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7

A HISTORY OF LAND MAMMALS IN
THE WESTERN HEMISPHERE

•?&&&■

THE MACMILLAN COMPANY

HH> VOMC - KMTON - CHICAGO - DALLAS

MACMILLAN k CO., Lmrr»D

LONDON - lUlHUAY ■ CALCUTTA

HILtOUIIfll

THE MACMILLAN CO. OF CANADA, 1

A

HISTORY OF LAND MAMMALS

IN THE

WESTERN HEMISPHERE

BY
WILLIAM B. ^C°TT

Ph.D. (Heidelberg), Hon.D.Sc. (Harvard & Oxford), LL.D. (Uuiv. of Pennsylvania)

BLAIR PROFESSOR OF GEOLOGY AND PALEONTOLOGY
IN PRINCETON UNIVERSITY

ILLUSTRATED WITH St PLATES AND MORE THAN 100 DRAWINGS

BY BRUCE HORSFALL

Ntfo Horfc
THE MACMILLAN COMPANY

1913

All rights reserved

Copyright, 1913,
By THE MACMILLAN COMPANY.

Set up and electrotyped. Published November, 1913.

NortoooD fJrfff

J. 8. Cashing Co. — Berwick & Smith Co.

Norwood, Mass., U.S.A.

De&tcateD

TO

MY CLASSMATES
HENRY FAIRFIELD OSBORN and FRANCIS SPEIR

IX MEMORY OF A NOTABLE SUMMER AFTERNOON

IN 1876 AND IN TOKEN OF FORTY

YEARS7 UNCLOUDED FRIENDSHIP

356603

Speak to the earth and it shall teach thee.

— Job, xii, 8.

Can these bones live ?

— Ezekiel, xxxvii, 3.

PREFACE

One afternoon in June, 1876, three Princeton undergraduates
were lying under the trees on the canal bank, making a languid
pretence of preparing for an examination. Suddenly, one of the
trio remarked : " I have been reading an old magazine article
which describes a fossil-collecting expedition in the West ; why
can't we get up something of the kind?" The others replied, as
with one voice, " We can ; let's do it." This seemingly idle talk
was, for Osborn and myself, a momentous one, for it completely
changed the careers which, as we then believed, had been mapped
out for us. The random suggestion led directly to the first of the
Princeton palaBontological expeditions, that of 1877, which took
us to the u Bad Lands " of the Bridger region in southwestern
Wyoming. The fascination of discovering and exhuming with
our own hands the remains of the curious creatures which once
inhabited North America, but became extinct ages ago, has proved
an enduring delight. It was the wish to extend something of
this fascinating interest to a wider circle, that occasioned the
preparation of this book.

The western portion of North America has preserved a marvel-
lous series of records of the successive assemblages of animals
which once dwelt in this continent, and in southernmost South
America an almost equally complete record was made of the
strange animals of that region. For the last half-century, or
more, many workers have cooperated to bring this long-vanished
world to light and to decipher and interpret the wonderful story
of mammalian development in the western hemisphere. The task
of making this history intelligible, not to say interesting, to the
layman, has been one of formidable difficulty, for it is recorded
in the successive modifications of the bones and teeth, and without

some knowledge of osteology, these records are in an unknown

ix

X PREFACE

tongue. To meet this need, Chapter III gives a sketch of the
mammalian skeleton and dentition, which the reader may use as
the schoolboy uses a vocabulary to translate his Latin exercise,
referring to it from time to time, as may be necessary to make
clear the descriptions of the various mammalian groups. Techni-
cal terms have been avoided as far as possible, but, unfortunately,
it is not practicable to dispense with them altogether. The
appended glossary will, it is hoped, minimize the inconvenience.

No one who has not examined it, can form any conception of
the enormous mass and variety of material, illustrating the history
of American mammals, which has already been gathered into the
various museums. A full account of this material would require
many volumes, and one of the chief problems in the preparation
of this book has been that of making a proper selection of the
most, instructive and illuminating portions of the long and com-
plicated story. Indeed, so rapid is the uninterrupted course of
discovery, that parts of the text became antiquated while in the
press and had to be rewritten. As first prepared, the work
proved to be far too long and it was necessary to excise several
chapters, for it seemed better to cover less ground than to make
the entire history hurried and superficial. The plan of treatment
adopted involves a considerable amount of repetition, but this is
perhaps not a disadvantage, since the same facts are considered
from different points of view.

The facts which are here brought together have been ascer-
tained by many workers, and I have borrowed with the greatest
freedom from my fellow labourers in the field of palaeontology.
As every compiler of a manual finds, it is not feasible to attribute
the proper credit to each discoverer. Huxley has so well explained
the situation in the preface to his " Anatomy of Vertebrated Ani-
mals," that I may be permitted to borrow his words : " I have
intentionally refrained from burdening the text with references ;
and, therefore, the reader, while he is justly entitled to hold me
responsible for any errors he may detect, will do well to give me
no credit for what may seem original, unless his knowledge is
sufficient to render him a competent judge on that head."

PREFACE XI

A book of this character is obviously not the proper place for
polemical discussions of disputed questions. Whenever, there-
fore, the views expressed differ widely from those maintained by
other palaeontologists, I have attempted no more than to state, as
fairly as I could, the alternative interpretations and my own
choice between them. Any other course was forbidden by the
limitations of space.

It is a pleasure to give expression to my sincere sense of grati-
tude to the many friends who have helped me in an unusually
laborious undertaking. Professor Osborn and Dr. Matthew have
placed at my disposal the wonderful treasures of the American
Museum of Natural History in New York and in the most liberal
manner have supplied me with photographs and specimens for
drawings, as well as with information regarding important dis-
coveries which have not yet been published. Dr. W. J. Holland,
Director of the Carnegie Museum in Pittsburgh, has likewise gen-
erously provided many photographs from the noble collection under
his charge, kindly permitting the use of material still undescribed.
To Professor Charles Schuchert, of Yale University, I am also
indebted for several photographs.

The figures of existing animals are almost all from photographs
taken in the New York and London zoological gardens, and I
desire to thank Director Hornaday, of the Bronx Park, and Mr.
Peacock, of the London garden, for the very kind manner in
which they have procured these illustrations for my use. The
photographs have been modified by painting out the backgrounds
of cages, houses, and the like, so as to give a less artificial appear-
ance to the surroundings.

To my colleagues at Princeton I am under great obligations
for much valuable counsel and assistance. Professor Gilbert van
Ingen has prepared the maps and diagrams and Dr. W. J. Sinclair
has devoted much labour and care to the illustrations and has also
read the proofs. Both of these friends, as also Professors C. H.
Smyth and E. G. Conklin and Drs. Farr and McComas, have read
various parts of the manuscript and made many helpful sugges-
tions in dealing with the problems of treatment and presentation.

Xll PREFACE

For thirteen years past I have been engaged in the study of
the great collections of fossil mammals, gathered in Patagonia by
the lamented Mr. Hatcher and his colleague, Mr. Peterson, now
of the Carnegie Museum. This work made it necessary for me
to visit the museums of the Argentine Republic, which I did in
1901, and was there received with the greatest courtesy and kind-
ness by Dr. F. Moreno, Director, and Dr. Santiago Roth, of the
La Plata Museum, and Dr. F. Ameghino, subsequently Director
of the National Museum at Buenos Aires. To all of these gentle-
men the chapters on the ancient life of South America are much
indebted, especially to Dr. Ameghino, whose untimely death was
a great loss to science. It is earnestly to be hoped that the heroic
story of his scientific career may soon be given to the world.

Finally, I desire to thank Mr. Horsfall for the infinite pains
and care which he has expended upon the illustrations for the
work, to which so very large a part of its value is due.

While the book is primarily intended for the lay reader, I can-
not but hope that it may also be of service to many zoologists,
who have been unable to keep abreast of the flood of palteonto-
logical discovery and yet wish to learn something of its more
significant results. How far I have succeeded in a most difficult
task must be left to the judgment of such readers.

Princeton, N.J.,
June 1, 1913.

CONTENTS

CHAPTER I

PAGE

Methods of Investigation — Geological 1

CHAPTER II
Methods op Investigation — PaljEontological .... 29

CHAPTER III
The Classification of the Mammalia 50

CHAPTER IV
The Skeleton and Teeth of Mammals 61

CHAPTER V

The Geographical Development of the Americas in Cenozoic

Times 99

CHAPTER VI
The Geographical Distribution of Mammals 135

CHAPTER VII
The Successive Mammalian Faunas of North and South America 192

CHAPTER VIII
HI8T0RT OF the Perissodactyla 288

CHAPTER IX
History of the Artiodactyla 358

CHAPTER X
History of the Proboscidea 422

t • •

1111

XIV CONTENTS

CHAPTER XI

PAGE

History of the IAmblypoda and ICondylarthra .... 443

CHAPTER XII
History of thk JToxodontia (or jNotoungulata) . . . 461

CHAPTER XIII
History of the jLitopterna and jAstrapotheria .... 489

CHAPTER XIV
History of the Carnivora 516

CHAPTER XV
History of the Primates 577

CHAPTER XVI
History of the Edentata 589

CHAPTER XVII
History of the Marsupialia 624

CHAPTER XVIII
Modes of Mammalian Evolution 645

GLOSSARY 665

INDEX 675

t Extinct.

A HISTORY OF LAND MAMMALS IN
THE WESTERN HEMISPHERE

1

A HISTORY OF LAND MAMMALS IN
THE WESTERN HEMISPHERE

CHAPTER I

METHODS OP INVESTIGATION — GEOLOGICAL

The term Mammal has no exact equivalent in the true
vernacular of any modern language, the word itself, like its
equivalents, the French Mammifkre and the German Sduge-
thier, being entirely artificial. As a name for the class Linnaeus
adopted the term Mammalia, which he formed from the Latin
mamma {i.e. teat) to designate those animals which suckle
their young ; hence the abbreviated form Mammal, which has
been naturalized as an English word. " Beast/ ' as employed
in the Bible, and " Quadruped' ' are not quite the same as
mammal, for they do not include the marine forms, such as
whales, dolphins, seals, walruses, or the flying bats, and they
are habitually used in contradistinction to Man, though Man
and all the forms mentioned are unquestionably mammals.

In attempting to frame a definition of the term Mammal,
it is impossible to avoid technicalities altogether, for it is the
complete unity of plan and structure which justifies the in-
clusion of all the many forms that differ so widely in habits
and appearance. Mammals are air-breathing vertebrates, which
are warm-blooded and have a ^-chambered heart ; the body cavity
is divided into pleural and abdominal chambers by a diaphragm ;
except in the lowest division of the class, the young are brought
forth alive and are always suckled, the milk glands being universal
throughout the class. In the great majority of mammals the body

2 LAND MAMMALS IN THE WESTERN HEMISPHERE

is clothed with hair; a character found in no other animals.
In a few mammals the skin is naked, and in still fewer there
is a partial covering of scales. The list of characters common
to all mammals, which distinguish them from other animals,
might be indefinitely extended, for it includes all the organs
and tissues of the body, the skeletal, muscular, digestive, ner-
vous, circulatory, and reproductive systems, but the two or
three more obvious or significant features above selected will
suffice for the purposes of definition.

While the structural plan is the same throughout the entire
class, there is among mammals a wonderful variety of form,
size, appearance, and adaptation to special habits. It is as
though a musician had taken a single theme and developed it
into endless variations, preserving an unmistakable unity
through all the changes. Most mammals are terrestrial, living,
that is to say, not only on the land, but on the ground, and
are herbivorous in habit, subsisting chiefly or exclusively upon
vegetable substances, but there are many departures from this
mode of life. It should be explained, however, that the term
terrestrial is frequently used in a more comprehensive sense for
all land mammals, as distinguished from those that are aquatic
or marine. Monkeys, Squirrels, Sloths and Opossums are
examples of the numerous arboreal mammals, whose structure
is modified to fit them for living and sleeping in the trees,
and in some, such as the Sloths, the modification is carried so
far that the creature is almost helpless on the ground. An-
other mode of existence is the burrowing or fossorial, the animal
living partly or mostly, or even entirely underground, a typical
instance of which is the Mole. The Beaver, Muskrat and Otter,
to mention only a few forms, are aquatic and spend most of
their life in fresh waters, though perfectly able to move about
on the land. Marine mammals, such as the Seals and Whales,
have a greatly modified structure which adapts them to life in
the sea.

Within the limits of each of these categories we may note

METHODS — GEOLOGICAL 3

that there are many degrees of specialization or adaptation to
particular modes of life. Thus, for example, among the marine
mammals, the Whales and their allies, Porpoises, etc., are so
completely adapted to a life in the seas that they cannot come
upon the land, and even stranding is fatal to them, while the
Seals frequently land and move about upon the shore. It
should further be observed that mammals of the most diverse
groups are adapted to similar modes of existence. Thus in one
natural group or order of related forms, occur terrestrial, burrow-
ing, arboreal and aquatic members, and the converse state-
ment is of course equally true, that animals of similar life-
habits are not necessarily related to one another, and very
frequently, in fact, are not so related. Among the typically
marine mammals, for example, there are at least three and
probably four distinct series, which have independently be-
come adapted to life in the sea.

Before attempting to set forth an outline of what has
been learned regarding the history of mammalian life in the
western hemisphere, it is essential to give the reader some con-
ception of the manner in which that knowledge has been ob-
tained. Without such an understanding of the methods em-
ployed in the investigation the reader can only -blindly accept
or as blindly reject what purports to be the logical inference
from well-established evidence. How is that evidence to be
discovered ? and how may trustworthy conclusions be derived
from it ?

The first and most obvious step is to gather all possible in-
formation concerning the mammals of the present day, their
structure (comparative anatomy), functions (physiology), and
their geographical arrangement. This latter domain, of the
geographical distribution of mammals, is one of peculiar signif-
icance. Not only do the animals of North America differ radi-
cally from those of Central and South America, but within the
limits of each continent are more or less well-defined areas,

4 LAND MAMMALS IN THE WESTERN HEMISPHERE

the animals of which differ in a subordinate degree from those
of other areas. The study of the modern world, however,
would not of itself carry us very far toward the goal of our
inquiries, which is an explanation, not merely a statement, of
the facts. The present order of things is the outcome of an
illimitably long sequence of events and can be understood only
in proportion to our knowledge of the past. In other words, it
is necessary to treat the problems involved in our inquiry
historically; to trace the evolution of the different mammalian
groups from their simpler beginnings to the more complex and
highly specialized modern forms ; to determine, so far as that
may be done, the place of origin of each group and to follow
out their migrations from continent to continent.

While we shall deal chiefly, almost exclusively, with the
mammals of the New World, something must be said regard-
ing those of other continents, for, as will be shown in the sequel,
both North and South America have, at one time or another,
been connected with various land-masses of the eastern hemi-
sphere. By means of those land-connections, there has been
an interchange of mammals between the different continents,
and each great land-area of the recent world contains a more or
less heterogeneous assemblage of forms of very diverse places
of origin. Indeed, migration from one region to another has
played a most important part in bringing about the present
distribution of living things. From what has already been
learned as to the past life of the various continents and their
shifting connections with one another, it is now feasible to
analyze the mammalian faunas of most of them and to separate
the indigenous from the immigrant elements. Among the
latter may be distinguished those forms which are the much
modified descendants of ancient migrants from those which
arrived at a much later date and have undergone but little
change. To take a few examples from North America, it may
be said that the Bears, Moose, Caribou and Bison are late
migrants from the Old World; that the Virginia and Black-

METHODS — GEOLOGICAL 5

tailed Deer and the Prong-horned Antelope are of Old World
origin, but their ancestors came in at a far earlier period and
the modern species are greatly changed from the ancestral
migrants. The Armadillo of Texas and the Canada Porcupine
are almost the only survivors, north of Mexico, of the great
migration of South American mammals which once invaded
the northern continent. On the other hand, the raccoons
and several families of rodents are instances of indigenous types
which may be traced through a long American ancestry.

Fully to comprehend the march of mammalian development,
it thus becomes necessary to reconstruct, at least in outline,
the geography of the successive epochs through which the
developmental changes have taken place, the connections and
separations of land-masses, the rise of mountain ranges, river
and lake systems and the like. Equally significant factors in
the problem are climatic changes, which have had a profound
and far-reaching effect upon the evolution and geographical
spread of animals and plants, and the changes in the vegetable
world must not be ignored, for, directly or indirectly, animals
are dependent upon plants. To one who has paid no atten-
tion to questions of this kind, it might well seem an utterly hope-
less task to reconstruct the long vanished past, and he would
naturally conclude that, at best, only fanciful speculations,
with no foundation of real knowledge, could be within our
reach. Happily, such is by no means the case. Geology offers
the means of a successful attack upon these problems and,
although very much remains to be done, much has already
been accomplished in elucidating the history, especially in its
later periods, with which the story of the mammals is more
particularly concerned.

It is manifestly impossible to present here a treatise upon the
science of Geology, even in outline sketch. Considerations of
space are sufficient to forbid any such attempt. Certain things
must be taken for granted, the evidence for which may be
found in any modern text-book of Geology. For example,

6 LAND MAMMALS IN THE WESTERN HEMISPHERE

it is entirely feasible to establish the mode of formation of
almost any rock (aside from certain problematical rocks, which
do not enter into our discussion) and to determine whether it
was laid down in the sea, or on the land, or in some body of
water not directly connected with the sea, such as a lake or
river. With the aid of the microscope, it is easy to discriminate
volcanic material from the ordinary water-borne and wind-
borne sediments and, in the case of the rocks which have
solidified from the molten state, to distinguish those masses
which have cooled upon the surface from those which have
solidified deep within the earth.

While the nature and mode of formation of the rocks mav
thus be postulated, it will be needful to explain at some length
the character of the evidence from which the history of the
earth may be deciphered. First of all, must be made clear the
method by which the events of the earth's history may be
arranged in chronological order, for a history without chronology
is unintelligible. The events which are most significant for
our purpose are recorded in the rocks which are called stratified,
bedded or sedimentary, synonymous terms. Such rocks were
made mostly from the debris of older rocks, in the form of
gravel, sand or mud, and were laid down under water, or, less
extensively, spread by the action of the wind upon a land-
surface. Important members of this group of rocks are those
formed, more or less completely, from the finer fragments
given out in volcanic eruptions, carried and sorted by the wind
and finally deposited, it may be at great distances from their
point of origin, upon a land-surface, or on the bottom of
some body of water. Stratified or bedded rocks, as their
name implies, are divided into more or less parallel layers or
beds, which may be many feet or only a minute fraction of an
inch in thickness. Such a division means a pause in the pro-
cess of deposition or a change in the character of the material
deposited over a given area. Owing to the operation of
gravity, the layers of sediment are spread out in a horizontal

METHODS — GEOLOGICAL 7

attitude, which disregard the minor irregularities of the bottom,
just as a deep snow buries the objects which lie upon the surface.

A moment's consideration will show that, in any series of
stratified rocks which have not been greatly disturbed from
their original horizontal position, the order of succession or
superposition of the beds must necessarily be the chronological
order of their formation. (Fig. 1.) Obviously, the lowest beds
must have been deposited first and therefore are the oldest of
the series, while those at the top must be the newest or
youngest and the beds intermediate in position are inter-
mediate in age. This inference depends upon the simple prin-
ciple that each bed must have been laid down before the next
succeeding one can have been deposited upon it. While this
is so clear as to be almost self-evident, it is plain that such a
mode of determining the chronological order of the rocks of the
earth's crust can be of only local applicability and so far as
the beds may be traced in unbroken continuity. It is of no
direct assistance in correlating the events in the history of
one continent with those of another and it fails even in com-
paring the distinctly separated parts of the same continent.
Some method of universal applicability must be devised before
the histories of scattered regions can be combined to form a
history of the earth. Such a universal method is to be found
in the succession of the forms of life, so far as that is recorded in
the shape of fossils, or the recognizable remains of animal and
vegetable organisms preserved in the rocks.

This principle was first enunciated by William Smith, an
English engineer, near the close of the eighteenth century,
who thus laid the foundations of Historical Geology. In the
diagram, Fig. 2, is reproduced Smith's section across England
from Wales to near London, which shows the successive
strata or beds, very much tilted from their original horizontal
position by the upheaval of the sea-bed upon which they were
laid down. The section pictures the side of an imaginary
gigantic trench cut across the island and was constructed by a

LAND MAMMALS IN THE WESTERN HEMISPHERE

METHOD8 — GEOLOGICAL 9

simple geometrical method from the surface exposures of the
beds, such as mining engineers continually employ to map the
underground extension of economically important rocks, and
shows how an enormous thickness of strata may be studied
from the surface. The older beds are exposed at the western
end of the section in Wales and, passing eastward, successively
later and later beds are encountered, the newest appearing at
the eastern end. Very many of the strata are richly fossiliferous,
and thus a long succession of fossils was obtained in the order
of their appearance, and this order has been found toehold good,
not only in England, but throughout the world. The order

SklcA »fth0 Sueeffiion of STRA 1>t and tkur rzkiivtsUttiudes

Fig. 2. — William Smith's section across the south of England. The vertical scale is

exaggerated, which makes the inclination of the beds appear too steep.

N. B. The original drawing is in colore, which are not indicated by the dotted strata.

of succession of the fossils was thus in the first instance actually
ascertained from the succession of the strata in which they are
found and has been verified in innumerable sections in many
lands and is thus a matter of observed and verifiable fact, not
merely a postulate or working hypothesis. Once ascertained,
however, the order of succession of living things upon the earth
may be then employed as an independent and indispensable
means of geologically dating the rocks in which they occur.
This is the palceontological method, which finds analogies in
many other branches of learned inquiry. The student of
manuscripts discovers that there is a development, or regular
series of successive changes, in handwriting, and from the hand-
writing alone can make a very close approximation to the date
of a manuscript. The order in which those changes came about

10 LAND MAMMALS IN THE WESTERN HEMISPHERE

was ascertained from the comparative study of manuscripts,
the date of which could be ascertained from other evidence,
but, when once established, the changes in handwriting are
used to fix the period of undated manuscripts. Just so, the
succession of fossils, when learned from a series of superposed
beds, may then be employed to fix the geological date of
strata in another region. Similarly, the archaeologist has
observed that there is an evolution or development in every
sort of the work of men's hands and therefore makes use of
coins, inscriptions, objects of art, building materials and methods,
etc., to date ancient structures. In the German town of Trier
(or Treves) on the Moselle, the cathedral has as a nucleus a
Roman structure, the date and purpose of which had long been
matters of dispute, though the general belief was that the
building had been erected under Constantine the Great. In
the course of some repairs made not very long ago, it became
necessary to cut deep into the Roman brickwork, and there,
embedded in the undisturbed mortar, was a coin of the emperor
Valentinian II, evidently dropped from the pocket of some
Roman bricklayer. That coin fixed a date older than which the
building cannot be, though it may be slightly later, and it well
illustrates the service rendered by fossils in determining geo-
logical chronology.

Other methods of making out the chronology of the earth's
history have been proposed from time to time and all of them
have their value, though none of them renders us independent
of the use of fossils, which have the pre-eminent advantage of
not recurring or repeating themselves at widely separated inter-
vals of time, as all physical processes and changes do. An
organism, animal or plant, that has become extinct never
returns and is not reproduced in the evolutionary process.

Great and well founded as is our confidence in fossils as
fixing the geological date of the rocks in which they occur, it
must not be forgotten that the succession of the different kinds
of fossils in time was first determined from the superposition of

METHODS — GEOLOGICAL 1 1

the containing strata. Hence, it is always a welcome con-
firmation of the chronological inferences drawn from the study
of fossils, when those inferences can be unequivocally estab-
lished by the succession of the beds themselves. For example,
in the Tertiary deposits of the West are two formations or
groups of strata, called respectively the Uinta and the White
River, which had never been known to occur in the same region
and whose relative age therefore could not be determined by
the method of superposition. Each of the formations, however,
has yielded a large number of well-preserved fossil mammals,
and the comparative study of these mammals made it clear
that the Uinta must be older than the White River and that
no very great lapse of time, geologically speaking, occurred
between the end of the former and the beginning of the latter.
Only two or three years ago an expedition, from the American
Museum of Natural History discovered a place in Wyoming
where the White River beds lie directly upon those of the
Uinta, thus fully confirming the inference as to the relative
age of these two formations which had long ago been drawn
from the comparative study of their fossil mammals.

The palaeontological method of determining the geological
date of the stratified rocks is thus an indispensable means of
correlating the scattered exposures of the strata in widely
separated regions and in different continents, it may be with
thousands of miles of intervening ocean. The general principle
employed is that close similarity of fossils in the rocks of the
regions compared points to an approximately contemporaneous
date of formation of those rocks. This principle must not,
however, be applied in an offhand or uncritical manner, or it
will lead to serious error. In the first place, the evolutionary
process is a very slow one and geological time is inconceivably
long, so that deposits which differ by some thousands of years
may yet have the same or nearly the same fossils. The method
is not one of sufficient refinement to detect such relatively
small differences. To recur to the illustration of the develop-

LAND MAMMALS IN THE WESTERN HEMISPHERE

METHODS — GEOLOGICAL 1 3

ment in handwriting, the palaeographer can hardly do more
than determine the decade in which a manuscript was written ;
no one would expect him to fix upon the exact year, still less the
month, from the study of handwriting alone. As is the month
in recorded human history, so is the millennium in the long
course of the earth's development.

In the second place, there are great differences in the con-
temporary life of separate regions and such geographical differ-
ences there have always been, so far as we can trace back the
history of animals and plants. A new organism does not
originate simultaneously all over the world but, normally
at least, in a single area and spreads from that centre until it
encounters insuperable obstacles. Such spreading is a slow
process and hence it is that new forms often appear in one re-
gion much earlier than in others and in the very process of ex-
tending their range, the advancing species may themselves
be considerably modified and reach their new and distant homes
as different species from those which originated the movement.
Extinction, likewise, seldom occurs simultaneously over the
range of a group, but now here and now there in a way that
to our ignorance appears to be arbitrary and capricious. The
process may go on until extinction is total, or may merely
result in a great restriction of the range of a given group, or
may break up that range into two or more distinct areas.

Of such incomplete extinctions many instances might be
given, but one must suffice. The camel-tribe, strange as it
may appear, originated in North America and was long con-
fined to that continent, while at the present day it is repre-
sented only by the llamas of South America and the true
camels of Asia, having completely vanished from its early
home. These facts and a host of similar ones make plain how
necessary it is to take geographical considerations into
account in all problems that deal with the synchronizing of the
rocks of separate areas and continents.

Properly to estimate the significance of a difference in the

14 LAND MAMMALS IN THE WESTERN HEMISPHERE

fossils of two regions and to determine how far it is geographical,
due to a separation in space, or geological and caused by separa-
tion in time, is often a very difficult matter and requires a vast
amount of minute and detailed study. Once more, the princi-
ple involved is illustrated by the study of manuscripts. Down
to the time when the printing press superseded the copyist,
each of the nations of Europe had its own traditions and its
more or less independent course of handwriting development.
A great monastery, in which the work of copying manuscripts
went on century after century, became an independent geo-
graphical centre with its particular styles. Thus the palae-
ographer, like the geologist, is confronted by geographical prob-
lems as well as by those of change and development in general.

In addition to the method of geologically dating the rocks
by means of the fossils which they contain, there are other ways
which may give a greater precision to the result. Climatic
changes, when demonstrable, are of this character, for they may
speedily and simultaneously affect vast areas of the earth's
surface or even the entire world. From time to time in the
past, glacial conditions have prevailed over immense regions,
several continents at once, it may be, as in one instance in
which India, South Africa, Australia, South America were
involved. The characteristic accumulations made by the
glaciers in these widely separated regions must be contempora-
neous in a sense that can rarely be predicated of the ordinary
stratified rocks. Such climatic changes as the formation and
disappearance of the ice-fields give a sharper and more definite
standard of time comparisons than do the fossils alone, and
yet the fossils are in turn needed to show which of several
possible glacial periods are actually being compared.

Again, great movements of the earth's crust, which involve
vast and widely separated regions and bring the sea in over
great areas of land, or raise great areas into land, which had
been submerged, may also yield more precise time-measure-
ments, because occurring within shorter periods than do

METHODS — GEOLOGICAL

15

notable changes in the system of living things. Such changes
in animals and plants may be compared to the almost imper-
ceptible movement of the hour-hand of a clock, while the re-
corded climatic revolutions and crustal movements often supply
the place of the minute-hand. It is obvious, however, that
if the hour-hand be wanting, the minute-hand alone can be of
very limited use. There have been a great many vast submer-
gences and emergences of land in the history of the earth, and
only the fossils can give us the assurance that we are comparing
the same movement in distant continents, and not two similar
movements separated by an enormous interval of time.

It may thus fairly be admitted that it is possible to arrange
the rocks which compose the accessible parts of the earth's
crust in chronological order and to correlate in one system the
rocks of the various continents. The terms used for the more
important divisions of geological time are, in descending order
of magnitude, era, period, epoch, age or stage, and the general
scheme of the eras and periods, which is in almost uniform use
throughout the world, is given in the table, which is arranged
so as to give the succession graphically, with the most ancient
rocks at the bottom and the latest at the top.

Cenozoic era

Mesozoic era

Palaeozoic era

Pre-Cambrian eras

Quaternary period
Tertiary period
Cretaceous period
Jurassic period
Triassic period
Permian period
Carboniferous period
Devonian period
Silurian period
Ordovician period
Cambrian period

Algonkian period
Archaean period

16 LAND MAMMALS IN THE WESTERN HEMISPHERE

It must not be supposed that all the divisions of similar
rank, such as the eras, for example, were of equal length, as
measured by the thickness of the rocks assigned to those divi-
sions. On the contrary, they must have been of very unequal
length and are of very different divisibility. The Pre-Cambrian
eras, with only two periods, were probably far longer than
all subsequent time, and all that the major divisions imply
is that they represent changes in the system of life of
approximately equivalent importance. It is impossible to
give any trustworthy estimate of the actual lengths of
these divisions in years, though many attempts to do so
have been made. All that can be confidently affirmed is
that geological time, like astronomical distances, is of in-
conceivable vastness and its years can be counted only in
hundreds of millions.

To discuss in any intelligible manner the history of mammals,
it will be necessary to go much farther than the above table
in the subdivision of that part of geological time in which
mammalian evolution ran its course. As mammals repre-
sent the highest stage of development yet attained in the
animal world, it is only the latter part of the earth's history
which is concerned with them ; the earlier and incomparably
longer portion of that history may be passed over. Mammals
are first recorded in the later Triassic, the first of the three
periods which make up the Mesozoic era. They have also
been found, though very scantily, in the other Mesozoic periods,
the Jurassic and Cretaceous, but it was the Cenozoic era that
witnessed most of the amazing course of mammalian develop-
ment and diversification, and hence the relatively minute sub-
divisions necessary for the understanding of this history deal
only with the Cenozoic, the latest of the great eras.

In the subjoined table the periods and epochs are those
which are in general use throughout the world, the ages and
stages are those which apply to the western interior of North
America, each region, even of the same continent, requiring a

METHODS — GEOLOGICAL

17

different classification. The South American formations are
given in a separate table, as it is desirable to avoid the appear-
ance of an exactitude in correlation which cannot yet be at-
tained.

Quaternary period

Tertiary period

CENOZOIC ERA

Recent epoch

Pleistocene epoch = Glacial and Inter-
glacial stages.

Pliocene epoch
Miocene epoch
Oligocene epoch
Eocene epoch
Paleocene epoch

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Lower

Upper

Middle

Lower

Upper

Lower

Upper

Lower

Upper
Lower

Continuing the subdivision of the Tertiary period still
farther, we have the following arrangement :

TERTIARY PERIOD (North America)

Upper Wanting

Middle Blanco age

Thousand Creek age
Snake Creek age
Republican River age

Loup Fork age
Deep River age
Arikaree age
John Day age
White River age

Uinta age
Middle Bridgerage

Wind River age
Wasatch age
Torrejon age
Puerco age

Fort Union

18 LAND MAMMALS IN THE WESTERN HEMISPHERE

This is a representative series of the wide-spread and manifold
non-marine Tertiary deposits of the Great Plains, but a much
more extensive and subdivided scheme would be needed to
show with any degree of fullness the wonderfully complete
record of that portion of the continent during the Tertiary
period. A much more elaborate table will be found in Pro-
fessor Osborn's "Age of Mammals/ ' p. 41. There are
some differences of practice among geologists as to this
scheme of classification, though the differences are not
those of principle. No question arises concerning the reality
of the divisions, or their order of succession in time,
but merely as to the rank or relative importance which
should be attributed to some of them, and that is a very
minor consideration.

Much greater difficulty and, conseor n n 4 more radical

differences of interpretation arise s . *nst is made to

correlate or synchronize the sma1? * found in

the various continents, with or . e of the

geographical differences in contemp «c\v6en Eu-

rope and North America there has always i certain pro-

portion of mammalian forms in common, a pre portion that
was at one time greater, at another less, and this community
renders the correlation of the larger divisions of the Tertiary
in the two continents comparatively easy, and even in the minor
subdivisions very satisfactory progress has been made, so
that it is possible to trace in some detail the migrations of
mammals from the eastern to the western hemisphere and
vice versa. Such intermigrations were made possible by the
land-bridges connecting America with Europe across the
Atlantic, perhaps on the line of Greenland and Iceland, and
with Asia where now is Bering Strait. These connections were
repeatedly made and repeatedly broken during the Mesozoic
and Cenozoic eras down to the latest epoch, the Pleistocene.
By comparing the fossil mammals of Europe with those of
North America for any particular division of geological time,

METHODS — GEOLOGICAL 1 9

it is practicable to determine whether the way of intermigra-
tion was open or closed, because separation always led to greater
differences between the faunas of the two continents through
divergent evolution.

Correlation with South America is exceedingly difficult and
it is in dealing with this problem that the widest differences of
opinion have arisen among geologists. Through nearly all
the earlier half of the Tertiary period the two Americas were
separated and, because of this separation, their land mammals
were utterly different. Hence, the lack of elements common
to both continents puts great obstacles in the way of establish-
ing definite time-relations between their geological divisions.
Only the marine mammals, whales and dolphins, were so far
alike as to offer some satisfactory basis of comparison. When,
in the later Tf> ' ; \ "■ land-connection was established between
the two c k ^ -ons °f mammals from each to the

other beg r ~ Wward there were always certain

elements c is there are to-day. In spite of the

continuous ; ,ihemy the present faunas of North and

South Amu , e very strikingly different, South America

being, with the exception of Australia, zoologically the most
peculiar region of the earth.

In the following table of the South American Cenozoic, the
assignment of the ages to their epochs is largely tentative,
especially as regards the more ancient divisions, and repre-
sents the views generally held by the geologists of Europe and
the United States ; those of South America, on the contrary,
give an earlier date to the ages and stages and refer the older
ones to the Cretaceous instead of the Tertiary.

CENOZOIC ERA (South America)

Quaternary period

Recent epoch

Pleistocene epoch — Pampean Beds,
Brazilian caverns

20

LAND MAMMALS IN THE WESTERN HEMISPHERE

Tertiary period

Pliocene epoch

Miocene epoch

Oligocene epoch

Eocene epoch

Monte Hermoso age
Catamarca age
Parand age
Santa Cruz age

«

Patagonian age
Deseado age (Pyrothe-

rium Beds)
Astraponotus Beds
Casa Mayor age (Noto-

stylops Beds)

The Pleistocene and Pliocene deposits are most widely dis-
tributed over the Pampas of Argentina, but the former occur
also in Ecuador, Brazil, Chili, and Bolivia. The other forma-
tions cover extensive areas in Patagonia, and some extend into
Tierra del Fuego.

We have next to consider the methods by which past geo-
graphical conditions may be ascertained, a task which, though
beset with difficulties, is very far from being a hopeless under-
taking. As has already been pointed out, it is perfectly
possible for the geologist to determine the circumstances of
formation of the various kinds of rocks, to distinguish terrestrial
from aquatic accumulations and, among the latter, to identify
those which were laid down in the sea and those which were
formed in some other body of water. By plotting on a map
all the marine rocks of a given geological date, an approximate
estimate may be formed as to the extension of the sea over the
present land for that particular epoch. It is obvious, however,
that for those areas which then were land and now are covered
by the sea, no such direct evidence can be obtained, and only
indirect means of ascertaining the former land-connections
can be employed. It is in the treatment of this indirect evi-
dence that the greatest differences of opinion arise and, if two
maps of the same continent for the same epoch, by separate
authors, be compared, it will be seen that the greatest dis-

METHODS — GEOLOGICAL 21

crepancies between them are concerning former land-connec-
tions and extensions.

The only kind of indirect evidence bearing upon ancient
land-connections, now broken by the sea, that need be con-
sidered here is that derived from the study of animals and plants,
both recent and fossil. All-important in this connection is
the principle that the same or closely similar species do not
arise independently in areas between which there is no con-
nection. It is not impossible that such an independent origin
of organisms which the naturalist would class as belonging to
the same species may have occasionally taken place, but, if so,
it must be the rare exception to the normal process. This
principle leads necessarily to the conclusion that the more
recently and broadly two land-areas, now separated by the
sea, have been connected, the more nearly alike will be their
animals and plants. Such islands as Great Britain, Sumatra
and Java must have been connected with the adjacent mainland
within a geologically recent period, while the extreme zoological
peculiarity of Australia can be explained only on the assumption
that its present isolation is of very long standing. The princi-
ple applies to the case of fossils as well as to that of modern
animals, and has already been made use of, in a preceding
section, in dealing with the ancient land-connections of North
America. It was there shown that the connection of this
continent with the Old World and the interruptions of that
connection are reflected and recorded in the greater or less
degree of likeness in the fossil mammals at any particular epoch.
Conversely, the very radical differences between the fossil
mammals of the two Americas imply a long-continued separa-
tion of those two continents, and their junction in the latter
half of the Tertiary period is proved by the appearance of
southern groups of mammals in the northern continent, and of
northern groups in South America.

Inasmuch as the connection between North and South
America still persists, the geology of the Isthmus of Panama

22 LAND MAMMALS IN THE WESTERN HEMISPHERE

should afford testimony in confirmation of the inferences
drawn from a study of the mammals. Of course, the separating
sea did not necessarily cross the site of the present isthmus ;
it might have cut through some part of Central America, but
a glance at the map immediately suggests the isthmus as the
place of separation and subsequent connection. As a matter of
fact, isthmian geology is in complete accord with the evidence
derived from the mammals. Even near the summit of the hills
which form the watershed between the Atlantic and the Pacific
and through which the great Culebra Cut passes, are beds of
marine Tertiary shells, showing that at that time the land was
completely submerged. This does not at all preclude the
possibility of other transverse seas at the same period ; indeed,
much of Central America was probably under the sea also, but
the geology of that region is still too imperfectly known to
permit positive statements.

When several different kinds of testimony, each inde-
pendent of the other, can be secured and all are found
to be in harmony, the strength of the conclusion is thereby
greatly increased. Many distinct lines of evidence support
the inference that North and South America were com-
pletely severed for a great part of the Tertiary period.
This is indicated in the clearest manner, not only by the
geological structure of the Isthmus and by the mammals,
living and extinct, as already described, but also by the fresh-
water fishes, the land-shells, the reptiles and many other
groups of animals and plants.

The distribution of marine fossils may render the same sort
of service in elucidating the history of the sea as land-mammals
do for the continents, demonstrating the opening and closing
of connections between land-areas and between oceans. The
sea, it is true, is one and undivided, the continental masses
being great islands in it, but, nevertheless, the sea is divisible
into zoological provinces, just as is the land. Temperature,
depth of water, character of the bottom, etc., are factors that

METHODS — GEOLOGICAL 23

limit the range of marine organisms, as climate and physical
barriers circumscribe the spread of terrestrial animals. Pro-
fessor Perrin Smith has shown that in the Mesozoic era Bering
Strait was repeatedly opened and closed, and that each opening
and closing was indicated by the geographical relationships of
the successive assemblages of marine animals that are found
in the Mesozoic rocks of California and Nevada. When
the Strait was open, the coast-line between North America
and Asia was interrupted and the North Pacific was cooled by
the influx of water from the Arctic Sea. At such times,
sea-animals from the Russian and Siberian coasts extended their
range along the American side as far south as Mexico, and no
forms from the eastern and southern shores of Asia accompanied
them. On the other hand, when the Strait was closed, the
Arctic forms were shut out and the continuous coast-line and
warmer water enabled the Japanese, Indian, and even Mediter-
ranean animals to extend their range to the Pacific coast of
North America. A comparison of the marine fishes of the
two sides of the Isthmus of Panama shows an amount and
degree of difference between the two series as might be expected
from the length of time that they have been separated by the
upheaval of the land.

In working out the geographical conditions for any particular
epoch of the earth's history, it is possible to go much farther
than merely gaining an approximate estimate of the distribu-
tion of land and sea; many other important facts may be
gathered from a minute examination of the rocks in combina-
tion with a genetic study of topographical forms. By this
physiographical method, as it is called, the history of several
of the great mountain-ranges has been elaborated in great detail.
It is quite practicable to give a geological date for the initial
upheaval and to determine whether one or many such series
of movements have been involved in bringing about the present
state of things. Similarly, the history of plains and plateaus,
hills and valleys, lake and river systems, may be ascertained,

24 LAND MAMMALS IN THE WESTERN HEMISPHERE

and for the earths later ages, at least, a great deal may be
learned regarding the successive forms of the land-surfaces
in the various continents. It would be very desirable to ex-
plain the methods by which these results are reached, but this
could hardly be done without writing a treatise on physiog-
raphy, for which there is no room in this chapter. We must
be permitted to make use of the results of that science without
being called upon to prove their accuracy.

No factor has a more profound effect in determining the
character and distribution of living things than climate, of
which the most important elements, for our purpose, are
temperature and moisture. One of the most surprising results
of geological study is the clear proof that almost all parts of
the earth have been subjected to great vicissitudes of climate,
and a brief account of the evidence which has led to this un-
looked for result will not be out of place here.

The evidence of climatic changes is of two principal kinds,
(1) that derived from a study of the rocks themselves, and (2)
that given by the fossils of the various epochs. So far as the
rocks laid down in the sea are concerned, little has yet been
ascertained regarding the climatic conditions of their formation,
but the strata which were deposited on the land, or in some

•

body of water other than the sea, often give the most positive
and significant information concerning the circumstances of
climate which prevailed at the time of their formation. Cer-
tain deposits, such as gypsum and rock-salt, are accumulated
only in salt lakes, which, in turn, are demonstrative proof of
an arid climate. A salt lake could not exist in a region of
normal rainfall and, from the geographical distribution of such
salt-lake deposits, it may be shown that arid conditions have
prevailed in each of the continents and, not only once, but many
times. As a rule, such aridity of climate was relatively local
in extent, but sometimes it covered vast areas. For example,
in the Permian, the last of the Palaeozoic, and the Triassic, the
first of the Mesozoic periods (see Table, p. 15) nearly all the

METHODS — GEOLOGICAL 25

land-areas of the northern hemisphere were affected, either
simultaneously or in rapid succession.

Until a comparatively short time ago, it was very generally
believed that the Glacial or .Pleistocene epoch, which was so
remarkable and conspicuous a feature of the Quaternary period,
was an isolated phenomenon, unique in the entire history of
the earth. Now, however, it has been conclusively shown
that such epochs of cold have been recurrent and that no less
than five of these have left unmistakable records in as many
widely separated periods of time.

When the hypothesis of a great " Ice Age " in the Pleistocene
was first propounded by the elder Agassiz, it was naturally
received with general incredulity, but the gradual accumula-
tion of proofs has resulted in such an overwhelming weight
of testimony, that the glacial hypothesis is now accepted as one
of the commonplaces of Geology. The proofs consist chiefly
in the characteristic glacial accumulations, moraines and drift-
sheets, which cover such enormous areas in Europe and North
America and, on a much smaller scale, in Patagonia, and in the
equally characteristic marks of glacial wear left upon the
rocks over which the ice-sheets moved. Many years later
it was proved that the Permian period had been a time of
gigantic glaciation, chiefly in the southern hemisphere, when
vast ice-caps moved slowly over parts of South America,
South Africa, Australia and even of India. The evidence is
of precisely the same nature as in the case of the Pleistocene
glaciation. In not less than three more ancient periods,
the Devonian, Cambrian, and Algonkian, proofs of glacial
action have been obtained.

While the rocks themselves thus afford valuable testimony
as to the climatic conditions which prevailed at the time and
place of their formation, this testimony is fragmentary, missing
for very long periods, and must be supplemented from the
information presented by the fossils. As in all matters where
fossils are involved, the evidence must be cautiously used, for

26 LAND MAMMALS IN THE WESTERN HEMISPHERE

hasty inferences have often led to contradictory and absurd
conclusions. When properly employed, the fossils give a more
continuous and complete history of climatic changes than can,
in the present state of knowledge, be drawn from a study
of the rocks alone. For this purpose plants are particularly
useful, because the great groups of the vegetable kingdom are
more definitely restricted in their range by the conditions of
temperature and moisture than are most of the correspondingly
large groups of animals. Not that fossil animals are of no
service in this connection ; quite the contrary is true, but the
evidence from them must be treated more carefully and criti-
cally. To illustrate the use of fossils as recording climatic
changes in the past, one or two examples may be given.

In the Cretaceous period a mild and genial climate prevailed
over all that portion of the earth whose history we know, and
was, no doubt, equally the case in the areas whose geology
remains to be determined. The same conditions extended
far into the Arctic regions, and abundant remains of a
warm-temperate vegetation have been found in Greenland,
Alaska and other Arctic lands. Where now only scanty and
minute dwarf willows and birches can exist, was then a luxuri-
ant forest growth comprising almost all of the familiar trees of
our own latitudes, a most decisive proof that in the Cretaceous
the climate of the Arctic regions must have been much warmer
than at present and that there can have been no great accumu-
lation of ice in the Polar seas. Conditions of similar mildness
obtained through the earlier part of the Tertiary. In the
Eocene epoch large palm-trees were growing in Wyoming and
Idaho, while great crocodiles and other warm-country reptiles
abounded in the waters of the same region.

It is of particular interest to inquire how far the fossils of
Glacial times confirm the inferences as to a great climatic
change which are derived from a study of the rocks, for this
may be taken as a test-case. Any marked discrepancy be-
tween the two would necessarily cast grave doubt upon the

METHODS — GEOLOGICAL 27

value of the testimony of fossils as to climatic conditions. The
problem is one of great complexity, for the Pleistocene was not
one long epoch of unbroken cold, but was made up of
Glacial and Interglacial ages, alternations of colder and milder
conditions, and some, at least, of the Interglacial ages had a
climate warmer than that of modern times. Such great
changes of temperature led to repeated migrations of the
mammals, which were driven southward before the advancing
ice-sheets and returned again when the glaciers withdrew
under the influence of ameliorating climates. Any adequate
discussion of these complex conditions is quite out of the
question in this place and the facts must be stated in simplified
form, as dealing only with the times of lowered temperature
and encroaching glaciers.

The plants largely fail us here, for little is known of Glacial
vegetation, but, on the other hand, a great abundance of the
fossil remains of animal life of that date has been collected, and
its testimony is quite in harmony with that afforded by the
ice-markings and the ice-made deposits. Arctic shells in the
marine deposits of England, the valley of the Ottawa River
and of Lake Champlain, Walruses on the coast of New Jersey,
Reindeer in the south of France, and Caribou in southern New
England, Musk-oxen in Kentucky and Arkansas, are only a
few examples of the copious evidence that the climate of the
regions named in Glacial times was far colder than it is to-day.

I have thus endeavored to sketch, necessarily in very
meagre outlines, the nature of the methods employed to re-
construct the past history of the various continents and the
character of the evidence upon which we must depend. Should
the reader be unconvinced and remain sceptical as to the possi-
bility of any such reconstruction, he must be referred to the
numerous manuals of Geology, in which these methods are
set forth with a fulness which cannot be imitated within the
limits of a single chapter. The methods are sound, consisting
as they do merely in the application of " systematized common

28 LAND MAMMALS IN THE WESTERN HEMISPHERE

sense7 ' (in Huxley's phrase) to observed facts, but by no means
all applications of them are to be trusted. Not to mention
ill-considered and uncritical work, or inverted pyramids of
hypothesis balanced upon a tiny point of fact, it should be
borne in mind that such a complicated and difficult problem
as the reconstruction of past conditions can be solved only by
successive approximations to the truth, each one partial and
incomplete, but less so than the one which preceded it.

CHAPTER II

METHODS OF INVESTIGATION — PAI^EONTOLOGICAL

Palaeontology is the science of ancient life, animal and
vegetable, the Zoology and Botany of the past, and deals with
fossils. Fossils are the recognizable remains or traces of animals
or plants, which were buried in the rocks at the time of the
formation of those rocks. In a geological sense, the term rock
includes loose and uncompacted materials, such as sand and
gravel, as well as solid stone. Granting the possibility of so
determining the relative dates of formation of the rocks, that
the order of succession of the fossils in time may be ascertained
in general terms, the question remains : What use, other than
geological, can be made of the fossils? In dealing with this
question, attention will be directed almost exclusively to the
mammals, the group with which this book is concerned.

As a . preliminary to the discussion, something should be
said of the ways in which mammals became entombed in the
rocks in which we find them. In this connection it should be
remembered that, however firm and solid those rocks may be
now, they were originally layers of loose and uncompacted
material, deposited by wind or water, and that each layer
formed in its turn the surface of the earth, until buried by fresh
accumulations upon it, it may be to enormous depths.

One method of the entombing of land-mammals, which has
frequently been of great importance, is burial in volcanic dust
and so-called ash, which has been compacted into firm rock.
During a great volcanic eruption enormous quantities of such
finely divided material are ejected from the crater and are
spread out over the surrounding country, it may be for dis-

29

30 LAND MAMMALS IN THE WESTERN HEMISPHERE

tances of hundreds of miles. Thus will be buried the scattered
bones, skeletons, carcasses, that happen to be lying on the sur-
face ; and if the fine fragments are falling rapidly, many animals
will be buried alive and their skeletons preserved intact. A
modern instance of this is given by the numerous skeletons of
men and domestic animals buried in the volcanic ash which
overwhelmed Pompeii in 79 a.d. Pliny the Younger, who
witnessed that first recorded eruption of Vesuvius, tells us in
a letter written to Tacitus, that far away at Misenum, west of
Naples, it was often necessary to rise and shake off the falling
ashes, for fear of being buried in them. In the Santa Cruz
formation of Patagonia (see p. 124), which has yielded such a
wonderful number and variety of well-preserved fossils, the
bones are all found in volcanic dust and ash compacted into
a rock, which is usually quite soft, but may become locally-
very hard. The Bridger formation of Wyoming (p. 110) and
the John Day of eastern Oregon (p. 116) are principally made
up of volcanic deposits ; and no doubt there are several others
among the Tertiary stages which were formed in the same
way, but have not yet received the microscopic study necessary
to determine this.

Much information concerning the mammalian life of the
Pleistocene, more especially in Europe and in Brazil (p. 211),
has been derived from the exploration of caverns. Some of
these caves were the dens of carnivorous beasts and contain
multitudes of the bones of their victims, as well as those of
the destroyers themselves. Others, such as the Port Ken-
nedy Cave, on the Schuylkill River above Philadelphia, the
Frankstown Cave in central Pennsylvania, the Conard Fissure
in Arkansas, are hardly caverns in the ordinary sense of the
word, but rather narrow fissures, into which bones and car-
casses were washed by floods, or living animals fell from above
and died without being able to escape. The bones are mostly-
buried in the earth which partially or completely fills many
caverns and may be covered by a layer of stalagmite, derived

METHODS — PALiEONTOLOGICAL 31

from the solution and re-deposition of the limestone of the
cavern-walls, by the agency of percolating waters.

A mode of preservation which is unfortunately rare is ex-
emplified by the asphaltic deposits near Los Angeles, at Rancho
La Brea, which have been very fully described by Professor
J. C. Merriam of the University of California. The asphalt
has been formed by the oxidation and solidification of petro-
leum, which has risen up through the Pleistocene rocks
from the oil-bearing shales below. At one stage in the con-
version of petroleum into asphalt, tar-pools of extremely viscid
and adhesive character were, and still are, formed on the surface
of the ground ; and these pools were veritable traps for mam-
mals and birds and for the beasts and birds of prey which came
to devour the struggling victims.

"The manner in which tar or asphalt pools may catch un-
suspecting animals of all kinds is abundantly illustrated at
the present time in many places in California, but nowhere
more strikingly than at Rancho La Brea itself, where animals
of many kinds have frequently been so firmly entrapped that
they died before being discovered, or if found alive were extri-
cated only with the greatest difficulty. As seen at this locality,
the tar issuing from springs or seepages is an exceedingly
sticky, tenacious substance which is removed only with the
greatest difficulty from the body of any animal with which it
may come in contact. Small mammals, birds, or insects
running into the soft tar are very quickly rendered helpless by
the gummy mass, which binds their feet, and in their struggles
soon reaches every part of the body. Around the borders of
the pools the tar slowly hardens by the evaporation of the
lighter constituents until it becomes as solid as an asphalt pave-
ment. Between the hard and soft portions of the mass there
is a very indefinite boundary, the location of which can often
be determined only by experiment, and large mammals in many
cases run into very tenacious material in this intermediate
zone, from which they are unable to extricate themselves."

32 LAND MAMMALS IN THE WESTERN HEMISPHERE

The foregoing account refers to what may actually be
observed at the present time; in regard to the Pleistocene,
Professor Merriam says: "In the natural accumulation of
remains at the tar pools through accidental entangling of ani-
mals of all kinds, it is to be presumed that a relatively large
percentage of the individuals entombed would consist of young
animals with insufficient experience to keep them away from
the most dangerous places, or with insufficient strength to
extricate themselves. There would also be a relatively large
percentage of old, diseased, or maimed individuals that lacked
strength to escape when once entangled. In the census of
remains that have been obtained up to the present time the
percentages of quite young, diseased, maimed, and very old
individuals are certainly exceptionally large. ... In addi-
tion to the natural accumulation of animal remains through
the entangling of creatures of all kinds by accidental encoun-
tering of the tar, it is apparent from a study of the collections
obtained that some extraordinary influence must have brought
carnivorous animals of all kinds into contact with the asphalt
with relatively greater frequency than other kinds of animals.
In all the collections that have been examined the number
of carnivorous mammals and birds represented is much greater
than that of the other groups. . . . Whenever an animal of
any kind is caught in the tar, its struggles and cries naturally
attract the attention of carnivorous mammals and birds in
the immediate vicinity, and the trapped creature acts as a
most efficient lure to bring these predaceous animals into the
soft tar with it. It is not improbable that a single small bird
or mammal struggling in the tar might be the means of en-
trapping several carnivores, which in turn would naturally
serve to attract still others. ... In the first excavations
carried on by the University of California a bed of bones was
encountered in which the number of saber-tooth and wolf
skulls together averaged twenty per cubic yard." *

1 Memoirs of the University of California, Vol. I, pp. 209-211.

METHODS — PALiEONTOLOGICAL 33

As the animals were thus entombed alive, it would be ex-
pected that a large number of complete skeletons would be
preserved, but this is not the case: " connected skeletons are
not common." This scattering and mingling of the bones
were due partly to the trampling of the heavier animals in
their struggles to escape, but, in more important degree, to
the movements within the tar and asphalt.

In arid and semi-arid regions great quantities of sand and
dust are transported by the wind and deposited where the
winds fail, or where vegetation entangles and holds the dust.
Any bones, skeletons or carcasses which are lying on the
surface will thus be buried, and even living animals may be
suffocated and buried by the clouds of dust. An example of
such wind-made accumulations is the Sheridan formation
(Equus Beds, see p. 131), which covers vast areas of the Great
Plains from Nebraska to Mexico and contains innumerable
bones, especially of horses. In this formation in northwestern
Kansas, Professor Williston found nine skeletons of the large
peccary (\Platygonus hptorhinus) , lying huddled together, with
their heads all pointing in the same direction, and in the upper
Miocene (p. 121) of South Dakota Mr. Gidley discovered six
skeletons of three-toed horses tfNeohipparion whitneyi) crowded
together, killed and buried probably by a sandstorm. Similar
illustrations might be gathered from many other parts of the
world.

Swamps and bogs may, especially under certain conditions,
become the burial places of great numbers of animals, which
venture into them, become buried and are unable to extricate
themselves. Especially is this true in times of great drought,
when animals are not only crazed with thirst, but very much
weakened as well, and so unable to climb out of the clinging
mud. In an oft-quoted passage, Darwin gives a vivid
description of the effects of a long drought in Argentina be-
tween the years 1827 and 1830. " During this time so little

d f Extinct.

34 LAND MAMMALS IN THE WESTERN HEMISPHERE

rain fell, that the vegetation, even to the thistles, failed;
the brooks were dried up, and the whole country assumed the
appearance of a dusty high road." "I was informed by an
eyewitness that the cattle in herds of thousands rushed into
the Parana, and being exhausted by hunger they were unable
to crawl up the muddy banks, and thus were drowned. The
arm of the river which runs by San Pedro was so full of putrid
carcasses, that the master of a vessel told me that the smell
rendered it quite impassable. Without doubt several hundred
thousand animals thus perished in the river; their bodies
when putrid were seen floating down the stream ; and many in
all probability were deposited in the estuary of the Plata. All
the small rivers became highly saline, and this caused the death
of vast numbers in particular spots; for when an animal
drinks of such water it does not recover. Azara describes the
fury of the wild horses on a similar occasion, rushing into the
marshes, those which arrived first being overwhelmed and
crushed by those which followed. He adds that more than
once he has seen the carcasses of upwards of a thousand wild
horses thus destroyed. . . . Subsequently to the drought of
1827 to 1832, a very rainy season followed, which caused great
floods. Hence it is almost certain that some thousands of
the skeletons were buried by the deposits of the very next
year." *

In the arid and desolate regions of the interior of South
Australia is a series of immense dry lakes, which only occasionally
contain water and ordinarily "are shallow, mud-bottomed or
salt-encrusted claypans only." One of these, Lake Calla-
bonna, is of great interest as having preserved in its soft mud
many remains of ancient life, of creatures which were mired
in the clay and destroyed, as has been described by Dr. E. C.
Stirling. ' ' There is, however, compensation for the unpromis-
ing physical features of Lake Callabonna in the fact that its
bed proves to be a veritable necropolis of gigantic extinct

Voyage of a Naturalist, Amer. ed., pp. 133-134.

METHODS — PALiBONTOLOGICAL 35

marsupials and birds which have apparently died where they
lie, literally, in hundreds. The facts that the bones of in-
dividuals are often unbroken, close together, and, frequently,
in their proper relative positions, the attitude of many of
the bodies and the character of the matrix in which they are
embedded, negative any theory that they have been carried
thither by floods. The probability is, rather, that they met
their deaths by being entombed in the effort to reach food or
water, just as even now happens in dry seasons, to hundreds
of cattle which, exhausted by thirst and starvation, are unable
to extricate themselves from the boggy places that they have
entered in pursuit either of water or of the little green herbage
due to its presence. The accumulation of so many bodies
in one locality points to the fact of their assemblage around
one of the last remaining oases in the region of desiccation
which succeeded an antecedent condition of plenteous rains
and abundant waters.' '

It is a very general experience in collecting fossil mammals
to find that they are not evenly or uniformly distributed
through the beds, but rather occur in "pockets/' where great
numbers of individuals are crowded together, while between
the " pockets' f are long stretches of barren ground. It is
equally common to find the bones thickly distributed in cer-
tain layers, or beds, and the layers above and below entirely
wanting in fossils. The reasons for this mode of occurrence
have been partially explained in the foregoing paragraphs,
but the reason differs for each particular mode of entombment.
The important part played by drought in causing such ac-
cumulation of closely crowded bodies in swamps and mud-
holes is indicated in the quotations from Darwin and Stirling ;
but similar accumulations may take place on hard ground,
as was observed in central Africa by Gregory. "Here and
there around a water hole we found acres of ground white
with the bones of rhinoceroses and zebra, gazelle and ante-
lope, jackal and hyena. . . . These animals had crowded

36 LAND MAMMALS IN THE WESTERN HEMISPHERE

around the dwindling pools and fought for the last drops of
water/ ' l Even in normal seasons springs and water holes
and the drinking places in streams are the lurking places
of beasts of prey and crocodiles, so that great accumula-
tions of bones are made around these spots. A succession
of unusually severe winters frequently leads to great
mortality among mammals, as happened in Patagonia in
the winter of 1899, when enormous numbers of Guanaco
perished of starvation on the shore of Lake Argentine,
where they came to drink.

Bones which are exposed on the surface of the ground
decay and crumble to pieces in the course of a very few years ;
and if they are to be preserved as fossils, it is necessary that
they should be buried under sedimentary or volcanic deposits.
Several such modes of burial have been described in the fore-
going paragraphs, but there are other and equally important
methods, which remain to be considered.

The deposits made by rivers are often extremely rich in
fossils, and most of the Tertiary formations of the Great Plains
are now ascribed to the agency of rivers. The flood-plain of
a stream, or that part of its basin which is periodically over-
flowed, is gradually built up by the layers of clay and silt
thrown down by the relatively still waters of the flooded
area, and scattered bones, skeletons or carcasses that may have
been lying on the ground before the freshet are buried in the
deposits. Bones covered up in this manner frequently show
the marks of teeth of rodents or carnivores which have gnawed
them when lying exposed. Deposits made in the stream-
channels, where the current was swiftest, are of coarser materials
such as gravel and sand, and these often contain the skeletons
of animals which were drowned and swept downward by the
flooded stream. When the Bison (the mistakenly so-called
Buffalo) still roamed in countless herds over the western plains,
immense numbers of them were drowned in the upper Missouri

1 J. W. Gregory, The Great Rift Valley, p. 268.

METHODS — PALiEONTOLOGICAL 37

River by breaking through the ice, when they attempted to
cross at times when the ice had not attained its winter thickness,
or was weakened by melting in the spring. No doubt, the bed
of that river contains innumerable bones of the Bison. Fre-
quently, too, animals are caught in quicksands and, unable
to escape, are buried in the soft mass ; fossil skeletons which
are preserved in sandstones in an erect or standing position
are usually to be interpreted in this manner.

The sedimentary accumulations formed in lakes and ponds
sometimes yield fossil bones or skeletons in considerable
numbers, which have, for the most part, been derived from the
carcasses of animals carried into the lake by streams. A newly
drowned mammal sinks to the bottom and, if sufficient sediment
be quickly deposited upon it, it may be anchored there and
fossilized as a complete skeleton. Otherwise, when distended by
the gases of putrefaction, the body will rise and float on the
surface, where it will be attacked and pulled about by croco-
diles, fishes and other predaceous creatures. As the bones
are loosened in the course of decomposition, they will drop
to the bottom and be scattered, now here, now there, over a wide
area.

Land mammals are rarely found in marine rocks, or such
deposits as were made on the sea-bottom; but the remains
of marine mammals, whales, porpoises, dolphins, seals, etc.
are often found in large numbers. In principle, the method
of entombment is the same as in the case of lakes, but currents
may drift to some bay or cove multitudes of carcasses of these
marine mammals. At Antwerp, in Belgium, incredible quanti-
ties of such remains have been exposed in excavations and in
all probability were drifted by currents into a quiet and shal-
low bay, which was subsequently converted into land.

While the foregoing account by no means exhausts the
various methods of accumulation and burial of the skeletons
and scattered bones of mammals, it covers the more important
of these methods sufficiently for a general understanding of

38 LAND MAMMALS IN THE WESTERN HEMISPHERE

the different processes. In whatever manner the preservation
may have been effected, there is great difference in the rel-
ative abundance and completeness among the fossils of the
various kinds of mammals which were living at the same time
and in the same area. It need hardly be said, that the more
abundant any species was, the better was the chance of its
being represented among the fossils ; hence, gregarious species,
living in large herds, were more likely to be preserved than
those which led a solitary existence, or were individually rare.
Most of the hoofed mammals are and apparently always have
been gregarious, and are therefore much better represented
among the fossils, and are, in consequence, better known than
the beasts of prey, which, of necessity, were individually less
numerous and generally solitary in habits. Not only this,
but large and medium-sized mammals, with strong and heavy
bones, were better fitted to withstand the accidents of entomb-
ment and subsequent preservation than small creatures with
delicate and fragile skeletons. The mere dead weight of over-
lying sediments often crushes and distorts the bones, and the
movements of uplift, compression, folding and fracture, to which
so many strata have been subjected, did still further damage
to the fossils. The percolating waters, which for ages have
traversed the porous rocks, often attack and dissolve the bones,
completely destroying the minute ones and greatly injuring
those which are massive and strong. In consequence of all
those accidents it frequently happens that only the teeth,
the hardest and most resistant of animal structures, and it
may be the dense and solid jaw-bones, are all that remain
to testify of the former existence of some creature that long
ago yanished from the earth. Very many fossil mammals are
known exclusively from the teeth, and it is this fact which makes
the exact study of teeth so peculiarly important to the palae-
ontologist.

In view of all these facts, it is not surprising that con-
cerning the history of many mammalian groups we have but

METHODS — PALiBONTOLOGICAL 39

scanty information, or none at all, while in the case of others
the story is wonderfully full and detailed. The latter are,
very generally, the groups which were not only numerically
abundant at all stages of their history, but also had skeletons
that were strong enough to resist destruction; while the
groups as to which there is little or no information are chiefly
of small and fragile animals, or such as were always rare.
For example, a great deal has been learned regarding the de-
velopment of horses and rhinoceroses in North America, but
the history of the tapirs is very unsatisfactorily known, be-
cause, while horses and rhinoceroses were common, tapirs
were solitary and rare. In Europe bats have been found in
the Eocene, Oligocene and Miocene, and there is no reason
to suppose that they were not equally ancient and equally
abundant in America ; but none have been found in the western
hemisphere in any formation older than the Pleistocene. All
things considered, the extraordinary fact is, not that so many
forms have irretrievably perished, but that so much has been
preserved, escaping all the chances of destruction.

As to the degree of preservation in fossil mammals, we have
to do almost entirely with bones and teeth. With very rare
exceptions, and those all of late geological date, the viscera,
muscles, skin, hair, horns, hoofs and claws have been com-
pletely destroyed and have vanished without leaving a trace.
In northern Siberia the gravel soil is permanently frozen to
a depth of several hundred feet and contains the intact carcasses
of elephants and rhinoceroses of Pleistocene date and notably
different from any species of these animals now in existence.
Sometimes such a carcass is disinterred from a bluff by the
cutting action of a stream and is in a state of nearly complete
preservation, with hide, hair and flesh almost as in an animal
freshly killed. From these remains it has been learned that
the fMammoth was an elephant densely covered with hair and
wool, just as he was depicted in the carvings and cave-paintings

t Extinct.

40 LAND MAMMALS IN THE WESTERN HEMISPHERE

of Pleistocene Man in Europe, where fMammoth bones have
been abundantly found, and also that there were Siberian
rhinoceroses similarly protected against the cold. fMammoth
remains with hide and flesh, but much less complete, have like-
wise been found in Alaska.

In a cavern in southern Patagonia an expedition from the
La Plata Museum discovered, with the remains of a gigantic,
extinct fground-sloth, large pieces of the skin still covered
with hair and affording most welcome information as to the
colouration of these most curious animals. The skin had been
preserved from decay by deep burial in dry dust. Mummies
of Pleistocene rodents have been found in the dry caves of
Portugal, whereas in the ordinary caves which are damp or
wet, only bones are preserved. x ^>tely, as has been

said, such instances of complete ^ . are very rare, and

none are known of mammals more cz ' * than those of the
Pleistocene epoch.

In general, it may be said th* ^au 0. jv the geological
antiquity of a skeleton is, the greater is the chemical alteration
which it has undergone. Bones of Pleistocene or later date
have, as a rule, suffered little change beyond the loss of more
or less of their animal matter, the amount of such loss depending
chiefly upon exposure to the air. Bones which, for thousands
or tens of thousands of years, have been buried in dense cave-
earth, in an antiseptic peat-bog, or in asphalt, are often per-
fectly sound and fresh when taken up. Skeletons of the ante-
cedent (Tertiary) period are, on the other hand, very frequently
petrified; that is to say, the original substance of the bones
has been completely removed and replaced by some stony
material, most commonly lime or flint. This substitution took
place very gradually, molecule by molecule, so that not only
is the form of the bone or tooth most accurately reproduced,
but the internal, microscopic structure is perfectly retained
and may be studied to as great advantage as in the case of
modern animals.

t Extinct.

METHODS — PALiEONTOLOGICAL 41

While, save in the rarest instances, only the hard parts of
fossil mammals remain to testify of their structure, very im-
portant information as to the size, form and external character
of the brain may be secured from " brain-casts/ ' which may
be natural or artificial. The pressure of the mud, sand or
other material, in which the fossil was embedded, filled up all
openings in the skeleton and, as the brain decayed and dis-
appeared, its place was taken by this material, which subse-
quently hardened and solidified and quite accurately reproduces
the external form and character of the brain. When a fossil
skull is exposed and shattered by weathering, the natural
brain-cast often remains intact, and a great many such speci-
mens are in the collections. An artificial cast is made by saw-
ing open the crr rty, cleaning out the stony matrix
which fills it ami. Ling liquid gelatine or plaster of
Paris into the cfr u These artificial casts are often quite
as satisfactory p -mal ones.

As has beeu'oiiorftt "a^o^e, the history of the mammals is
recorded, save in a very few instances, in terms of bones and
teeth and, to the uninitiated, it might well seem that little
could be accomplished with such materials. However, it is
the task, and the perfectly feasible task, of palaeontology to
make these dry bones live. It is a current and exceedingly
mischievous notion that the palaeontologist can reconstruct
a vanished animal from a single bone or tooth and, in spite of
repeated slayings, this delusion still flourishes and meets one
in modern literature at every turn. No doubt, much of the
scepticism with which attempts to restore extinct animals
are met by many intelligent people is traceable to the wide-
spread belief that such off-hand and easy-going methods
are used in the work. So far from being able to make a trust-
worthy reconstruction from a few scattered bones, competent
palaeontologists have been sometimes led completely astray
in associating the separated parts of the same skeleton. More
than once it has happened that the dissociated skull and feet

42 LAND MAMMALS IN THE WESTERN HEMISPHERE

of one and the same animal have been assigned to entirely
different groups, just because no one could have ventured, in
advance of experience, to suppose that such a skull and teeth
could belong to a creature with such feet. In all these cases
(and they are few) the error has been finally corrected by
the discovery of the skeleton with all its essential parts in
their natural connection.

While the number of complete skeletons of Tertiary mam-
mals as yet collected is comparatively small, it is often possible
to construct a nearly complete specimen from several imperfect
ones, all of which can be positively shown to belong to the same
species. Such composite skeletons are almost as useful as
those in which all the parts pertain to a single individual,
though in making the drawings it is not easy to avoid slight
errors of proportion. It must not be supposed that no success-
ful restoration of missing bones is practicable ; on the contrary,
this can often be done very easily, but only when all the essential
parts of the skeleton are known.

Even if an unlimited number of perfect skeletons were
available, of what use would they be? A skeleton is a very
different looking object from a living animal, and how is it
possible to infer the latter from the former? Do the many
restorations of extinct mammals which this book owes to the
skill of Mr. Horsfall and Mr. Knight deserve any other con-
sideration than that due to pleasing, graceful or grotesque
fancies, with no foundation of solid fact? To answer these
questions, it is necessary first to consider the relations of the
bony structure to the entire organism and then to discuss the
principles in accordance with which the restorations have been
made.

The skeleton is far from being merely the mechanical frame-
work of the animal. Such a frame-work it is, of course, but
it is much more than that ; it is the living and growing expres-
sion of the entire organism and is modified, not only by age,
but by the conditions of the environment and accidental cir-

METHODS — PALiEONTOLOGICAL 43

cumstances as well. The bones of the same individual differ
very materially in early youth, maturity and old age ; so long
as the animal lives, its bones are perpetually changing, slowly
it is true, but with ready response to needs. Not only that,
but dislocated bones may and frequently do develop entirely
new joints, and their internal structure is remodelled to meet
the requirements of stresses differing in character or direction
from those of normal, uninjured bones. The general form
and proportions of any mammal are determined chiefly by
its muscular system and this may be directly and confidently
inferred from its skeleton, for the muscles which are of im-
portance in this connection are attached to the bones and leave
their indelible and unmistakable mark upon them. In any
good text-book of anatomy this extremely intimate relation
of bone and muscle is made clear ; and it is shown how each
attachment of muscle, tendon and ligament is plainly indicated
by rough lines, ridges, projections or depressions, which speak
a language intelligible enough to those who have learned to
interpret it. Given the skeleton, it is no very difficult
task to reconstruct the muscular system in sufficient detail.
Further, the teeth afford valuable information as to the food,
habits and appearance of the animal, for the bulk of the viscera,
a significant element in the general form, is principally con-
ditioned by the character of the diet.

Beasts of prey, which live by catching and devouring other
animals, have a certain likeness to one another, even though
they are in no wise related, except as all mammals are. The
Thylacine, or so-called "Tasmanian Wolf" (Thylacynus
cynocephalus) , a marsupial and related to the opossums, is
deceptively like the true wolves in appearance, although be-
longing to an order (Marsupialia) almost as widely separated
from that to which the wolves belong (Carnivora) as two
mammalian groups well can be. This resemblance is as clearly
indicated by the skeletons as by the living animals themselves,
though the fundamental differences of structure which dis-

44 LAND MAMMALS IN THE WESTERN HEMISPHERE

tinguish the marsupial from the carnivore are no less clearly-
displayed. Large herbivorous mammals too, though referable to
very different orders, bear a strong resemblance to one another,
the characteristic differences, so far as the living animal is
concerned, appearing chiefly in the head. It was this general
likeness that induced Cuvier to form his order, "Pachyder-
mata," which comprised elephants, rhinoceroses, hippopota-
muses, tapirs, etc., animals that are now distributed into no
less than three separate orders; aside from the head, all of
these forms are quite distinctly similar in appearance.

Of course, the external features, such as ears, tail, skin and
hair, are most important factors in the general make-up of
any mammal; and, as to these matters, the fossils leave us
largely in the lurch, save in the all too rare cases, like the Si-
berian fMammoth, in which these external features are actually-
preserved. Two artists may so restore the same animal as
to result in two very different pictures, and no one can posi-
tively decide between them; just as two modern mammals,
which are closely related and have very similar skeletons, may
yet differ markedly in outward appearance, because of the
different character of the skin, as do, for example, the Bornean
and Indian rhinoceroses. Yet even in dealing with purely-
external features, we are not left altogether to conjecture.
Ears of unusual size or form frequently leave some indication
of this on the skull, and the presence or absence of a proboscis
can nearly always be inferred with confidence from the char-
acter of the bones of the nose and muzzle. The length and
thickness of the tail may be generally directly deduced from
the caudal vertebrae, but whether it was close-haired and
cylindrical, or bushy, or tufted at the end, or flat and trowel-
shaped, as in the Beaver, is not determinable from the bones
alone.

Most uncertain of all the characters which determine;
outward appearance are the hair and the pattern of colouration ;
the Horse and Zebra differ much more decidedly in the living

METHODS — PAUEONTOLOGICAL 45

form than their skeletons would lead one to expect, as do also
the Lion, the Tiger and the Leopard. The curious and ex-
ceptional colour-pattern of the Okapi, that remarkable giraffe-
like animal but lately discovered in the equatorial forests of
western Africa, could never have been inferred from a study
of the skeleton alone. However, even in the problem of colour-
patterns there is more to go upon than sheer guess-work, for
certain definite principles of animal colouration have been
ascertained ; the great difficulty lies in the application of these
principles to a particular case. It is quite certain that the
naked, hairless skin is never primitive, but always a compara-
tively late acquisition and, in many mammalian orders, is
not found at all. Aside from a few domesticated animals,
this type of skin occurs only in very large herbivorous mammals
living in warm climates, such as elephants, rhinoceroses and
hippopotamuses, in a few burrowers, and in marine mammals,
like the walruses, whales, porpoises, etc. Useful hints as to the
colouring of ancient and extinct forms may be gathered from

46

LAND MAMMALS IN THE WESTERN HEMISPHERE

a study of series of living animals, such as lizards and butter-
flies, in which the development of a definite scheme of coloura-
tion may be followed step by step. Young animals very fre-
quently retain more or less distinct traces of the ancestral
colouration, which disappear in the adult, for the develop-
ment of the individual is, in some respects at least, an abbre-
viated and condensed recapitulation of the history of the species.
In many mammals which, in the adult condition, have a solid
body-colour, the young are striped or spotted, a strong indi-
cation that these mammals were derived from striped or spotted
ancestors. Thus, the Wild Boar has a uniform body-colour
in the full-grown stage, but the pigs are longitudinally striped ;
many deer are spotted throughout life, as in the Fallow Deer,
the Axis Deer of India and others, but the great majority of
the species, including all the American forms, have uniform
colouration, while the fawns are always spotted. Lion cubs

are also spotted and the adults have a uniform tawny colour,
and many such examples might be given.

The study of colouration among existing animals has led
to the conclusion that in mammals the primitive colour-

- PALuBONTOLOGICAL

47

pattern was that of stripes, either longitudinal or transverse
and more probably the former. In the second stage these
bands break up into spots, which still show the longitudinal
arrangement and may be either light on a dark ground, or
dark on a light ground. In a third stage the spots may again
coalesce into stripes, the course of which is at right angles to
that of the original stripes, or the spots may disappear, leaving
a uniform body-colour, lighter or white on the belly. These
changes of colour-pattern have not proceeded at a uniform
rate in the various mammalian groups, or even within the same
group, for an all-important factor is the mode of life of the
particular animal. In general, it may be said that the scheme
of colour is such as to render
its possessor inconspicuous, or
even invisible, and many a
creature that seems to be very
conspicuous and striking in a
museum case can hardly be
seen at all when in its natu-
ral surroundings. Thus, Arctic
mammals and birds, in their
winter dress, are white ; desert
animals are tawny or sandy-
brown ; forest animals are frequently striped or spotted ; while
those that live on open plains are more commonly of uniform
colouration. There are exceptions to these rules, but they
hold good for the most part. From careful comparative study
of the teeth and skeletons a clew may be gained as to the
habits of animals and from the habits something may be
inferred as to the colouration.

It would, however, be misleading to claim a greater au-
thority for these attempts at restoring a long-vanished life
than can fairly be ascribed to them. The general form and
proportions of the head, neck, body, tail, limbs and feet may be
deduced with a high degree of accuracy from the skeleton,

Fio. 6. — Tajrirw terratrit, 3 days old.
Compare with Fin. 137. p. 320. (By
permission of W. S. Berridge, London.)

48 LAND MAMMALS IN THE WESTERN HEMISPHERE

while the external characters of skin, hair and colouration are
largely conjectural, but not altogether imaginary. It cannot
be doubted that among the extinct mammals were many which,
owing to some uncommon growth of subcutaneous fat, or some
unusual local development of hair, were much more curious and
bizarre in appearance than we can venture to represent them.
If, for example, the Camel, the Horse, the Lion and the Right
Whale were extinct and known only from their skeletons,
such restorations as we could make of them would assuredly
go astray in some particulars. The Camel would be pictured
without his hump, for there is nothing in the skeleton to suggest
it ; the forelock, mane and characteristic tail of the Horse and
the Lion's mane would certainly not be recognized ; while the
immense development of blubber in the head of the Whale
gives to it a very different appearance from that which the
skull would seem to indicate. Such cases are, however, ex-
ceptional and restorations made by competent hands from
complete skeletons probably give a fair notion of the appearance
of those animals when alive.

It will thus be sufficiently plain that the work of restora-
tion is beset with difficulties, but that there is no good ground
for the uncritical scepticism which summarily rejects the re-
sults as being purely fanciful, or for the equally uncritical
credulity which unhesitatingly accepts them as fully and inT
contestably accurate. It is altogether likely that one of the
main sources of error consists in making the extinct animal
too closely resemble some existing species which is selected as
a model.

Too much space has perhaps been devoted to the problem
of restoring the external form of these extinct mammals,
a problem which, after all, is of distinctly subordinate impor-
tance. The most valuable results which may be gained
from a study of these fossil mammals are the answers which
they afford to the great questions of relationship, classification
and genetic descent, and the light which they throw upon the

METHODS — PALiEONTOLOGICAL 49

processes of evolution and the course of geographical arrange-
ment. The bones and teeth afford admirable means of tracing
the gradual steps of modification by which the modern
mammals have arisen from very different ancestors and of
following their wanderings from region to region and continent
to continent. It is to these questions that most of the subse-
quent chapters are devoted.

CHAPTER III

THE CLASSIFICATION OF THE MAMMALIA

The terminology and nomenclature of science form a great
barrier, which only too often shuts out the educated layman
from following the course of investigation and keeping abreast
of the discoveries in which he may be particularly interested.
No more frequent and heartfelt complaint is uttered than that
which decries the " scientific jargon, " and one might be tempted
to think that this jargon was a superfluous nuisance, delib-
erately adopted to exclude the uninitiated and guard the
secrets of the temple from the curious intruder. As a matter
of fact, however, this terminology, though an unquestionable
evil from one point of view, is an indispensable implement of
investigation and description. Ordinary language has far
too few words for the purpose and most of the words that
might be used lack the all-important quality of precision.
The vernacular names of animals and plants are notoriously
inexact and, even when not inaccurately employed, are not
sufficiently refined and destinctive for scientific use. This
is pre-eminently true of the New World, where the European
settlers gave the names of the creatures with which they had
been familiar at home to the new animals which they found in
the western hemisphere. Some of these names, such as deer,
wolf, fox, bear, are accurate enough for ordinary purposes,
while others are ludicrously wrong. The bird that we call the
Robin is altogether different from his European namesake, and
the great stag, or Wapiti, is commonly called "Elk," a name
which properly belongs to the Moose. In short, it is impossible
to gain the necessary accuracy and abundance of vocabulary

50

CLASSIFICATION OF THE MAMMALIA 51

without devising an artificial terminology, drawn chiefly from
Greek and Latin.

In dealing with fossils, the difficulty of nomenclature be-
comes formidable indeed. The larger and more conspicuous
mammals of the modern world are more or less familiar to all
educated people, and such names as rhinoceros, hippopotamus,
elephant, kangaroo, will call up a definite and fairly accurate
image of the animal in question. For the strange creatures
that vanished from the earth ages before the appearance of
Man there are no vernacular names and it serves no good pur-
pose to coin such terms. To the layman names like Uinta-
therium or Smilodon convey no idea whatever, and all that can
be done is to attempt to give them a meaning by illustration
and description, using the name merely as a peg upon which
to hang the description.

The system of zoological classification which is still in use
was largely the invention of the Swedish naturalist Linnaeus,
who published it shortly after the middle of the eighteenth
century. As devised by Linnseus, the scheme was intended
to express ideal relationships, whereas now it is employed to
express real genetic affinities, so far as these can be ascertained.
The Linnsean system is an organized hierarchy of groups,
arranged in ascending order of comprehensiveness. In this
scheme, what may be regarded as the unit is the speciesy a
concept around which many battles have been waged and
concerning which there is still much difference of opinion and
usage. Originally a term in logic, it first received a definite
meaning in Zoology and Botany from John Ray (1628-1705)
who applied it to indicate a group of animals, or plants, with
marked common characters and freely interbreeding. Linnaeus,
though not always consistent in his expressions on the subject,
regarded species as objective realities, concrete and actual
things, which it was the naturalist's business to discover and
name, and held that they were fixed entities which had been
separately created. This belief in the fixity and objective

52 LAND MAMMALS IN THE WESTERN HEMISPHERE

reality of species was almost universally held, until the publica-
tion of Darwin's " Origin of Species" (1859) converted the
biological world to the evolutionary faith, which declares that
the only objective reality among living things is the individual
animal or plant.

According to this modern conception, a species may be
defined as signifying a " grade or rank assigned by systematists
to an assemblage of organic forms which they judge to be more
closely interrelated by common descent than they are related to
forms judged to be outside the species " (P. Chalmers Mitchell).
The technical name of a species, which is either in Latin, or in
latinized form, is in two words, one of which designates the
genus (see below) and the other the particular species of that
genus, as, for example, Equus caballns, the species Horse, E.
przewalskii, the Asiatic Wild Horse, E. asinus, the species
Ass, etc. In order to identify a species, the genus to which
it belongs must be stated, hence the term, binomial system
of nomenclature, which Linnaeus introduced, becoming tri-
nomial when the name of a subspecies is added, a modern re-
finement on the older method. A very large species {i.e.
one which is represented by great numbers of individuals),
extending over a very large area, is often divisible into groups
of minor rank, as varieties} geographical races or subspecies.
Taking the species as the unit in the scheme of classification,
the varieties and subspecies may be considered as fractions.

There is great difference of usage among writers on sys-
tematic zoology in the manner of applying the generally ac-
cepted concept of species, some making their groups very much
more comprehensive than others, according as they are
" lumpers" or "splitters," to employ the slang phrase. The
difficulty lies in the fact that there are no fixed and definite
criteria, by which a given series of individuals can be surely
distinguished as a variety, a species or a genus ; it is a matter
for the judgment and experience of the systematist himself.
The individuals of a species may differ quite widely among

CLASSIFICATION OF THE MAMMALIA 53

themselves, provided that they are all connected by inter-
gradations, and the more or less constant varieties or sub-
species are to be distinguished from the individual variants,
which are inconstant and fluctuating. No two specimens
agree exactly in every particular, but if a very large suite of
them be compared, it will be found that the great majority
depart but little from the average or norm of the species, and
the wider the departure from the norm, the fewer the indi-
viduals which are so aberrant. Taking so easily measured a
character as size, for example, and measuring several hundred
or a thousand representatives of some species, we see that a
large majority are of average size, a little more or a little less,
while very large or very small individuals are rare in propor-
tion to the amount by which they exceed or fall short of the
norm. Subspecies or varieties are marked by differences
which are relatively constant, but not of sufficient importance
to entitle them to rank as species.

A group of the second rank is called a genus, which may
contain few or many species, or only a single one. In the latter
case the species is so isolated in character that it cannot prop-
erly be included in the same genus with any other species.
A large genus, one containing numerous species, is frequently
divisible into several subgenera, each comprising a group of
species which are more similar to one another than they are
to the other species of the genus.

The third of the main groups in ascending order is the
family, which ordinarily consists of a number of genera united
by the possession of certain common characters, which, at
the same time, distinguish them from other genera, though
a single isolated genus may require a separate family for its
reception. Just as it is often convenient to divide a genus
into subgenera, so families containing many genera are usually
divisible into subfamilies, as indicative of closer relationships
within the family. The name of the family is formed from
that of the genus first described or best known, with the

54 LAND MAMMALS IN THE WESTERN HEMISPHERE

termination -idee, while that for the subfamily is -ince. To
take an example, all the genera of cats, living and extinct, are
assembled in the family Felidae (from the genus Felis) which
falls naturally into two subfamilies. One of these, the Felinae,
includes the true cats, a very homogeneous group, both the
existing and the extinct genera ; the other subfamily, that of
the highly interesting series of the " Sabre-tooth Tigers,"
called the tMachairodontinra, comprises only extinct forms.

The fourth principal rank or grade is the order, distin-
guished by some fundamental peculiarity of structure and
usually including a large number of families. Some of the
orders, however, contain but a single family, a single genus,
or even, it may be, a single species, because that species is in
important structural characters so unlike any other that it
cannot properly be put into the same order with anything else.
Such isolation invariably implies that the species or genus in
question is the sole survivor of what was once an extensive
series. As in the case of the family and the genus, it is often
necessary to recognize the degrees of closer and more remote
affinity by the use of suborders. Existing Artiodactyla, or
even-toed hoofed animals, an enormous assemblage, may con-
veniently be divided into four suborders : (1) Suina, swine and
the Hippopotamus; (2) Tylopoda, the Camel and Llama;
(3) Tragulina, " mouse-deer/7 or chevrotains; (4) Pecora, or
true ruminants, deer, giraffes, antelopes, sheep, goats, oxen,
etc. In nearly all of the orders such subordinal divisions are
desirable and it is frequently useful to employ still further
subdivisions, like superfamilies, which are groups of allied
families within the suborder, sections and the like.

In the Linnsean scheme, the next group in ascending rank
is the class, which includes all mammals whatsoever, but the
advance of knowledge has made it necessary to interpolate
several intermediate grades between the class and the order,
which, in the descending scale, are subclass, infraclass, cohort,

t Extinct.

CLASSIFICATION OF THE MAMMALIA 55

superorder and others, while above the class comes the sub-
kingdom of Vertebrata, or animals with internal skeletons,
which includes mammals, birds, reptiles, amphibians and
fishes.

A word should be said as to the conventions of printing
technical names. The names of all species are, in American
practice, printed in small letters, but. many Europeans write
specific terms which are proper nouns or adjectives with a
capital. Generic, family and all groups of higher rank are
always written with a capital, unless used in vernacular form,
e.g. Artiodactyla and artiodactyls. It is also a very general
custom to give capitals to vernacular names of species, as the
Mammoth, the Coyote, the Black Bear. Genus and species
are almost invariably in italics, groups of higher rank in roman.

Such a scheme of classification as is outlined above has a
decidedly artificial air about it and yet it serves a highly use-
ful purpose in enabling us to express in brief and condensed
form what is known or surmised as to the mutual relationships
of the great and diversified assemblage of mammals. The
scheme has been compared to the organization of an army into
company, battalion, regiment, brigade, division, army corps,
etc., and there is a certain obvious likeness ; but the differences
go deeper, for an army is an assemblage of similar units,
mechanically grouped into bodies of equal size. A much closer
analogy is the genealogical or family tree, which graphically
expresses the relationships and ramifications of an ancient and
wide-spread family, though even this analogy may easily be
pushed too far. Blood-relationship is, in short, the under-
lying principle of all schemes of classification which postulate
the theory of evolution.

The system of Linnaeus, as expanded and improved by
modern zoologists, has proved itself to be admirably adapted
to the study of the living world ; but it is much more difficult
to apply it to the fossils, for they introduce a third dimension,
so to speak, for which the system was not designed. This

56 LAND MAMMALS IN THE WESTERN HEMISPHERE

third dimension is the successive modification in time of a
genetically connected series. The cumulative effect of such
modifications is so great that only very elastic definitions
will include the earlier and later members of an unbroken series.
In attempting to apply the Linnaean system to the successive
faunas {i.e. assemblages of animals) which have inhabited the
earth, palaeontologists have employed various devices. One
such method is to classify each fauna without reference to
those which precede and follow it, but this has the great draw-
back of obscuring and ignoring the relationships, to express
which is the very object of classification. Another and more
logical method is to treat species and genera as though they
belonged to the present order of things, for these groups,
particularly species, were relatively short-lived, when regarded
from the standpoint of geological time, and either became so
modified as to require recognition as new species and genera, or
died out without leaving descendants. Groups of higher rank,
families, orders, etc., are treated as genetic series and include
the principal line or stock and such side-branched as did not
ramify too widely or depart too far from the main stem. Under
the first arrangement, the horses, a long history of which has
been deciphered, would be divided into several families ; under
the second, they are all included in a single family.

One of the most interesting results of palaeontological
study is the discovery that in many families, such as the horses,
rhinoceroses and camels, there are distinct series which in-
dependently passed through parallel courses of development,
the series of each family keeping a remarkably even pace in
the degree of progressive modification. Such a minor genetic
series within a family is called a phylum, not a very happy
selection, for the same term had been previously employed
in a much wider sense, as equivalent to the subkingdom. In
both uses of the term the underlying principle, that of genetic
series, is the same ; the difference is in the comprehensiveness
of meaning.

CLASSIFICATION OF THE MAMMALIA 57

It must be admitted that no method, yet devised, of apply-
ing the Linnsean scheme to the fossils is altogether satisfactory,
and indeed it is only the breaks and gaps in the palseontological
record which makes possible any use of the scheme. Could
we obtain approximately complete series of all the animals
that have ever lived upon the earth, it would be necessary to
invent some entirely new scheme of classification in order to
express their mutual relationships.

In the present state of knowledge, classification can be made
only in a preliminary and tentative sort of way and no doubt
differs widely from that which will eventually be reached.
So far as the mammals are concerned, part of the problem would
seem to be quite easy and part altogether uncertain. Some
mammalian groups appear to be well defined and entirely
natural assemblages of related forms, while others are plainly
heterogeneous and artificial, yet there is no better way of
dealing with them until their history has been ascertained.
The mutual relations of the grand groups, or orders, are still
very largely obscure.

The class Mammalia is first of all divided into two sub-
classes of very unequal size. Of these, the first, PROTO-
THERIA, is represented in the modern world by few forms,
the so-called Duck-billed Mole {Ornithorhynchus paradoxus)
and Spiny Anteaters {Echidna) of Australia. They are
the lowest and most primitive of the mammals and retain
several structural characters of the lower vertebrates. Their
most striking characteristic is that the young are not brought
forth alive, but are hatched from eggs, as in the reptiles, birds
and lower vertebrates generally.

The second subclass, EUTHERIA, which includes all
other mammals, is again divided into two very unequal groups
or infraclasses. One of these, Didelphia, contains but a single
order, the Marsupialia, or pouched mammals, now in existence,
and is also very primitive in many respects, though far more
advanced than the Prototheria. The young, though born alive,

58 LAND MAMMALS IN THE WESTERN HEMISPHERE

are brought forth in a very immature state and, with the excep-
tion of one genus (Perameles) the foetus is not attached by
a special structure, the placenta, to the womb of the mother.
Like the Prototheria, the Marsupials, which were once spread
all over the world, are at present almost entirely confined to
Australia and the adjoining islands, the Opossums of North
and South America, and one small genus (Ccenolestes) in the
latter continent being the exceptions to this rule of distribution.
The second and vastly larger infraclass, the Monodelphia,
is characterized by the placenta, a special growth, partly
of foetal and partly of maternal origin, by means of which the
unborn young are attached to the mother and nourished during
the foetal period ; they are born in a relatively mature state
and are generally able to walk immediately after birth and
resemble their parents in nearly all respects.

The vast assemblage of placental mammals, which range
over all the continents, are divided into numerous orders, most
of which appear to be natural groups of truly related forms,
while some are but doubtfully so and others again are clearly
unnatural and arbitrary. As has already been pointed out,
the mutual relationships of these orders, as expressed in
groups of higher than ordinal rank, offer a much more difficult
problem, chiefly because our knowledge of the history of mam-
mals is most deficient just where that history is most important
and significant, namely, in its earlier portion. In many in-
stances, the evolution of genera and families may be followed
out within the limits of the order in a very convincing way,
but very rarely can the origin of an order be demonstrated.
When the history began to be full and detailed,the orders had
nearly all been established, and, until the steps of their diver-
gence and differentiation can be followed out, their mutual
relationships can be discussed only from the standpoint of
their likenesses and differences. In the valuation of these, there
' is much room for difference of opinion, and such difference
is not lacking. On the other hand, concerning the number

CLASSIFICATION OF THE MAMMALIA 59

and limits of the orders themselves there is very general
agreement.

In the following table only the major groups are included
and those which are extinct are marked with a dagger (f).
The scheme is almost identical with that given in Professor
Osborn's "Age of Mammals/' the few points in which I should
prefer a somewhat different arrangement being waived in the
interests of uniformity and avoidance of confusion. A few
changes are, however, made in matters which I regard as too
important to ignore.

I. Subclass PROTOTHERIA. Egg-laying Mammals.

1. Order fPROTODONTA.

2. Order MO NOTRE MAT A, e.g. the Duck-billed Mole and Spiny

Anteaters.
II. Subclass EUTHERIA. Viviparous Mammals.

A. Infraclass DIDELPHIA. Pouched Mammals.

1. Order t TRICONODONTA.

2. Order MARSUPIALIA.

a. Suborder Polyprotodonta. Opossums, carnivorous and

insectivorous Marsupials.
6. Suborder Diprotodonta. Herbivorous Marsupials;

Kangaroos, etc.
c. Suborder t Allotheria.

B. Infraclass MONODELPHIA. Placental Mammals.
A A. Cohort UNGUICULATA. Clawed Mammals.

1. Order t TRITUBERCULATA.

2. Order INSECTIVORA. Insect-eating Mammals.

a. Suborder Lipotyphla, e.g. Moles, Hedgehogs, Shrews, etc.
6. Suborder t Hyopsodonta.

c. Suborder t Proglires.

d. Suborder Menotyphla, e.g. Tree and Jumping Shrews.

3. Order t TILLODONTIA.

4. Order DERMOPTERA. The Flying Lemur.

5. Order CHIROPTERA. Bats.

6. Order CARNIVORA. Beasts of Prey.

a. Suborder t Creodonta. Primitive Flesh-eaters.
6. Suborder Fissipedia. Wolves, Bears, Weasels, Cats, etc.
c. Suborder Pinnipedia. Marine Carnivores — Seals and
Walruses.

7. Order RODENTIA. Gnawing Mammals.

a. Suborder Duplicidentata, e.g. Hares, Rabbits, Pikas.

60 LAND MAMMALS IN THE WESTERN HEMISPHERE

b. Suborder Simplicidentata, e.g. Squirrels, Marmots,
Beavers, Rats, Mice, Porcupines, etc.

8. Order fT-fiNIODONTIA.

9. Order EDENTATA.

a. Suborder Pilosa. Hairy Edentates, e.g. Sloths, Ant-
eaters, etc.

6. Suborder Loricata. Armoured Edentates, e.g. Armadil-
los, t Glyptodonts.

10. Order PHOLIDOTA. Scaly Anteaters or Pangolins.

11. Order TUBULIDENTATA. The Aard Vark.
BB. Cohort PRIMATES. Mammals with nails.

12. Order PRIMATES.

a. Suborder Lemuroidea. Lemurs.
6. Suborder Anthropoidea. Monkeys, Apes, Man.
CC. Cohort UNGULATA. Hoofed Mammals.

13. Order t CONDYLARTHRA.

14. Order fAMBLYPO DA.

15. Order ARTIODACTYLA. Even-toed Hoofed Mammals.

a. Suborder t Artiodactyla Primitiva.

b. Suborder Suina. Swine, Peccary, Hippopotamus.

c. Suborder Tylopoda. Camels, Llama, Guanaco.

d. Suborder Tragulina. Mouse-deer or Chevrotains.

e. Suborder Pecora, e.g. Deer, Antelopes, Sheep, Oxen, etc.

16. Order PERISSODACTYLA. Odd-toed Hoofed Mammals.
a. Suborder Chelodactyla, e.g. Horses, Tapirs, Rhi-
noceroses, etc.

6. Suborder t Ancylopoda. t Chalicotheres.

17. Order PROBOSCIDEA. Elephants and f Mastodons.

18. Order t BARYTHERIA.

19. Order f EMBRITHOPODA.

20. Order SIRENIA. Sea-cows and Dugongs.

21. Order HYRACOIDEA. Conies.

22. Order t TOXODONTIA.
a. Suborder t Tozodonta.
6. Suborder t Typotheria.

c. Suborder t Entelonychia.

d. Suborder fPyrotheria.

23. Order t ASTRAPOTHERIA.

24. Order t LITOPTERNA.

DD. Cohort CETACEA. Whales, Dolphins, Porpoises.

25. Order t ZEUGLODONTIA.

26. Order ODONTOCETI. Toothed Whales, Dolphins,

Porpoises.

27. Order MYSTACOCETI. Whalebone Whales.

CHAPTER IV

THE SKELETON AND TEETH OF MAMMALS

With very rare exceptions, and those only of the latest
geological period (Quaternary) , the fossil remains of mammals
consist only of bones and teeth. The evolutionary changes,
so far as these are preserved, are recorded therefore in terms of
dental and skeletal modifications. To render these changes
intelligible, it is necessary to give some account of the mam-
malian skeleton and teeth, with no more use of technical
language than is unavoidable; ordinary speech does not
furnish a sufficient number of terms, nor are most of these
sufficiently precise. With the aid of the figures, the reader
may easily gain a knowledge of the skeleton which is quite
adequate for the discussion of fossil series, which will follow
in the subsequent chapters.

I. The Skeleton

I. The most obvious distinction of the skeletal parts is
into axial and appendicular portions, the former comprising
the skull, backbone or vertebral column, ribs and breastbone
or sternum, and the latter including the limb-girdles, limbs
and feet. In the axial skeleton only the ribs and certain bones
of the skull are paired, but in the appendicular all the bones
are in pairs, for the right and left sides respectively.

The skull is a highly complex structure, made up of many
parts, most of which are immovably fixed together, and per-
forming many functions of supreme importance. In the first
place, it affords secure lodgement and protection for the brain
and higher organs of sense, those of smell, sight and hearing,

61

62

LAND MAMMALS IN THE WESTERN HEMISPHERE

and second, it carries the teeth and, by its movable jaws,
enables these to bite, to take in and masticate food. The
portion of the skull which carries the brain, eyes and ears, is
called the cranium, and the portion in front of this is the face,
the boundary between the two being an oblique line drawn
immediately in front of the eye-socket (Fig. 7). A great

Ex.0.

-co*.

Fio. 7. — Skull of Wolf (Cants occidentalis) . P. M x., premaxillary. Mx., maxillary.
Na., nasal. L., lachrymal. Ma., malar or jugal. Fr., frontal. Pa., parietal.
Sq., squamosal. Zyg., zygomatic process of squamosal. O.S., orbitosphenoid.
PL, palatine. M., mandible, cor., coronoid process of mandible, m.c, condyle
of mandible, ang., angular process of mandible, p.g., postglenoid process of
squamosal. Ty., tympanic (auditory bulla), mas., mastoid, p.oc., paroccipital
process, con., occipital condyle. Ex.0., exoccipital. S.O., supraoccipital.

deal of the endless variety in the form of the skull of different
mammals depends upon the differing proportions of cranium
and face. In the human skull, for example, the cranium is
enormously developed and forms a great dome, while the face
is shortened almost to the limit of possibility ; the skull of the
Horse, on the other hand, goes to nearly the opposite extreme
of elongation of the facial and shortening of the cranial region.
The posterior surface of the skull, or occiput, is made up of
four bones, which in most adult mammals are fused into a
single occipital bone. At the base of the occiput is a large
opening, the foramen magnum, through which the spinal cord
passes to its junction with the brain ; and on each side of the
opening is a large, smooth, oval prominence, the occipital
condyles, by means of which the skull is articulated with the

SKELETON AND TEETH 63

neck. The paroccipital processes are bony styles of varying
length, which are given off, one on each side external to the
condyles. The boundary of the occiput is marked by a ridge,
the occipital crest, which varies greatly in prominence, but is
very well marked in the more primitive forms and tends to
disappear in the more highly specialized ones. The roof
and much of the sides of the cranium are formed by two pairs
of large bones, the parietals behind and the frontals in advance ;
along the median line of the cranial roof, where the two parietals
meet, is usually another ridge, the sagittal crest, which joins
the occipital crest behind. The sagittal crest also varies
greatly in prominence, being in some mammals very high and
in others entirely absent, and, like the occipital crest, is a prim-
itive character; as a rule, it is longest and highest in those
mammals which have the smallest brain-capacity. As pointed
out by Professor Leche, the development of the sagittal crest
is conditioned by the relative proportions of the brain-case and
the jaws. Powerful jaws and a small brain-case necessitate
the presence of the crest, in order to provide sufficient surface
of attachment for the temporal muscles, which are important
in mastication, while with large brain-case and weak jaws the
crest is superfluous. Though the brain-case proper may be
quite small, yet it may have its surface enormously increased
by great thickening of the cranial bones, as is true of elephants
and rhinoceroses, and in them sufficient surface for attachment
is afforded to the muscles without the development of a crest.
The structure of these cranial bones, more particularly of
the parietals, is subject to important changes ; in most mam-
mals they are of moderate thickness and have dense layers,
or il tables/' forming the outer and inner surfaces and, between
these, a layer of spongy bone. In many large mammals,
however, especially those which have heavy horns or tusks, the
cranial bones become enormously thick and the spongy layer
is converted into a series of communicating chambers, or
minuses, the partitions between which serve as braces, thus

64

LAND MAMMALS IN THE WESTERN HEMISPHERE

making the bone very strong in proportion to its weight.
Sinuses are very generally present in the frontals and communi-
cate by small openings with the nasal passage, even in genera

?io. 8. — Skull of Wolf, top view.

P.Mx., pre maxillary Na., iiaaaJ.
Ma., malar or jugal. L., lachrymal.
Fr., frontal. Sq., aquamoaal. Pa.,
parietal. S.O., «u preoccipital.

Fio. 9. — Skull of Wolf, view of baee.
P.Mx., premazillary. Mx., palatioe
process of maxillary. PL. palatine.
Ft., frontal. Pi., parietal. Ma.,
malar or jugal. Sq., glenoid cavity
of aquamoaal. B.S., baaiaphenoid.
B.O., bnsi occipital. Ty., tympanic
(auditory bulla), p.oc., paroccipital
process. con., occipital condyle,
S.O.. aupraoccipital.

of moderate size and with-
out horns or tusks. The
frontals form the roof of
the eye-sockets, or orbits, and usually there is a projection
from each frontal, which marks the hinder border of the
orbit and is therefore called the postorbital process. The roof
of the facial region is made by the nasals, which are com-
monly long and narrow bones, but vary greatly in form and

SKELETON AND TEETH 65

proportions in different mammals; in those which have a
proboscis, like tapirs and elephants, or a much inflated snout,
such as the Moose (Alee) or the Saiga Antelope (Saiga tatarica)
the nasals are always very much shortened and otherwise
modified in form.

The anterior end of the skull is formed by a pair of rather
small bones, the premaxillaries, which carry the incisor teeth ;
they bound the sides of the nasal opening, or anterior nares,
reaching to the nasals, when the latter are of ordinary length ;
they also form the front end of the hard or bony palate, which
ades the nasal passage from the mouth. The mamillaries,
•r upper jaw-bones, make up nearly all of the facial region on
each side and send inward to the median line from each side
*■ bony pldte which together constitute the greater part of the
*rd palatra^he remainder of the upper teeth are implanted
the ma IJMjIxjes. A varying proportion of the hinder part
v the hdrjl pMate is formed by the palatines, which also en-
close the posterior nares, the opening by which the nasal passage
enters the back part of the mouth. The maxillary of each
side extends back to the orbit, which it bounds anteriorly and
in the antero-superior border of which is the usually small
lachrymal. The inferior, and more or less of the anterior,
border of the orbit is made by the cheek-bone (malar or jugal)
which may or may not have a postorbital process extending
up toward that of the frontal ; when the two processes meet,
the orbit is completely encircled by bone, but only in monkeys,
3ipes and Man is there a bony plate given off from the inner
side of the postorbital processes, which extends to the cranial
"wall and converts the orbit into a funnel-shaped cavity. For
Most of its length, the jugal projects freely outward from the
^ide of the skull and extends posteriorly beneath a similar bar
*>t bone, the zygomatic process of the squamosal. This process
«,nd the jugal together constitute the zygomatic arch, which on
^ach side of the skull stands out more or less boldly, and the
«ze and thickness of which are subject to great variation in

66 LAND MAMMALS IN THE WESTERN HEMISPHERE

different mammals, the massiveness of the arch being pro-
portional to the power of the jaws. One of the principal
muscles of mastication (the masseter) is attached to the zygo-
matic arch.

The squamosal itself is a large plate, which makes up a great
part of the side- wall of the cranium and articulates above with
the frontal and parietal ; it also supports the lower jaw, the
articular surface for which is called the glenoid cavity. The
lower jaw is held in place by the postglenoid process, which is
a projection, usually a transverse ridge, behind the cavity.
Back of the postglenoid process is the entrance to the middle
ear, the auditory meatus, which may be merely an irregular hole,
or a more or less elongated tube. The meatus is an opening
into the tympanic, a bone which at birth is a mere ring and in
some mammals remains permanently in that condition, but
as a rule develops into a swollen, olive-shaped auditory bulla,
which sometimes reaches enormous proportions, especially
in nocturnal mammals. The labyrinth of the internal ear is
contained in the periotic, a very dense bone which is con-
cealed in the interior of the cranium, but in many mammals
a portion of it, the mastoid, is exposed on the surface between
the squamosal and occipital.

The lower jaw-bone (inferior maxillary, or mandible) is the
only freely movable element of the skull; it consists of two
halves which meet anteriorly at the chin in a contact of greater
or less length, called the symphysis. In nearly all young
mammals and in many adult forms the two halves of the lower
jaw are separate and are held together at the symphysis only
by ligaments, while in others, as in Man, they are indistinguish-
ably fused to form a single bone. Each half consists of two
portions, a horizontal part or ramus and an ascending ramus
or vertical part ; the former supports all of the lower teeth, and
its length, depth and thickness are very largely conditioned by
the number and size of those teeth. The ascending ramus is
a broad, rather thin plate, divided at the upper end into two

SKELETON AND TEETH 67

portions, the hinder one of which terminates in the condyle,
a rounded, usually semicylindrical projection, which fits into
the glenoid cavity of the squamosal. The anterior portion
of the ascending ramus ends above in the coronoid process, which
serves for the insertion of the temporal muscle, the upper
portion of which is attached to the walls of the cranium and
thus, when the muscle is contracted, the jaws are firmly closed ;
the coronoid process passes inside of the zygomatic arch. The
lower jaw is therefore a lever of the third order, in which the
power is applied between the weight (i.e. the food, the resistance
of which is to be overcome) and the fulcrum, which is the
condyle. At the postero-inferior end of the ascending ramus
is the angle, the form of which is characteristically modified
in the various mammalian orders and is thus employed for
purposes of classification.

The hyoid arch is a U-shaped series of small and slender
bones, with an unpaired element closing the arch below;
each vertical arm of the U is attached to the tympanic of its
own side and the whole forms a flexible support for the tongue,
but with no freely movable joint like that between the lower
jaw and the squamosal.

The mammalian skull in its primitive form may be thought
of as a tube divided into two parts, of which the hinder one is
the brain-chamber, or cranial cavity, and the forward one the
nasal chamber or passage. With the growth of the brain and
consequent enlargement of the cranium, this tubular character
is lost ; and various modifications of the teeth, jaws and facial
region, the development of horns and tusks, bring about the
many changes which the skull has undergone.

This brief sketch of the skull-structure is very incomplete,
several of its elements having been altogether omitted and only
those parts described which are needful in working out the
history and descent of the various mammalian groups.

The second portion of the axial skeleton is the backbone,
or vertebral column, which is made up of a number of separate

68 LAND MAMMALS IN THE WESTERN HEMISPHERE

bones called vertebras. These are so articulated together as to
permit the necessary amount of flexibility and yet retain the
indispensable degree of strength. The function of the back-
bone is a twofold one : (1) to afford a firm support to the body
and give points of attachment to the limbs, and (2) to carry the
spinal cord, or great central axis of the nervous system, in such
a manner that it shall be protected against injury, a matter of
absolutely vital necessity.

> While the vertebra differ greatly in form and appearance in
the various regions of the neck, body and tail, in adaptation
to the various degrees of mobility and strength which are
required of them, yet they are all constituted upon the same
easily recognizable plan. The principal mass of bone in each
vertebra is the body, or centrum, which is typically a cylinder,
or modification of that form, and the two ends of the cylinder
are the faces, by which the successive vertebrae are in contact
with one another. In the living animal, however, the successive
centra are not in actual contact, but are separated by disks of
cartilage (gristle) which greatly add to the elasticity of the
column. From the upper surface of the centrum arises an
arch of bone, the neural arch, enclosing with the centrum the
neural canal, through which runs the spinal cord. As already
mentioned, the protection of the spinal cord is essential to the
life of the animal, yet this protection must be combined with
a certain flexibility, both lateral and vertical. Mere contact
of the centra, even though these be held in place by ligaments,
would not give the column strength to endure, without dis-
location, the great muscular stresses which are put upon it.
Additional means of articulation between the successive
vertebrae are therefore provided, and these vary in size, form
and position in different regions of the backbone, in nice adjust-
ment to the amount of motion and degree of strength needed
at any particular part of the column. Of these additional
means of articulation, which are called the zygapophyses, each
vertebra has two pairs, an anterior and a posterior pair, placed

SKELETON AND TEETH 69

upon the neural arch. From the summit of the arch arises
the neural spine, a more or less nearly straight rod or plate of
bone, which may be enormously long or extremely short,
massive or slender, in accordance with the muscular attach-
ments which must be provided for. Finally, should be men-
tioned the transverse processes, rod-like or
plate-like projections of bone, which arise,
one on each side of the vertebra, usually
from the centrum, less commonly from the
neural arch ; these also differ greatly in form
and size in the various regions of the column.
Anatomists distinguish several other pro- fiq 10 —First dorsal
cesses of the vertebra, but for our purpose vertebra of Wolf

•x . . j. j. i xi_ • x from the front, en..

it is not necessary to take these into con- centrum. r.t facet

sideration. for the head °f the

Five different regions of the backbone The tuberci^f the

may be distinguished, in each of which the rib- tr- traMvene

_x i j./s j • i x • j.' Process. jw.*.,ante-

vertebrae are modified m a characteristic rior «ygapophyses.
way. There is (1) the cervical region, or n*p" neural 8pine*
neck, the vertebrae of which, among mammals (with only one
or two exceptions) are always seven in number, however long
or short the neck may be; the immoderately long neck of
the Giraffe has no more and the almost invisible neck of
the Whale has no less, and thus the elongation of the neck
is accomplished by lengthening the individual vertebrae and
not by increasing their number. (2) Those vertebrae to
which ribs are attached are named dorsal or thoracic and
can always be recognized by the pits or articular facets
which receive the heads of the ribs. (3) Behind the dorsal
is the lumbar region, or that of the loins, made up of a num-
ber of vertebrae which carry no ribs. The dorso-lumbars are
known collectively as the trunk-vertebrce and are generally
quite constant in number for a given group of mammals, though
often differently divided between the two regions in different
members of the same group. In the Artiodactyla, for example.

70 LAND MAMMALS IN THE WESTERN HEMISPHERE

there are very constantly 19 trunk-vertebrae, but the Hippo-
potamus has 15 dorsals and 4 lumbars, the Reindeer (Rangifer)
14 D., 5 L., the Ox (Bos taurus) 13 D., 6 L., the Camel (Camelus
dromedarius) 12 D. and 7 L. (4) Next follows the sacrum,
which consists of a varying number of coalesced vertebrae.
The number of sacral vertebrae varies from 2 to 13, but is
usually from 3 to 5. (5) Finally, there are the caudal vertebrae,
or those of the tail, which are extremely variable in number
and size, depending upon the length and thickness of the tail.

We must next consider briefly some of the structural features
which characterize the vertebrae of the different regions.
(1) The length of the neck varies greatly in different mammals
and, up to a certain point, flexibility increases with length, but,
as the number of 7 cervicals is almost universally constant
among mammals and the lengthening of the neck is accom-
plished by an elongation of the individual vertebrae, a point
is eventually reached, where greater length is accompanied
by a diminution of mobility. For instance, in the Giraffe
the movements of the neck are rather stiff and awkward, in
striking contrast to the graceful flexibility of the Swan's neck,
which has 23 vertebrae, more than three times as many.

The first two cervical ver-
tebrae are especially and pecul-
iarly modified, in order to
support the skull and give to

Fig. ii.— Atlas of Wolf, anterior end and it the necessary degree of mo-
ieft side, cot., anterior cotyles. n.c, .... , , ,-« „
neural canal, n.a., neural arch, tr., Dlllty Upon the neck. The first

transverse process, v. a., posterior vertebra, or atlas, is hardly

opening of the canal for the vertebral .

artery. more than a ring of bone with

a pair of oval, cuplike depres-
sions (anterior cotyles) upon the anterior face (superior in
Man) into which are fitted the occipital condyles of the skull.
By the rolling of the condyles upon the atlas is effected
the nodding movement of the head, upward and down-
ward, but not from side to side; this latter movement is

SKELETON AND TEETH 71

accomplished by the partial rotation of skull and atlas to-
gether upon the second vertebra in a manner presently to be
explained. On the hinder aspect are two articular surfaces
(posterior cotyles) in shape like the anterior pair, but very much
less concave, which are in contact with corresponding surfaces
on the second vertebra. The neural arch of the atlas is broad
and low and the neural canal is apparently much too large
for the spinal cord, but, in fact, only a part of the circular
opening belongs to the neural canal. In life, the opening is
divided by a transverse ligament into an upper portion, the
true neural canal, and a lower portion, which lodges a pro-
jection from the second vertebra. The atlas usually has no
neural spine and never a prominent one; the transverse
processes are broad, wing-like plates and each is perforated by
a small canal, which transmits the vertebral artery.

The second vertebra, or axis, is a little more like the ordi-
nary vertebra, having a definite and usually elongate centrum,
on the anterior end of which are the two ar-
ticular surfaces for the atlas. Between these
is a prominent projection, the odontoid pro- Wi
cess, which fits into the ring of the atlas and
has a special articulation with the lower bar ^£^7*2*2
of that ring. In most mammals the odon- toid process, cot., an-

, • i 11 M • i . terior cotyles. n.a.,

toid process is a bluntly corneal peg, varying neural arch n8p
merely in length and thickness, but in many neurai spine, pu.,

I i j r i.u • -x j • a posterior aygapophy-

long-necked forms the peg is converted into a «*. tr., transverse Pro-
semicylindrical spout, convex on the lower ce88*. ».«'•. anterior

opening of canal for

side and concave above. The neural spine of the vertebral artery.
the axis is almost always a relatively large, ?•""•• v0****™ open-

° mg of the same.

hatchet-shaped plate, which is most developed
in the carnivorous forms, and the transverse processes are com-
monly slender rods.

The five succeeding cervical vertebrae are much alike, though
each one has a certain individuality, by which its place in the
series may readily be determined. The centrum has a convex

72

LAND MAMMALS IN THE WESTERN HEMISPHERE

anterior and concave posterior face, which in long-necked ani-
mals form regular "ball and socket" joints; neural spines are

frequently wanting and, when present, are almost

always short and slender ; the zygapophyses are

very prominent and are carried on projections

which extend before and behind the neural arch ;

Fio. 13. — Fifth the transverse processes are long, thin plates and,

cervical verte- except in the seventh cervical, are usually pierced

aide0 *r.°trans- by the canal for the vertebral artery, but in a

verse process. few forms {e.g. the camels) this canal pierces the

" posterior

of neural arch.

(2) The dorsal or thoracic vertebrae have more

v.a

opening
canal for the
vertebral ar-
tery. pr.*.and or less cylindrical centra, with nearly flat faces,

pt.z., anterior ancj on ^ centra for the most part at their ends,

and posterior ' r ■ '

*ygapophyses. are the concave facets for the rib-heads. The
spine neura transverse processes are short and rod-like and

most of them articulate with the tubercles of the
ribs. The zygapophyses are smaller than in the cervical region,
less prominent and less oblique ; the anterior pair, on the front
of the neural arch, face upward and the posterior pair down-
ward. The neural spines are very much longer
than those of the neck and those of the anterior
dorsals are often of relatively enormous length,
diminishing toward the hinder part of the region.
(3) The lumbar vertebrae are almost always
heavier and larger than those of the dorsal region ;
they carry no ribs and their neural spines and
transverse processes are broad and plate-like and
the latter are far larger and more prominent than
those of the dorsals. As an especial degree of
strength is frequently called for in the loins, to-
gether with a greater flexibility than is needed
in the dorsal region, the modes of articulation
between the successive vertebrae are more com-
plex, sometimes, as in the Edentata, most elabo-

Fio. 14. — First
dorsal vertebra of
Wolf, left side.
c, centrum, r.,
anterior rib-
facet, r"., pos-
terior rib-facet.
tr., transverse
process. pr.t.
pt.z., anterior and
posterior zyga-
pophyses. n.sp.,
neural spine.

SKELETON AND TEETH

rately so. Taking the dorso-
lumbars, or trunk-vertebra, as a
single series, we may note that
in a few mammals (e.g. the ele-
phants) all the neural spines

process, en., centrum, pr.t. and pl.t.,
anterior and posterior tygapophyses.
n.ap., neural spine.

the great majority of forms
this backward inclination ceases
near the hinder end of the dor-
sal region, where there is one vertebra with erect spine, while
behind this point the spines slope forward.

(4) The sacral vertebra, varying from 2 to 13 in number,
are fused together solidly into one piece, the combined centra
forming a heavy mass and the neural canals a
continuous tube, while the neural spines are
united into a ridge. As a rule, only the first
two vertebra of the sacrum are in contact with
the hip-bones, to support which they have de-
veloped special processes, the remainder of the
mass projecting freely backward.

(5) The caudal vertebra vary greatly, in
accordance with the length and thickness of the
tail. In an animal with well-developed tail
several of the anterior caudals have the parts
and processes of a typical vertebra, centrum,
neural arch and spine, zygapophyses and transverse processes.
Posteriorly, these gradually diminish, until only the centrum
is left, with low knobs or ridges, which are
the remnants of the various processes. A
varying number of long, cylindrical centra,
diminishing backward in length and diame-
ter, complete the caudal region and the ver-
tebral column. In some mammals, chevron
bones are attached to the under side of the
anterior and middle caudals ; these are forked, Y-shaped bones.

Fio. 16. —Sacrum
of Wolf, upper
side. 1, II. Ill,
first, second and
third sacral verte-
bra, pi., surface
for attachment to
hip-bone.

Fio. 17, — Caudal verte-
bra! of Wolf, from ante-
rior and middle parte of
the tail. Letters M in
Fig. 15.

74

LAND MAMMALS IN THE WESTERN HEMISPHERE

which form a canal for the transmission of the great blood-ves-
sels of the tail.

The ribs, which are movably attached to the backbone,
together with the dorsal vertebrae and breast-bone, compose
the thorax, or chest The articulation with the vertebrae is
by means of a rounded head ; in most cases the head has two

distinct facets, the pit being formed half on
the hinder border of one dorsal vertebra and
half on the front border of the next suc-
ceeding one, but posteriorly the pit is often
shifted, so as to be on a single vertebra. A
second articulation is by means of the tu-
bercle, a smooth projecting facet on the con-
vexity of the rib's curvature and near the
head; the tubercle articulates with the
transverse process of its vertebra. The ribs,
in general, are curved bars of bone, which
in small mammals generally and in the
clawed orders are slender and rod-like, while
in the hoofed mammals they are broader,
thinner and more plate-like, especially the
anterior ones. The number of pairs of ribs
is most commonly 13, but ranges among
existing mammals from 9 in certain whales to 24 in the Two-toed
Sloth (Chokepus didactylus) . The complex curvature of the
ribs, outward and backward, is such that, when they are drawn
forward (in Man upward) by muscular action, the cavity of
the thorax is enlarged and air is drawn into the lungs, and
when they are allowed to fall back, the cavity is diminished
and the air expelled.

Below, a varying number of the ribs are connected by the
cartilages in which they terminate with the breast-bone
(sternum) ; sometimes these cartilages are ossified and then
form the sternal ribs, but there is always a flexible joint between
the latter and the true ribs. In certain edentates, notably

Fig. 18. — Ribs of Wolf
from anterior and
middle parts of the
thorax, cp., head, t.,
tubercle.

SKELETON AND TEETH 75

the anteatere and the extinct f ground-sloths, these sternal ribs,
at their lower ends, are provided with head and tubercle, for
articulation with the sternum.

The sternum, or breast-bone, is made up of a number of
distinct segments, usually broad and flat, but often cylindrical,
which may unite, but far more commonly remain separate
throughout life. The number, size and form of these segments
often give useful characters in
classification. The first seg-
ment, or manubrium, has quite
a different shape from the suc-
ceeding ones and is consider-
ably longer.

II. The appendicular
skeleton consists of the limb-
girdles and the bones of the
limbs and feet. The limb-
girdles are the means of at-
taching the movable limbs to
the body, so as to combine
the necessary mobility with
strength. The anterior, or
shoulder-girdle, has no direct
articulation with the vertebral
column, but is held in place by
muscles; it is made up of
the shoulder-blade and collar-
bone, though very many mam-
mals have lost the latter.

The shoulder-blade, Or Fia. IB. — Sternum and rib-cartilages of
... , ... , . Wolf, lower side. P.S., manubrium,

scapula, is a broad, thin, plate- x 3 ™hiBternum
like bone, which contracts be-
low to a much narrower neck, ending in a concave articular
surface, the glenoid cavity, for the head of the upper arm-bone,
the two together making the shoulder-joint. On the outer side

LAND MAMMALS IN THE WESTERN HEMISPHERE

the blade is divided into two parts by a prominent ridge,
the spine, which typically ends below in a more or less con-

Fio. 21. — Left scapula or Hone.
This figure is much more reduced

than Fig. 20.

spicuous projection, the acromion, which may, however, be
absent, its prominence being, generally speaking, correlated
with the presence of the
collar bone. A hook-like
process, the coracoid, rises
from the antero-internal
side of the glenoid cavity
and varies greatly in size
in the different groups of
mammals; though it usu-
ally appears to be merely a
position of process of the scapula, with
which it is indistinguish-
ably fused, yet its development shows it to be a separate ele-
ment and in the lowest mammals (Prototheria), as in the rep-

SKELETON AND TEETH

77

tiles and lower vertebrates generally, it is a large and im-
portant part of the shoulder-girdle and articulates with the
sternum.

The collar-bone, or clavicle, is a complexly curved bar,
which, when present and fully developed, extends from the
forward end of the sternum to the acromion, the projecting
lower end of the scapular spine, supporting and strengthening
the shoulder-joint. In many
mammalian orders, notably all
existing hoofed animals, the

Clavicle has become Superfluous Fio. 23. -Left clavicle of Man, front ride.

and is lost more or less com-
pletely ; it may be said, in general, that the clavicle is devel-
oped in proportion to the freedom of motion of the shoulder-
joint and to the power of rotation of the hand upon the arm.
In arboreal animals, such as monkeys, in which the hand
rotates freely and the arm moves in any direction on the
shoulder, the clavicle is large and fully developed, as it also is
in Man. Many burrowing mammals (e.g. the moles) have
very stout clavicles.

The posterior, or pelvic, girdle is composed on each side of
a very large, irregularly shaped bone, which is firmly attached
to one or more of the coalesced vertebrae which form the sacrum
and thus affords a solid support to the hind leg. Each half

of the pelvis, or hip-
bone, is made up of
three elements, called
respectively the ilium,
ischium and pubis,
which are separate in
the very young animal,
indistinguishably fused
in the adult. The three
elements unite in a deep, hemispherical pit, the acetabulum,
which receives the head of the thigh-bone, a perfect ex-

Fio. 24. — Left hip-bone of Wolf. //., ilium. /«.,
ischium. P., pubis, ac., acetabulum.

78

LAND MAMMALS IN THE WESTERN HEMISPHERE

txt.t.

ample of the "ball and socket joint.' ' In the inferior median
line the two pubes meet and may become coalesced, in a sym-
physis, the length of which differs in various mammals. The
pelvis and sacrum together form a short, wide tube, the diame-
ter of which is normally greater in the female skeleton than in
the male.

The limbs are each divided into three segments, which
in the anterior extremity are the arm, fore-arm and hand
(or fore foot) and in the posterior extremity are the thigh, leg
and foot (or hind foot), and there is a general correspondence
between the structure of these segments in the fore and hind
legs, however great the superficial difference. The bones of

the limbs, as distinguished from
those of the feet, are the long bones
and, except in a few very large and
heavy mammals, are essentially
hollow cylinders, thus affording
the maximum strength for a given
weight of bone; the cavity of a
long bone contains the marrow
and hence is called the medullary
cavity. In the young mammal
each of the long bones consists of
three parts, the shaft, which makes
up much the greater part of the
length, and at each end a bony
cap, the epiphysis. Growth takes
place by the intercalation of new
Fiq. 25. — Left humerus of Wolf, from material between the shaft and the

the front and outer sides, the latter . t , .L lL ,

somewhat oblique, a., head, int.t., epiphyses; when the three parts

internal tuberosity. ext.L, external unite, gTOWth Ceases and the ani-
tuberosity. be., bicipital groove. 1 . j ij

dl., deltoid ridge, sh., shaft. «., mal 1S adult.

supinator ridge, int. epi. internal The Superior Segment of the

epicondyle. «./. anconeal foramen.

*r., trochlea. */■'., trochlea, posterior fore limb has a single bone, the

side, ext. epi external epicondyle. humerus, the Upper end of which
a J. anconeal fossa. ' *rr

it t

ext epi

SKELETON AND TEETH

79

I Jiff-

*

is the rounded, convex head, which fits into
the glenoid cavity of the shoulder-blade, form-
ing the joint of the shoulder; in front of
the head are two prominent and sometimes
very large projections for muscular attach-
ment, the external and internal tuberosities, sep-
arated by a groove, in which play the two ten-
dons of the biceps muscle and is therefore called
the bicipital groove. In a few mammals, such as

the Horse, Camel and Giraffe,
the groove is divided into two
by a median tubercle or ridge.
From the external tuberosity
there generally passes down
the front face of the shaft a
rough and sometimes very
prominent ridge, the deltoid
crest, to which is attached the
powerful deltoid muscle. At
the lower end of the humerus is the trochlea,
an irregular half-cylinder, for articulation with
the two bones of the fore-arm and vary-
ing in form according to the relative sizes
of those bones. On each side of the troch-
lea is frequently a rough prominence, the epi-
condyle, and above the inner one is, in many
mammals, a perforation, the epicondylar fora-
men, for the passage of a nerve. Extending
up the shaft from the outer epicondyle is a
rough crest, the supinator ridge, to which is
attached one of the muscles that rotate the
hand and is conspicuously developed in those
Fio. 27.— Left hu- mammals which have the power of more or

menifl of Man, iess free rotation and especially in burrow-
front side. Let- .

ten as in Fig. 25. ers. On the postenor face of the humerus,

Fig. 26. — Left hu-
merus of Horse,
front side. i.L, in-
ternal tuberosity.
ex.t., external tu-
berosity. 6c., out2r
part of bicipital
groove, dt., del-
toid ridge, *., su-
pinator ridge, tr.,
trochlea.

i fit..

tn

80 LAND MAMMALS IN THE WESTERN HEMISPHERE

juBt above the trochlea, is a large, deep pit, the anconeal
fossa.

The two bones of the fore-arm, the radius and ulna, are,
in most mammals, entirely separate from each other, but in
certain of the more highly specialized hoofed animals are
immovably eoossified. Primitively, the two bones were of

O

©

Fto. 28. — Left fore-arm bone* of Wolf,

front side. A., radius. (/., ulna, ol.,
olecranon. A., head of radius.

?io. 29. — Left fore-aim bones of Man,
front aide. Letters as in Fig. 28. The
small obj ect at the right of each figure is
theheodof the radius, seen from above.

nearly equal size, but in most of the mammalian orders there
is a more or less well-defined tendency for the radius to enlarge
at the expense of the ulna. These bones are normally crossed,
the radius being external at the upper end and passing in front
of the ulna to the inner side of the arm. The radius varies
considerably in form in accordance with the uses to which the

SKELETON AND TEETH

81

hand is put; if the capacity of rotation is re-
tained, the upper end, or head, of the radius is
small, circular or disk-like, covering little of the
humeral trochlea, but when the head of the radius
is broadened to cover the whole width of the
humerus, then all power of rota-
tion is lost. (Cf . Figs. 28 and 29.)
As a rule, the radius broadens
downward and covers two-thirds
or more of the breadth of the
wrist-bones.

The ulna is longer than the
radius, its upper end being ex-
tended into a heavy process, the
olecranon, or anconeal process,
into which is inserted the tendon
of the great triceps muscle, the Fl0i 30.— coe*-
contraction of which straightens
the arm ; this process is the bony
projection at the back of the el-
bow-joint. Below the olecranon
is a semicircular articular con-
cavity, which embraces the hume-
ral trochlea and its upper angle fits into the
anconeal fossa of the humerus. The ulna con-
tracts and grows more slender downwards and
its lower end covers but one of the wrist-bones.
While in the more primitive mammals, and in
those which retain the power of rotating the
hand, the ulna has nearly or quite the same
thickness as the radius, it is often much more

I

Fio. 31.— Left fore-
arm bones of the
Tapir (Tapirus

Bified bones of
left fore-arm of
Horse, front

the uloa is coo-
cealed by the

dills- V., ulna,
head of radius. .

sigmoid notch of slender and in the more highly specialized of
eranon. N.B. This the hoofed animals, such as the horses, camels
figure is on * much ancj {j^g ruminants, the radius carries the en-
Fig. 30. tire weight and the ulna has become very slen-

82 LAND MAMMALS IN THE WESTERN HEMISPHERE

der, more or less of its middle portion is lost and the two ends
are coossified with the radius, so that the fore-arm appears to
have but a single bone. The reverse process of enlarging the
ulna and reducing the radius is very rare and practically con-
fined to the elephant tribe.

The fore foot, or hand, for which the term manus may be
conveniently employed, is divisible into three parts, correspond-
ing in ourselves to the wrist, back and palm of the hand, and
the fingers. The bones of the wrist constitute the carpus,

Fio. 33. — Left manus of Man. S„ sea
phoid. L.. lunar. Pi,., pyramidal (pisi-
form not shown). Tm., trapeiium. Td..

trapezoid. M , magnum. Un., unciform.
Other letters as in Fig. 32.

Fin 32. — Left manus of Wolf, front
side. SL., scapho-lunar. Py., pyram-
idal. Pit., pisiform. Tm., trape-
iium. Td., trapezoid. M., magnum.
V., unciform. Mc.I-V. first to fifth
metacarpals. Ph.l, first phalanx.
Ph.t, second phalanx. Ung., ungual
phalanx. 1, first digit, or polleX. Il-V,
second to fifth digits.

those of the back and palm the metacarpus, and those of the
fingers the phalanges.

The carpus consists primitively of nine distinct bones,
though one of these, as will be shown later, is not a true carpal.
These bones are of a rounded, subangular shape, closely ap-

SKELETON AND TEETH 83

pressed together, with very little movement between them, and
are arranged in two transverse rows. The upper row con-
tains four bones, which enumerating from the inner side are
the scaphoid, lunar, pyramidal (or cuneiform) and pisiform.
The scaphoid and lunar support the radius, while the ulna
rests upon the pyramidal. The pisiform, though very con-
stantly present, is not a true carpal, but an ossification in
the tendon of one of the flexor muscles, which close the fingers ;
it projects more or less prominently backward and articulates
with the ulna and pyramidal. The second row is also made
up of four bones, which, from within outward, are the trape-
zium, trapezoid, magnum and unciform. The relations of the
two rows vary much in different mammals and the arrange-
ment may be serial or alternating; thus, the scaphoid rests
upon the trapezium and trapezoid and usually covers part of
the magnum ; the lunar may rest upon the magnum only,
but very much more frequently is equally supported by the
magnum and unciform and the pyramidal by the latter only.
The ninth carpal is the central, which, when present and dis-
tinct, is a small bone, wedged in between the two rows. Few
existing mammals have a separate central, which, though
present in the embryo, has coalesced with the scaphoid in the
great majority of forms. In the more advanced and differ-
entiated mammals the number of carpals may be consider-
ably reduced by the coossification of certain elements or
the complete suppression and loss of others. In all existing
Carni vora and a few other mammals the scaphoid and lunar
are united in a compound element, the scapho-lunar (or, more
accurately, the scapho-lunar-central) ; hoofed animals with
a diminished number of toes generally lose the trapezium,
and other combinations occur. The second row of carpals
carries the metacarpals, and primitively the trapezium, trape-
zoid and magnum are attached each to one metacarpal and
the unciform has two.

The metacarpus consists typically of five members, a num-

Si LAND MAMMALS IN THE WESTERN HEMISPHERE

bor which is never exceeded in any normal terrestrial mammal ;
the members are numbered from the inner side, beginning with
the thumb or pollex, from I to V. Many mammals have
fewer than five metacarpals, which may number four, three,
two or only one ; the third is never lost, but any or all of the
others may be suppressed, and functionless rudiments of them
may long persist as splints or nodules. The metacarpals are
elongate, relatively slender and of more or less cylindrical
shape ; but the form varies considerably in different groups,
according to the way in which the hand is used. When em-
ployed for grasping, as in many arboreal animals and pre-
eminently in Man, the pollex is frequently opposable to the
other fingers and enjoys much freedom of motion. In the
camels and true ruminants the third and fourth metacarpals
are coossified to form a cannon-bone (see Fig. 43, p. 91), but the
marrow cavities and the joints for the phalanges remain
separate.

The phalanges in land mammals never exceed three in each
digit, except the pollex, which, when present and fully developed,
has but two. The phalanges are usually slender in proportion
to their length, but in very heavy hoofed animals they are short
and massive. The terminal joint is the ungual phalanx, which
carries the nail, claw, or hoof, its shape varying accordingly.

The hind leg is constituted in very much the same manner
as the fore, but with certain well-marked and constant dif-
ferences. The thigh-bone, or femur, is usually the longest and
stoutest of the limb-bones and in very large animals may be
extremely massive. At the upper end is the hemispherical
head, which is set upon a distinct neck and projects inward and
upward, fitting into the acetabulum of the hip-bone. Nearly
all land mammals have a small pit on the head of the femur,
in which is inserted one end of the round ligament, while the
other end is attached in a corresponding depression in the
floor of the acetabulum. This ligament helps to hold the thigh-
bone firmly in place and yet allows the necessary freedom of

SKELETON AND TEETH 85

movement. On the outer side of the upper end of the femur
U a large, roughened protuberance, which often rises higher

Fia. 34. — Left femur of Wolf, front side
A., head, gt.tr,, great trochanter, tr.t,
second trochanter, int. con., internal
condyle, r.g., rotular groove, ezt.
con., external condyle.

Fio. 36. — Left femur of Horse, tr .3,
third tiochanter. Other letters sa in
Fig. 34. than which thia drawing is
very mueh more reduced.

than the head and is called the great trochanter; another, the
second or lesser trochanter, is a small, more or less conical prom-
inence on the inner side of the shaft, below the head. These
two processes are well-nigh universal among land mammals ;
and in a few of the orders occurs the third trochanter, which
arises from the outer side of the shaft, usually at or above the
middle of its length. Though comparatively rare in the
modern world, the third trochanter is an important feature,
and the early members of most, if not all, of the mammalian
orders possessed it. The shaft of the femur is elongate and,
except in certain very bulky mammals, of nearly cylindrical
shape. The tower end of the bone is thick and heavy and bears

86 LAND MAMMALS IN THE WESTERN HEMISPHERE

on the posterior side two large, rounded prominences, the
condyles, which articulate with the shin-bone to form the

knee-joint. On the anterior side is a broad, shal-

Ofjl low groove, the rotular groove , in which glides
*? the patella, or knee-cap. The patella is a large
ossification, of varying shape, in the tendon com-
mon to the four great extensor muscles of the
thigh, the action of which is to straighten the leg.
"*"* The lower leg, like the fore-arm, has two

bones, which, however, are always parallel, never
tnt«w. crossed, and have no power of rotation. Of

mur oTwoif1 in^ these, the inner one is the shin-bone, or tibia,
side of lower end. which is always the larger and alone enters into

cjct. con., external . % ■* ... mi i it • j i /»i >

condyle, int. the knee-joint. The external bone is the fibula,
con., internal which is almost entirely suppressed in certain

condyle, r.g., rot- ,.,, • v j * i_ ,1 L j

uiar groove, highly specialized forms, such as the horses and
Above, are two ruminants, the tibia carrying the whole weight.

views of the left . .

patella, anterior The upper end of the tibia is enlarged and ex-
ridel internal tends over that of the fibula ; it has two slightly

concave surfaces for articulation with the con-
dyles of the femur, the approximate edges of which are raised into
a bifid spine. The upper part of the shaft is triangular, with one
edge directed forward, and the superior end of this edge is rough-
ened and thickened to form the cnemial crest, to which is at-
tached the patellar ligament. The middle portion of the shaft is
rounded and the lower end broad and usually divided by a ridge
into two grooves or concavities for the ankle-bone ; from the in-
ner side of this end projects downward a tongue-like process, the
internal malleolus, which prevents inward dislocation of the ankle.
The fibula is relatively stoutest in the less advanced mam-
mals and is usually straight and slender, with enlarged ends,
the lower one forming the external malleolus, which serves to
prevent outward dislocation of the ankle. In many forms
the fibula is coossified with the tibia at both ends, and in the
most highly specialized hoofed animals, such as the horses,

SKELETON AND TEETH

87

camels and true ruminants, the bone has apparently disap-
peared. The young animal, however, shows that the ends
of the fibula have been retained and the shaft completely lost ;
the upper end is in the adult firmly fused with the tibia and,

IM. ***

Fio. 37. —Bones of left
lower leg of Wolf, front
aide. T., tibia. F.,
fibula, sp. spine of
tibia, en. cnemial
crest, t.m., internal
malleolus, e.m., ex-
ternal malleolus.

im

Fig. 38. — Bones of left
lower leg of Horse
(much more reduced),
en. cnemial crest. F.t
lower end of fibula,
coossified with tibia.
Other letters as in
Fig. 37.

Fio. 39. — Bones cf lower
leg, left side, of Tapir.
T., tibia. F., fibula.
sp., spine of tibia, en.,
cnemial crest. i.m.t in-
ternal malleolus, e.m.,
external malleolus.
N.B. This figure is on
a much larger scale than
Fig. 38.

in the horses, the lower end is also, but this remains separate
in the ruminants and camels, forming the malleolar bone,
which is wedged in between the tibia and the heel-bone.
Because of its importance in holding the ankle-bone in place,
this lower end of the fibula is never lost in any land mammal.
The hind foot, or pes, like the manus, is clearly divisible

LAND MAMMALS IN THE WESTERN HEMISPHERE

into three parts, the bones of which are
called respectively the tarsus, metatarsus
and phalanges, and the correspondence in
structure between manus and pes is close
and obvious. The tarsus consists typi-
cally of seven bones, which are tightly
packed and rarely permit any movement
between them. The upper row of the tar-
sus consists of two bones, which are pe-
culiarly modified to form the ankle-joint
and heel ; on the inner side is the ankle-
bone, or astragalus, the shape of which is
highly characteristic of the various mam-
malian orders. The upper or posterior
portion of the astragalus,
according to the position
of the foot, is a pulley
which glides upon the
Fio.40. — Left pee of Wolf, lower end of the tibia

front side, Cal., calca- , . , ,, „ ,

neum. a>„ astrajaiiu. and is held hrmly in
n.. navicular, ch., m- piace by the internal and

boid. Cn.l.Cn.t.Cn.S, \ J

internal, middle and ex- the external malleolus.

ternalruneiforms. Mil, ^[^ th(J pUUey_Iike

rudimentary first meta-

tarsal, ml ii-v. nwond surface the astragalus
'di ,* «™ftakafiBB *' usually contracts to a

Ph. 1, first phalanx. -

narrow neck, which ends

Una., ungual phalanx. a . i_ j

/. rudimentary hallux. ™ * fl*t <>r COnveX head.

ii-v, second to fifth The astragalus is sup-
ported behind (or be-
neath) by the heel-bone, or calcaneum, which
is elongate and extends well above (or behind) Flo
the remainder of the tarsus ; it frequently has m
a distinct articulation with the fibula, but more at
commonly is not in contact with that bone.
The astragalus rests upon the navicular, which

n. Note the targe.
si*- of ATI. /, the met-
atarsal of the first
digit, or hallux. Let-
ters as in Fig. 40, ex-
cept Cb„ cuboid.

SKELETON AND TEETH 89

is moulded to fit its head and corresponds in position to the cen-
tral of the carpus, but, unlike that carpal, it is a very important
element and is never suppressed or lost in any land mammal.
The navicular, in turn, rests upon three bones of the second row,
which are called respectively the internal, middle and external cu-
neiform, which correspond to the trapezium, trapezoid and mag-
num of the carpus and to which are attached the three inner met-
atarsals, one to each. Finally, the cuboid, the external element
of the second row, is a large bone, which supports the calcaneum
and often part of the astragalus and to which the fourth and
fifth metatarsals are attached ; it is the equivalent of the unci-
form in the manus. The number of tarsals is more constant
than that of the carpals, but some suppressions and coossi-
fications do occur.

The long bones of the pes constitute the metatarsus, which
is the counterpart of the metacarpus. There are never more
than five metatarsals in any normal mammal, but there may be
any number less than five, down to a single one. In form and
size the metatarsals of any given mammal are usually so like
the metacarpals, that it requires some experience to distinguish
them, but when either manus or pes is especially adapted
to some particular kind of work, there may be very decided
differences between metatarsals and metacarpals. For example,
the burrowing forefoot of the moles is very different from the
hind foot, which has undergone but little modification, and
even more striking is the difference between the wing of a bat
and its foot. Many other instances of a less extreme diver-
gence might be enumerated, but when manus and pes are used
only for locomotion, as in nearly all hoofed animals and many
other mammals, the metacarpals and metatarsals are very
similar. When there is a difference in number, it is the general
rule that there are fewer metatarsals; an instance of this is
found in the tapirs, which have four toes in the front foot and
three in the hind. Forms which have a cannon-bone in the
manus have it also in the pes, and some, like the peccaries and

90 LAND MAMMALS IN THE WESTERN HEMISPHERE

the jumping rodents called jerboas, have it only in the pes.
The first (or inner) metatarsal, that of the great toe, or hallux,
is sometimes opposable to the others, as in the monkeys, apes
and lemurs.

The word metapodial is a useful general term which in-
cludes both metacarpals and metatarsals. A metapodial
with its phalanges is a digit, a term often employed because
of the ambiguity which arises in the use of the words "fingers"
and "toes," and is applicable to both fore and hind feet.

Normally, the phalanges of the pes are so like those of the
manus as to require no particular description ; and only when
the two pairs of extremities are specialized for entirely different
function, is there any notable divergence between the pha-
langes of manus and pes.

Before leaving the subject of the skeleton, it will be well
to explain the terms used in describing the gait and manner of
using the feet. When the entire sole of the foot is in contact
with the ground and weight is thrown upon the heel-bone, or

calcaneum, the gait is said to
be plantigrade and is exem-
plified in Man, bears, raccoons
and many other mammals.
The Dog is digitigradey that is
to say, the feet in the stand-
ro. «. -Left pes of Black Bear (Ursus 'mS position are nearly erect

americanut), showing the plantigrade gait, and the WllSt and heel are
T.9 tibia. F., fibia. Cal., calcaneum. • j i • i_ t_ ji j

As., astragalus. N.. navicular. Cn.S, raised high above the gTOUnd )

external cuneiform. Cb., cuboid. Mt.V, the weight is bome Upon ball-
fifth metatarsal, -iii

like pads, one under the pha-
langes of each functional digit and one under the metapo-
dials. The digitigrade gait is found not only in all the dogs
and cats, but in many other Carnivora and in the camels and
llamas, as well. Transitions between the plantigrade and
digitigrade gait are so numerous and gradual, that such terms as
semi-plantigrade and semi-digitigrade are sometimes necessary.

SKELETON AND TEETH

An animal is said to be unguli-
grade when the weight is carried
entirely upon the hoofs and is
used only of hoofed animals ; ex-
amples are the horses, pigs, deer,
antelopes, oxen, etc. The so-
called "knee" of a horse is really
his wrist and the "hock" is the
heel, so that the feet make nearly
half the apparent length of ths
legs. Certain very large and
massive animals, such as the rhi-
noceroses and elephants, are un-
guligrade in a modified sense ;
the foot is a heavy column, seem-
ingly a part of the leg, and the
weight is borne upon a great pad
of elastic tissue, with the hoofs
disposed around its periphery. A
very peculiar mode of locomotion
is exemplified by certain of the
Edentata, in the forefoot of the
existing Ant Bear (Myrmeco-
pkaga jubata) and in both ex-
tremities of some of the later
representatives of the extinct
tground-sloths, or fGravigrada.
Here the weight is carried upon
the outer edge of the foot, the
palm and sole being turned in-
ward. No term has been sug-
gested for this very exceptional
gait, which is a modified form of plantigradism.

Fir.. 43. — Left pes of Patagonian Deer
(liippvcumcluit buulcus), showing the
unguligrade gait. T., tibia. F., lower
end of fibula (malleolar hone). Cat.,
calcaneum. .-Is., astragalus. f/.Cb.,
eooosiried cuboid and navicular. Mi.
Ill, ML IV, cannon-bone, formed by
the coSssification of the third and
fourth metatarsals. V., Rudimen-
tary fifth digit.

VC£ LAND MAMMALS IN THE WESTERN HEMISPHERE

II. The Teeth

It was pointed out in Chapter II (p. 38) that very often
( he tooth are all that remains to us of extinct genera and species
of mammals, and it may be further noted that the teeth are
vory characteristic and often suffice to fix the systematic position
of a genus. Since, therefore, the teeth play such an uncom-
monly important part as fossils and are so pre-eminently useful
to the palaeontologist, it is necessary to give some general
account of them.

Among the mammals the teeth display a very great variety
of size and form in accordance with the manner in which they
are used. Primarily, the function of the teeth is to seize and
masticate food, and the kind of food habitually eaten by any
animal is well indicated by the form of its teeth. The beasts
of prey have teeth adapted for shearing flesh and crushing
bones ; plant-feeders have teeth fitted for cropping plants and
triturating vegetable tissues; insect-eaters have teeth with
numerous sharp-pointed cusps, or it may be, no teeth at all,
swallowing without mastication the insects which they capture,
etc. Among animals that have similar diet there is very
great difference in the form and elaborateness of the grinding
apparatus and it is often possible to follow out the steps of
evolutionary change, by which, from simple beginnings, a high
degree of complexity has been attained. In addition to the
uses of the teeth as organs of mastication, they frequently
serve as weapons of offence or defence. In the flesh-eaters
which capture living prey they are formidable offensive
weapons, and the fangs of the Lion or the Wolf are instances
familiar to every one ; but the tusks of the elephants or the
hippopotamuses have nothing to do with the taking of prey.
Several Old World deer, which have no antlers or very small
ones, possess scimitar-like upper tusks, with which they are
able to defend themselves very effectually.

In the lower vertebrates, such as reptiles and fishes, the

SKELETON AND TEETH 93

number of teeth is usually indefinite and they continue to
be shed and replaced, as needed, throughout life ; but in each
species of mammal, aside from abnormalities, the number is
fixed and constant. Mammalian teeth are very generally
divisible into four categories • (1)
the incisors, or front teeth, which
in the upper jaw are inserted in
the premaxillary bones, (2) the
canines, or eye-teeth, which are
never more than one on each side

Fio. 44. — Dentition of Wolf, left side.
Of each jaw, Or four m all, (3) the i.S, third incisor. C\, canine, p. /,

premolars, Called in Man the bi- ** Premolar p. 4, fourth premolar.
r ' m.l, first molar.

cuspids, the anterior grinding

teeth which have predecessors in the milk-series and (4) the
molars, the posterior grinding teeth which have no such pred-
ecessors.

It is customary and convenient to express the numbers and
kinds of teeth of a given mammalian species by means of a
"dental formula" ; for example, in Man the formula is:
* h c h V $ 9 m h X 2 =32 ; the reason for the multiplication by
two is that the figures deal only with one side of the mouth
and must be doubled to give the sum total. Just because,
however, the two sides are alike, it is usual to take the doubling
for granted. Written out in full, the formula means that Man
has two incisors, one canine, two premolars and three molars
on each side of each jaw, the horizontal line indicating the
division between upper and lower teeth. The number of teeth
is frequently not the same in the upper and lower jaws ; for
instance, the formula for the Sheep is : i #, c {, p f , m §, X 2 = 32 ;
the total is the same as in Man, but the arrangement is entirely
different. The meaning is that in the Sheep there are no upper
incisors or canines, but three incisors and a canine are present
in each half of the lower jaw, with three premolars and three
molars on each side above and below. The Dog gives still
another formula :i$,c{, p \, m £ , X 2 = 42. What is called the

94 LAND MAMMALS IN THE WESTERN . HEMISPHERE

typical formula for the higher terrestrial mammals above the
grade of the marsupials and which is but rarely exceeded, is
i h c\y V i> m i > X 2 = 44, though most existing mammals have
fewer teeth than this. Compared with the typical formula, the
Dog has lost but two teeth, the third upper molar on each
side, while Man and the Sheep have each lost twelve.

As every one knows from his own experience, mammals
normally have two sets of teeth, the first, temporary, or milk-
dentition, in the young anijnal, and the second, or permanent
dentition, in the adult. The milk-dentition, when fully
developed, consists of incisors, canines and premolars, which
usually agree in number, though often not in form, with the
permanent teeth which replace them in the adult. The milk-
teeth are frequently more conservative than the permanent
ones and retain ancestral characters which have disappeared
in the adult series, thus affording welcome information as to
lines of descent and steps of evolutionary change. While
there can be little doubt that the development of more than
one dentition, or set of teeth, is the primitive condition among
mammals and was derived by inheritance from their lower
vertebrate ancestors, in which there was an indefinite succession
of teeth ; yet there are many mammals in which the milk-
dentition is greatly reduced or altogether lost. In some, the
milk-teeth are shed and replaced before birth, in others only
the germs of the milk-teeth are formed and never cut the gum,
while in others again all traces of the temporary series have
vanished. This complete loss of the milk-teeth, like the pres-
ence of a great number of simple and similar teeth in the
dolphins and porpoises, or the total absence of teeth, as in the
anteaters and whalebone whales, is a secondary and derivative
condition, never a primitive one.

The structure of mammalian teeth varies greatly, from the
simplest slender cones to enormous and highly complicated
apparatus, and, in order to comprehend the significance of
these differences, we must look a little more. closely into the

io. 44a. — First upper
molar, right aide of
Deer (Odoeoifeus). On
the left, the maati-
catingaurface; heavy
black line, - enamel.
On the right, external

and roots. Brachyo-

SKELETON AND TEETH 95

materials of which the teeth are constructed and the manner

in which those materials are combined. In all primitive

mammals and in many of the higher and

more advanced ones (including Man) a tooth

is composed of the crown, or portion which

is exposed above the gum, and the roots* one

or more in number, by means of which the

tooth is firmly inserted in the jaw-bone ; the

roots are at least partly formed before the

tooth comes into use. Such a tooth is said

to be short or low-crowned, or brachyodont.

In many plant-feeders, such as horses,

cattle, elephants, beavers, etc., the teeth

continue to grow in height for a long time

and do not form roots until late in life, or perhaps not at all.

Such teeth are said to be long- or high-crowned, or hypsodonl, and

in very many instances the development of brachyodont into
hypsodont teeth may be fol-
lowed through every step of
the change. The advan-

|a^jj§7*51 / taSe °^ *ne change is ob-

t^V^r j | / vious in lengthening the

animal's life, especially in
those which feed upon abra-
sive substances, like grass,
for the growth of the teeth
long continues to make up
for the loss through wear.
Serious trouble has often
been caused for captive el-
ephants by giving them too

Fio. 45. — First upper molar, left aide, of a fos- soft food, SO that the growth
nil horse (Bquu* tp.). Oo the right, external * .. , .. . , ,

aide. On the left, the grinding surface, °f the **«"> ls not P">perly

showing two stages of wear. Heavy black balanced by abrasion. Still

line, enamel ; white, dentine; shaded. cement. , , .

HyjKodont, roots not yet formed. another category of teeth is

96

LAND MAMMALS IN THE WESTERN HEMISPHERE

\ \s^2&

Fig. 46. — Dentition of Beaver (Castor
canadensis), m. S, last molar, p. 4,
last premolar, i. , scalprif orm incisors ;
enamel face black, dentine in vertical
lines.

the rootless, which are of simple form, like those of an armadillo,
and grow throughout life, never forming roots. The chisel-like,

or scalprif orm incisors of the ro-
dents do not cease to grow while
the animal lives ; they are kept
of constant length by continual
use, and the arrangement of
harder and softer tissue is such
that the sharp edge is main-
tained; through accident or
malformation it sometimes hap-
pens that the upper and lower
teeth fail to meet, then the con-
tinued growth causes them to form curved hoops in the mouth,
locking the jaws and bringing death by starvation to the un-
fortunate animal.

The typical mammalian tooth is composed of three kinds
of tissue, all differing in structure and hardness and called
respectively (1) dentine, (2) enamel, (3) cement. (1) The
dentine, or ivory, is the indispensable tissue of the tooth ; the
other kinds may be absent, but never the dentine. Chemically,
it is like bone, but the microscope shows that its structure is
quite different from that of true bone, being composed of an
immense number of fine tubules, which radiate from the
" pulp-cavity/ ' or chamber which contains the blood-vessels
and nerves, these entering the tooth through the canals of the
roots. The tubules of the dentine lodge excessively fine
fibrillae of the nerve and that is why the cutting into a live
tooth is so painful an operation. (2) The enamel, which is
the hardest of all animal tissues, has a polished and shining
appearance and is arranged in a mosaic of microscopic prisms,
closely packed together, which in most mammals are solid,
but in the marsupials, with some exceptions, are tubular.
The enamel normally covers the entire crown of the tooth,
but does not extend upon the roots, where its superior hardness

SKELETON AND TEETH 97

would be of no advantage. In several instances, always as
a secondary specialization, the enamel does not cover the whole
crown, but is arranged in vertical bands, it may be on one
side only, or at intervals around the tooth. The scalpriform
incisors of the rodents, already alluded to, have the enamel
band on the front face of the tooth ; the softer dentine behind
wears away more rapidly, keep-
ing the cutting surface bevelled,
like the edge of a chisel, while
the hard enamel forms the sharp
edge. In some instances the en-
amel is absent altogether and the
teeth are composed entirely of
dentine, as in the elephant tusk. Fl°- ,47 7,s""°" : ^S"* fl'°r,CT

' K molar of the Indian Elephant (Elt-

In all the Edentata, SUch as pha» maximiu). Enamel, heavy

sloths and armadillos, both liv- ISLSSST ""^
ing and extinct, that have any

teeth at all, the teeth have no enamel, but in some of the
fossil forms the place of the missing enamel is taken by a
harder dentine and thus the effect of differential hardness
is secured.

(3) The cement is simply bone, both chemically and in
microscopic structure ; it is not quite so hard as dentine, but
it is less affected by the fluids of the mouth and the juices of
the food. In the brachyodont or low-crowned tooth, Buch as
a human molar, the cement merely forms a sheath over the
roots and does not appear upon the crown, but in many
hypsodont teeth, those of horses and elephants, for example,
the cement completely encases the entire tooth in a thick layer,
filling up all the depressions and irregularities of the enamel
surface and making a freshly erupted and unworn tooth look
like a shapeless lump. When the cement and the enamel
covering are partially worn through, the masticating surface
is made up of three distinct substances, each having a dif-
ferent degree of hardness and thus, through unequal wear,

98 LAND MAMMALS IN THE WESTERN HEMISPHERE

the grinding surface is always kept rough and therefore efficient.
Not all hypspdont teeth have the cement covering, but in
such teeth the differing degrees of hardness of enamel and
dentine suffice to keep a rough surface, though not so
effectively.

CHAPTER V

THE GEOGRAPHICAL DEVELOPMENT OP THE AMERICAS IN

CENOZOIC TIME8

I. Tertiary Period

In the interior regions of western North America the transi-
tion from the Mesozoic to the Cenozoic was so gradual that
there is great difficulty in drawing the line between them and
therefore, as might be expected, there is much difference of
opinion as to just where that line should be drawn. From
one point of view, the matter is of no great consequence ; but
from another, it is of the utmost importance, for, unless the
events in different continents can be approximately syn-
chronized, it will often prove a hopeless undertaking to trace
the course of migration of the various mammalian groups and
determine their place of origin and primary home. Until
a definitive answer can be given to the question as to when
the Cenozoic era began, many significant points must be left
in doubt, and much remains to be done in the geology of the
Far West before that definitive solution can be reached.

1. Paleocene Epoch

So far as North America is concerned, the best available
evidence points to the conclusion that we should regard the
Fort Union, Puerco and Torrejon as the most ancient of the
Cenozoic formations (see Table, p. 17), though retaining so
many features of Mesozoic life that a separate division of the
Tertiary, the Paleocene epoch, is made for them. Such a sepa-
ration is not the common practice in this country, where it is
more usual to employ the terms "Lowest" or "Basal" Eocene.

99

100 LAND MAMMALS IN THE WESTERN HEMISPHERE

In my judgment, however, the balance of advantage is in favour
of giving to this so-called Basal Eocene a rank equivalent to
that of the four other universally recognized and admitted
epochs of the Tertiary period. No marine rocks of Paleocene
date have yet been found in North America, which indicates
that the continent was at least as extensive as it is now. The
very scanty development of deposits representing this epoch
in Europe renders the comparison with the fossils of the Old
World unsatisfactory and hence leads to uncertainty, when it
is attempted to determine the land-connections of the time.
During the Mesozoic era the shallow Bering Sea had repeatedly
been elevated into a land joining North America with Asia
and had as often been depressed, so as to separate the conti-
nents and allow the waters of the Arctic Ocean to mingle with
those of the Pacific. A like alternation of junction and separa-
tion went on during the Tertiary and Quaternary periods and,
by a comparison of the fossil mammals of Europe and America
for any particular division of geological time, it is almost
always feasible to say whether the two continents were con-
nected, or altogether separated. This statement does not
imply that the proportion of common elements in the two
faunas during epochs of continental connection was a con-
stant one at all times, for that was by no means true. Mere
land-connections or separations are not the only factors which
limit the spread of terrestrial animals ; if they were, the com-
munity of forms between North and South America would
be much greater than it actually is. Climatic barriers are of
almost equal importance in determining animal distribution,
and changes of climate may greatly alter the conditions of
migration between connected continents. As the connections
between North America and the Old World were probably in
high latitudes, where the seas are narrow, changes of climate
produced a greater effect upon migration than they could have
done had the land-bridges been in the tropical or warm tem-
perate zones. That these vicissitudes of climate really did

GEOGRAPHICAL DEVELOPMENT OP THE AMERICAS 101

occur and are not mere guesses to bolster up a tottering hy-
pothesis, there is abundant evidence to prove.

In the Paleocene, or most ancient epoch of the Tertiary
period, the geographical condition of North America was ap-
proximately as follows: The continent had attained nearly
its modern outlines and on the Atlantic and Pacific coasts
probably extended farther seaward than it does to-day. Florida,
however, and perhaps a narrow strip of the northern Gulf
coast were still submerged, the Gulf of Mexico opening broadly
into the Atlantic. It is very probable that the continent was
connected with the Old World by a land occupying the site
of Bering Sea and perhaps also by way of Greenland and the
North Atlantic ; and there is some evidence, though not al-
together convincing, that it was also joined to South America.
The great mountain ranges were largely what they now are,
though subsequent upheavals greatly modified the Rocky
Mountains, Sierra Nevada and the ranges of the Pacific coast,
while the lofty St. Elias Alps of Alaska were not in existence.
The region of high plateaus, between the Rockies and the
Sierras, was much less elevated than it is now. The Appala-
chians, which were of far more ancient date than the western
ranges, had been worn down by ages of weathering and stream-
erosion into a low-lying, almost featureless plain, with some
scattered peaks rising from it here and there, of which the moun-
tains of western North Carolina were the highest. In general,
it may be said that while the average height of the continent
above the sea-level may have been as great or greater than at
present, yet the inequalities of surface appear to have been
less marked, and both along the Atlantic coast and in the in-
terior were vast stretches of plains.

The Paleocene formations of the western interior are of
non-marine or continental origin. In northwestern New
Mexico is the typical area of the Puerco and Torrejon, a series of
beds 800 to 1000 feet in thickness and for the most part quite
barren of fossils, but there are two horizons, one near the top

102 LAND MAMMALS IN THE WESTERN HEMISPHERE

and the other near the bottom of the series, which have yielded
a very considerable number of fossil mammals, and of these
the lower is the Puerco, the upper the Torrejon. The Fort
Union is quite different in character and is composed of great
areas of sandstone and clay rocks, with a maximum thickness
of 2000 feet, in eastern Wyoming, South Dakota, Montana
and the adjoining parts of Canada. The modes of formation
of these beds have not yet been fully determined ; that they
may have been partly laid down in shallow lakes is indicated
by the masses of fresh-water shells in certain localities. In
others are preserved multitudes of leaves, which have given a
very full conception of the plants of the time, and great swamps
and bogs have left the traces of their presence in beds of lignite,
or imperfectly formed coal. Deposits made on the flood-
plains of rivers and wind accumulations are probably also
represented. "Vast stretches of subtropical and more hardy
trees were interspersed with swamps where the vegetation was
rank and accumulated rapidly enough to form great beds of
lignite. Here were bogs in which bog iron was formed. Amid
"the glades of these forests there wandered swamp turtles, alli-
gators, and large lizards of the characteristic genus Champ-
sosaurus" (Osborn, p. 100).

Fort Union mammals are relatively rare and most of those
that have been found are very fragmentary ; they are amply
sufficient, however, to demonstrate the Paleocene date of the
beds and to make it probable that they include both the Puerco
and the Torrejon faunas.

The climate, as shown by the plants, was much milder and
more uniform than that of the Recent epoch, though some in-
dication of climatic zones may already be noted. The vegeta-
tion was essentially modern in character ; nearly all our modern
types of forest-trees, such as willows, poplars, sycamores, oaks,
elms, maples, walnuts and many others, were abundantly
represented in the vast forests which would seem to have covered
nearly the entire continent from ocean to ocean and extended

GEOGRAPHICAL DEVELOPMENT OP THE AMERICAS 103

north into Alaska and Greenland, where no such vegetation
is possible under present conditions. Numerous conifers were
mingled with the deciduous trees, but we do not find ex-
clusively coniferous forests. Palms, though not extending
into Greenland, flourished magnificently far to the north of
their present range. On the other hand, the Paleocene flora
of England points to a merely temperate climate, while that
of the succeeding Eocene was subtropical.

South America. — Nothing is definitely known concerning
the condition of Central America and the West Indies and very
little as to South America. As no marine rocks of Paleocene
date have been found in any of these regions, it may be inferred
that all the existing land areas were then above the sea, and there
is some evidence that South America was much more extended
in certain directions than now. From the character and dis-
tribution of modern plants, fresh-water fishes, land and fresh-
water shells, there is strong reason to believe that in late
Mesozoic times a land-bridge connected Brazil with equatorial
Africa and this connection may have continued into the Pale-
ocene, though it is only fair to observe that some highly com-
petent authorities deny the reality of this bridge. There is
also evidence, though incomplete, of a connection between
South America and Australia by way of the Antarctic continent,
and it is clear that that polar region could not have had the
rigorous climate of the present time. In the upper part of
the Cretaceous, the last of the Mesozoic periods, there was
a possibility of migration, however indirect, between every
continent and every other, for the huge land reptiles called
Dinosaurs have been found in the non-marine Cretaceous
rocks of every continent, which could not have been the case,
had any of the great land areas been isolated. There is no
known reason to assume that the land-bridges were essentially
different in the Paleocene.

104 LAND MAMMALS IN THE WESTERN HEMISPHERE

2. Eocene Epoch

North America. — The Eocene witnessed quite extensive
geographical changes, though but little is known of it in Central
or South America, or the West Indies. Along the Atlantic
and Gulf coasts of the United States there was an extensive
submergence of the coastal plain, the sea covering the southern
half of New Jersey and extending thence to the southwestward
in an ever broadening band, through the South Atlantic and
Gulf states. Northern Florida was under water and the Gulf
extended as a narrow sound, known as the "Mississippi Em-
bayment, " up the valley of that river to southern Illinois and
westward into Texas. The Embav * wa^nresent in the
Cretaceous and again in the r 31* known

whether it persisted through rsdyit did

not, as the whole Atlantic coast u is*e stood

at a higher level then than n^ .nation of

Mexico and Central America during the , - < known

in any save the vaguest manner, it is evi laere was

then a broad communication between t **a*J the

Pacific, completely severing North and Soi unerica, though
the place of this transverse sea has not b en fixed. On the
Pacific side, a long, narrow arm of the sea occupied what is now
the great valley of California, extending north into Oregon and
Washington. It will be noted that in North America the
Eocene sea was almost confined to the neighbourhood of the
present coast-lines, nowhere penetrating very far inland, except
in the Mississippi Embayment, and thus differing widely from
the condition of Europe at that epoch, where much of what is

#

now land was submerged. The greatly expanded Mediter-
ranean covered most of southern Europe, where the great
mountain ranges, the Pyrenees, Alps, etc., had not yet been
formed. Very important, from the point of view of American
geography, is the fact that Europe was completely separated
from Asia by a narrow strait or sea, which ran down the eastern

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 105

Fio, 48. — Map of North America during the Eocene epoch. The present limits of (he
continent are ahown in outline ; white areas - land ; horUontal lines - sea ; dotted
areas — non-marine deposits ; black circles with white dots - active volcanoes.

(After Schu chert.)

106 LAND MAMMALS IN THE WESTERN HEMISPHERE

side of the Ural Mountains from the Arctic Ocean and joined
the enlarged Mediterranean. During the existence of this
Ural Sea any land connection of North America with Europe
must necessarily have been by means of a North Atlantic
bridge, or by one across the Arctic Sea, since communication
with Asia by way of Alaska would not have reached eastern
Europe.

Any such general statement of geographical conditions
during the Eocene as the foregoing sketch, cannot but be to
some extent misleading, because it brings together, as con-
temporary, arrangements which were, in some cases at least,
separated by considerable intervals of time and which were
subject to continual change. Along nearly all coasts the posi-
tion of the sea was quite different in the latter part of the epoch
from what it had been in the earlier portion. On the north
side of the Gulf of Mexico, for example, the sea retreated from
time to time, and the successive divisions of the Eocene rocks
are so arranged that the later ones are farther to the south.
Limitations of space, however, forbid the attempt to follow
out these minor changes.

In the western interior are found extensive non-marine
or continental deposits of Eocene date, which must be con-
sidered more in detail, because of the highly important bearing
which they have upon mammalian history. With the excep-
tion of a few small areas in Colorado, these deposits are all
situated in the plateau region west of the Rocky Mountains,
and were made of the debris of older rocks washed down by
rain and rivers and deposited in broad basins. Some of them
are the sediments of shallow or temporary lakes, and one series,
at least, is made up of volcanic ash and dust showered upon
the land, or into water of no great depth. The oldest of these
Eocene stages, known as the Wasatch (see Table, p. 17) covers
a very large region, though in a discontinuous manner ; the
principal area begins in New Mexico, where it lies over the
Torrejon, of the Paleocene, and extends far to the north through

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 107

,v\:x

-\ \

*%

\ c<

108 LAND MAMMALS IN THE WESTERN HEMISPHERE

western Colorado and eastern Utah to the Uinta Mountains,
around the eastern end of which it passes in a narrow band and
then expands again over southwestern Wyoming. A second
area is in the Big Horn Basin of northwestern Wyoming and
southern Montana, and probably two small areas in southern
Colorado are of the same date. The Wasatch beds are richly
fossiliferous and have yielded a most interesting and important
series of mammals, which were far more advanced than those
of the Paleocene ; and, at first sight, the student is tempted
to believe that they must be of very much later date. A more
critical examination shows that this appearance of a great
lapse of time between the Paleocene and the Wasatch is decep-
tive; the more advanced and characteristic of the Wasatch
mammals were obviously not the descendants of ancestors
in the North American Paleocene, but were altogether new-
comers to this continent, immigrants from some region which
cannot yet be identified. On the other hand, a considerable
number of the old, indigenous types still persisted, and these,
when compared with their Paleocene ancestors, are found not
to have changed so much as to require a very great length of
time, geologically speaking, for the degree of development
involved. This is the earliest recorded one of the great waves
of mammalian migration which invaded North America
down almost to our own time.

The same wave of migration extended to Europe, and that
there was a broad and easy way of communication between
that continent and North America is plain, for the similarity
between the Wasatch mammals and those of the corresponding
formation in France, the Sparnacian, is remarkably close.
At no subsequent time were the mammalian faunas of North
America and Europe so nearly identical as during the Wasatch-
Sparnacian age, which is especially remarkable when the dis-
crepancy is noted between the vast stretches of the Wasatch
(150,000 square miles) and the very limited areas in France.

If, as is probable, the Ural Sea was in existence at that time,

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 109

the land-connection with Europe must have been across
the North Atlantic, most likely from Greenland eastward. At
the present time a land-bridge in such high latitudes would be
of little service in bringing about a similarity of mammals in the
two continents, for the severity of the Arctic climate would be
as effective a barrier against the intermigration of all save the
Arctic mammals as the ocean itself; but in the mild and genial
Eocene climate the latitude of the bridge was of small conse-
quence.

The second of the Eocene stages, the Wind River — Green
River, is found in two very different phases. The Wind River
phase occupies the basin of that stream, north of the Wind
River Mountains in central Wyoming, and in the Big Horn
Basin of the same state it very extensively overlies the Wasatch,
and in this phase the sediments are very like those of the latter,
flood-plain and wind accumulations. A widely distant area
of this stage occurs in the Huerfano Canon in Colorado. The
Wind River beds contain numerous mammals which were
clearly sequential to those of the Wasatch, of which they were
the more or less modified descendants. With two possible
exceptions, there were no new immigrants and the connection
with the Old World may have been already severed, as it as-
suredly was in the succeeding age, the Bridger, though diver-
gent development had not yet had time to produce the very
striking differences in the mammals of North America from
those of Europe, which characterized the Bridger.

The Green River phase is a thick body of finely laminated
"paper shales," which seem to have been deposited in a very
shallow lake and occupy some 5000 square miles of the Green
River valley in southern Wyoming and northern Utah, where
they overlie the Wasatch, just as do the Wind River beds in
the Big Horn Basin. These fine-grained and thinly laminated
shales have preserved, often in beautiful perfection, countless
remains of plants, insects and fishes, but no traces of mammals,
other than footprints, have been found.

110 LAND MAMMALS IN THE WESTERN HEMISPHERE

The third of the Eocene stages of the interior is the Bridger
of southern Wyoming and northeastern Utah, where it lies
upon the Green River shales, but overlaps these shales both
eastward and westward, extending out upon the Wasatch.
The Bridger beds are largely made up of volcanic ash and dust
deposited partly upon the land and partly in shallow or tem-
porary lakes. The frequency with which the remains of fishes,
crocodiles and fresh-water shells are found indicates deposition
in water, and the large crystals of gypsum which are abundant
in certain localities show that the water became salt, at least
occasionally. From the immense mass of volcanic debris, it
is evident that volcanic activity broke out at this time on a
much greater scale than had been known in that region since
the Cretaceous period. Two different horizons, or substages,
are distinguishable in the Bridger, lower and upper, each of
which has its distinct mammalian fauna, though the two are
very closely allied. Their difference from the contemporary
mammals of Europe is very great, hardly any genera being
common to the two continents. So striking a difference in-
dubitably points to a severance of the land-connection, a sever-
ance which, as was shown above, probably took place during
the Wind River stage, for its effects would not be immediately
apparent ; time would be required for the operation of diver-
gent evolution, the fauna of each continent developing along
its own lines, to make itself so strongly felt. Had the connec-
tion never been renewed, North America, on the one hand, and
Eurasia on the other, would to-day be utterly different from the
zoological point of view, instead of containing, as they do,
a great many identical or closely similar animals of all classes,
a likeness due to subsequent migrations.

The fourth and last of the stages referred to the Eocene
is the Uinta, the geological position of which is the subject
of much debate; almost as good reasons can be brought
forward for placing it in the Oligocene as in the Eocene, so
nearly is it on the boundary line between those two epochs.

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 111

The Uinta is found in the Green River valley of northeastern
Utah and northwestern Colorado, where it lies upon the upper
Bridger and is the latest of the important Tertiary formations
to be found in the plateau region west of the Rocky Mountains.
It is probable that the separation of North America from the
Old World still continued, for, as a whole, the Uinta fauna
is totally different from that of the upper Eocene of Europe.
There were, however, a few doubtful forms, which may prove
to be the outposts of a renewed invasion.

The Eocene climate was decidedly warmer than the present
one, and subtropical conditions extended over the whole United
States and perhaps far into Canada. On the other hand,
signs of increasing aridity in the western part of the continent
are not wanting, and that must have resulted in a great shrink-
age of the forests and increase of the open plains. The vegeta-
tion was essentially the same as in the Paleocene, when it had
already attained a modern character, the differences from the
present being chiefly in regard to geographical distribution.
Large palms were then flourishing in Wyoming and Idaho,
and another indication of a warm climate is furnished by the
large crocodiles which abounded in all of the Eocene stages.

So far as North America was concerned, the Eocene epoch
was brought to a close by extensive movements of the earth's
crust, which more or less affected the entire continent and were
registered both on the sea-coasts and in the mountain ranges
of the interior. Upheaval added a narrow belt of land along
the Atlantic and Gulf coasts and the Mississippi Embayment
was nearly closed. On the Pacific side the sea withdrew from
the great valley of California and Oregon, and in the interior
the plateau region was elevated by a great disturbance, which
also increased the height of the western mountains.

Our knowledge of Eocene land-mammals in North America
is almost wholly derived from the formations of the western
United States, but it may be inferred from the uniform climatic
conditions that there were no very great geographical dif-

112 LAND MAMMALS IN THE WESTERN HEMISPHERE

ferences among the animals. This inference is confirmed by
the discovery of a Bridger genus, very fragmentary but identi-
fiable, in the marine Eocene of New Jersey.

South America. — No Eocene rocks, marine or continental,
are known in the West Indies or Central America, but the latter
region has been so imperfectly explored that no great impor-
tance can be attached to this fact. North and South America
were separated completely, as is proved by the entire dis-
similarity of their mammalian faunas, but the position of the
transverse sea or strait cannot be determined. There is much
reason to believe that the Greater Antilles were connected
into a single large land, which has been called "Antillia"
and may have been joined to the mainland of Central America.
Certain marine rocks in Patagonia and Chili have been re-
ferred to the Eocene by South American geologists, but the
reference is almost certainly erroneous, the rocks in question
being much more probably Miocene. The Andes, probably
throughout their length and certainly in their southern half,
stood at a much lower level than they do now, and, no doubt,
were rising, either slowly and steadily, or periodically and more
rapidly, throughout the whole Tertiary period. At all events,
their present height in the south is due to movements in the
Pliocene or later. Continental deposits of Eocene date have
been discovered only in northern Patagonia (Casa Mayor)
where they occupy depressions in the worn and eroded sur-
faces of the Cretaceous rocks; the mode of their formation
has not been carefully studied.

There is great uncertainty as to the status of the land-
bridge which, it is believed, in the Cretaceous period connected
South America with Africa. Some of the evidence goes to
show that the connection persisted throughout the Eocene
epoch, but the testimony is that of fragmentary and therefore
imperfectly understood fossils and is far from being unequivocal.
The connection with Antarctica probably continued.

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 113

3. Oligocene Epoch

North America. — The Oligocene, or third of the Tertiary
epochs, was a time of great significance in the history of the
American mammals and of great geographical changes in the
West Indian and Central American regions, but in North
America proper the changes were not so widespread. On the
Atlantic coast the marine Oligocene is but scantily displayed
except in the Florida peninsula, where it is found in a thick-
ness of some 2000 feet, but it is well developed along the north
shore of the Gulf of Mexico, where the coast-line followed
that of the Eocene, only a little farther to the south, marking
the retreat of the sea at the end of the Eocene. The Gulf
Stream entered the Atlantic over the site of northern Florida
and flowed northward nearer the coast than it does to-day,
in consequence of which warm-water conditions extended far
to the north and West Indian shells flourished on the New
Jersey coast. In the middle Oligocene part of northern Florida
was elevated into an island and the water over much of the
remainder of the peninsula became shallower, but this did
not greatly alter the course of the Gulf Stream. The Pacific
encroached upon the western shore of Oregon and British
Columbia and very extensively upon that of Alaska, where
strata no less than 10,000 feet thick are assigned to this
epoch.

In the western interior Oligocene formations are among
the most important and widely spread of the continental
Tertiaries and are divisible into two principal stages and each
of these again into three substages. Of these, the older or
White River stage covers a vast region in northeastern Colo-
rado, western Nebraska, eastern Wyoming and southern
South Dakota, with separate areas in the Black Hills, North
Dakota and the Northwest Territory of Canada. The de-
posits are believed to be chiefly of fluviatile origin, and many
of the ancient stream-channels, some of great size, may still

114 LAND MAMMALS IN THE WESTERN HEMISPHERE

Explanation tta in Fig. 48.

GEOGRAPHICAL DEVELOPMENT OP THE AMERICAS 115

be traced, filled with the consolidated sands and gravels of
the old rivers. The country was very flat and the divides
between the streams very low, so that in seasons of flood
great regions were converted into shallow, temporary lakes,
in which were deposited the finer silt and mud, but were dry
for most of the year. The volcanic activity which had gone
on so impressively in the Bridger Eocene was renewed in
White River times, as is proved by thick beds of pure volcanic
ash, which must have been carried long distances by the wind,
for they occur far from any volcanic vent.

The White River fauna is more completely known than
that of any other Tertiary formation of this continent. The
first discovery of these fossils was made more than 70 years
ago and since then oft-repeated expeditions have brought to
light an astonishing number and variety of mammals. Not
only are these beds remarkable for the immense quantity of
material which they have yielded, but also for its complete-
ness and beauty of preservation, a most unusual number of
skeletons having been obtained. The mammals demonstrate
that the land-connection with the Old World had been re-
established, for many European genera, which could not have
been derived from an American ancestry, are found in the
White River beds. At the same time, there was no such
proportion of forms common to both continents as there had
been in the Wasatch-Sparnacian stage of the lower Eocene,
each having many genera and even families which did not
extend their range into the other. The reason for this remark-
able and, at first sight, inexplicable difference between the
lower Eocene and the lower Oligocene is probably to be found
in climatic changes, in consequence of which relatively fewer
genera were able to take advantage of the reopened connection ,
which lay far to the north. The White River mammals, like
those of the Recent epoch, are thus divisible into two groups
or elements, one set indigenous and descended from ancestors
which are found in the American Eocene, and the other com-

1 1 0 LAND MAMMALS IN THE WESTERN HEMISPHERE

potted of late immigrants from the Old World. Migrants
from North America likewise made their way to Europe.

The upper continental Oligocene of the interior has re-
ceived the peculiar appellation of the John Day, from the river
of that name in eastern Oregon, a large part of which was
buried to a depth of 3000 or 4000 feet in stratified volcanic
ash and tuff. This great mass of finely divided volcanic
material was derived from the craters of the Cascade Moun-
tains to the westward; a long-continued series of eruptions
would be needed to form such thick accumulations at such
a distance from the sources of supply. The John Day evi-
dently succeeded the White River very closely in time, but
is marked by the disappearance of almost all the European
migrants. This fact, together with the absence of any new
immigrant genera, is evidence that the connection had again
been broken and it was not renewed until after a considerable
lapse of time.

There are many reasons for believing that the Oligocene
climate marked the beginning of the very long and gradual
process of refrigeration which culminated in the glacial con-
ditions of the Pleistocene epoch, but the change was slight
and probably chiefly affected the far north. The climate,
however, remained notably warmer than the present one of
the same extra-tropical latitudes, as is abundantly proved by
the fossils. The Atlantic coast, as noted above, was bathed
in warm waters, the plants of the Alaskan Oligocene point
to temperate conditions and the vegetation of Europe was
subtropical, palms growing in the north of Germany. The
change which was distinctly to be noted in the Great Plains
region of North America was probably due rather to the ele-
vation and increased altitude of the western interior than to
general climatic alteration. Crocodiles are very rare indeed
in the White River beds and those that have been found all
belong to dwarf species, while none are known from the John
Day. Unfortunately, hardly anything has been ascertained

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 117

concerning the Oligocene vegetation of the region, but the
reptiles indicate diminished warmth.

South America. — Marine Oligocene strata have great
extent around the Gulf of Mexico and the Caribbean Sea, and
the distribution of these shows that Antillia was broken up
by great submergences, the islands of the Greater Antilles
being much smaller than they are to-day. The greater part
of Central America and the Isthmus were under water, a
broad sea, broken only by scattered islands, separating North
and South America. Very little is known of the Oligocene in
the latter continent save a non-marine formation in northern
Patagonia, the Deseado stage (or Pyrotherium Beds), which,
like the Eocene of the same region, occupies depressions in
the worn and irregular surface of the Cretaceous rocks. The
attribution of the Deseado to the Oligocene is open to some
doubt, because of the entire absence in its mammalian fauna
of any elements which are also found in the northern hemi-
sphere. Hence, there are no means of direct comparison.

4. Miocene Epoch

North America. — The Atlantic and Gulf coasts, which
had been raised in the Oligocene, were again depressed, almost
restoring the Eocene coast-line, the chief differences being
the presence of the Florida islands and the nearly complete
closing of the Mississippi Embay ment. There was a remark-
able change in the marine fauna from that of Oligocene times ;
a cool current flowed southward along the coast and entered
the Gulf of Mexico through the strait between the Florida
island and the mainland, bringing the northern animals with
it and driving out the tropical forms. This complete faunal
change, which might fairly be called a revolution, was the most
sudden and striking in the Tertiary history of the continent.

On the Pacific coast also there was a depression, which
caused a renewed transgression of the sea. The Coast Range
formed a chain of reefs and islands in the Miocene sea, which

118 LAND MAMMALS IN THE WESTERN HEMISPHERE

again filled the great valley of California, except in the northern
part of what is now the Sacramento Valley, where there was
an accumulation of continental deposits. The immense thick-
ness (5000 to 7000 feet) of the California Miocene is largely
made up of volcanic material, which testifies to the great
activity of the vents. In the Sierras, the height of which was
increased in the upper Miocene, there was also a great display
of vulcanism, recorded in the lava-flows and tuffs of the time.
In the region of Lower California and northwestern Mexico
considerable changes of the coast-line took place during the
Miocene; in the earlier half of the epoch the Gulf of Cali-
fornia was much shorter and narrower than it is to-day and
the peninsula was broadly united with the mainland to the
east as well as to the north. A wide submergence marked
the upper Miocene, reducing the peninsula to a long, narrow
island and enlarging the gulf considerably beyond its present
limits, flooding an extensive area in northwestern Mexico and
sending a small bay into southeastern California. There were
great disturbances in the course of the epoch, for in the Santa
Cruz Mountains near San Francisco the lower Miocene strata
were crumpled into folds, before those of the upper Miocene
were deposited upon them. British Columbia, Washington
and Oregon were invaded by the sea, which extended up the
valley of the Columbia River and its southern tributary, the
Willamette, though here the beds are far thinner than those
of California. Much of Alaska, both on the north and west
coasts and in the valley of the Yukon, was submerged, and the
land-connection with Asia appears to have been broken. This
is made probable not only by the submergence of the Alaskan
coast, but also by the fact that the marine animals of the Cali-
fornia coasts and shoal waters, which could not migrate across
the ocean, were quite unlike the contemporary forms of the
eastern Asiatic shore, which would hardly have been the case,
had a continuous coast-line united the two continents. On the
other hand, there was a renewed connection with Europe, as

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 119

120 LAND MAMMALS IN THE WESTERN HEMISPHERE

is shown by the appearance of Old World land-mammals,
beginning scantily in the lower and becoming numerous in
the middle Miocene. This connection, it will be remembered,
had been interrupted during the upper Oligocene. Many
students of the problem have maintained that the land-bridge
was by way of the West Indies and the Mediterranean lands,
but such a bridge would not account for the facts of mammalian
distribution, which would seem to require its location in the
far north.

Several distinct lines of evidence go to prove that the
junction of the Americas dates from the Miocene, possibly
from the beginning of it. The absence of Atlantic species
from the Pacific Miocene is an indication that the passage
from ocean to ocean had been closed, and this is confirmed by
the geology of the Central American and Isthmian region.
In the middle Miocene of Oregon and Nebraska have been
found remains, which are unfortunately too incomplete for
altogether convincing identification, but which can be inter-
preted only as belonging to the extinct and most characteristi-
cally South American group of edentates, the fground-sloths or
fGravigrada ; if this reference is correct, the fact of the junc-
tion cannot be questioned.

Continental deposits of Miocene date, chiefly accumula-
tions made by rivers and the wind, cover vast areas of the west-
ern interior, though but rarely to any considerable depth.
These have been divided into several stages and have received
various names; the lower Miocene, known as the Arikaree,
Harrison or Rosebud, overlies the White River in South Dakota,
western Nebraska and eastern Wyoming, with smaller areas in
Montana and Colorado. In the deposits of this stage there
are no mammals of indisputably Old World type, though a few
which I consider to be such are a probable indication of re-
newed connection with Europe. The middle Miocene is
found typically in central Montana, where it is called the

t Extinct.

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 121

Deep River (or Smith River) stage, but occurs also in numerous
small, scattered and widely separated areas in Oregon,
Wyoming, Colorado and Texas, with local names in these
different states. It is most likely that these middle Miocene
formations are not strictly contemporaneous in the geological
sense, but rather form a closely connected and successive series.
The mammals of the Deep River stage leave no doubt that the
way of migration from the Old World was again open.

The Loup Fork, or upper Miocene, itself susceptible of
further subdivision, is by far the most extensive of the Miocene
formations and covers much of the Great Plains region, in
separate areas, from South Dakota far into Mexico. Perhaps
also referable to the upper Miocene is a small, but very inter-
esting formation, the Florissant, which is in the South Park
of Colorado ; it was made by very fine volcanic material
showered into a small and shallow lake. The finely laminated
papery shales of the Florissant have preserved countless
plants and insects and many fishes, and these throw very
welcome light upon the vegetation and climatic conditions
of the epoch and afford an interesting contrast to the fauna
and flora of the Green River shales of the lower or middle
Eocene. That the Florissant shales are Miocene, no one
questions, but their isolated position and the fact that they
have yielded no mammals make it somewhat doubtful whether
they belong in the middle or later part of the epoch.

In the western portion of the continent vulcanism was dis-
played on a grand scale during the Miocene. Mention has
already been made of the quantity of volcanic material in the
marine Miocene of California and also in the lavas and tuffs
of the Sierras. The magnificent cones, such as Mts. Hood
and Tacoma, which are the glory of the Cascades, are believed
to date from this time. In Idaho and eastern Oregon and
Washington are the immense lava-fields of the Columbia
River, which are, partly at least, of Miocene date and were
chiefly extruded through great fissures, the lava flooding the

122 LAND MAMMALS IN THE WESTERN HEMISPHERE

valleys and plains in a fiery sea of molten rock. In Oregon
these lavas rest upon the upper Oligocene (John Day stage)
and middle Miocene beds are deposited upon them, which
fixes their date sufficiently. In the Yellowstone Park was
piled up a huge mass of volcanic products, lava-flows and beds
of ash and tuff, to a thickness of several thousand feet. The
ash-beds have preserved the petrified forests, with their tree-
trunks still standing one above another; one locality in the
Park shows seven such forests, each one killed and buried
by a great discharge of ash and then a new forest established
and growing upon the surface of the accumulation. In the
tuffs are leaf-impressions which permit identification of the
plants.

In the latter part of the Miocene and at its close there were
important crustal movements, which affected all the Pacific
coast mountain ranges, though this epoch was no such time of
mountain making in America as it was in the Old World.
The principal elevation of the Coast Range in California and
Oregon was due to these movements, and the Sierras and the
plateaus of Utah and Arizona were increased in height. On
the Atlantic side the Florida island was joined to the mainland
and thus the present shape of the continent was almost exactly
gained.

The Miocene climate of North America, as indicated by
the plants of Florissant, the Yellowstone Park and Oregon, was
distinctly milder than at present, a southern vegetation of
warm-temperate character extending to Montana and perhaps
much farther north, but it was not so warm as it had been
in the Eocene, and palms are not found in any of the localities
mentioned, nor do crocodiles occur in any of the northern
Miocene formations. In Europe the climate of the early
Miocene was considerably warmer than in North America,
the vegetation of central and western Europe being very much
like that of modern India. This difference between the two
sides of the Atlantic was probably due, in large part, to the

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 123

manner in which Europe was broken and intersected by arms
and gulfs of the warm southern sea. In the latter half of the
epoch, however, the climate became colder, the subtropical
flora giving way to a distinctly temperate one.

South America. — In Central America, where marine Oli-
gocene beds are of great extent, no Miocene is known, and on
the Isthmus Oligocene is the latest marine formation, except
a narrow fringe of Pleistocene on the Caribbean coast. These
facts and others already cited lead to the conclusion that in
the Miocene the connection of the Americas was complete and
that the Isthmus was considerably broader than at present,
extending nearly to Jamaica. The condition of the Greater
Antilles is but vaguely understood, but they were involved in
the general elevation of the Caribbean region and were at
least as large as they are now and may have been considerably
larger, and Cuba was perhaps joined to Central America, as
Hayti probably was.

In South America proper nearly the whole of Patagonia
was submerged by the transgression of a shallow, epiconti-
nental sea, in which were accumulated the beds of the Pata-
gonian stage, containing an exceedingly rich and varied as-
semblage of marine fossils, an assemblage which has very little
in common with the contemporary formations of the northern
hemisphere. . It is this lack of elements common to the northern
faunas which has led to the long debate concerning the geo-
logical date of the Patagonian formation, the South American
geologists very generally referring it to the Eocene. How-
ever, the occurrence of genera of Cetaceans (whales and dol-
phins), which are also found in the Miocene of Maryland and
Virginia, is very strong evidence that the proper date of the
Patagonian is Miocene. A continuous coast-line, or at least
an unbroken continuity of shoal-water conditions, seems neces-
sary to account for the similarity of the Patagonian fossils
with those of New Zealand and Australia, and that this con-
nection was by way of the Antarctic continent is indicated by

124 LAND MAMMALS IN THE WESTERN HEMISPHERE

the occurrence of similar fossils in the South Shetland Islands,
an Antarctic group. On the Chilian coast the Navidad forma-
tion, which is believed to be approximately contemporaneous
with the Patagonian, has so different a fauna as to point to
some kind of a barrier between the Atlantic and the Pacific,
and this barrier, Dr. von Ihering holds, was the land-extension
from South America to Antarctica.

After some oscillations of retreat and advance, the seawith-
drew from Patagonia and the terrestrial accumulations of the
Santa Cruz stage were formed. These beds are partly com-
posed of river-deposits, but chiefly of more or less consolidated
volcanic ash or tuff, and have yielded a surprising number of
beautifully preserved mammals. No other assemblage of
South American Tertiary Mammalia is so well known and
understood as the Santa Cruz fauna, and the very large number
of all but complete skeletons which have been found strongly
suggests that many of the animals were buried alive in the
showers of volcanic ash. The Santa Cruz fauna is completely
and radically different from any of the North American as-
semblages, and at that time no immigrant from the north had
penetrated so far as Patagonia.

In the upper Miocene the Andes stood at a much lower
level than they do now ; fossil plants, some of them collected
at a great height in the mountains, are the remains of a luxuri-
ant and purely tropical flora nearly identical with the vegeta-
tion of the modern forests of Bolivia and Brazil. Such a
vegetation could not exist at the altitudes where the fossils
occur and these demonstrate a great elevation of the mountains
since those leaves were embedded. The same mild climatic
conditions which prevailed in the northern hemisphere during
the Miocene must also have characterized Patagonia, sub-
tropical shells extending far to the south of their present
range.

Whatever may have been true of the land-bridge connecting
South America with Africa during the early Tertiary epochs,

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 125

it must have been submerged in the Miocene, otherwise there

would not have been the open pathway for the Cetacea of

Patagonia to reach the Atlantic coast of North America and

vice versa.

5. Pliocene Epoch

North America. — The Pliocene of North America is not
nearly so well displayed or so satisfactorily known as the pre-
ceding Tertiary epochs, and only of comparatively late years
has it been recognized at all upon the Atlantic coast. The
Atlantic and Gulf shores had very nearly their present outlines,
but with some notable differences. It would seem that the
northeastern portion of the continent stood at a higher level
than it does now, north Greenland being joined with the islands
of the Arctic archipelago and Newfoundland with Labrador,
the Gulf of St. Lawrence then being land. From Nova Scotia
to southern New Jersey the coast-line was many miles to the
east and south of its present position, but the sea encroached
here and there upon the shores of Virginia, the Carolinas and
Georgia, and southern Florida was mostly under water, as was
also a narrow strip of the Gulf coast from Florida to Texas
and along the east of Mexico. On the Pacific side of the con-
tinent the marine Pliocene is far thicker and more important
than on the east coast and in California is largely made up of
volcanic materials. Quite extensive disturbances in this
region had marked the close of the Miocene, the strata of which
in the Coast Range had been violently compressed and folded.
An elevation of the land had caused the sea to withdraw from
the central valley of California and had restored Lower Cali-
fornia to its peninsular conditions, reducing the gulf to the
narrow limits which it had had in the lower Miocene and ex-
tending southern Mexico to the west and south. British
Columbia and southeastern Alaska stood at higher than their
present levels and the countless islands of that region were
part of the mainland. Bering Strait was closed, for at least
a great part of the epoch, and, as a continuous shore-line was

126 LAND MAMMALS IN THE WESTERN HEMISPHERE

Fig. 52. — Map of North America during the Pliocene epoch, Bering Strait open. Ex-
planation as in Fig. 48. (Modified from Schuchert.)

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 127

thus formed and a way of migration opened, the marine fauna
of California and Japan became closely similar.

In the interior, the Pliocene continental formations and
faunas followed so gradually upon those of the Miocene, that
there is great doubt as to where the line between them should
be drawn. These interior formations are mostly of small
extent and are very widely scattered, and much remains to
be learned regarding the mammals of the epoch. In northern
Kansas are the Republican River beds, which are so doubtfully
Pliocene, that they may almost equally well be called upper-
most Miocene. Other lower Pliocene stages, representing
various divisions of time, are the Alachua of northern Florida,
the Snake Creek of western Nebraska, the Thousand Creek and
Virgin Valley of northwestern Nevada and the Rattlesnake
of Oregon. Probably middle Pliocene is the Blanco of north-
western Texas, a valley cut in the middle and lower Miocene
rocks and filled in with Pliocene deposits. Possibly upper
Pliocene, or, it may be, lowest Pleistocene, are the Peace
Creek of southwestern Florida and the so-called "Loup River"
(not Loup Fork) of western Nebraska.

The volcanic activity of the Rocky Mountain and Pacific
coast regions, which was so remarkable in the Miocene, con-
tinued into and perhaps through the Pliocene. The great
outflow of light-coloured lava which built up the central
plateau of the Yellowstone Park is referred to the Pliocene,
and some of the enormous fissure-eruptions which formed the
vast Columbia River fields of black basaltic lava were probably
Pliocene, as some were demonstrably Miocene. Both of these
epochs were remarkable for volcanic activity in the western
part of the continent.

The Pliocene climate, as may be inferred from the plants
and marine shells, was colder than that of the Miocene, and
refrigeration was progressive, as is shown by the proportion of
Arctic shells in the Pliocene beds of the east coast of England,
rising from 5 per cent in the oldest to more than 60 per cent

128 LAND MAMMALS IN THE WESTERN HEMISPHERE

in the latest beds. In the Arctic regions the cold must have
been severe, at least during the latter half of the epoch, for
in the succeeding Pleistocene we find an Arctic fauna already
fully adapted to the extreme severity of present day polar
conditions and time was necessary for such an adaptation.
In the western interior the climate was not only colder, but
also drier than it had been in the Miocene, the desiccation
which had begun in the latter epoch becoming progressively
more and more marked.

South America. — The Greater Antilles were larger than
at present and Cuba was much extended, especially to the
southeastward, and was probably connected with the main-
land, not as one would naturally expect, with Yucatan, but
with Central America ; this island, it is most likely, was cut
off from Hayti. The Isthmian region was considerably broader
than it is now and afforded a more convenient highway of
intermigration. Costa Rica was invaded by a Pliocene
gulf, but it is not yet clear whether this persisted for the whole
or only a part of the epoch. In the Argentine province of
Entrerios is a formation, the Parand, which is most probably
Pliocene, though it may be upper Miocene. This formation
is largely marine and shows that the present Rio de la Plata
was then a gulf from the Atlantic. A few northern hemisphere
mammals in the Parand beds show that the migration had
advanced far into South America, A large part of Patagonia
was again submerged beneath the sea, which extended to the
Andes in places, but just how general the submergence was,
it is impossible to say, for the Cape Fairweather formation has
been largely carried away by erosion and only fragments of
it remain. Along the foothills of the Andes these beds are
upturned and raised several thousand feet above the sea-level,
a proof that the final upheaval of the southern mountains took
place at some time later than the early Pliocene. Continental
formations of Pliocene date are largely developed in Argentina ;
the Araucanian stage is in two substages, one in the province

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 129

of Catamarca, where the beds are much indurated and were
involved in the Andean uplift, the other, of unconsolidated
materials, is at Monte Hermoso near Bahia Blanca on the
Atlantic coast. The very small proportion of northern ani-
mals in the Araucanian beds is surprising, but not more so than
the almost complete absence of South American types in the
upper Miocene and lower Pliocene of the United States. Inter-
migration between the two Americas would seem to have been
a much slower and more difficult process than between North
America and the Old World, and the reason for the difference
is probably the greater climatic barriers involved in a migration
along the lines of longitude. Upper Pliocene is found in the
Tarija Valley of Bolivia and probably also in Ecuador, in both
of which areas the proportion of northern animals was very
greatly increased.

II. Quaternary Period

The Quaternary period was a time of remarkable geo-
graphical and climatic changes, which had the profoundest
and most far-reaching effects, partly by migration and partly
by extinction, upon the distribution of animals and plants,
effects which are naturally more obvious than those of earlier
geological events, just because they were the latest. It is cus-
tomary to divide the period into two epochs, (1) the Pleis-
tocene or Glacial, and (2) the Recent, which continues to the

present day.

1. Pleistocene Epoch

When Louis Agassiz first suggested (1840) the idea of a time,
comparatively recent in the geological sense, when northern
and central Europe was buried under immense sheets of
slowly moving ice, like the " ice-cap' ' of modern Greenland,
the conception was received with incredulity. Nearly thirty
years passed before this startling theory gained the general
acceptance of geologists, but now it is one of the common-
places of the science, for no other hypothesis so well explains
the complicated phenomena of Pleistocene geology. One great

130 LAND MAMMALS IN THE WESTERN HEMISPHERE

obstacle to the acceptance of the glacial theory was the sup-
posed fact that the Pleistocene glaciation was something quite
unique in the history of the earth, a violent aberration in
the development of climates. Now, however, we have every
reason to believe that at least three other and very ancient
periods had witnessed similar climatic changes and that ' ' ice-
ages" were recurrent phenomena. This is not the place to
discuss or even to summarize the evidence which has convinced
nearly all geologists of the reality of Pleistocene glacial con-
ditions on a vast scale in Asia, Europe and, above all, in North
America. The reader who may wish to examine this evidence
will find an admirable presentation of it in Vol. Ill of the
" Geology " of Professors Chamberlin and Salisbury.

North America. — There has long been a difference of
opinion among students of the Pleistocene as to whether the
glaciation was single, or several times renewed. That there
were many advances and retreats of the ice, is not denied ;
the question is, whether there were truly interglacial stages,
when the ice altogether disappeared from the continent and
the climate was greatly ameliorated. The present tendency
among American and European geologists is decidedly in
favour of accepting several distinct glacial stages (Chamberlin
and Salisbury admit six of these) separated by interglacial
stages, and for this there are very strong reasons. While it
is out of the question to present the evidence for this conclusion
here, one or two significant facts may be noted. On the north
shore of Lake Ontario, near Toronto, are certain water-made
deposits, which rest upon one sheet of glacial drift and are
overlaid by another. The fossils of the aqueous sediments
are in two series, upper and lower, of which the older and
lower contains plants and insects indicative of a climate con-
siderably warmer than that of the same region to-day and
corresponding to the temperature of modern Virginia. In
the upper and newer beds the fossils show the return of cold
conditions, much like those of southern Labrador, and this

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 131

was followed by the reestablishment of the ice, as recorded
in the upper sheet of drift. Even far to the north, on the
Hudson's Bay slope, an interglacial forest is embedded between
two glacial drift-sheets. In Iowa and South Dakota numerous
mammals of temperate character occur in interglacial beds.

At the time of their greatest extension, the glaciers covered
North America down to latitude 40° N., though the great
terminal moraine, which marks the ice-front and has been
traced across the continent from Nantucket to British
Columbia, describes a very sinuous line. The ice was not a
homogeneous sheet, moving southward as a whole, but flowed
in all directions away from several, probably four, centres
of accumulation and dispersal. At the same time, the western
mountain ranges had a far greater snow-supply than at present,
and great glaciers flowed down all the valleys of the Rocky
Mountains as far south as New Mexico and in the Sierras to
southern California, while the Wasatch, Uinta and Cascade
ranges and those of British Columbia and Alaska were heavily
glaciated, but, strange to say, the lowlands of Alaska were
free from ice. During the periods of greatest cold the rain-
belt was displaced far to the south of its normal position,
bringing a heavy precipitation to regions which are now ex-
tremely arid. In the Great Basin were formed two very large
lakes; on the east side, rising high upon the flanks of the
Wasatch Mountains, was Lake Bonneville, the shrunken and
pygmy remnant of which is the Salt Lake of Utah, and on the
west side, in Nevada, was Lake Lahontan. Lake Bonneville,
which was nearly two-thirds the size of Lake Superior, dis-
charged northward into the Snake River, a tributary of the
Columbia, but Lahontan had no outlet. Each of these lakes had
two periods of expansion, with a time of complete desiccation
between them.

Over the Great Plains the principal Pleistocene formation
is that known as the Sheridan, or, from the abundance of
horse-remains which are entombed in it, the Equus Beds.

132 LAND MAMMALS IN THE WESTERN HEMISPHERE

These beds extend as a mantle of wind-drifted and compacted
dust from South Dakota to Texas and in places contain multi-
tudes of fossil bones; they correspond to one of the early
interglacial stages and in South Dakota pass underneath a
glacial moraine.

The upheaval which came at or near the end of the Pliocene
had raised the continent, or at least its northeastern portion,
to a height considerably greater than it has at present, and this
must have facilitated the gathering of great masses of snow ;
but before the end of the Pleistocene a subsidence of the same
region brought about important geographical changes. The
depression, which lowered the coast at the mouth of the Hudson
about 70 feet below its present level, increased northward to
600 feet or more in the St. Lawrence Valley and allowed the
sea to invade that valley and enter Lake Ontario. From this
gulf ran two long, narrow bays, one far up the valley of the
Ottawa and the other into the basin of Lake Champ lain. The
raised beaches, containing marine shells and the bones of whales,
seals and walruses, give eloquent testimony of those vanished
seas. The recovery from this depression and the rise of the
continent to its present level inaugurated the Recent epoch.

When the ice had finally disappeared, it left behind it
great sheets of drift, which completely changed the surface
of the country and revolutionized the systems of drainage by
filling up the old valleys, only the largest streams being able
to regain their former courses. Hundreds of buried valleys
have been disclosed by the borings for oil and gas in the Middle
West, and these, when mapped, show a system of drainage
very different from that of modern times. Innumerable
lakes, large and small, were formed in depressions and rock-
basins and behind morainic dams, the contrast between the
glaciated and non-glaciated regions in regard to the number
of lakes in each being very striking.

On the west coast events were quite different; marine
Pleistocene beds in two stages are found in southern Cali-

GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 133

fornia. The upheavals late in the Pleistocene, or at its close,
were far greater than on the Atlantic side, 4000 feet in south-
eastern Alaska, 200 feet on the coast of Oregon and rising again
to 3000 feet in southern California ; all the western mountain
ranges and plateaus were increased in height by these move-
ments. The volcanoes continued to be very active, as may be
seen from the lava-sheets and streams in Alaska, all the Pacific
states, Arizona and New Mexico.

South America. — No such vast ice-sheets were formed in
the southern hemisphere as in the northern. Patagonia was
the only part of South America to be extensively covered with
ice and there traces of three glaciations have been observed,
of which the first was the greatest and reached to the Atlantic
coast, and there were great ice-masses on the coast of southern
Chili. Mountain glaciers existed throughout the length of the
Andes across the Equator to 11° N. lat., the elevation increas-
ing northward to the tropics. The surface of the great Argentine
plain of the Pampas between 30° and 40° S. lat. is covered
with a vast mantle, largely of wind-accumulated dust, the Pam-
pean, which is the sepulchre of an astonishing number of great
and strange beasts. The Pampean formation corresponds
in a general way to the Sheridan or Equus Beds of North
America, but involves a much greater lapse of time, beginning
earlier, possibly in the late Pliocene, and apparently lasting
through the entire Pleistocene. While largely of seolian origin,
the Pampean seems to be in part made of delta deposits
laid down by rivers. One striking difference between the
Pampean, on the one hand, and the Sheridan and the loess of
the Mississippi Valley and of Europe, on the other, is that the
former is in many places much more consolidated and stony,
which gives it a false appearance of antiquity. Another and
very rich source of Pleistocene mammals is found in the lime-
stone caves of eastern Brazil, which have yielded an incredible
quantity of such material, but not in such a remarkably per-
fect state of preservation as the skeletons of the Pampean.

134 LAND MAMMALS IN THE WESTERN HEMISPHERE

Very little is known of the Pleistocene in the West Indies,
though probably to this date should be assigned the notable
oscillations of level which are recorded in the raised sea-
terraces of Cuba and other islands. The Windward groups
were joined, at least in part, to the continent and large extinct
rodents reached Antigua, which would not be possible under
present conditions. The Isthmus of Panama was 200 feet
or more higher than it is now and correspondingly wider, but
was depressed to a lower than the present level, and finally
raised to the height it now has. Marine beds, of presumably
Pleistocene date and certainly not older, extend from the
Caribbean shore to Gatun, some seven miles, and are nowhere
more than a few feet above sea-level.

The question of Pleistocene climates is a very vexed one
and is far from having received a definitive answer. Limita-
tions of space forbid a discussion of the problem here and I
shall therefore merely state the conclusions which seem best
supported by the evidence so far available. Such immense
accumulations of ice might be due either to greatly increased
snow-fall, or to a general lowering of the temperature. The
balance of testimony is in favour of the latter factor and no
great refrigeration is required. Professor Penck has calcu-
lated that a reduction of 6° or 7° in the average yearly tem-
perature would restore glacial conditions in Europe. Even
the tropics were affected by the change, as is shown not only
by the glaciation of the Andes, but also by Mt. Kenya, which
is almost on the Equator in eastern Africa and still has glaciers.
The presumably Pleistocene ice covered the whole mountain
like a cap, descending 5400 feet below the present glacier
limit. It was pointed out above that the interglacial stages
had greatly ameliorated climatic conditions and that, in some
of them at least, the climate was warmer than it is to-day in
the same localities. The cause of these astonishing fluctuations
and of the climatic changes in general, to which Geology
bears witness, still remains an altogether insoluble mystery.

CHAPTER VI

THE GEOGRAPHICAL DISTRIBUTION OP MAMMALS

To every one who has paid the slightest attention to the
subject, it is a familiar fact that different parts of the earth
have different animals; school-children learn from their
geographies that kangaroos are found in Australia, the Hippo-
potamus in Africa, the Tiger in southern Asia, armadillos and
llamas in South America. These examples are all taken
from distant lands, yet the zoological difference between two
given land-areas is by no means proportional to the distance
between them. An Englishman landing in Japan finds him-
self surrounded by animals and plants very like and often iden-
tical with those which he left at home, while the narrow Strait
of Lombok, east of Java, separates two profoundly different
regions. In crossing Mexico from east to west, the traveller
meets very different animals in closely adjacent areas ; and,
at first sight, the arrangement of animals appears to be so
capricious as to admit of no formulation in general laws.

In pre-Darwinian times, when it was the almost universal
belief that each species had been separately created and was
exactly fitted to the region which it inhabits, no explanation
of the geographical arrangement of animals was possible, but
the acceptance of the theory of evolution demanded that such
an explanation should be found. A failure to devise any ra-
tional and satisfactory account of the geography of animal
life would be a fatal weakness in the evolutionary theory, hence
the facts of distribution were subjected to a renewed and search-
ing analysis as one of the best means of critically testing the
new doctrine. Not that the subject had received no attention

135

136 LAND MAMMALS IN THE WESTERN HEMISPHERE

before the publication of Darwin's book ; on the contrary, it
had attracted much interest as a study of facts, and this study
was one of the principal avenues by which Darwin approached
his great generalization. In his autobiographical fragment
he tells us : "I had been deeply impressed by discovering in
the Pampean formation great fossil animals covered with
armour like that on the existing armadillos ; secondly, by the
manner in which closely allied animals replace one another in
proceeding southward over the Continent ; and third, by the
South American character of most of the productions of the
Galapagos archipelago and more especially by the manner in
which they differ slightly in each island of the group/ '

Obviously, before attempting to explain the facts of the
geographical distribution of mammals, we must first ascertain
what those facts are. The following brief sketch of the terms
used in describing geographical arrangement is summarized
from Mr. Wallace's " Island Life/'

Though with fluctuating boundaries and subject to slow
secular changes, a mammalian species is limited to a fairly
definite area, which may be of immense or very restricted
extent, and throughout which it may be found in greater or
less abundance. Many species, however, are not distributed
continuously over the areas which they inhabit, but occur only
in suitable stations adapted to their habits and mode of life.
Thus, some will be found only where there are trees, others in
the neighbourhood of water, others only on open plains, etc.
A specific area is then the whole extent of country within which
the species may be found, while the stations are the limited
districts contained in the area which are exactly suited to the
habits of the species in question ; these stations may be hun-
dreds of miles apart, as in the case of mountain-tops, or they
may be close together. A marsh-living species, for example,
will occur in all the marshes throughout its area, whether these
be many or few, near together or widely scattered ; for such
a species marshes are its stations.

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 137

Generic areas differ in character according as the genus
is large, that is, comprising many species, or small and having
but few species, or, it may be, a single one. The species, as
a rule, occupy each its own area, and the areas may be entirely
distinct, or they may be contiguous and more or less extensively
overlapping, though it seldom happens that two or more
species of the same genus inhabit exactly the same area. Often
some physical feature, such as a range of high mountains, a
great river, the edge of a forest, plain or desert, exactly defines
the limits of species of the same genus. The Amazon, for
example, acts as such a boundary to many species. It was
to this change of related species from one area to another that
Darwin referred in the passage quoted above, saying that he
had been deeply impressed ' i by the manner in which closely
allied animals replace one another in proceeding southward
over the Continent [i.e. South America]." On the other hand,
the overlapping of areas may be very extensive, and one species
of great range may cover the whole area of another and much
more besides.

A remarkable example of the widely separated areas of
species belonging to the same genus is that of the tapirs. Of
this genus there are two or three species in Central and South
America and one inhabiting the Malay Peninsula and Borneo,
almost as wide a separation as the size of the earth permits.
Discontinuous distribution of this character can be explained
in terms of the evolutionary theory only in one of two ways.
Either (1) the American and Asiatic species developed inde-
pendently of one another from different ancestors, or (2) the
regions intervening between these widely separated areas once
formed a continuous land, occupied by species of the genus
which have become extinct. From all that we know concern-
ing the operation of the evolutionary process, the first alterna-
tive may be set aside as altogether improbable, and, even had
we no information concerning the history of the tapirs and
their former distribution, the second explanation would be

138 LAND MAMMALS IN THE WESTERN HEMISPHERE

chosen as incomparably the more likely. As a matter of
fact, we have definite knowledge that tapirs once ranged all
over Europe and North America and doubtless over northern
Asia, as well, and, further, that North America was joined to
Asia by a land occupying the place of the shallow Bering Sea,
at a time when the tapirs were able to take advantage of this
means of passing from one continent to the other. Such
appears to be the invariable explanation of discontinuous dis-
tribution, though we may not always be able to give so clear
a proof of it.

The genera of a family are distributed in much the same
fashion as the species of a genus, but, as a rule, much more
widely. While no genus of terrestrial mammals is cosmo-
politan (i.e. universally distributed), at least as genera are de-
fined and limited by most modern systematists, certain families
are represented in every continent. If the extremely peculiar
and isolated Australian continent be excepted, the number
of such cosmopolitan families is considerable and wide separa-
tion between the genera is frequent. Of the camel family,
for instance, one genus, that of the true Camel (Camelus),
is confined to the northern hemisphere and the Old World,
the other (Lama), comprising the Llama, Guanaco, etc., is
found only in the southern hemisphere and the New World.
Less extreme instances of the discontinuous distribution of
a family are common enough.

The principles of distribution are the same when applied
to families and orders. Most of the mammalian orders are
very widely distributed and many are cosmopolitan, except
for Australia, though some are confined to one or two conti-
nents. TKfe monotremes are limited to Australia and Tas-
mania, the marsupials to Australia and the Americas, the
edentates to the latter, the elephants and hyracoids to Africa
and Asia. Carnivores and rodents, on the contrary, are found
in every continent, even Australia.

We have next to inquire what is the nature of the obstacles

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 139

or barriers that prevent the indefinite spread of terrestrial
mammals, so that the mammalian fauna of the whole earth,
and even of a single continent, is not uniform, but highly
variegated. The rate of multiplication of animals is so rapid
that, under normal conditions, the animal population is always
pressing hard upon the means of subsistence and every species
that is increasing in numbers must constantly extend its range
in search of food. Every species would increase indefinitely,
if there were no countervailing checks. Were all the young
to survive and breed in their turn, "even large and slow-breed-
ing mammals, which only have one at a birth, but continue
to breed from eight to ten successive years, may increase
from a single pair to 10,000,000 in forty years " (Wallace).
Evidently, a species must spread from its place of origin until
stopped by insuperable obstacles, the most obvious of which
are wide seas. A few land mammals are not only excellent
swimmers, but will cross straits without hesitation, as the
Guanaco has been seen to swim the Straits of Magellan ; for
the great majority, however, a very few miles of sea form an
impassable barrier. As was shown above, a broad or deep river
is sufficient to limit many species, as the Santa Cruz River
in Patagonia marks the southern boundary of the armadillos.

Important geographical changes, such as the joining of
lands that before were separate, or the dividing of continuous
lands by transgressions and incursions of the sea, must neces-
sarily have a profound effect upon the distribution of land
mammals. Separated land-areas, however similar may have
been their faunas at the time of separation, will, through the
operation of the divergent evolutionary process, grow more
unlike in proportion to the length of time that the separation
continues. Regions which have been severed within a short
time (in the geological sense of a short time) are zoologically
very similar or even identical, while those that have long been
isolated are correspondingly peculiar. Attention has already
been called, in another connection, to the contrasted cases

140 LAND MAMMALS IN THE WESTERN HEMISPHERE

of such great continental islands as Great Britain, Java,
Sumatra, etc., on the one hand, and Australia, on the other.
The continental islands, which have but lately been detached
from the neighbouring main lands, are hardly more peculiar
zoologically than equal areas of the adjoining continents,
while the long-continued isolation of Australia has made it
the most peculiar region of the earth. Climatic changes, which,
as we saw in Chapter I, have indubitably taken place many
times, have also had a great effect in shifting the distribution
of mammals, which in its present form is the outcome of a
very long series of geographical and climatic changes, on the
one hand, and of adaptive changes in the animals themselves,
on the other.

Of almost equal importance as a barrier is climate and
especially temperature. Not that similar climates can pro-
duce similar forms in separate areas. Regions of almost
exactly similar climate in Australia, Africa and South America
have totally different faunas, but, within continuous land-areas,
the most effective of barriers is temperature. This acts dif-
ferently in the case of limiting the northward spread of south-
ern forms and the southward spread of northern species. Dr.
Merriam's long study of this problem has led him to the con-
clusion that southern species are bounded on the north by the
temperature of the breeding season, in which the total quantity
of heat must reach a certain minimum, while " animals and
plants are restricted in southward distribution by the mean tem-
perature of a brief period covering the hottest part of the year."
On the Pacific coast there is a remarkable mingling in the same
areas of species which, east of the high mountains, are dis-
tributed in sharply separated zones. This is explained by the
mild and equable climate of the coastal belt, where the hottest
season of the year does not reach the limiting maximum for
the northern species, while the total quantity of heat in the
breeding season is sufficient to enable southern species to
thrive and maintain themselves.

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 141

Dr. Merriam thus sums up the effects of climatic factors
upon distribution: " Humidity and other secondary causes
determine the presence or absence of particular species in
particular localities within ttieir appropriate zones, but tem-
perature pre-determines the possibilities of distribution; it
fixes the limits beyond which species cannot pass." "Con-
currently with these changes in vegetation from the south
northward occur equally marked differences in the mammals,
birds, reptiles, and insects. Among mammals the tapirs,
monkeys, armadillos, nasuas, peccaries, and opossums of
Central America and Mexico are replaced to the northward
by wood-rats, marmots, chipmunks, foxes, rabbits, short-
tailed field-mice of several genera, shrews, wild-cats, lynxes,
short-tailed porcupines, elk, moose, reindeer, sables, fishers,
wolverines, lemmings, musk-oxen, and polar bears."

Dr. J. A. Allen has reached closely similar conclusions.
"Of strictly climatic influences, temperature is by far the most
important, although moisture plays an influential part. Where
a low temperature prevails life, both animal and vegetable, is
represented by comparatively few forms ; under a high tem-
perature it is characterized by great diversity and luxuriance.
Within the Arctic Circle the species of both animals and plants
are not only few, but they are widely distributed, being for
the most part everywhere the same. Under the tropics they
are a hundred fold more numerous and of comparatively re-
stricted distribution." "The influence of temperature is
perhaps most strikingly displayed in the distribution of life
upon the slopes of a high mountain, especially if situated near
the tropics. While its base may be clothed with palms and
luxuriant tropical vegetation, its summit may be snow-capped
and barren. . . . The animal life becomes likewise corre-
spondingly changed, tropical forms of mammals, birds, and
insects of the lower slopes gradually giving place to such as
are characteristic of arctic latitudes." " The effect of humidity
upon plant life is thus obvious, but it is equally potent, though

142 LAND MAMMALS IN THE WESTERN HEMISPHERE

less evident, upon animal life. Many animals . . . are so
fitted for a forest life, as regards both food and shelter, that
their very existence depends upon such surroundings. . . .
Thus moisture alone may determine the character of life over
extensive regions/ '

While climate is thus the most important of the barriers
which determine distribution in continuous land-areas, the
absence of any particular species from a given region is no
proof that the climate is unsuitable to that species. This is
sufficiently shown by the manner in which animals introduced
into a new country often run wild and multiply to an incredible
extent, as the rabbits have done in Australia, the Mongoose
in Jamaica, horses on our western plains, horses and cattle
on the Pampas of Argentina, etc.

Topographical features, such as a»8t*rtdtintain-ranges and
plateaus, also limit many s^ - * <f ot only by the difficulty of
crossing them, but a) /* ;ct which they have upon

temperature and r A. / or this reason long ranges of

mountains and table-lano y- ' >rry a northern fauna very

far to the south of its < y mge, as do the mountain-

systems of North Ame . . **i , very conspicuous manner.
The great Mexican plateau is zoologically a part of North
America, while the low coastal lands as far as southeastern
Texas have Central American affinities.

A different kind of obstacle to the spread of a species into
a new area may be the pre-occupation of that area by another
species. The pre-occupier may be one that plays so similar
a part in the economy of nature as to leave no opportunity
for the newcomer to establish itself. On the other hand,
the obstructing form may be an active enemy and of a totally
different character from the intruder, as in the case of the
Tse-tse Fly in parts of Africa. The bite of the fly is fatal to
horses and oxen, so that these mammals are unable to enter
the fly-infested regions. Many times in the course of the
Tertiary period various mammals reached North America

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 143

from the south or from the Old World, which were unable to
gain a permanent foothold and speedily died out. At this
distance of time it is seldom, if ever, possible to explain why
a species which succeeded in reaching this continent could
not maintain itself, though the most probable assumption is
that the forms already in possession of the land were an in-
superable obstacle to the intruders.

The rate of dispersal of a species into new areas may be
fast or slow, according as the conditions are more or less favour-
able. Newly introduced insect-pests, like the Gypsy and the
Brown-tailed Moths in New England, often spread with por-
tentous rapidity; and introduced mammals have frequently
taken possession of vast areas in a surprisingly short time.
One of the most remarkable of these cases is cited by Darwin.
"In the time of Sarmiento (1580) these Indians had bows and
arrows, now long since disu ^*v then also possessed some

horses. This is a very t showing the extraor-

dinarily rapid multiplication ^os n South America.

The horse was first lander it: bs Ayres in 1537 and the
colony being then for a tn d>. d, Jthe horse ran wild ; in
1580, only forty-three yeai itv.. ^rds, we hear of them at
the Strait of Magellan !" (" Voyage of a Naturalist," pp. 232-
233.) In this example, something must be allowed for human
agency, but even so, it is very surprising.

In the case of lands newly raised above the sea and con-
necting formerly separated areas, it is necessary that they should
first be taken possession of by vegetation, before they can
become passable by animals, for the migration of mammals
from continent to continent is an entirely distinct phenomenon
from the annual migration of birds. The latter, though a fact
familiar to every one, is an unexplained mystery, and it is some-
what unfortunate that the same term should be used for the
completely different process of the spread of mammals into
newly opened land. This spread is purely unconscious and is
due to the pressure of increasing numbers upon the means of

/

144 LAND MAMMALS IN THE WESTERN HEMISPHERE

subsistence, each new generation ranging farther and farther
from the original home of the species and continuing so to
extend until some insuperable obstacle is encountered. When
a sea-barrier is removed by upheaval and the newly formed
land rendered habitable for mammals through the invasion
of plants, the interrupted process is resumed and an inter-
change of species between the areas thus connected is brought
about. The interchange is, however, always an incomplete
one, certain forms not being able so to extend their range,
because of climatic differences, pre-occupation or some such
barrier.

It is customary to give a graphic expression to the facts
of animal distribution by dividing the land surface of the earth
into districts which are characterized by their faunas. It is
not possible to construct a geographical scheme which will
be equally satisfactory for all classes of animals, because the
geological date of most rapid development and diffusion was
so different in the various classes. The geographical and
climatic conditions which favoured a particular geographical
arrangement of one class had been so completely altered that
the class coming in later could not attain a similar distribution.
For this reason, land mammals are chosen as affording the best
criteria; their adaptability is such that they are found all
over the earth, their dispersal is primarily dependent upon the
arrangement and connections of the continental land-masses,
modified by the topographical and climatic conditions, and
they, with the birds, are the latest of the vertebrate classes to
assume a dominating importance. Their history is the most
fully known and falls within the best understood portion of the
earth's history, making it possible to follow their migrations
with a precision which is seldom feasible for the other classes
of animals, and thus to correlate the successive physical and
organic changes. A particularly great advantage which mam-
mals possess for this purpose is that the mutual relationships
of the various kinds are better understood than in the case of

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 145

most other groups of animals. It is true that we shall find a
great many unsolved problems, upon which the most divergent
opinions are held, but the main outlines of the scheme are quite
generally agreed upon.

Many plans for the zoological division of the continental
areas have been proposed by various writers on the subject,
some differing very radically from others. It would be useless
and tedious to review even the more important of the many
proposals and suggestions which have been made in the last
half-century ; and we may, with advantage, adopt an eclectic
scheme which has been slowly reached by successive approx-
imations to a satisfactory arrangement.

Just as in political geography it is found necessary to rec-
ognize divisions of different rank and scope, like nation, state,
county, township, the facts of zoological geography require
divisions of different orders of importance. Thus, in descend-
ing order, the terms realm, region, subregion, province, etc.
are commonly employed, but unfortunately they are often
used loosely and even interchangeably ; yet it is desirable to
attach a more or less precise significance to each and more
terms are needed for an accurate expression of the many
complex facts.

The extreme zoological peculiarity of Australia is recognized
by making that continent and its adjoining islands one of the
great primary divisions, of which the other includes all the
rest of the world; the former is characterized by its almost
exclusively marsupial fauna, while the other continents are
inhabited by the Monodelphia or placental mammals. Aside
from Australia, by far the most isolated and peculiar region
of the earth is South America, and this fact is expressed by
constituting it into a realm, or division of the second order, and
to this realm is given the name Neogcea. The remaining con-
tinents, North America, Europe, Asia and Africa, make up
the other realm, Arctogcea, in which there is an unmistakable
general likeness among the mammals. The three continents

146 LAND MAMMALS IN THE WESTERN HEMISPHERE

of the Old World form a vast, connected land-mass, and the
final separation of North America from this great complex
is an event of geologically recent date. For reasons that will
be made clear in the course of the history, the junction of the
two Americas has had comparatively little effect upon the
zoology of the northern continent, except in its tropical portion.
It is obvious from a glance at the map, that the great zoological
divisions are of very unequal size, but the arrangement is made
on the basis of degrees of difference in the mammalian faunas.
These degrees of difference are, in turn, an expression of length
of separation or of the difficulty of communication between
connected lands.

The following table gives the major divisions of the earth
apart from Australia:

I. NEOGiEic Realm. Neotropical Region. — South and Central America,
lowlands of Mexico, the West Indies.

{ 1. Malagasy Region. — Madagascar.

2. Ethiopian Region. — Africa south of the Sahara
Desert.

3. Oriental Region. — Southern peninsulas of Asia,
Malay Archipelago.

4. Holarctic Region. — N. Africa, Europe, Asia,
(except southern part), boreal N. America.

5. Sonoran Region. — Remainder of N. America
(except lowlands of Mexico).

North America, as is expressed by this scheme, is zoolog-
ically composite ; the northern half, including nearly all of
Canada, belongs to the vast Holarctic Region, which also
comprises Europe, Africa north of the Sahara and Asia north
of the Himalaya Mountains. The remainder of the continent,
exclusive of the Mexican coastal lowlands, is set off as the
Sonoran Region. Inasmuch as we have here to do with
broadly continuous land-areas, not demarcated by great physi-
cal features, and as the genera and species of mammals differ
greatly in regard to their ability to withstand a wide range
of climatic variations, it is not to be expected that the boun-

II. Arctog.eic Realm.

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS

147

daries between the regions which make up North America
should be very sharply drawn. It is not surprising, therefore,
to find a transition zone, extending all across the continent,
in which the Holarctic and Sonoran faunas mingle, or that
Central America should, in considerable measure, be transi-
tional to South America, though zoologically a part of the latter.

Fio. 53. — Zoological Divisions of North A

(After Mcmam.)

148 LAND MAMMALS IN THE WESTERN HEMISPHERE

Or. Merriam's arrangement, which deals only with North
America without reference to the Old World, divides the land
into a series of transcontinental zones, which he calls the
Arctic, Boreal, Upper and Lower Sonoran and Tropical.
These zones have very irregular and sinuous boundaries, which
follow lines of equal temperature (isothermal lines) during the
breeding season, May, June and July, the tortuous boundaries
being conditioned by topographical features, which deflect
the isothermal lines.

PlO. 64. — Polar Bear (Thalarctus ntaritimus) . — By permission of the N.Y. Zoolog. Soc.

The Arctic zone is part of a circumpolar area, which is very
much the same in North America, Asia and Europe; and in any
of these continents the fauna differs much more from that of
the contiguous zone to the south than from the Arctic fauna
of another continent. There are some local differences, but
the characteristic mammals of this Arctic zone are the Polar
Bear, Arctic Fox, Musk Ox, Barren-ground Caribou, Lemming,

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS

- By permission of tht

150 LAND MAMMALS IN THE WESTERN HEMISPHERE

Arctic Hare, and a marmot. Most, if not all, of these forms are
of Old World origin.

The American portion of the great Holarctic region is
called by Mr. Lydekker, who uses Wallace's term, the "Cana-
dian subregion," and by Dr. Merriam the "Boreal region." Not
that there is any difference of principle involved in this varying
nomenclature, for Dr. Merriam says: "It so happens that the
Boreal element in America resembles that of Eurasia so closely
that in the judgment of many eminent authorities the two
constitute a single primary region — - a view in which I heartily
concur." The Canadian or Boreal subregion of the Holarctic
is the great belt of coniferous forest, which extends obliquely
across North America from Alaska to New England ; its
frontier with the Arctic zone is the northern limit of trees and

Fm. 57. — Arctic Fox in summer dreas. — By permission of the N.Y. Zooiog. Soc.

it is divided from the Transition zone approximately by the
line of latitude 45° N., though with a sinuous course, and it
is carried far to the south by the wooded heights of the Appa-
lachian, Rocky and Sierra Nevada Mountains, and along the
Pacific coast, the mixed character of which has already been
explained ; it extends almost to San Francisco. The sub-

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS

151

region is further divisible into northern and southern belts,
called the Hudsonian and Canadian faunas, the limit between
them approximately following the isothermal line of 57° F.
The mammals of this subregion are largely of Old World
origin, many of them coming in with the great immigrations
of the Pliocene and Pleistocene epochs; but there are also
native American elements and even one genus of South American
origin, the Short-tailed or Canada Porcupine (Erethizon).

In considering the mammals of this subregion, it should be
remembered that they are not uniformly distributed through-
out even one subdivision, but in a scattering way and in ac-
cordance with their habits and stations, and also in accordance
with a gradual change to
the south, following the
changing temperature. The
Muskrat will not be found
far from water or the Por-
cupine from woods. Espe-
cially characteristic of the
Canadian subregion are the
Old World types of deer,
none of which range farther
south than the Transition
zone. The Wapiti, errone-
ously called the Elk (Cervua
canadensis), is very closely
allied to the European Stag
(C elapkus) and still more
closely to the Stag of the
Thian Shan in Central Asia
(C. eustephanus). So great Soc-

is the resemblance, that some naturalists would refer all three
forms to a single species. The Moose (Alee americanus), which
should be called the Elk, is so near to the Scandinavian Elk
(A. machlis) that it is hardly distinguishable as a separate

152

LAND MAMMALS IN THE WESTERN HEMISPHERE

species, and the Woodland Caribou {Rangifer caribou) is the
American representative of the Lapland Reindeer (R. tarandus).
The so-called Rocky Mountain Goat (Oreamnos montanus), a
peculiar and aberrant
form of the Chamois
subfamily of the Ante-
lopes, is confined to the
subregion. The Moun-
tain Sheep {Oris Mon-
tana, 0. dalli) are rep-
resented by three or
four species, one of
which extends into the
Sonoran region, as does
also the Bison, wrongly called Buffalo (Bison bison), which is
nearly allied to the European B. bonasus. In Caesar's time
the European Bison (German, Wisent) ranged through Ger-
many and is described in his account of the Hercynian Forest ;
but the advance of civilization has almost exterminated it,
only a few small herds being maintained by the most rigid
protection in Russia
and in the Carpathian
Mountains. Of the Car-
nivora, the weasels, mar-
tens, Fisher, Mink and
Ermine are Boreal, as
are the Wolverene (Gulo)
and the Grey Wolf (Car-
nis), the three last-
named extending also
into the Arctic zone. Es-
sentially Boreal, though
reaching and entering the Sonoran, are the bears (Ursus),
the red foxes (Vulpes), the otters (Lutra) and the Old World
shrews (Sorex), while the Star-nose Mole (Condylura) and

Fin. 60. — MinkfLi

of thcN.Y. Zoolog. 9oc

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 153

the mole-shrews (Urotrichus) do not extend south of the
Transition zone. Probable intruders from the south into
the Boreal subregion are the pumas, or " mountain lions/ '
which just enter the subregion, the Canada Lynx (Lynx
rufus) and one species of skunks (Mephitis), the Raccoon
(Procyon lotor), Badger (Taxidea americana) and the Ameri-
can deer (Odocoileus) . A large number of rodents are char-
acteristically Boreal : marmots, or woodchucks (Marmota) , the
Sewellel (Aplodontia rufa), lemmings (My odes), Jumping Mouse
(Zapus), the Canada Porcupine (Erethizon dorsatus) and the
pikas, " tailless or whistling hares' ' (Ochotona). Boreal ro-
dents that enter the Sonoran are the chipmunks (Tamias),
beavers (Castor), meadow-mice (Microtus), the Muskrat (Fiber
zibethicus). The white-footed mice (Sitomys) and the wood-
rats (Neotoma) are southern rodents that reach or enter the
Boreal.

Between the Boreal subregion and the Sonoran region is
the Transition zone, which follows all the complex windings of
the boundary lines. It covers most of New England, New
York, Pennsylvania and southern Ontario; passing through
southern Michigan and Wisconsin, it bends northward over
Minnesota and covers most of North Dakota, Manitoba and
the plains of the Saskatchewan, then turns abruptly south-
ward and includes eastern Montana and parts of South Dakota
and Nebraska. Crossing Wyoming, it follows around the
northern edge of the Great Basin to the plains of the Columbia.
The three great mountain-systems carry the zone far to the
south and arms of it extend along the Appalachians to northern
Georgia, along the Rockies to New Mexico, and it follows the
Sierras to southern California. "The Transition zone, as
its name indicates, is a zone of overlapping Boreal and Sono-
ran types. Many Boreal genera and species here reach the
extreme southern limits of their distribution and many Sonoran
genera and species their northern limits. But a single mam-
malian genus (Synaptomys) [one of the field mice] is restricted

154 LAND MAMMALS IN' THE WESTERN HEMISPHERE

a

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 155

166 LAND MAMMALS IN THE WESTERN HEMISPHERE

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 157

FlO. 67. — Woodland Caribou (Rangifer caribou). — By permission of the
N.Y. Zodlog. Soc.

158 LAND MAMMALS IN THE WESTERN HEMISPHERE

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 159

160 LAND MAMMALS IN THE WESTERN HEMISPHERE

Fio. 72. — Boreal Mammals. A. Blaok-footed Fprret [Muxtda nigripee). B. Otter
(Lutra cinadensis). C. Jumping Mouse (Znpm Audsonius]. — A and £ by permiB-
Bion of the N.Y. Zoolog. Soc. C, by permission of W. S. Berridge, London.

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 161

to the Transition zone. ... A number of species, however,
seem to be nearly or quite confined to this zone " (Merriam).
The most characteristic portion of North America, zoolog-
ically speaking, is the Sonoran region of Dr. Merriam, the
Warm Temperate of Dr. Allen. It crosses the continent
from ocean to ocean, its northern boundarj' following for most
of the way the 43d parallel of latitude, but over the Great

Plains and Great Basin, on each side of the Rocky Mountains
and the high plateaus, it extends to lat. 48°. On the south,
it takes in the greater part of Mexico, covering all of the table-
land of that country, the lowlands of which belong to the South
American or Neotropical region. The Sonoran is invaded from
the north by the long branches from the Boreal and Transition
zones, which follow the three great mountain-systems in the
manner already explained, and the Mexican plateau permits
the similar invasion of Neotropical territory by the Sonoran
fauna. Characteristic Sonoran genera, none of which extend
into the Boreal, are the opossums (Didelphis), in the southern
part a peccary (Tagassu) or "Wild Texas Pig," representative
of a family of swine quite different from the true pigs of the Old

162 LAND MAMMALS IN THE WESTERN HEMISPHERE

World, and an armadillo (Tatu). A very isolated form is
the Prong-horned Antelope (Antilocapra americana) ; there
are several species of the typically American deer (Odocoileus)
which differ in important respects from those of the eastern

hemisphere, and the Bison was very abundant until exterminated
by Man. Bison, antelope and deer also reach or extend into
the Boreal zone, but the former, or Wood Bison, is probably
a different species from the plains animal.

The grey foxes (Urocyon), Coyote (Cants latrans), large
Timber Wolf (Canis occidentals), the Caxomistle (Bassaris-
cus), the Coati (Arasua), Raccoon (Procyon), Badger (Taxi-

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 163

dea), three genera of skunks, pumas, several species of lynx
and some bears (Ursus) represent the Carnivora, though one
species each of raccoon, skunk, badger, puma and lynx range

into the Boreal. The American types of shrews {Blarina)
and moles (Scalops and Scapanus) are characteristic of the
Sonoran, though partially shared with the Boreal. A great

many peculiar rodents inhabit the Sonoran ; cotton-rats (Sig-
modori), pocket-gophers (Geomys, etc.), several genera of the
beautiful little kangaroo-rats (Dipodomys, etc.) ; while the

164

LAND MAMMALS IX THE WESTERN HEMISPHERE

%

^#■^1^

prairie-dogs (Cynomyx), the white-footed mice (Silomys),
wood-rats {Xeotoma) and one genus of pocket-gophers (Thom-
omys) are chiefly Sonoran, but have Boreal representatives.
The flying squirrels
(Sciuropterus) , t rue
squirrels (Sciurus),
ground-squirrels (Sper-
mophilus), rabbits (Le-
pus) , wolves (Canis)
and otters {Lutra) have
very wide range
through both the Bo-
real and Sonoran, but
have many more spe-
cies in the latter region.
The Sonoran region
may be divided into
the upper and lower Sonoran zones, which are demarcated
by temperature and are of transcontinental extent. Each of
these zones may, in turn, be subdivided into arid and humid
provinces, but our purpose does not necessitate entering into
such refinements.

The Neotropical, which is the only region of the Neogseic
realm, comprises the West Indian islands, all of Central
and South America and the lowlands of Mexico, extending
a short distance into southeastern Texas. Of its four sub-
regions, the most typical is (1) the Brazilian, which includes
not only Brazil, but all of South America east of the Andes and
as far south as Paraguay, and is a vast area of tropical forests.
(2) The Chilian subregion takes in the west coast, the high
Andes and the southern end of the continent, south of the
Brazilian subregion ; it is a country chiefly of open plains and
high mountains, and a few deserts, of which South America
lias less than any other continent, except Europe, which has
none. (3) The Central American subregion reaches from the

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 165

166 LAND MAMMALS IN THE WESTERN HEMISPHERE

FlO. 80. — Raccoon {Procyon lotor). — By permission of the N.Y. Zoolog. Soc.

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 167

LAND MAMMALS IN THE WESTERN HEMISPHERE

N.Y. Zoolog. Soc.

— By permission of the

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 169

Fia. 86. — Lynx (Lynx ■mfua}. — By permission of the N.Y. Zodlog. Soc.

170 LAND MAMMALS IN THE WESTERN HEMISPHERE

Isthmus of Panama to Mexico, the lowlands of which are in-
cluded and even a small portion of southeastern Texas. (4)
The West Indian subregion includes all the islands of that
archipelago, except Trinidad, which is a fragment of the con-

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 171

tinent, detached at a comparatively recent date ; the southern
extremity of Florida also belongs to this subregion.

The two subregions into which continental South America
is divided are not altogether satisfactory and will doubtless
require change when the distribution of South American
mammals has been more accurately determined.

By permission of

"Richness combined with isolation is the predominant
feature of Neotropical Zoology, and no other region can
approach it in the number of its peculiar family and generic
types " (Wallace). Just as North America has received many
immigrants from the Old World, so it has sent many mi-
grants into South America, materially changing the character
of the Neotropical mammalian fauna, but these intruders may
be readily identified and almost seem to be out of place in their
new surroundings. Not all of these northern migrants were

172

LAND MAMMALS IN THE WESTERN HEMISPHERE

able to maintain their footing in the southern continent and
several became extinct during and at the close of the Pleistocene
epoch, as was even more markedly the case with the southern
forms which invaded the northern continent.

There are two families of monkeys in the forested areas
of South America, both very different from those of the Old
World. One of these families, the marmosets (Hapalidse), dif-
fers from all other monkeys in several particulars, most obvious
of which are the long claws on the feet and the non-opposable
thumb. The second family (Cebidae) comprises forms which
are superficially much more like those of the eastern hemi-
sphere, but many of them have prehensile tails, which are used
as efficient grasping organs.

Insectivora are entirely absent from the South American

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS

173

continent, but some shrews (Blarina) have entered Central
America from the north and a very curious genus is represented
by one species in Cuba (Solenodon cubanus) and another in
Hayti (5. paradoxus). These remarkable animals are, strange

Flo. 01.— Solenodon cvbai

of the N.Y. ZoSlog. S

to relate, most nearly allied to the tenrecs (Centetes) of Mada-
gascar and by some authorities are placed in the same family.
The Carnivora are quite numerous and varied and rather
peculiar, but they all belong to northern families and are the
more or less modified descendants of northern immigrants.
The dogs (Canidte) belong to genera not represented else-
where and form a considerable assemblage of interesting types.
There are no true wolves or foxes, but several species of fox-like

LAND MAMMALS IN THE WESTERN HEMISPHERE

By permission of

wolves (Cerdocyon), with bushy tails, are common, especially in
the plains regions. The Bush-Dog {Iclicyon venaticus) , a small,
short-legged animal, is very peculiar. The musteline or weasel
family (Mustelidae) is rather scantily represented. There are
no badgers and but few skunks (Spilogale and Conepatus) ;

THE GEOGRAPHICAL DISTRIBUTION OP MAMMALS 175

FlO. 94. — Tayrn {Taj/ra tayra). — By permission of W. S. Berridge, London.

weasels are absent, but their place is taken by the Grison
(Galera vittata) and Tayra (Tayra layra) and in the far south
Lyncodon palagonicus. These animals are peculiar in having
a lighter colouration on the back than on the belly. There
are two or three species of otter (Lutra). The raccoons
(Procyon) have a very wide range in South America, as in the

- By permission of

176

LAND MAMMALS IN THE WESTERN HEMISPHERE

northern continent, and the curious, long-snouted coatis
(Nasua), which just enter the Sonoran region, are typically
Neotropical. The Spectacled Bear (Tremarctos ornatus) is the
only member of the family that occurs in South America and
is confined to the highlands of Peru and Chili. The cat family
is quite numerously represented ; the Jaguar (Felis onca) , which
ranges from Texas to Patagonia, is a large spotted cat, rivalling

Fig. 96. — Ocelot (F this partialis}, —By permission of the N.Y. Zootog.

the Leopard in size and ferocity; the Ocelot (F. pardalis,
Arkansas to Paraguay) is smaller and streaked and blotched
rather than spotted. The pumas differ little from those
of North America, and there are many small cats, spotted,
clouded and of solid colour, but no lynxes, which are essentially
northern types.

Hoofed animals are not numerously represented in South
America. The only existing Perissodactyla of the western
hemisphere are the tapirs (Tapirus) of Central and tropical
South America, a very remarkable contrast to the ancient
faunas, especially of the northern continent, as will be shown
in the sequel. The Artiodactyla are more varied, though very
scanty in comparison with those of the Old World ; even North
America, which has but a poor representation of these animals.

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 177

By permission of the

178

LAND MAMMALS IN THE WESTERN HEMISPHERE

is much richer than the southern continent, where, indeed,
all the hoofed animals are the descendants of comparatively
recent immigrants from the north and none are truly autoch-
thonous. Members of three different artiodactyl suborders
occur in the Neotropical region; the peccaries (Tagassu)
extend through Central and South America to Paraguay,

Fio. 99. — Vicuna (Lama ricunta).— By permission of Ihu N.Y. Zofilog,

though also entering the Sonoran region in Texas. Most
interesting are the members of the camel family, which are
very distinct from the true Camel of Asia. Tierra del Fuego
and the Patagonian plains support great herds of the Guanaco
(Lama huanacus), which extends along the Andes to Ecuador
and Peru, where it is associated with the Vicuna (L.vicunia),
a smaller and more slenderly built species. The Vicuna does
not range south of Bolivia. Just as the mountain systems of
North America carry the Boreal and Transition faunas through
nearly the whole breadth of the Sonoran region, so the high

THE GEOGRAPHICAL DISTRIBUTION OP MAMMALS

179

Andes afford a pathway by which the mammals of the south
temperate zone extend their range to the equator.

The suborder Pecora of the Artiodactyla is represented in
the Neotropical region only by the deer family (Cervidte), of
which there are several genera (or subgenera), all of them
North American as distinguished from the Old World type,

iceola). — By permission of the

but some are so peculiar that they must have had a relatively
long South American ancestry. The Virginia Deer (Odo-
coileus virginianits) of the northern United States is a com-
paratively large animal, becoming much smaller in Florida
and the Southwest. The type extends through Mexico and
Central America to Guiana and Peru, the Neotropical forms
being so small and having such weak antlers that they are
referred to separate species. Another type is the Marsh Deer

180

LAND MANUALS IN THE WESTERN HEMISPHERE

(Blastoceros paludosus) of eastern South America, which has
short, stout antlers, each beam with two double bifurcations ;
there are other species of the same genus, such as the Pampas
Deer of Argentina (B. bezoarticus). In the Andes of Peru and
Chili and the forests of western Patagonia are two species
of a genus which bears the preposterous name of Hippocamelus

and in which the antlers are simply forked. The vernacular
name of these animals is "Huemul." Peculiarly Neotropical
are the little brockets, which hardly exceed a height of two
feet at the shoulder, with simple spike-like antlers not more
than three inches long ; the genus, Mazama, has several species,
one of which occurs as far north as the state of Puebla in Mexico.
"The smallest of all deer is the Chilian pudu (Pudua pvdu),

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 181

a creature not much larger than a hare, with almost rudimen-
tary antlers" (Lydekker). Old World types of deer, such
as the Wapiti, Moose and Caribou, of the Boreal and Transi-
tion zones of North America, are entirely absent from the
Neotropical region.

South America has an astonishingly rich and varied assem-
blage of rodents, both indigenous and immigrant, but the

— By permission of

former are much the more important, varied and abundant.
Of the four divisions of the order, all of which are represented,
three are immigrants from the north and the fourth is autoch-
thonous, but this far outnumbers the other three combined.
The hares and rabbits have but very few species, one of which
occurs in Brazil and is separated by a very wide interval from
the one in Costa Rica, while the pikas are absent. Of the squir-
rel division, only the true squirrels are found, and of these there
are many species, the ground-squirrels, marmots, prairie-dogs

182

LAND MAMMALS IN THE WESTERN HEMISPHERE

and beavers all being lacking. In the same way the rat and
mouse division is represented by a single family. The vesper
or white-footed mice (Sitomys) have invaded the southern
continent and a number of peculiar genera have arisen there, but
all of northern ancestry, such as the groove-toothed mice
(Rheithrodon) and the fish-eating rats (Ichthyomys). The

Flo. 103. — Braiilio.ii Tree Porcupine (Coendou prektntilU) . — By permission of the
N.Y. ZoQlog. Soc.

voles, or meadow-mice, the muskrats, jumping mice, kan-
garoo-rats and pocket-gophers of the northern continent are
all absent. While the immigrant suborders have thus but
one family each in South America, the case is very different
with the fourth or porcupine group, of which that continent
is to-day, as it has been for ages past, the headquarters. No
less than six families and twenty-nine genera are known, ail
of the genera and four of the families being restricted to the
Neotropical region. Contrast this assemblage with the ex-
treme scantiness of this group in North America, where but
a single genus, the Short-tailed or Canada Porcupine (Ere-

Fiq. 104. — Neotropical rodents. A. Viii-aoha (VUcaccuf). B. Para (Agouti paca).

C. Rock Cavy (Cacia rupe«fn'«). D. Wat<T-Ho«, or Carpincho (Hydrorlurrus) .

D. by permission of the N.Y. ZoSlog. Soc. A. B, C, by permission of W. 9.
Berridge, London.

(183)

184

LAND MAMMALS IN THE WESTERN HEMISPHERE

thizon) represents it, and that is a late immigrant from the
south.

It would lead us too far to attempt a description of this
horde of curious and interesting rodents, so only a few of the
more striking and characteristic forms can be mentioned.
There are two genera of porcupines (Coendou and Chcetomys),
both arboreal, which belong in the same family as the North
American Bretkizon, but are distinguished by their long,
prehensile tails, which they use, as monkeys and opossums

Fia. 105. — Chinchilla (Chinchilla laniger). — By permission of W. S. Berridge, Loudon.

do, for grasping and climbing. The very large family of the
Octodontidae has 17 Neotropical genera and four others are
found in Africa. The Degu (Octodon) of Chili, Bolivia and
Peru has the appearance of a large rat with tufted tail ; the
tuco-tucos (Ctenomys) are extremely abundant burrowers in
Patagonia, where they honeycomb the ground over wide areas.
The spiny rats (Eckimys and Lonckeres) are so called from their
appearance, not because they are related to the true rats ;
they have numerous horny spikes through the fur of the back.
The Coypu (Myocastor) is a large, aquatic animal, remotely
like the northern Muskrat, and the Hutias (Capromys and

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS

185

Plagiodontia) are arboreal and found only in Cuba, Hayti and
Jamaica. The chinchillas (Chinchilla and Lagidium) of the
Andes and the Vizcacha (Viacaccia) of the Argentine plains
have somewhat the appearance of hares, but with long and
bushy tails. The cavies, to which the familiar, misnamed
Guinea-Pig (Cavia porcellus) belongs, are a very characteristic
family ; besides the true cavies, it includes the Patagonian
Mara (Dolichotis), a large, long-legged, long-eared, short-
tailed creature, and the Water-Hog, or Carpincho (Hydro-
chcerus), an aquatic animal, as its name implies, and much the

largest of existing rodents ; it occurs in the warmer regions,
south to Argentina. The heavy Paca (Agouti) and the
slender-limbed Agouti (Dasyprocta) make up another family.
Altogether, this assemblage of the porcupine-like suborder
of rodents is a very remarkable one and in no other region
of the earth is anything like it to be found.

With the exception of one genus of armadillos, which has
invaded Texas, the entire order of the Edentata is at present
confined to the Neotropical region, the so-called edentates
of the Old World now being removed to other orders. The

lSt) UNO MAMMALS IN THE WESTERN HEMISPHERE

Kdeiitata, which were once far more varied and abundant than
thov now are, comprise three groups of animals so bizarre and
strange t'1** they seem more like fabulous creatures than
actual, living mammals. One group, or suborder, is that of
tin* sloths (Tardigrada), arboreal, shaggy animals, with short,

,

tEHHrTr _fli

SffTl

air 11

L 1 1

HL -^9uk

''*J

Flu. 107. — Three-loed Sloth (Bradypi.n (rirtaciyfuj). — By permission of the
N.Y. ZoSlog. Soc.

almost monkey-like head and no tail ; their very long legs
and hook-like feet make them nearly helpless on the ground,
but are very useful for hanging from the branches of the trees,
in which the creatures live. Indeed, the sloths are the only
mammals which habitually hang in a suspended position.

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 187

Two genera of sloths inhabit the tropical forests, between which
the most obvious difference is that in one (Bradypua) the fore-
foot has three toes, and in the other (Ckolcepus) two.

The suborder of the anteaters (Vermilingua) is more varied,
and is the only one of the order to which the term "edentate"

— By permission of

applies strictly, for they alone in the order are altogether
toothless. The great Ant-Bear (Myrmecophoga jubata), which
may reach a total length of seven feet, has an extravagantly
long, slender and nearly cylindrical head, long, shaggy, black
and white hair and an immense, bushy tail ; the forefeet are
armed with huge, sharp-pointed claws, which are used .for
tearing open ant-hills, and when occasion arises, as formidable
weapons of defence, for the Ant-Bear can successfully repulse
even the Jaguar. In walking, the claws are curved inward
and the preposterous beast rests his weight upon the outside
edges of the forefeet, while the hind feet apply the sole to the
ground, as does a bear or raccoon. The Collared Anteater
(Tamandua) is much smaller and mainly arboreal in habits.
It has a short-haired, black body, with a white stripe down the

LAND MAMMALS IN THE WESTERN HEMISPHERE

Fig. 109. — Act-Bear {MyrmtcophaQa jubata) . — By permission of the N. V. Zoolog. Soc.

back, white neck and limbs, a colour-pattern which gives to
the animal the appearance of wearing a close-fitting black
jacket ; the long tail, which has some cross bars, is short-
haired, very different from the extremely bushy tail of the Ant-
Bear. The little Two-toed Anteater {Cyclopes didactylus),

Flo. 1 10. — Collared Anteater {Tamandua tetradattyla). — By permission of the
N.Y. Zoolog. Soc.

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 189

hardly larger than a rat, is exclusively arboreal and has a pre-
hensile tail, like so many other South American mammals.
Sloths and anteaters are forest animals and are not found west
of the Andes or south of Paraguay.

The third existing suborder of edentates is that of the arma-
dillos (Dasypoda), which have a very complete armour of bony
scutes, ossifications in the skin, covered with scales of horn.
They are all more or less burrowers in habit and omnivorous

in diet, eating roots, insects, worms, etc. ; the extraordinary
rapidity with which they burrow into the ground is almost
their only way of escape from pursuit, but in one genus, Toly-
pevies, the animal can roll itself into a bail, completely pro-
tected by mail all around. The armadillos -are much more
varied than the anteaters or sloths and have a wider geo-
graphical range, extending from Texas to Patagonia. The
head, which is long-snouted, is protected by a shield made up
of numerous horn-covered platesof bone, and the tail is encased
in a tubular sheath of more or less regular rings, each ring
of bony plates and horny scales. The body-shield, or cara-
pace, which covers the back and sides, consists of an anterior
and posterior buckler, in which the plates are immovably

190 LAND MAMMALS IN THE WESTERN HEMISPHERE

attached to one another by their edges, and between the two
is a series of movable, overlapping bands, the number of which
varies in the different genera. In the little Pichiciago (Chlamy-
dophorus truncatus) the head and back are covered with four-
sided plates of horn, the bony scutes being small and thin and
much reduced. The carapace has no bucklers, but about 20
transverse rows of plates, and is attached along only the middle
line of the back and beneath it the body is covered with silky,

white fur; the rump is covered with a solid shield of bone,
placed nearly vertically and covered with thin scales, and is
notched below for the tail, altogether a most exceptional
arrangement. Seven or more distinct genera of armadillos
are found in the Neotropical region and they display a great
range in size ; the Giant Armadillo of Brazil (Priodontes) is
a yard or more in length, while the little Zaedyus of Patagonia
is smaller than a rabbit and, least of all, the Pichiciago is but
five inches long.

Two families of marsupials occur in South America. The
opossums are much more numerous and varied than in North
America; three genera and a large number of species, some
not larger than mice, range through the forested parts of the
continent. Of particular interest is the little Ccenolestes,

THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 191

which has two species, with two enlarged lower front teeth,
the sole survivors of a group which is abundantly represented
in the Tertiary deposits of Patagonia.

The fauna of the Central American subregion is less rich
and characteristic than that of the Brazilian and is, to a cer-
tain extent, transitional to that of the Sonoran region of North
America, several genera proper to the latter region extending
into it, which are not known to pass the Isthmus of Panama,
such as shrews, a fox and one of the pocket-mice. The West
Indian islands are exceedingly poor in mammals, a great con-
trast to the East Indian, or Malay, Archipelago ; only a few
rodents, insectivores and bats occur in them.

J

CHAPTER VII

THE SUCCESSIVE MAMMALIAN FAUNAS OP NORTH AND SOUTH

AMERICA

The natural method of telling a story is to begin at the
beginning and go on to the end, but to deal in that manner with
the many different assemblages of mammals which have in
turn inhabited the western hemisphere has the great draw-
back of beginning with a time when everything was utterly
strange to the modern eye. Could the reader be carried back
to the far distant days of the Paleocene epoch, he would find
himself in a completely unfamiliar world ; and there is therefore
a real practical advantage in reversing the story and starting
with the end and thus proceeding gradually from the more
to the less familiar. The foregoing chapter gave a sketch
of the more striking and characteristic mammals which inhabit
the Americas to-day, and we may now take a step backward
to the epoch immediately preceding our own, the Pleistocene.

As was shown in Chapter V, the Pleistocene was a time of
many and great climatic vicissitudes, periods of cold, when the
northern part of the continent was buried under great ice-
sheets, alternating with far milder periods, when the climate
was much as at present, or even warmer. These climatic
changes necessitated many changes in the distribution of ani-
mals and plants, increasing cold driving them southward, while
the return of more genial conditions permitted the northward
migration of southern forms. The effects of these changes of
climate are still plainly visible in the geographical arrangement
of living beings in the northern continents and many anomalies
of distribution, otherwise inexplicable, are thus made clear.

192

SUCCESSIVE MAMMALIAN FAUNAS 193

Attention was long ago directed to the fact that the tops of
high mountains support a flora and fauna which, on the low-
lands, will be found only hundreds, or even thousands, of miles
to the northward. The plants which grow on the summits
of the White Mountains of New Hampshire recur in Labrador,
but not in the intervening area; the vegetation and animals
of the high Alps are those of the Arctic regions, and many
similar instances might be cited. Hooker and Darwin were
the first to find a highly probable explanation of this curious
phenomenon by referring it to the climatic changes of the Pleis-
tocene epoch. During the last period of cold and glaciation,
the northern plants and animals were driven far to the south
and occupied the lowlands along the ice-front and well beyond
it ; when milder conditions gradually returned, the northern
forms not only retreated northward, but also ascended the
mountains, as the latter were freed from ice, and thus became
cut off as isolated colonies. The general explanation of " dis-
continuous distribution' ' (see p. 138) is thus always the same,
viz., that the intervening regions were once occupied by the
forms now so widely separated, which, for one reason or another,
have vanished from the connecting areas.

I. Quaternary Faunas

North America. — The Quaternary faunas of North America
are extremely difficult to correlate and place in chronological
order, because, for the most part, they are found in locally
restricted areas, such as tar-pools, bogs, caverns and similar
places. Professor Osborn has, however, succeeded in making
an admirable arrangement, which, though it will doubtless
be corrected and expanded by future research, represents
a most important advance. Of the general problem he says :-
' ' The study of the mammals of the Quaternary has by no means
progressed so far in America as in Europe ; it will be many
years before the faunistic succession can be worked out with
such chronologic accuracy and precision as has at last been

o

194 LAND MAMMALS IN THE WESTERN HEMISPHERE

attained by European geologists and palaeontologists." Ac-
cording to Osborn's arrangement, there are three principal
successive Pleistocene faunas, two of which appear to have
coincided with interglacial stages, and the third with the last
reestablishment of glacial conditions on a grand scale. Re-
garding the details of these faunas, there still remains much
uncertainty, and consequently there will be no attempt made
here to do more than discriminate between the general Pleis-
tocene assemblage, on the one hand, and that of the last cold
period, on the other. It must be emphasized that we are as
yet unable to assert that all of the animals listed together were
actually living at the same time.

It is probable that the Pleistocene fossils already obtained
give us a fairly adequate conception of the larger and more
conspicuous mammals of the time, but no doubt represent
very incompletely the small and fragile forms. With all its
gaps, however, the record is very impressive; "the early and
mid-Pleistocene life of North America is the grandest and
most varied assemblage of the entire Cenozoic Period [i.e.
era] of our continent " (Osborn). There is the further ad-
vantage that the fossils have been gathered over a very great
area, extending from ocean to ocean and from Alaska to Central
America. Thus, their wide geographical range represents
nearly all parts of the continent and gives us information con-
cerning the mammals of the great forests, as well as of the great
plains.

Those divisions of the early and middle Pleistocene which
enjoyed milder climatic conditions had an assemblage of mam-
mals which, from one point of view, seems very modern, for
most of the genera, and even many of the species, which now
inhabit North America, date back to that time. From the
geographical standpoint, however, this is a very strange fauna,
for it contains so many animals now utterly foreign to North
America, to find near relatives of which we should have to go
to Asia or South America. Some of these animals which

SUCCESSIVE MAMMALIAN FAUNAS

195

*-2^Ty*,-

Fig. 113. — Some of the more characteristic Pleistocene mammals, reduced to a uniform
scale, with a pointer dog (in the frame) to show relative sizes. — 1. t Columbian
Elephant (Elephas fcolumbi). 2. Giant f Ground-Sloth (f Megalonyz jeffersoni).
3. tStag-Moose (fCervalces scotti). 4. "{American Mastodon (^Mastodon ameri-
canus). 5. t Giant Beaver (f Castoroides ohioensis). 6. t Texas Horse (Equus -f scotti) .
7. t Sabre-tooth Tiger (f Smilodon calif ornicus) .

196 LAND MAMMALS IN THE WESTERN HEMISPHERE

now seem so exotic, such as the llamas, camels and horses, were
yet truly indigenous and were derived from a long line of
ancestors which dwelt in this continent, but are now scattered
abroad and extinct in their original home, while others were
migrants that for some unknown reason failed to maintain
themselves. Others again are everywhere extinct.

Most surprising, perhaps, in a North American landscape,
is the presence of the Proboscidea, of which two very distinct
kinds, the fmastodons and the true elephants, are found together.
Over nearly the whole of the United States and southern
Canada, and even with sporadic occurrence in Alaska, ranged
the "("American Mastodon (f Mastodon americanus) which was
rare in the plains, but very abundant in the forested regions,
where it persisted till a very late period and was probably
known to the early Indians. This animal, while nearly related
to the true elephants, was yet quite different from them in
appearance, as will be immediately seen on comparing 1 and 4,
Fig. 113, p. 195. The most obvious external difference was the
comparative shortness of the legs in the fMastodon, which
did not exceed and seldom attained a height of 9 ft. 6 in.
at the shoulder ; the head also was lower and more flattened.
The teeth were very different from those of the elephants ;
the grinding teeth were much smaller and simpler, being low-
crowned and rooted and having three or four high, transverse,
enamel-covered crests, without cement. The tusks were
elephant-like except that in the male there was a single small
tusk in the lower jaw, which cannot have been visible exter-
nally ; this is a remnant of an earlier stage of development,
when there were two large tusks in the lower as well as the
upper jaw. The creature was covered with long, coarse,
dun-coloured hair; such hair has been found with some of
the skeletons.

Of true elephants, the North American Pleistocene had three
species. Most interesting of these is the northern or Siberian
fMammoth (Elephas ^primigenius) , a late immigrant from

SUCCESSIVE MAMMALIAN FAUNAS 197

northern Asia, which came in by way of Alaska, where Bering
Land (as we may call the raised bed of Bering Sea) connected
it with Asia. The fMammoth was abundant in Alaska,
British Columbia and all across the northern United States
to the Atlantic coast. Hardly any fossil mammal is so well
known as this, for the carcasses entombed in the frozen gravels
of northern Siberia have preserved every detail of structure. It
is thus definitely known that the fMammoth was well adapted
to a cold climate and was covered with a dense coat of wool
beneath an outer coating of long, coarse hair, while the con-
tents of the stomach and the partially masticated food found
in the mouth show that the animal fed upon the same vegeta-
tion as grows in northern Siberia to-day. The grinding teeth
were very high, cement-covered, and composed of many thin
plates of enamel, dentine and cement, and were closely similar
to those of the existing Indian Elephant (E. maximus) . In size
this is the smallest of the three Pleistocene species, 9 feet at
the shoulder. The fMammoth was not peculiar to Siberia
and North America, but extended also into Europe, where it
was familiar to Palaeolithic Man, as is attested by the spirited
and lifelike carvings and cave-paintings of that date. Thus,
during some part of the Pleistocene, this species ranged around
the entire northern hemisphere.

Closely related to the fMammoth and in some cases hardly
distinguishable from it, is the fColumbian Elephant (E.
\colwribi) which, however, attained a considerably larger size,
as much as 11 feet, rivalling the largest African elephants of
the present time. The head was very high and had a curiously
peaked appearance, and the tusks in old males curved inward,
overlapping at the tips. From the likeness in teeth and
skeleton to the fMammoth, it may be inferred, though some-
what doubtfully, that the fColumbian Elephant was clothed
with hair, but not so heavily as the fMammoth, which was
a northern species, the Columbian form replacing it southward,
and ranging over the whole United States, including Florida

LAND MAMMALS IN THE WESTERN HEMISPHERE

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SUCCESSIVE MAMMALIAN FAUNAS 199

and even throughout the table-land of Mexico. The areas
of the two species overlapped along the northernmost United
States, but are elsewhere distinct.

A third species was the huge "("Imperial Elephant (E. ^impera-
tor), the largest of American forms, to which Osborn's calcula-
tions give the almost incredible height of 13 ft. 6 in. This
great creature was characterized not only by its enormous
stature, but also by the proportionately very large size of its
grinding teeth, and was a survivor from the preceding Pliocene
epoch ; it is not known to have passed beyond the middle Pleis-
tocene and was thus the first of the species to become extinct.
In geographical range, the tlmperial Elephant was a western
form, extending from the Pacific coast almost to the Mississippi
River, east of which it has never been found, and from Ne-
braska southward to the City of Mexico. The meaning of this
distribution is probably that this elephant shunned the forests
and was especially adapted to a life on the open plains. Over
most of its area the winters were severe, and this fact makes
it likely that the animal was clothed with hair, but nothing is
definitely known on this point.

Many other hoofed animals, far more than now inhabit
North America, are found in this Pleistocene fauna. The
Perissodactyla were represented by horses and tapirs, but not
by rhinoceroses ; it might seem superfluous to say that there
were no rhinoceroses, but, as a matter of fact, that family had
a long and varied American history and became extinct only
during or at the end of the Pliocene epoch. The horses were
extremely numerous, both individually and specifically, and
ranged, apparently in great herds, all over Mexico and the
United States and even into Alaska. All the known species
(at least ten in number) belong to the genus Equus, but the
True Horse (E. caballus), to which all the domestic breeds are
referred, is not represented. The smallest known member of the
genus is the pygmy E.^tau of Mexico. E.^fratemus, likewise
a very small species, is found especially in the southeast, but

200

LAND MAMMALS IN THE WESTERN HEMISPHERE

extended as far north as Pennsylvania and west to Nebraska.
On the other hand, E.^giganteua of Texas exceeded the
heaviest modern draught-horses in size and was the largest of
the American species; of other Texan forms, one (E.fycotti)
resembled Burchell's Zebra (E.burchelli) in the proportions
of head and neck, body and limbs, while another {E.\semi-
plicatus) was more ass-like. The forest horse of the eastern

states has been named E.^pectinatus, an animal of moderate
size. The Great Plains must have been fairly covered with
enormous herds of horses, the countless bones and teeth of
which, entombed in the Sheridan formation, have given to it
the name of "Equus beds." The most abundant of the plains
species is E. \complicatus, a horse of about 14J hands in height
(i.e. 4 feet 10 inches at the shoulder) which also ranged down
the Mississippi Valley nearly or quite to the Gulf of Mexico.
In California was E.\ocddentalis, equalling Ejcomplicatus in
size, but with much more simple teeth, and associated with

SUCCESSIVE MAMMALIAN FAUNAS 201

it the much larger E.1[pacificusf which was inferior only to
E.^giganteus and therefore the second largest of the American
Pleistocene horses. •

To one who knows nothing of the geological history of
North America it would be natural to suppose that the Pleis-
tocene horses must have been immigrants from the Old World,
which failed to establish themselves permanently here, since
they completely disappeared before the discovery of the con-
tinent by Europeans. This would, however, be a mistaken
inference, for North America was for long ages the chief area
of development of the equine family, which may here be
traced in almost unbroken continuity from the lower Eocene
to the Pliocene. On the other hand, it is quite possible that
some of the species were immigrants.

Tapirs, which are now confined to southern Asia, Central
and South America, were not uncommon in the forested parts
of eastern North America as far north as Pennsylvania, but
they have not been found west of the Mississippi in the plains
region. Two species are known, a larger and heavier one,
Tapirus^haysii, and a smaller one which seems to be identical
with the living T. terrestris of Central and South America.
Like the horses, the tapirs had a long history of development
in North America and may well have originated here, but
they withdrew from the continent in the Pleistocene, probably
yielding to the last of the glacial advances.

There was likewise a much greater variety of Artiodactyla
than North America can boast at the present day ; some were
autochthonous, but, for the most part, they were migrants
from the eastern hemisphere, where the great group of the true
ruminants (Pecora) passed through the greater part of its
development and where its headquarters still are. Indigenous
were the peccaries, or American swine, which still occur from
Texas south to Brazil. In Pleistocene time they ranged over
nearly all of the United States, as far northward as Pennsylvania,
and across the plains to the Pacific coast ; they were represented

202 LAND MAMMALS IN THE WESTERN HEMISPHERE

by two genera, now extinct, one of which (^Platygonus) had
crested grinding teeth and much longer legs than the modern
peccaries. Another indigenous group, strange as that may seem,
is the suborder (Tylopoda) of the camels and llamas, both of
which are represented in the North American Pleistocene, the
descendants of a very long American ancestry. Some of
these tylopodans were far larger than existing forms, and at
least one species extended its range to Alaska.

Of ultimately Old World origin, but through a considerable
line of descent in America, were the typically American deer
{Odocoileus) of which the Virginian and Black-tailed species
are familiar modern instances. Whether or not the Old
World types, the Caribou (Rangifer) and Wapiti {Cervus
canadensis) had reached the western hemisphere, is a matter
of some doubt ; if present at all, they must have been com-
paratively rare. The Moose {Alee americanus)9 on the other
hand, had already appeared, but seems to have been confined
to the western half of the continent, its presence in the east
being questionable. The mistakenly named " Rocky Mountain
Goat" (Oreamnos montanus), which is an antelope of the
chamois group, was an apparently late arrival in the Pleistocene,
while the peculiar Prong-Buck (Antilocapra americana), which
is very different from any of the Old World antelopes, was
present in the early part of the epoch. The descent of this
remarkable animal is still a problem, but not improbably it
was derived from the " deer-antelopes" of the Miocene and
Pliocene, the last of which occurred in the early Pleistocene.
Mr. Gidley has announced the surprising discovery in Mary-
land of a large antelope hardly distinguishable from the
African Eland (Taurotragus). Other late arrivals from the
Old World were several forms allied to the existing Musk Ox
(Ovibos) ,at least two genera of which tfPreptoceras and ]Eucera-
therium) have been found in California. A surprising number
of species of Bison occurred in the Pleistocene, no less than
seven of which are recognized as distinct, ranging from Florida

SUCCESSIVE MAMMALIAN FAUNAS

203

to Alaska. It is not likely that all these species coexisted at
the same time, but we cannot yet determine their order of
succession, though the modern species, B. bison, was probably
the latest to arise. Most of these species were much larger

than B. bison, and some were gigantic, such as B.\latifrons,
which had a spread of horns of 6 feet and is found through the
Mississippi Valley, and B.^crassicornis of Alaska.

Preying upon this great assemblage of hoofed animals was
a corresponding array of Carnivora, most of which were in-
digenous and derived from American stocks, but there was a
considerable migrant element also, such as the bears and
badgers. Nearly all the modern kinds of flesh-eaters found

204 LAND MAMMALS IN THE WESTERN HEMISPHERE

in the North America of to-day were already here in the
Pleistocene, minks, weasels, martens, skunks, otters, badgers,
wolverenes, raccoons, foxes, wolves, coyotes, pumas, etc., etc.,
but there were several others which are either now extinct or no
longer to be found in this continent. Of the extinct types much
the most striking were the several species of fsabre-tooth tigers
{]Smilodony see Frontispiece) which have been found in the
greater part of the United States and no doubt ranged over the
whole. These were massive, short-tailed and rather short-
legged, but very muscular and powerful, cat-like animals, in
which the upper canine teeth were converted into great,
recurved, scimitar-like tusks. These large beasts of prey,
which about equalled the Leopard in height, but were far
heavier, belonged to a group which, at one time or another,
spread over nearly the whole world and persisted much later
and attained a larger size and higher development in the
western hemisphere than in the eastern. They had a very
long American ancestry, from the lower Oligocene to the end
of the Pleistocene, but the place of their origin is still un-
known. In addition to the pumas and lynxes, there were
some very large true felines (Felis ^atrox and F jimperialis) ,
which closely resembled the Lion (F. leo) in size, appearance
and structure, and have been found in California and the
Mississippi Valley ; probably these great cats were immigrants,
but they may represent a native development of Miocene and
Pliocene stock ; the history of the family is too imperfect for a
decision of this question.

Besides coyotes and wolves which are indistinguishable
from existing species, there were some very large wolves, now
extinct, of which the commonest and most widely distributed
was Canis ^dirus (also called C jindianensis) so abundant in
the asphalts of southern California. Bears were not so com-
mon in the middle Pleistocene and have not been found in the
older part of that epoch, though they probably had already
reached North America from the Old World, where they orig-

SUCCESSIVE MAMMALIAN FAUNAS 205

inated. Their absence from the older Pleistocene (Equus
Beds) may be accounted for by the fact that those beds con-
tain a fauna of the open plains, while bears are chiefly forest-
living animals. An extinct type of the family is the group
of species which constitute the fshort-f aced bears i^Arctotherium) ,
very large and powerful creatures, with remarkably shortened
jaws, which have been found from ocean to ocean. The smaller
beasts of prey, badgers, weasels, etc., were, as intimated above,
substantially the same as now.

The rodents of the Pleistocene were very nearly in their
modern stage of development, most of the genera and many
of the species surviving to present times. Just what members
of the order were introduced from the Old World, the imperfect
and fragmentary history will not permit us to say, but some
interesting South American immigrants should be noted. One
of these, the Capybara or so-called Water-Hog (Hydrochcerus
capybara), the largest of existing rodents, failed to gain a per-
manent foothold, but another South American form, the Short-
tailed or Canada Porcupine (Erethizon dorsatus) , common
all over the United States in the Pleistocene, has maintained
itself to the present day. One especially peculiar form, not
derived from South America or the Old World, is the fGiant
Beaver tfCastoroides), one species of which, fC. ohioensisf was
as large as a Black Bear and occurred in the later Pleistocene,
while a smaller species (fC. species indet.) is found in the more
ancient deposits of the epoch. In almost all respects ]Cas-
toroides was simply a gigantic beaver, but the grinding teeth
were remarkably like those of the South American Capybara
{Hydrochosrus) , so much so that it has been mistakenly re-
ferred to the same family by some authorities.

By far the strangest elements of the Pleistocene faunas
were the two suborders of gigantic edentates, the fGravigrada,
or fground-sloths, and the fGlyptodontia, which might well be
called giant armadillos, if that name were not already in use
for a living Brazilian animal. Both suborders are completely

206 LAND MAMMALS IN THE WESTERN HEMISPHERE

extinct, but they long played a very conspicuous r61e in South
America, where they originated and whence the North American
representatives migrated. The fground-sloths were great,
unwieldy, herbivorous animals covered with long hair, and
in one family (fMylodontidse) there was a close-set armour
of pebble-like ossicles in the skin, not visible externally ; they
walked upon the outer edges of the feet, somewhat as the Ant-
Bear (Myrmecophaga) uses his fore paws, and must have been
very slow-moving creatures. Their enormous claws may have
served partly as weapons of defence and* were doubtless
used also to drag down branches of trees and to dig roots and
tubers. Apparently, the latest of these curious animals to
survive was the very large \Megalonyx, which, it is interesting
to note, was first discovered and named by Thomas Jefferson.
The animals of this genus were very abundant in the forests
east of the Mississippi River and on the Pacific coast, much
less common in the plains region, where they would seem to
have been confined to the wooded river valleys. The still
more gigantic f Megatherium, which had a body as large as that
of an elephant and much shorter, though more massive legs,
was a southern animal and has not been found above South
Carolina. ^Mylodon, smaller and lighter than the preceding
genera, would seem to have entered the continent earlier and to
have become extinct sooner ; it ranged across the continent,
but was much commoner in the plains region and less so in the
forested areas than \Meqalonyx, being no doubt better adapted
to subsisting upon the vegetation of the plains and less de-
pendent upon trees for food.

The fGlyptodonts were undoubtedly present in the North
American Pleistocene, but the remains which have been col-
lected so far are very fragmentary and quite insufficient to
give us a definite conception of the number and variety of them.
It will be better therefore to defer the description of these
most curious creatures until the South American Pleistocene
is dealt with, as they were incomparably more varied and

SUCCESSIVE MAMMALIAN FAUNAS 207

characteristic in that continent. In North America they have
been found only in Mexico and the southern United States.

The many and great climatic changes which took place in
the Pleistocene led to very extensive migrations of mammals
from one part of the continent to another, as the conditions of
temperature and moisture changed. In Interglacial stages,
when the climate was much ameliorated, southern species
spread far to the north, as when the fMastodon ranged into
Alaska, and the Manatee, or Sea-Cow, of Florida waters, came
up the coast to New Jersey, while the increasing cold of on-
coming glaciation caused a reverse movement and drove
northern and even Arctic forms far to the south. Thus, the
Musk-Ox, the Caribou and the northern fMammoth came
south beyond the Ohio and the Potomac, and the Walrus was
found on the South Atlantic coast. It is these migratipns which
give such a mixed character to the Pleistocene faunas from the
climatic point of view, as it is often very difficult to correlate
or synchronize the fossiliferous deposits with the Glacial and
Interglacial stages, though this has been definitely accomplished
in several very important instances.

The latest of the Pleistocene faunas is less completely
known than those of the earlier and middle portions of the
epoch, for but few localities have yet been discovered with
any extensive series of fossils. As worked out by Osborn,
this fauna coincided with the last Glacial stage and was a greatly
reduced and impoverished assemblage as compared with those
of the middle and lower Pleistocene, though it is not safe to
argue that all the animals not found in this fauna were already
extinct, for the known list is still far too short to be entirely
representative. The American fMastodon (t Mastodon ameri-
canus, see p. 196) was still abundant in the forested regions and
was apparently able to withstand severe winter temperatures,
as certainly was the fMammoth (Elephas ^-primigenius, see
p. 196), which was so abundant in the coldest part of Siberia
and which extended south to the Potomac, presumably at this

208 LAND MAMMALS IN THE WESTERN HEMISPHERE

time. Horses were still present in North America, though
apparently in greatly diminished numbers and variety. Tapirs
have not been found, though they may have lingered on in the
southern regions. The typically North American genus of deer
(Odocoileus) was, of course, well represented, and Old World
types had a much more southerly distribution than at present.
The Caribou (Rangifer caribou) came down into Pennsylvania
and Ohio, the Moose (Alee americanus) into Kentucky and
Kansas, and the Wapiti {Cervus canadensis) is reported as far
south as Florida. A very remarkable animal is the Stag-
Moose {^Cervalces scotti), the best preserved skeleton of which
is that in the museum of Princeton University. This was
found in a shell-marl beneath a peat-bog at Mt. Hermon,
N. J., north of the great terminal moraine , and therefore most
probably this particular individual dates from a time not
earlier than the beginning of the final retreat of the ice.

^Cervalces, as its name implies, was in some respects inter-
mediate between the Stag {Cervus) and the Moose {Alee) ;
in general proportions it most nearly resembled the latter,
having a short neck, long body and very long legs ; but the skull
differed in many respects from that of the Moose, especially in
parts which show that the great, inflated snout and pre-
hensile upper Up had no such development in the extinct as in
the living form. The antlers were unique among the known
members of the deer family, resembling those of the Moose,
though much less palmated and with the addition of great
trumpet-shaped plates. The feet were large, almost as large
as in the Caribou, and the whole structure indicates an animal
well fitted to travel through deep snows and flourish in severe
winters.

Even more typically northern than the Caribou were the
Musk-Oxen, of which two genera occurred in the late Pleistocene.
One of these, 1[Symbos, is extinct and was characterized by its
short horns ; the other, Ovibos, is the genus to which the exist-
ing species, 0. moschaius and 0. wardi, belong and is now con-

SUCCESSIVE MAMMALIAN FAUNAS

210 LAND MAMMALS IN THE WESTERN HEMISPHERE

fined to the extreme north of the continent, the Arctic islands
and Greenland. The remains of Musk-Oxen have been found
mostly along the great terminal moraine which marks the
front of the last ice-invasion, but they occurred also as far
south as Oklahoma, and in Utah they ranged far to the south
of the ice-front. Nothing could be more conclusive evidence
of a climate much colder than the modern one than the presence
of Caribou and Musk-Oxen in the United States and of the
Walrus on the coast of Georgia.

The smaller animals were much as they are now, differing
only in range. The fsabre-tooth tigers, the last of a most
interesting line, persisted in the south, and an extinct genus of
skunks has been discovered in Arkansas, but otherwise the
Carnivora were entirely modern in character. Unfortunately,
these smaller animals are very incompletely known, much
the richest aggregation which has yet been found being
that collected by Mr. Brown in the Conard Fissure, Arkansas.
From this collection Mr. Brown has described thirty-seven
genera and fifty-one species of mammals, of which four genera
and twenty-four species are extinct. That is to say, less than
one-ninth of the genera and one-half of the species represent
extinct forms. Contrast this with the middle Pleistocene
assemblage found in the Port Kennedy cavern in eastern Penn-
sylvania, of sixty-four species with at least forty extinct ones.

The foregoing sketch, brief and imperfect as it necessarily
is, makes it sufficiently plain that North America during the
Pleistocene was far richer in mammalian life than it was when
the continent was first settled by Europeans. When we make
the proper allowance for the many forms which undoubtedly
remain to be discovered and for those which may have vanished
without leaving a trace behind them, the contrast becomes
all the more striking. Not only did Pleistocene North America
have substantially all the mammals that it now possesses, but
it had many more. The lions and fsabre-tooth tigers, the
gigantic f short-faced bears, the tapirs and many varieties of

SUCCESSIVE MAMMALIAN FAUNAS 211

horses, large and small, the camels and llamas, many species
of bisons, some of enormous proportions, several forms allied
to the Musk-Ox, the elephants and fm&stodons, the fgiant
beavers and South American water-hogs, the huge fground-
sloths and fglyptodonts, have all disappeared, leaving a con-
tinent, that, by contrast, is "zoologically impoverished."
The Pleistocene fauna was strangely mixed in character, the
free roads of migration bringing together Old World and South
American types, and mingling them with indigenous forms
in a cosmopolitan assemblage.

Turning to South America , we find in the pampas of Argen-
tina a wonderful museum of Pleistocene mammals, such as
occurs nowhere else in the known world, and this is supple-
mented by the very rich collections gathered from the caverns
of Brazil and from deposits of Ecuador and Bolivia, and thus
all the important regions of the continent, save the far south,
are well represented. These faunas are far stranger than the
corresponding ones of North America and differ more radically
from those of modern times, since they include a much larger
proportion of extinct types, and the extinctions have swept
away not only species and genera, but families and orders as
well.

The South American Pleistocene assemblage of mammals
is very clearly divisible into two elements : (1) the immigrants
from the north, which reached the southern continent in suc-
cessive waves of migration, that have left records of themselves
as early as the older Pliocene, perhaps even the upper Miocene,
and (2) the indigenous element, which had a very long history
of development in South America. To the immigrant class be-
longed all of the Carnivora, which therefore resembled their
North American relatives, but were less varied in character. Of
the bears, only the huge, fshort-faced kind (^Arctotherium, Fig.
275, p. 549) are known, and it is not likely that true bears existed
except in the Andes, as is also the case to-day. Of the cat
family, the fsabre-tooth tigers {^Smilodori) were as common in

212

LAND MAMMALS IN THE WESTERN HEMISPHERE

South America as in North, and, while there were no lions,
there were large cats nearly allied to the Jaguar and Puma, and
smaller ones, like the Ocelot. The dogs were quite numerously

Fig. 118. — Some of the commoner Pampean mammals, reduced to a uniform scale,
with a pointer dog (in the frame) to show the relative sizes. 1. t Dadicurua clavi-
caudatus. 2. fGlyptodon clavipes, t glyptodonts. 3. f Macrauchenia patachonica,
one of the f Litopterna. 4. t Pampas Horse (f Hippidion neogceum). 5. t Toxodon
burmeisteri, a ftoxodont. 6. ^Megatherium americanum. 7. f Mylodon robu&tus,
t ground-sloths.

represented by species resembling closely the existing South
American fox-like wolves and the Bush-Dog (Icticyon) and,
strange to say, by one which seems referable to the same

SUCCESSIVE MAMMALIAN FAUNAS 213

genus (Cyon) as the Dhole of India. The weasel family
(Mustelidse) were less numerous and varied than in the northern
continent, as they still are; coatis (Naaua) and raccoons
(Procyon) were abundant and one species of the latter was much
larger than any existing one; extinct species of skunk (Co-
nepatus)y tayra {Tayra) and otter (Lutra) were also present,
but the badgers, minks, martens and wolverenes were not.

The hoofed animals were represented by a great variety
of forms, both immigrant and indigenous, of which the latter
belonged to orders now entirely extinct. Horses were com-
mon in all parts of the continent, where fossils of this epoch
have been obtained, and are referable to two very distinct
groups: (1) to the typical genus Equus, of which three species
have been described, all somewhat more primitive than the
True Horse (E. caballus) and, like most of the Pleistocene
species of North America, with a certain resemblance to the
zebras and asses ; (2) to an extinct group of four genera, the
best known of which is \Hippidion. The species of this genus
(which has also been reported from North America, though
upon hardly sufficient evidence) had most exceptional characters
in the skull, and the head was relatively large and clumsy, with
narrow and very high facial region. The neck was com-
paratively short, the limbs heavy and the feet short. These
animals can hardly have been very swift runners. A very
interesting member of this group is ]Hyperhippidiumy a small
horse found in the Andes, with remarkably short feet, well
adapted for a mountain life. The only other perissodactyls
were tapirs, which ranged down to the Argentine pampas,
much farther south than now.

The Artiodactyla were much more varied; there were
peccaries, many species of llamas, which then extended into
Brazil, and were not confined, as at present, to the colder
portions of the continent. There were also numerous deer,
all of the South American type, and two different antelopes
have been reported, though that family has no representatives

214 LAND MAMMALS IN THE WESTERN HEMISPHERE

SUCCESSIVE MAMMALIAN FAUNAS 215

in the southern continent now. Several species of fmastodons
have been found in Brazil, Argentina, Bolivia and elsewhere,
but none of the true elephants. Why the fmastodons were
able to make their way into South America, while the elephants
were not, is one of the puzzling questions of mammalian dis-
tribution to which no answer can be given.

All the preceding types of hoofed animals, the horses,
tapirs, peccaries, llamas, deer, antelopes and fmastodons were
migrants from the north, and four of these, tapirs, peccaries,
llamas and deer, were able to gain a permanent footing in
South America and are more or less abundant there to-day,
while the horses, antelopes and "(mastodons failed to do so
and died out. In addition to these, there were the indigenous
types, which are now extinct and have never been found out-
side of the Neotropical region. An extremely peculiar creature,
^Macrauchenia, was the last surviving member of an order, the
fLitopterna, which for ages played a very important r61e in
South America. ^Macrauchenia was a large animal, somewhat
larger and of much heavier build than a camel, to which it
had a considerable, though entirely superficial, resemblance.
The head was relatively small and must have had quite a long
proboscis ; the neck was very long, suggesting that the animal
browsed upon trees, which is also indicated by the character
of the teeth ; the legs were long and stout, the feet short and
each provided with three toes. Another curious creature was
IfTypotherium, from which is named the group of the fTypo-
theria, which some authorities regard as a suborder, while
others assign to it a full ordinal rank.

The fTypotheres throughout the Tertiary period were
among the most abundant and characteristic of the South
American hoofed animals, and the genus fTypotherium was the
last of a very long series and was an animal of moderate size,
with chisel-shaped incisor teeth so like those of the rodents
that the genus was long referred to that order. Finally, we
have \Toxodon, type of the order fToxodontia, a ponderous

216 LAND MAMMALS IN THE WESTERN HEMISPHERE

SUCCESSIVE MAMMALIAN FAUNAS

217

beast, as large as a rhinoceros, which, there is some reason to
think, was largely aquatic in its habits. The first species of
this extraordinary creature was found by Charles Darwin,
who says of it: "Perhaps one of the strangest animals ever
discovered ; in size it equalled an elephant or megatherium,

Restored from a skeleton

but the structure of its teeth, as Mr. Owen states, proves
indisputably that it was intimately related to the Gnawers
[i.e. Rodentia] ... in many details it is allied to the Pachy-
dermata : judging from the position of its eyes, ears, and
nostrils, it was probably aquatic, like the Dugong and Manatee,
to which it is also allied." ' Modern views concerning the
relationships of ^Toxodon are very different from those advanced
by Darwin, but he gives a vivid picture of its diverse likenesses.
Neither ^Macrauchenia, ^Typotherium nor iToxodon has been

'Voyage of a Naturalist, Am. ed,, 1891, p. 82.

218 LAND MAMMALS IN THE WESTERN HEMISPHERE

found in the Brazilian caverns, but this is no doubt due to the
accidents of preservation, for the latter animal ranged north
to Nicaragua.

The rodents likewise were partially of immigrant and par-
tially of native stock. To the former belonged the few mice
and rats and a meadow-mouse (Microtus), a group not repre-
sented in present-day South America, and a rabbit. Very
much more abundant and varied were the indigenous forms, all
of which belonged to existing families and most of them to exist-
ing genera ; the tree-porcupines, cavies, agoutis, spiny-rats, viz-
cachas, capybaras, coypus, etc., were abundantly represented,
for the most part by extinct species.

The monkeys were of purely Neotropical type and several
modern genera, such as Cebus and Callithrix, and one very
large extinct genus, ^Protopithecus, of the same family, have
been found in the caverns of Brazil, but not in the pampas of
Argentina, which would seqm to have been a country of open
plains.

In the South America of to-day one of the most striking
and peculiar elements of the fauna is that formed by the Eden-
tata, the sloths, anteaters and armadillos, and this was even
more true of the same region in Pleistocene times. Anteaters
and sloths are very scantily represented, but this is merely
an accident of preservation; armadillos, on the other hand,
were very numerous both in Brazil and in Argentina, and, in
addition to many modern genera, there were several which
are no longer in existence, such as 1[Chlamydotherium, which
was a huge creature almost as large as a rhinoceros. Then
there were the two extinct suborders of the fglyptodonts
(fGlyptodontia) and the fground-sloths (fGravigrada) which
were astonishingly abundant in Argentina and which, as was
shown in a previous page (p. 205), were also well represented iit
North America.

Few more fantastic-looking mammals than the fglyptodonts
have ever been found ; the short, deep head, with its shield

SUCCESSIVE MAMMALIAN FAUNAS 219

of thick, bony plates, the huge carapace made up of innumerable
plates of bone firmly united at their edges and without the
movable bands of the armadillo carapace, the enormous tail-
sheath, the short legs and massive feet with broad hoofs,
must have given these animals rather the appearance of gigantic
tortoises than of mammals. The fglyptodonts were especially
numerous and varied in the Argentine pampas, and a stately
array of them is mounted in the museums of La Plata and
Buenos Aires ; in length, they ranged from six to twelve feet,
including the tail. The skeleton and carapace did not differ
very greatly in appearance among the various genera, but there
were great differences in the form and size of the bony sheath
enclosing the tail. In the genus 1[Gtyptodon the sheath was
composed throughout of movable overlapping rings, with
prominent spines on them ; in ^Sclerocalyptus the hinder half
of the sheath coalesced into a single piece, marked only by
the elaborate ornamentation of the horny scales, while in
^Dcedicurus the end had a tremendous, club-like expansion,
which must have been set with great horn-like spines. The
fglyptodonts were ponderous, slow-moving and inoffensive
plant-feeders, almost invulnerable to attack, and probably
used their massive tails, which could be freely swung from side
to side, as redoubtable weapons of defence, much as the alli-
gator uses his tail. In comparison with the bewildering variety
in South America, the few that made their way into North
America were quite insignificant.

Much the same statement applies to the fground-sloths,
and though these ranged far more widely through the northern
continent than did the fglyptodonts, they were but few in
comparison with the multitude which inhabited alike the
forests of Brazil and the plains of the south. Two of the three
genera of fground-sloths which occur in the North American
Pleistocene, ^Megatherium and \Mylodony are also found in
South America ; and though \Megalonyx has not yet been ob-
tained there, the family of which it is a member was represented.

220 LAND MAMMALS IN THE WESTERN HEMISPHERE

SUCCESSIVE MAMMALIAN FAUNAS 221

In size, these creatures varied from a tapir to an elephant,
though all were much shorter-legged than any elephant ; the
extremely massive tail, which the larger forms had, served to
support the huge body, when erected to tear down the branches
and leaves upon which these strange creatures fed.

Opossums were extremely numerous, especially in the
Brazilian caves, where in half a cubic foot of earth 400 jaws
were collected.

The Pleistocene mammalian fauna of South America was
a mixture of modern forms with ancient, vanished types similar
to that which we found in North America. The fground-
sloths and fglyptodonts, the flitopterns, "ftoxodonts and
ftypotheres, the antelopes, horses and fmastodons have all
disappeared from the continent, or vanished altogether from
the face of the earth.

II. Tertiary Faunas
1. Pliocene

North America. — No part of the Cenozoic history of North
America is so imperfectly recorded and so unsatisfactorily
known as that of the Pliocene, and the later portion of that
epoch is especially obscure. If the Peace Creek formation
of Florida is properly referred to the upper Pliocene, it would
show that the mammals of that time were substantially the
same as those of the early Pleistocene.

The only fauna, as yet discovered, which can be referred
to the middle Pliocene, is that of the Blanco beds of north-
western Texas, which have yielded but a scanty list of mostly
ill-preserved fossils. Obviously, these give us a very incom-
plete picture of the life of that time. The great fground-
sloths had already reached North America, and the genus
\MegalonyXj so common in the forested areas of Pleistocene
North America, was perhaps already in existence. The
fglyptodonts were likewise represented by one genus tfGlyp-

222 LAND MAMMALS IN THE WESTERN HEMISPHERE

totherium) which was distinguished by the simple rings of
the tail-sheath. No rodents have yet been found and only
a few of the Carnivora, though a large cat, a musteline and
a large f" bear-dog' ' are known. There were no true elephants,
but several species of fniastodons, all of which were different
from those of the Pleistocene ; and in some, grinding teeth,
though still low-crowned, had become much larger and more
complex, marking a stage of advance toward the elephan-
tine dentition. Horses of primitive type, the feet having
three functional toes instead of one, were relatively abundant.
Very large llama-like animals were present, but nothing has
been ascertained with regard to the deer and antelopes of the
time, and the only other representative of the Artiodactyla
yet recovered is a peccary, interesting as being a species of the
genus (\Platygonus) which became so abundant and wide-
spread in the Pleistocene. Scanty and incomplete as this
fauna is, it suffices to show that the middle Pliocene mammals
were much more primitive than those of the -Pleistocene.

The fauna of the Snake Creek formation in western
Nebraska and that of the presumably somewhat later beds
of northwestern Nevada, which are referable to the lower
Pliocene, may be considered together. The rodents, which
are not very fully represented, were quite modern in character
and belonged mostly to extinct species of modern genera,
such as hares, pocket-gophers, beavers, forerunners of the
fGiant Beaver, marmots, sewellels, etc. A remnant of a more
ancient world, especially characteristic of the Miocene, is
found in the remarkable burrowers, the horned tmyl&gaulids
which have been extinct since the lowel* Pliocene. Carnivora
were abundant, and members of all the families which inhabit
North America to-day have been obtained; wolves, f" bear-
dogs/ ' f" hyena-dogs' ' and forms like the Dhole of India were
common. The terms f"bear-dogs" and f" hyena-dogs' ' are
not to be understood as implying any relationships of these
animals to bears or hyenas, but merely a certain superficial

SUCCESSIVE MAMMALIAN FAUNAS 223

resemblance ; these were very large members of the dog family
(Canidse), now extinct. Mustelines, large and small, are
found, and possibly some bears had already made their way
from the Old World, but this is still uncertain. fSabre-tooth
tigers and true cats, some as large as lions and one species
fairly gigantic, were likewise characteristic of the time. There

"was a great wealth of horses, though the modern genus Equns
"was not among them ; all the genera are now extinct and all
"were three-toed. Several distinct phyla were represented,
some progressive and advancing toward the modern forms,
others conservative and stationary. Browsing horses with
low-crowned teeth, grazing horses with prismatic, cement -
covered teeth, heavier and lighter, larger and smaller, must
liave covered the plains and thronged the woods. Ancestral
tapirs were present, though far less common. A family which

224 LAND MAMMALS IN THE WESTERN HEMISPHERE

seems to be utterly exotic to North America, that of the rhinoc-
eroses, was present, and of these there were three or four series,
mostly without horns, or with a very small horn on the tip
of the snout. The extremely aberrant perissodactyls (fAncylo-
poda), in which the hoofs were converted into great claws,
perhaps persisted, but the evidence is not conclusive.

The Artiodactyla were, for the most part, totally different
from those of modern times, though several forms were an-
cestral to some now living. Peccaries more primitive than
the living genus were the only representatives of the swine-
like suborder; ancestral camels and llamas were among the
commonest of the hoofed animals and an extinct phylum, that
of the f" giraffe-camels " (jAlticamelus) continued over from
the Miocene. The giraffe-camels are so called, not because
of any actual relationships with the giraffes, but on account of
certain likenesses in the proportions of the animals compared.
^Alticamelus was a very large, camel-like creature, with remark-
ably elongate neck and limbs and comparatively small head,
which no doubt resembled the giraffes in browsing upon trees
which were above the reach of the ordinary camels and llamas
of the time. It was the terminal member of a series, or phylum,
which branched off from the main stock in Oligocene times and
pursued a course of development which was independent of
the principal series, but curiously parallel with it.

The deer of the lower Pliocene were little, graceful creatures
( ^Blastomeryx) which had no antlers, but the males were armed
with sabre-like upper canine tusks, so that they must have
resembled the Musk-Deer of Tibet, but were smaller and more
slender. The remarkable group of f" deer-antelopes/ ' now
extinct, was represented by fMerycodus, a dainty little creature,
less than two feet high at the shoulder, which had the antlers
and general appearance of a small deer, but the high-crowned
grinding teeth which most antelopes have. True antelopes
of two different lines were also present, though they are as yet
known from little more than the bony horn-cores; of these,

SUCCESSIVE MAMMALIAN FAUNAS 225

one is the flat-horned and the other the twisted-horned or
strepsicerine type, such as is illustrated by the Eland and Kudu
of modern Africa. The latter may, however, be related to
the peculiarly North American Prong-Buck (Antilocapra)
and not to the strepsicerine antelopes of the Old World. The
last survivors of an exclusively North American family, the
foreodonts, which were wonderfully numerous and varied
from the upper Eocene onward, are found here.

The fmastodons (jGomphotherium) of this formation had
well-developed tusks in the lower as well as in the upper jaw,
and in one species the chin-region or symphysis of the lower
jaw was greatly prolonged, an ancient feature.

That the South American edentates had already reached
the northern continent is sufficiently proved by remains of
fground-sloths, which are, however, too incomplete to permit
identification of the genus. fGlyptodonts have not yet been
found, but this fact does not demonstrate that they had not
accompanied the fground-sloths in their migration, for at no
time did they range so far north as Nebraska or northwestern
Nevada, and the only mammal-bearing formation of lower
Pliocene date known in the south, the Alachua Clay of Florida,
has yielded too scanty a list of fossils to make its negative
evidence at all conclusive on this point.

The mammals of the middle and especially of the lower
Pliocene were much stranger and more primitive than might
be inferred from the foregoing brief account. Except several
of the Rodentia and perhaps one or two of the Carnivora, the
genera are all extinct and such familiar terms as horses, rhinoc-
eroses, camels, etc., can be employed only in a very compre-
hensive sense, as equivalent to families.

The Pliocene of South America is involved in some obscurity ;
not that there is any question as to the formations, or their
order of succession, but there is much doubt as to the limits
of the epoch both above and below. The latest Pliocene
fauna, that of the Tarija Valley in Bolivia, was essentially the

Q

226 LAND MAMMALS IN THE WESTERN HEMISPHERE

same as that of the Pleistocene and contained a similarly large
proportion of migrant elements from the north, but it was evi-
dently older and many of the species were different. The two
divisions of the Araucanian fauna, contained in the beds of
Catamarca and Monte Hermoso respectively, are very much
alike and need not be given separate consideration. In one
respect these presumably upper Pliocene faunas formed a very
strong contrast to the mammalian assemblage of the Pleistocene,
and that is in the quite insignificant part taken by the migrants
from North America. Of the Carnivora there were but two
representatives, one referable to the raccoon family and one
to the dogs, while a hare and a small member of the Artio-
dactyla, of indeterminate family, complete the list of northern
forms, though this list will doubtless be extended by future
discovery. The peccaries, deer, antelopes, tapirs, horses,
fmastodons, cats, weasels, otters, squirrels, mice, etc. had not
reached the southern continent, or were still so rare that
remains of them have not been found. This rarity and relative
insignificance of the northern forms gave a very different aspect
to the fauna.

On the other hand, the indigenous South American groups
were very fully represented. Many kinds of opossums and
a few large carnivorous types, much like the so-called Tas-
manian Wolf (Thylacynus) , were the remnants of a much
larger assemblage of marsupials which inhabited South
America in the Miocene. Of the Edentata, there were great
abundance and variety, many large tglyptodonts and some
gigantic armadillos, as well as numerous examples of normal
size ; the fground-sloths, though somewhat smaller than those
of the Pleistocene, were mostly of gigantic size, and true or
arboreal sloths (Tardigrada) have been reported. The very
numerous rodents, with the exception of the intrusive hare,
all belonged to typically South American families. Some of
the rodents were gigantic and one (^Megamys), a member of
the Chinchilla family, was equal to a rhinoceros in size and

8UCCES8IVE MAMMALIAN FAUNAS 227

the largest known representative of the order. Especially
characteristic was the abundance of the cavy family (Caviidse).

The hoofed animals, with the single known exception of
the immigrant artiodactyl, all belonged to the autochthonous
orders, all of which are extinct at the present time. Fore-
runners of the extraordinary genus ^Macrauchenia, which was
one of the most conspicuous elements of Pleistocene life, were
quite common in the Pliocene and differed from the Pampean
genus chiefly in their smaller size and less advanced specializa-
tion. We find here also the last survivors of another family of
the fLitopterna, the fproterotheres (fProterotheriidse), which
imitated the horses in such a surprising manner that some
authorities believe them to have been actually related to those
perissodactyls. The Monte Hermoso genus {\Epitherium) had
feet which were wonderfully, though but superficially, like. those
of the three-toed horses. The fToxodonta were numerous and
most of them were large, ponderous animals ; one genus (fTVt-
godori) had the interesting peculiarity of a single median horn
on the forehead, much like that of a rhinoceros. Horned spe-
cies were always rare among the indigenous groups of South
American ungulates, and all that have been discovered so far
belonged to the ftoxodonts. The remaining group, that of the
fTypotheria, was also well represented, both by larger and by
very small forms, some no larger than a rabbit (1[Pachyru-
Jchos).

The presumably lower Pliocene (perhaps upper Miocene)
fauna of the Parand formation is as yet known only from very
fragmentary material. Representatives of the dogs, raccoons
and bears have been reported, but the identifications are doubt-
ful; at all events, these would seem to have been the most
ancient of the northern immigrants. A considerable number
f3f marsupials, both opossums and large predaceous types,
have been found. The rodents were very numerous, all
belonging to South American families and some of them very
large. The edentates were gigantic fground-sloths and tglyp-

222 LAND MAMMALS IN THE WESTERN HEMISPHERE

totherium) which was distinguished by the simple rings of
the tail-sheath. No rodents have yet been found and only
a few of the Carnivora, though a large cat, a musteline and
a large f" bear-dog" are known. There were no true elephants,
but several species of fmastodons, all of which were different
from those of the Pleistocene ; and in some, grinding teeth,
though still low-crowned, had become much larger and more
complex, marking a stage of advance toward the elephan-
tine dentition. Horses of primitive type, the feet having
three functional toes instead of one, were relatively abundant.
Very large llama-like animals were present, but nothing has
been ascertained with regard to the deer and antelopes of the
time, and the only other representative of the Artiodactyla
yet recovered is a peccary, interesting as being a species of the
genus (^Platygonus) which became so abundant and wide-
spread in the Pleistocene. Scanty and incomplete as this
fauna is, it suffices to show that the middle Pliocene mammals
were much more primitive than those of the Pleistocene.

The fauna of the Snake Creek formation in western
Nebraska and that of the presumably somewhat later beds
of northwestern Nevada, which are referable to the lower
Pliocene, may be considered together. The rodents, which
are not very fully represented, were quite modern in character
and belonged mostly to extinct species of modern genera,
such as hares, pocket-gophers, beavers, forerunners of the
fGiant Beaver, marmots, sewellels, etc. A remnant of a more
ancient world, especially characteristic of the Miocene, is
found in the remarkable burrowers, the horned tmylag&ulids
which have been extinct since the lowel* Pliocene. Carnivora
were abundant, and members of all the families which inhabit
North America to-day have been obtained; wolves, f" bear-
dogs/ ' t" hyena-dogs " and forms like the Dhole of India were
common. The terms t" bear-dogs" and f" hyena-dogs" are
not to be understood as implying any relationships of these
animals to bears or hyenas, but merely a certain superficial

SUCCESSIVE MAMMALIAN FAUNAS

223

resemblance ; these were very large members of the dog family
(Canidfe), now extinct. Mustelines, large and small, are
found, and possibly some bears had already made their way
from the Old World, but this is still uncertain. fSabre-tooth
tigers and true cats, some as large as lions and one species
fairly gigantic, were likewise characteristic of the time. There

was a great wealth of horses, though the modern genus Equus
was not among them ; all the genera are now extinct and all
were three-toed. Several distinct phyla were represented,
some progressive and advancing toward the modem forms,
others conservative and stationary. Browsing horses with
low-crowned teeth, grazing horses with prismatic, cement-
covered teeth, heavier and lighter, larger and smaller, must
have covered the plains and thronged the woods. Ancestral
tapirs were present, though far less common. A family which

230

LAND MAMMALS IN THE WESTERN HEMISPHERE

larger members of the group. The upper tusks were compar-
atively short and nearly straight and retained a band of enamel,
while the lower tusks were still shorter, chisel-shaped and so
worn as to prove that they were regularly used, no doubt in
cropping leaves ; the shortness of these lower tusks was com-
pensated for by the great elongation of the lower jaw. The

FiO. 125. — *Tcleoccrni /ojsiper, a Hhort-IeRged rhinoceros, with small nasal horn;
lower Pliocene and upper Miocene of Nebraska. Restored from a skeleton in
the American Museum of Natural History.

head was proportionately broad and low and, for Proboscidea,
these were small animals, not more than five or six feet high
at the shoulder. The body, limbs and feet had already at-
tained substantially their modern grade of structure, advance
among the Proboscidea being chiefly restricted to the teeth
and skull.

Four families of Perissodactyla were represented in the
upper Miocene. The rhinoceroses, which were very abun-
dant, were present in considerable variety ; some were hornless,
others had a single small horn on the end of the nose. Among
these rhinoceroses there was much difference in bodily pro-

SUCCESSIVE MAMMALIAN FAUNAS 225

«)ne is the flat-horned and the other the twisted-horned or
ctrepsicerine type, such as is illustrated by the Eland and Kudu
of modern Africa. The latter may, however, be related to
the peculiarly North American Prong-Buck (Antilocapra)
and not to the strepsicerine antelopes of the Old World. The
last survivors of an exclusively North American family, the
foreodonts, which were wonderfully numerous and varied
from the upper Eocene onward, are found here.

The fmastodons {\Gomphotherium) of this formation had
well-developed tusks in the lower as well as in the upper jaw,
and in one species the chin-region or symphysis of the lower
jaw was greatly prolonged, an ancient feature.

That the South American edentates had already reached
the northern continent is sufficiently proved by remains of
tground-sloths, which are, however, too incomplete to permit
identification of the genus. fGlyptodonts have not yet been
found, but this fact does not demonstrate that they had not
accompanied the fground-sloths in their migration, for at no
time did they range so far north as Nebraska or northwestern
Nevada, and the only mammal-bearing formation of lower
Pliocene date known in the south, the Alachua Clay of Florida,
has yielded too scanty a list of fossils to make its negative
evidence at all conclusive on this point.

The mammals of the middle and especially of the lower
Pliocene were much stranger and more primitive than might
be inferred from the foregoing brief account. Except several
of the Rodentia and perhaps one or two of the Carnivora, the
genera are all extinct and such familiar terms as horses, rhinoc-
eroses, camels, etc., can be employed only in a very compre-
hensive sense, as equivalent to families.

The Pliocene of South America is involved in some obscurity ;
not that there is any question as to the formations, or their
order of succession, but there is much doubt as to the limits
of the epoch both above and below. The latest Pliocene
fauna, that of the Tarija Valley in Bolivia, was essentially the

Q

232

LAND MAMMALS IN THE WESTERN HEMISPHERE

toreodontsinthealtogetherexceptionalformoftheskull. Graz-
ing foreodonts (-fMerychyus), of moderate and small size with
high-crowned teeth, were evidently quite common on the upper
Miocene plains. The fhomless deer and f" deer-antelopes"

Jp 1

~>Sm

m J

j|L )

*8fii

Restored from

differed but little from those of the lower Pliocene. Peccaries
were fairly abundant.

The upper Miocene fauna was especially characterized by
the large number of mammals, belonging to several different
orders, which had acquired the high-crowned, persistently
growing pattern of grinding teeth. Many of the horses,
camels, ruminants and rodents displayed this structure, and,

SUCCESSIVE MAMMALIAN FAUNAS 233

as was first pointed out by Kowalevsky, the explanation is
probably to be found in the spread of grassy plains at the ex-
pense of the forests. On account of the silica which they
contain, the grasses are very abrasive and rapidly wear the
teeth down. In adaptation to this new source of abundant
and nutritious food, many kinds of mammals developed a form
of tooth which was fitted to compensate by growth for the
loss through abrasion.

The middle Miocene, small areas of which occur in Montana,
eastern Oregon and northeastern Colorado, has received various
local names, the typical one being the Deep River of Montana.
Very probably, these scattered areas are not strictly contem-
poraneous, but form a closely connected series. That a land-
connection with the eastern hemisphere existed, is made clear
by the appearance of several unmistakably Old World types
of animals and the beginnings of migration from South America
are perhaps also to be noted, though this cannot be positively
stated. The evidence for the South American connection
is the finding in the middle Miocene of Oregon of what are
believed to be the earliest remains of fground-sloths yet dis-
covered in North America, but the material is too scanty for
altogether certain determination.

The smaller animals are not very well represented in the
middle Miocene faunas, as conditions appear to have been
unfavourable to their preservation; something is known of
them, nevertheless. The very curious extinct family of rodents
known as the fMylagaulidae, the presence of which was noted
in the upper Miocene and lower Pliocene, first appeared here.
These fmylagaulids, which were distantly related to the modern
Sewellel (Aplodontia rufa), were characterized by the great
enlargement and complication of one of the grinding teeth
in each jaw and the consequent reduction of the others. One
genus of this family, as in the Pliocene, had the peculiarity,
unique among rodents, of developing a large horn upon the nose,
like a miniature rhinoceros. Among the Carnivora, we find a

234 LAND MAMMALS IN THE WESTERN HEMISPHERE

great variety of dogs, large and small, all belonging to extinct
genera, as indeed is true of the other carnivores also. True
felines have been found, but as yet, none of the fsabre-tooth
series ; the abundance of the latter, however, in both preceding
and succeeding formations, is sufficient proof that the discovery
of them in the middle Miocene is merely a question of time.
Mustelines were present, and especially noteworthy is the
appearance of the first American otters, immigrants from the
Old World.

Of the hoofed animals, the most interesting are the Pro-
boscidea, the most ancient of which that are definitely deter-
minable in America occur in this horizon. The place of origin
and ancestry of these animals were long exasperating puzzles.
Appearing suddenly in the Miocene of Europe and North
America, in which regions nothing was known that could,
with any plausibility, be regarded as ancestral to them, they
might as well have dropped from the moon, for all that could
be told concerning their history. The exploration of the
Eocene and Oligocene beds of Egypt has dispelled the mystery
and shown that Africa was the original home of the group,
whence they gradually spread to every continent except
Australia. Little is known of these earliest American pro-
boscideans, but they were doubtless small fm&stodons of the
four-tusked type.

Among the Perissodactyla, the rhinoceroses were perhaps the
most conspicuous ; the native American stocks of this family
appear to have mostly died out and to have been replaced by
two or more phyla of immigrants from the Old World, some
of which were hornless, others had a small horn on the tip of
the nose and others again had a second and smaller horn on the
forehead. Tapirs, though unquestionably present, are rare as
fossils and not well known. Several distinct phyla of horses
may be distinguished, which were like small ponies in size,
but of more slender form ; they were all three-toed, but there
were marked differences among them with regard to the degree

SUCCESSIVE MAMMALIAN FAUNAS 235

to which the middle toe (the third of the original five) had been
enlarged to cany the whole weight and the lateral toes (second
and fourth) reduced to mere " dew-claws/ ' While browsing
horses, with low-crowned teeth, still persisted in large numbers,
we find also the extremely interesting beginnings of the highly
complex, cement-covered and high-crowned teeth of the graz-
ing kinds. The clawed fchaiicotheres were present, though
very little is known about them because of the fragmentary
character of the remains.

The Artiodactyla were much more varied and abundant,
though they did not rival the great assemblage of these ani-
mals found in the European Miocene. Of the peccaries little
more can be said than that they were present in these faunas.
The foreodonts were very numerous, both individually and
generically ; two stages of the proboscis-bearing kind are found
here together, the older, long-faced genus ('fPromerycochoerus)
surviving from the Oligocene, while the newer Miocene type was
short-faced and had a moderate proboscis (see Fig. 196, p. 373).
Others had more the proportions of peccaries and still others
were very small and presumably aquatic in habits. Camels
abounded, both the grazing kinds which were ancestral to
the modern forms of South America and Asia, and the great,
browsing fgiraffe-camels. The fhornless deer and the antlered
fdeer-antelopes were much like those of the Upper Miocene,
slender and graceful little creatures, and there were also con-
siderably larger ruminants (fDromomeryx) with straight, simple
and non-deciduous horns, which may be called antelopes.

The line of division between the lower Miocene and the
uppermost Oligocene is a very obscure and difficult one to
draw. Personally, I prefer to begin the Miocene with the
widespread formation of the Great Plains, which has been
variously named Arikaree, Harrison, Rosebud, etc., but this
is a moot point. Concerning the lower part of these beds
Osborn says: "They may be either: (1) Upper Oligocene or
(2) transitional from Oligocene to Miocene, or (3) of pure

236 LAND MAMMALS IN THE WESTERN HEMISPHERE

Fid. 127. — Gigantic t giraffe -cam el tfAlticameluM altut) from the middle Miocene
of Colorado. Restored from specimens in the American Museum of Natural
History.

SUCCESSIVE MAMMALIAN FAUNAS

237

Lower Miocene age." The upper division is referred to the
Miocene without question by any one, but for the purposes of
this rapid sketch it will be best to treat the two faunas to-
gether. This many-named formation, for which the term
Arikaree is here employed, as having priority, is found over
extensive areas of South Dakota, northern Nebraska and

Kin. 128. — Most ancient American Antelope (f Dromomtryx antilopina), middle
Miocene. Restored from specimens in the Carnegie Museum and Princeton
University.

central Wyoming. The fauna was almost entirely a* develop-
ment from that of the North American Oligocene, with very
little admixture of foreign elements, so that the land com-
munication with the eastern hemisphere must have been
difficult. In this, as in most of the Miocene formations, the
smaller mammals are not fairly represented, and it is evident
that much remains to be learned with regard to them ; this is
especially true of the upper division of this stage.

The rodents, which were fairly numerous, were directly
continuous with those of the upper Oligocene and included
forms which were more or less distantly connected with the

238 LAND MAMMALS IN THE WESTERN HEMISPHERE

modern hares, squirrels, beavers, sewellels, pocket-gophers and
kangaroo-rats. A few Insectivora of doubtful reference have
been found. Among the Carnivora there was also consider-
able variety : dogs, large and small, were abundant, but all
of them were decidedly primitive from the modern standpoint ;
the cats were represented both by the true felines, which
were probably immigrants, and by the fsabre-tooth series.
There were several large and powerful mustelines, or members
of the weasel family, which were likewise immigrants, one
of which resembles in many ways the modern Wolverene
(Gulo). Very interesting is the beginning of the raccoon
family (Procyonidae) or, at least, what is believed to be such,
which arose from a branch of the dogs ; this most ancient of
the raccoons was fPhlaocyon, a small and slender animal.

The earliest traces of the Proboscidea in America have
been reported from this formation, but the fragmentary speci-
mens are inconclusive. The Perissodactyla are among the
commonest fossils. The rhinoceroses belonged to native stocks,
including both the horned and hornless forms. The horned
genus (f Dicer atherium) differed from all other rhinoceroses
in having a transverse pair of horns on the nose, and the species
of the lower Miocene were quite small and light ; the hornless
genus tfCcenopus) was a larger and heavier animal. Tapirs
are rare as fossils and consequently not well known. While
there were several kinds of horses, they all agreed in having
short-crowned and relatively simple grinding teeth and three-
toed feet ; they were smaller and of lighter, more slender build
than those of the middle Miocene. The wonderful aberrant
perissodactyls with clawed feet, the fchalicotheres (suborder
t Ancylopoda) , appear to have been more abundant in the
Arikaree than at any other time in North America, though
their history in this continent extends from the middle Eocene
to the lower Pliocene. ]Moropus, the lower Miocene genus,
was as grotesque a creature as could well be imagined and, in
advance of experience, no one ever did imagine such a beast.

SUCCESSIVE MAMMALIAN FAUNAS 269

With rather small and somewhat horse-like head, long neck,
long fore limbs and shorter hind limbs, these extraordinary
animals united short, three-toed feet, which were armed with
enormous claws. The long persistence (to the Pleistocene of
Asia) and wide geographical range of the fchalicotheres are
sufficient evidence that their very unusual structure must

Miocene. Kestored Irom a skeleton in the Carnegie Museum, Pittsburgh.

have been advantageous to them, but the problem of their
habits and mode of life is still unsolved. From the character
of the teeth, the long neck and fore limbs, it may, however,
be inferred that they fed chiefly upon the leaves of trees.

Even more numerous and varied were the Artiodactyla.
Peccaries of a primitive sort were common, and we find the
last of the series of f" giant pigs," which had been a very con-
spicuous group throughout the Oligocene. The lower Miocene
genus, ^Dinohyus, was a monstrous beast, six feet or more in
height, with formidable canine tusks and a very long head
made grotesque by bony excrescences upon the skull and jaws.
For a pig, the legs were very long and the feet slender, having

240 LAND MAMMALS IN THE WESTERN HEMISPHERE

SUCCESSIVE MAMMALIAN FAUNAS 241

but two toes. The foreodonts were present in great num-
bers, both small and large forms; except for bodily stature
and modifications of the head, they all looked very much alike ;
\Merycochoerus, with its incipient proboscis, here made its
first appearance. The last representatives of a family (fHyper-
tragulidse) of small and graceful artiodactyls are found in this
formation. One of these (fSyndyoceras, see Fig. 215, p. 403),
an animal considerably larger than the existing Musk-Deer, was
in its way even more bizarre-looking than the fchalicotheres ;
with an antelope-like head, it had four horns, one pair over
the eyes, curving inward, and a shorter pair, with outward
curvature, on the muzzle. Another genus {^Hypertragulus)
was very much smaller and very slender.

The camels were beginning to diversify and give rise to
several phyla. One of the genera (1[Protomeryx), which did
not much exceed a sheep in size, prpbably represented the main
stock, which led to the camels and llamas of to-day. A second
(IfStenomylus) was a still smaller animal, with remarkably long
and slender legs, and might be called a " gazelle-camel/ '
while a third ( \Oxydactylusy see Fig. 209, p. 392) , which was larger
and apparently the beginning of the fgiraffe-camels, was note-
worthy for its long neck. All of these lower Miocene camels
had deer-like hoofs, the characteristic pad or cushion which gives
such an exceptional appearance to the "feet of modern llamas
and camels not being fully developed till a later period. A very
important new element in the North American fauna was the
appearance of the first deer (fBlastomeryx), which came in the
latter part of the Arikaree stage and were the forerunners of
a renewed immigration from the Old World, which had been
broken off during the upper Oligocene. This, however, is a
disputed point; Professor Osborn and Dr. Matthew believe
that these animals were truly indigenous and derived from a
long line of American ancestry. The same genus continued
through the middle Miocene, as we have already seen, and
therefore no further description of it is called for.

R

242

LAND MAMMALS IN THE WESTERN HEMISPHERE

The limits of the South American Miocene are very doubtful.
The Parana formation, here regarded as lower Pliocene, may
prove to be more properly referable to the upper Miocene.
No other upper Miocene is known.

To the earlier, probably middle, Miocene may be referred
the wonderful Santa Cruz fauna of Patagonia. It is extremely

difficult to convey to the reader any adequate conception of
this great assemblage of mammals, because most of them
belonged to orders which have altogether vanished from the
earth and are only remotely like the forms with which we are
familiar in the northern hemisphere. To one who knows only
these northern animals, it seems like entering another world
when he begins the study of the Santa Cruz fossils. If any
North American mammals had then entered South America,
which is not probable, they had not extended their range as
far as Patagonia. Marvellously rich and varied as the Santa

SUCCESSIVE MAMMALIAN FAUNAS

244 LAND MAMMALS IN THE WESTERN HEMISPHERE

Cruz fauna was, it did not contain everything that we should
expect to find in it; several recent families of undoubtedly
indigenous South American origin have left no ancestors in
the early Miocene formations. For this, there are several
obvious reasons. In part, these gaps in the history are merely
due to the accidents of collecting and some of them will almost
certainly be filled by future exploration. Other absentees will
probably never be found, because the Santa Cruz beds are
known only in the very far south, and the Miocene climate of
the region, though much milder and more genial than the
present one, must have been unsuitable for many tropical
animals. Again, the Patagc % of tha time appears to have
been a country of open pla . with f trees, and hence ar-
boreal forms were rare. '

While great numbers of ^e, fligh rirds, some of them

of enormous size, were t .mbed i volcanic ash and

dust which were spread ( er such reas and to such

great depths, the extreme scarcity of reptiles is surprising; a
few remains of lizards have been found, but no snakes, croc-
odiles, or tortoises, and we have no information as to the
plant-life of the region at that time. The mammals were al-
most all of small or moderate size ; only one or two species were
really large.

One very striking and characteristic feature of the Santa
Cruz fauna is the great abundance of marsupials which it
contained and which resembled more or less those of modern
Australia. There were no true Carnivora and their places
were taken by a variety of carnivorous marsupials, some of
which (e.g. ^Prothylacynus) were as large as wolves and were
closely similar to the so-called Tasmanian Wolf (Thylacynus).
Another genus (fBorhyama) had a short, bullet head, not un-
like a small Puma in appearance and, besides, there were many
smaller beasts of prey, in size like badgers and minks. Opos-
sums were common and there were many very small herbivorous
marsupials, which resembled, though perhaps but superficially,

SUCCESSIVE MAMMALIAN FAUNAS 245

the Australian phalangers. At the present day South America
contains no Insectivora, but in the Santa Cruz there was one
family (fNecrolestidae) of this order which bore considerable
resemblance to the " golden moles' ' of South Africa. An
extraordinary variety of rodents inhabited Patagonia in Santa
Cruz times, all of them belonging to the Hystricomorpha, or
porcupine suborder, and all referable to existing South Ameri-
can families. There were none of the northern forms of ro-
dents, neither rats, mice, squirrels, marmots, hares, nor
rabbits, but a very numerous assembly of tree-porcupines,
cavies, chinchillas, coypus and the like. The genera, though
closely allied to existing ones, are all extinct, and the animals
were very generally smaller than their modern descendants.
A few small monk' rs >f unmistakably Neotropical type have
been found, but \\ ler arbo^ yf Vand forest-living animals,

they are very, rare g the fo, „>.

The Edentata lore aba lant and diversified than at

any other time in fJo^ih American history of which the record
is preserved. Two of the modern subdivisions of this order
have not been certainly identified in the Santa Cruz collections,
the arboreal sloths and the anteaters, and though they may be
found there at any time, it will only be as stragglers from the
warmer forested regions to the north, where these forms had
doubtless long been present. Unfortunately, however, nothing
is directly known concerning the life of those regions in Miocene
times. On the other hand, three groups of edentates, two of
them now extinct, were very copiously represented in the Santa
Cruz formation, the armadillos, fglyptodonts and fground
sloths. Of the many armadillos, some quite large, others
very small, only a few can be regarded as directly ancestral
to those now in existence; the truly ancestral forms were
probably then living in the forests of Brazil and northern
Argentina, in the same areas as the ancestral tree-sloths and
anteaters. In comparison with the giants of the Pliocene
and Pleistocene, the Santa Cruz fglyptodonts were all small,

246 LAND MAMMALS IN THE WESTERN HEMISPHERE

the carapace rarely exceeding two feet in length, and, what
it is particularly interesting to note, they departed much less
widely from the armadillo type than did their gigantic suc-
cessors. The fground-sloths were present in actually bewild-
ering variety and they also were very small as compared with
the huge animals of the Pleistocene, none of them exceeding
the Black Bear in height or length, though proportionally
much more massive, and many were no bigger than foxes.
They had small heads, long bodies, heavy tails and short,
thick legs ; their teeth show that they were plant-feeders, but
their feet were armed with long, sharp and formidable claws.
Among this great host of Santa Cruz fground-sloths may
readily be noted the probable ancestors of the gigantic creatures
which were such characteristic elements of the Pliocene and
Pleistocene faunas.

There was an extraordinarily rich and varied assemblage of
hoofed animals, all utterly different from those of the northern
hemisphere and belonging to groups which have never been
found outside of South and Central America. Of these groups
there were five, which by different writers are variously re-
garded as orders or suborders, a matter of very secondary im-
portance. Individually, the commonest of the hoofed mam-
mals were the fToxodonta, which ranged in size from a sheep
to a tapir, heavily built and clumsy creatures, with absurdly
small, three-toed feet ; in some of the species there was a smaft
median horn on the forehead. As with the fglyptodonts and
fground-sloths, the contrast in size between the Santa Cruz
ancestors and the Pleistocene descendants was very striking.
A very numerous and varied group was that of the f Typotheria,
all small animals, some no larger than rabbits, others the size
of small foxes. It requires a decided effort to think of these
ftypotheres as being really hoofed animals at all, as their
whole appearance must have been much more like that of
rodents, yet their structure clearly demonstrates their near
relationship to the f toxodonts. Still a third group of the same

SUCCESSIVE MAMMALIAN FAUNAS 247

series, the f Entelonychia, is of great interest, for, as in the
f chalicotheres of the northern hemisphere, the hoofs had been
transformed into claws and their five-toed feet had a truly
grotesque appearance, not diminished by the long and power-
ful limbs and relatively small head.

This is the third example of that paradoxical creature, a
"hoofed animal" with claws instead of hoofs, and in each of
the three instances, there is every reason to believe, the trans-
formation proceeded independently. Among the perisso-
dactyls the fchalicotheres (p. 238) underwent this change;
in North America the f Agriochceridse, a family of artiodactyls,
had a very similar history, while in South America the f Entel-
onychia arose from the same stock as the ftoxodonts, with
which they were nearly allied. They were among the largest
animals of Santa Cruz times and ranged in size from an ox
to a rhinoceros.

There was a fourth group, the fAstrapotheria, concerning
which our knowledge is tantalizingly incomplete, some species
of which were the largest of known Santa Cruz mammals,
while others were much smaller. They had short, domed heads,
with a considerable proboscis, and were armed with formidable
tusks, which were the enlarged canine teeth, the only known
instance of large canine tusks among the indigenous South
American hoofed animals. The limbs were long and not very
massive, the feet short, five-toed and somewhat elephantine
in appearance. These bizarre animals would seem to have
held a rather isolated position among the South American
ungulates, and though they may be traced back to the most
ancient mammal-bearing beds of that continent, their relation-
ships are still obscure ; much more complete material must be
obtained before this problem can be definitely solved. Both
the fAstrapotheria and the fEntelonychia died out shortly
after the end of the Santa Cruz.

From many points of view the most interesting members of
the Santa Cruz fauna were the f Litopterna, an order which also

248 LAND MAMMALS IN THE WESTERN HEMISPHERE

went back to the earliest South American Tertiary. In the
Miocene and Pliocene the order was represented by two very
distinct families, the fMacrauchenidse and tProterotheriidae,
which were superficially very unlike. In the Santa Cruz beds
is found a genus (^Theosodon) which was apparently the di-
rect ancestor of the Pampean ^Macrauchenia. The Miocene
genus was a much smaller animal and had hardly more than
an incipient proboscis, but otherwise was very like its Pam-
pean successor; it was somewhat larger and heavier than a
Llama and probably bore some resemblance to that animal in
appearance. The long, narrow head, with its prehensile
upper lip, must have had an almost reptilian likeness from the
numerous uniform and sharp-pointed teeth with which the
front of the jaws was supplied ; the neck was elongate, the body
short and rather slender and the legs long, ending in three
nearly equal toes.

The tproterotheres, on the other hand, were almost the
only Santa Cruz ungulates which had nothing outrt or grotesque
about them to the eye. of one habituated to the faunas of the
northern hemisphere. They were small, graceful animals,
very like the Miocene horses of the north in their proportions,
though having much shorter necks and shorter, heavier heads.
In some genera of this family (e.g. fDiadiaphvrus, \Protero-
therium) the feet were three-toed and most surprisingly horse-
like in shape, but one genus (fThoatherium) was absolutely
single-toed, more completely monodactyl than any horse.
The horse-likenesses ran all through the skeleton and are so
numerous and so striking that several writers have not hesitated
to incorporate the fLitopterna with the Perissodactyla, but
this I believe to be an error. If the fproterotheres were not
perissodactyls, as I am convinced they were not, they afford
one of the most remarkable examples of convergent evolution
among mammals yet made known.

SUCCESSIVE MAMMALIAN FAUNAS 249

3. Oligocene

North America. — The John Day formation of eastern Oregon
represents the upper Oligocene and has yielded a very extensive
series of mammals, though with some obvious gaps that remain
to be filled by future work. The land-connection with the
Old World which had existed in the lower Oligocene and was
restored in the lower, or at latest in the middle, Miocene, was
interrupted in John Day times, and so the mammals assumed
a purely indigenous character.

No opossums or other marsupials have been found, and
nothing is known of the Insectivora. Of the Carnivora, there
were but three families, and one of these, the mustelines, was
represented but scantily by a few small species. Cats of the
fsabre-tooth subfamily were common and one species was
quite large, almost equalling the Jaguar in length ; but most of
the species were small, much smaller than the Pleistocene
members of the group. True cats are not definitely known
to have been present, but there were two genera {^Nimravus
and fArchcelurus) which have been called the " false fsabre-
tooths," which may prove to be referable to that series. The
dogs, on the other hand, were remarkably numerous and
diversified, more so than ever before or since ; none of them
was very large, the largest but little exceeding the Timber
Wolf in size, and some were extremely small ; but the number
of distinct genera and species and the differences among them
are quite remarkable. Both long and short-faced forms
and early stages of the f" bear-dogs/ ' and f" hyena-dogs/ '
and ancestral forms of the wolves and dholes may be distin-
guished, a truly wonderful assemblage. The rodents also
were numerous and varied, including ancient and extinct
genera of the beavers, squirrels, mice, pocket-gophers and
hares and the earliest distinguishable ancestors of the sewellels
(Aplodontiidae).

The remainder of the known John Day fauna was composed

250 LAND MAMMALS IN THE WESTERN HEMISPHERE

of artiodactyls and perissodactyls. The latter had suffered
serious losses as compared with the preceding or White River
stage. Up to and through White River times the perisso-
dactyls had held their own in actual diversity, though the
rise of the artiodactyls had put an end to the dominant position
which they had maintained in the Eocene. With the John
Day the actual decline may be said to have begun. The
rhinoceroses were represented chiefly by the fdiceratheres,
with a transverse pair of horns, some species of which were much
larger than those of the lower Miocene. Hornless rhinoceroses
have not yet been certainly found, though there is every rea-
son to believe that they then existed, as they unquestionably
did both before and after. Tapirs occurred but rarely and
the horses were individually abundant, though in no great
diversity ; they were smaller and lighter than the horses of
the lower Miocene. Enough has been found to demonstrate
the presence of the clawed f chalicotheres, but not to show how
they differed from their immediate successors.

In the number of individuals, species, genera and families,
the artiodactyls of the John Day much exceeded the perisso-
dactyls. The peccaries were numerous, but smaller and more
primitive than those of the succeeding age, as were also the
tgiant pigs, or fentelodonts, but the latter were very large.
The peculiarly North American family of the foreodonts was
very numerously represented, and one genus (fPromeryco-
cheerus), comprising animals not unlike the Wild Boar in size
and shape, was the probable beginning of the series of proboscis-
bearing foreodonts, which led to such grotesque forms in the
middle and upper Miocene. A family closely allied to the
foreodonts, and by many writers included in the latter, is the
very remarkable group of the f Agriochoeridae, which was dis-
tinguished by the long, stout and cat-like tail and by the
possession of claws instead of hoofs. The family is not known
to have existed later than the John Day and no trace of it
has been found in the succeeding formations. The camels

SUCCESSIVE MAMMALIAN FAUNAS 251

seem to be all comprised in a single genus (IfProtomeryz) which
was the same as that found in the lower Miocene. A very
small and dainty little creature {\Hypertragulus) belonged to
another family, the relationships of which are not clear.

To the middle and lower Oligocene is referred the great
White River formation of South Dakota, Nebraska,Wyoming,
etc., which is divisible into three clearly marked substages.
The White River contains the best-known fauna of all of the
North American Tertiaries, for collecting in these beds has
been carried on for more than sixty years, and a greater number
of complete and nearly complete skeletons has been secured
than from any of the other formations. It is plainly evident
that a land-connection existed with the Old World, which was
interrupted in the John Day, as is shown by the intermigration
of characteristic forms ; but some barrier, presumably climatic,
prevented any complete interchange of mammals, and very
many genera and even families remained confined to one con-
tinent or the other.

The aspect of the White River fauna changes in accordance
with the direction from which it is approached. If one comes
to the study of it from the Eocene, it displays a very modern
aspect, given by the almost complete disappearance of the
archaic groups of mammals and by the great multiplication
of genera and species belonging to the progressive orders.
These genera, it is true, are all extinct, but many of them stood
in an ancestral relationship to modern forms. On the other
hand, if approached from the Miocene side, the White River
mammals seem to be very ancient and primitive and very
different from anything that now lives. We speak of horses
and rhinoceroses, dogs and cats, in this fauna, but those terms
can be employed only in a very wide and elastic sense to desig-
nate animals more or less distantly allied to those of the present
day.

Several species of opossums, some of them very small, were
the only marsupials in North America then, as they are now.

Fig. 133. — 1. iArchaoiherium. 2. Ancestral camel (iPotbrotherium). 3. IMerycoido-
don. 4. lAgriochatrus. 5. Ancestral horse (iMcsohippux). 6. t H oplophoneus.
7. t Bothriodon. 8. iHycenodon. 9. fCursorial rhinoceros (t Hyracodon) . 10. fPro-
loceras. 11. Hornless rhinoceros (fCajnopu*).

(262)

SUCCESSIVE MAMMALIAN FAUNAS

253

There was quite a variety of Insectivora ; some were survivals
of a family that was abundant in the Eocene, others, like the
hedgehogs, moles and shrews, were probably immigrants.
Here we find the last of a group (order or suborder) of ancient
and primitive flesh-eaters, the fCreodonta, that had played a
great r61e in the Eocene and Paleocene of North America and

Fiq. 134. — White River ftitanothere (\Titanotherium robustum) reduced to the same

scale as Fig. 133.

Europe. In White River times but a single family (fHyaeno-
dontidae), with two genera, remained of the Eocene host. One
of these genera (fHemipsalodori), a very large beast of prey,
which was almost identical with the Old World genus ^Pterodon,
was confined to the lower substage of the White River beds in
the Northwest Territory of Canada; the other, fHycenodony
which was also an Old World form, was represented abundantly
in the United States by many species. In size, these species
ranged from a small fox to a large wolf, but they all had dis-
proportionately large heads, and small, weak feet, with blunt
claws, so that they must have been very curious-looking
creatures and were probably carrion-feeders rather than active
catchers of prey. The White River members of the family

254 LAND MAMMALS IN THE WESTERN HEMISPHERE

were migrants from the eastern hemisphere, for, though small
and primitive representatives of it occurred in the North
American Eocene, as well as in the corresponding formations
of Europe, the family appears to have died out in America
and to have been renewed by the Oligocene migration.

Coincident with this decline of the fcreodonts and, no doubt,
causally connected with it, was the rise of the true Carnivora,
which for the first time were numerous and were divisible into
three distinct families. Small and primitive representatives
of the wolves tfDaphamus) and possibly also of the foxes
(\Cynodictis) were quite common, and there were a few species
of the musteline family, evidently immigrants and the most
ancient yet found in America. There were several species of
the fsabre-tooth cats {\Dinictis and 1[Hoplophoneus) all of
which, except in the uppermost substage, were quite small,
few of them exceeding the Canada Lynx in size. A much
larger animal {\Eusmilus, also European) appeared in the
latter part of the stage. None of the true cats, or feline sub-
family, has been obtained. Nothing is yet known of the time
and place of origin of the fsabre-tooth series, for they ap-
peared at approximately the same date in Europe and America,
and in neither continent have any possible ancestors been found
in preceding formations. The -problem is like that of the
Proboscidea (see p. 234), but E}gypt has given no help in the
case of the fsabre-tooths, and, by a process of elimination,
we reach the conclusion that these strange creatures probably
arose somewhere in Asia and sent out migrants eastward and
westward.

The Rodentia were fairly abundant and present a strange
mixture of ancient and comparatively modern types. One
very common genus ('flschyromys), which was the last rem-
nant of a family almost limited to the North American
Eocene, was associated with the earliest American mice,
arboreal and ground squirrels, beavers and rabbits; some, if
not all, of these were immigrants.

SUCCESSIVE MAMMALIAN FAUNAS 255

The hoofed mammals were present in fairly bewildering
variety, but were restricted to the two orders of the Perisso-
dactyla and Artiodactyla. The Perissodactyla, while they
no longer had the relatively dominant position which they
held in the middle Eocene (see p. 270), had suffered no actual
loss ; and no less than seven families of them, or six by another
scheme of classification, had members in the North America
of White River times, a very notable difference from the
present order of things, when there are but three families in
the entire world, none of which enters North America. The
Eocene family of the ftitanotheres became extinct at the end
of the lower substage of the White River, but in that substage
there was a marvellous abundance of these huge beasts, some
of which were of almost elephantine stature and bulk. The
pair of great bony, horn-like protuberances on the nose varied
much in size and form in the different species, short to very
long, triangular, cylindrical, flattened and shovel-shaped,
and gave these ungainly creatures somewhat the appearance
of strange and very large rhinoceroses. The ftitanotheres
were a typically North American family, but sent migrants
to the Old World, at least two species reaching southeastern
Europe. Rhinoceroses too were extremely numerous and
diversified throughout the stage and are very plainly divisible
into three strongly contrasted series, which are sometimes
regarded as three subdivisions of the same family and some-
times put into two separate families. One of these series, the
fhyracodonts {^Hyracodori), was composed of small, long-
necked and long-legged, slender and lightly built, cursorial
animals, but with short, heavy heads, which gave them a
somewhat clumsy look ; having neither horns nor tusks, they
were entirely defenceless and depended for their safety upon
speed alone. The second series, or famynodonts (\Met-
amynodori), formed the very antithesis of the first, — large,
heavy, short-necked, and short-legged and probably amphibi-
ous in manner of life, they were armed with formidable

256

LAND MAMMALS IN THE WESTERN HEMISPHERE

tusks ; and their skulls were so curiously modified as to bear a
distinct resemblance to the skull of a huge carnivore. The
famynodonts migrated to the Old World and occur in the
Oligocene of France, but the fhyracodonts would seem never
to have left North America. The third series, that of the true
rhinoceroses, comprised several genera at different levels in

the White River beds {\Trigonias, ^Canopus, etc.) ; they were
of uncertain origin and it has not yet been determined whether
they were immigrants or of native stock. Many species have
been found, varying much in size, up to that of a modern tapir,
and not unlike one in proportions, for they were of lighter build
and had relatively longer legs than any existing rhinoceros.
The species of the lower and middle substages were all horn-
less, but in the uppermost substage we find skulls with a pair of
nasal horns in an incipient stage of development. This was the
beginning of the tp&ired-horned rhinoceroses (t Dicer atherium)
which so flourished in the John Day and the lower Miocene.

SUCCESSIVE MAMMALIAN FAUNAS 257

Of the horses there was no great variety and all the species
so far discovered are included in a single genus (jMesohippus),
though there was a decided increment in the size of the suc-
cessive species from the earlier to the later portion of the stage.
Looked at superficially, it seems absurd to call these little
creatures " horses' ' at all and the term can be justified only as
implying that they were ancestral members of the family.
The largest of the White River species hardly exceeded a sheep
in size and all of them had comparatively short necks, long
and slender legs and three-toed feet. The low-crowned grind-
ing teeth show that they were browsers, not grazers. The
abundant Eocene family of the fLophiodontidse made its last
appearance in the White River, where it was scantily repre-
sented by slender, long-legged animals (jColodon), with feet
singularly like those of the contemporary horses, except that
there were four toes in the front foot. Tapirs (jProtapirus)
were very much less common than rhinoceroses or horses and
were hardly half as large as the existing species of the family
and of relatively far more slender form; the development
of the proboscis had already begun. Lastly, the presence of
the clawed fchalicotheres has been reported from the lower
Oligocene of Canada, but the material is too fragmentary for
generic reference.

Though the number of artiodactyl families yet identified
among the White River fossils is no larger than that of the
perissodactyl families, the artiodactyls greatly preponderated
in individual abundance. The peccaries, which were fairly
common, resembled those of the John Day, but were consider-
ably smaller. Of the camels, there were two series, one of
which {\Eotylopus) , lately described by Dr. Matthew, is of yet
unknown significance, while the other {^Poebr other ium) was
apparently the ancestor common to all the subsequent phyla
of camels and llamas. This extremely interesting genus had
species which ranged in size from a gazelle to a sheep, had two
toes in each foot, a moderately elongate neck and teeth which

8

258 LAND MAMMALS IN THE WESTERN HEMISPHERE

were beginning to assume the high-crowned character. From
this it may be inferred that those animals were, partly at least,
of grazing habit, which was rare among White River ungulates,
most of which fed upon leaves and soft and succulent plants.
An extinct family, the fHypertragulidae, were a greatly diver-
sified group of dainty little creatures, one of which (^Hy-pisodus)
was no larger than a rabbit and had high-crowned teeth.
The other genera (1[Leptomeryx, ]Hypertragulus) must have
resembled in form and proportions the tiny little chevrotains
or " mouse-deer' ' of the East Indian islands. Late in the
age arose a larger form of this family, nearly equalling the
Musk-Deer in size, the extraordinary genus \Protocerasy which
was, especially the males, a grotesque object. The males had
a pair of upper canine tusks and two pairs of prominent long
protuberances on the skull. This, or some similar form, must
have been the ancestor of the still more bizarre \Syndyoceras
of the lower Miocene.

The t°re°donts were by far the commonest of White
River mammals, and evidently they roamed the woods and
plains in great herds. There were several species, larger and
smaller, of the abundant genus (1[Merycoidodon) but the largest
did not surpass a modern peccary in size and was somewhat
like that animal in appearance, but had a shorter head and
much longer tail. In the upper substage appeared a very
peculiar genus of this family (jLeptauchenia), animals with
short, deep, almost monkey-like heads, and presumably
aquatic in habits. The ^agriochosrids were very much less
common ; they may be described roughly as foreodonts with
very long, cat-like tails and clawed feet.

All of the foregoing artiodactyl families were exclusively
North American in Oligocene distribution; even the camels
did not reach Asia till the Pliocene, and the other families
never invaded the Old World at all. There were, however,
two additional families, which also occurred in the eastern
hemisphere, whence one of them, and possibly the other, was

SUCCESSIVE MAMMALIAN FAUNAS

259

derived. The unquestionably Old World family, that of the
fanthracotheres, was represented in the White River by two
genera {\Bothriodon and \Anthracotherium), which were shorts
legged, long-snouted, swine-like animals, which have no near
relations in the modern world. The other family, the fgiant

Restored from a skeleton in the American Museum of Natural History.

'pigs, which we have already met with in the lower Miocene
and upper Oligocene, is of doubtful origin, and nothing has yet
been found in the preceding formations of either North America
or Europe which can be regarded as ancestral to them. The
White River genus {\Archceotkerium) was very like the John
Day and Arikaree genera, but most of the species were much
smaller and some were not so large as a domestic pig. In the
uppermost beds, however, are found huge species, which
rivalled those of the subsequent formations. That these
strange animals were rooters and diggers and therefore pig-like
in habits is indicated by the manner in which the teeth are worn.

260 LAND MAMMALS IN THE WESTERN HEMISPHERE

SUCCESSIVE MAMMALIAN FAUNAS 261

South America. — The older continental Tertiary forma-
tions of South America cannot be correlated with those of North
America or Europe, because they have nothing in common.
Difficult as it is to give a correct and adequate conception of
the Tertiary mammalian life of the northern hemisphere to
one who has not made a study of it, it is far more difficult in
the case of South America. The stock of adjectives, such as
"peculiar," " bizarre/ ' "grotesque" and the like, already
overworked in dealing with northern forms, is quite hopelessly
inadequate where everything is strange. In addition to this,
we are seriously handicapped in treating of the Oligocene and
Eocene of South America by very incomplete knowledge.
Many fossils have been collected and named, but the great
majority of these are known only from teeth ; a few skulls
and limb-bones have been described, but no skeletons, and
therefore much is very uncertain regarding these faunas.

The Deseado formation (Pyrotherium Beds) has been
variously referred by different writers from the upper Creta-
ceous to the lower Miocene, but its most probable correlation
is with the Oligocene. Though most of the mammalian groups
are the same as those of the Santa Cruz, the proportions of the
various orders in the two faunas are very different, but, to
some extent, the difference is probably illusory and due to the
conditions of fossilization, for, as a rule, the small mammals
are much less frequent and well preserved in the older beds.
As in the Santa Cruz, the marsupials were the only predaceous
mammals, and some of them attained gigantic size; but no
such variety of these beasts of prey has been found in these
beds as occurred in the middle Miocene. In addition, there
were numerous small herbivorous marsupials. One of the
most striking differences from the Santa Cruz fauna was in
the very much smaller number of Edentata, which, instead of
being extremely common, are quite rare among the fossils.
No doubt there was a real and substantial difference in this
respect, but it was probably not so great as it seems, and the

262 LAND MAMMALS IN THE WESTERN HEMISPHERE

same three suborders are found in both formations. One of
the few "("ground-sloths that have been obtained was very-
large {^Octodontherium crassidens) , a much larger animal than
any species of the suborder that is known from the Santa Cruz.
The fglyptodonts were also rare, and only two genera and
species have been described from very scanty remains. Arma-
dillos, on the other hand, were much more common, and no less
than eleven genera have been named, three of which occurred
also in the Santa Cruz. Among these was the remarkable
genus 1[Peltephilus, in which the anterior two pairs of plates of
the head shield were modified into horn-like spines.

Equally striking was the remarkable diminution of the
Rodentia, as compared with those of the Santa Cruz, though,
of course, this is an inaccurate mode of stating the truth,
occasioned by the fact that we are following the history in
reverse order. It would be preferable to say that the rodents
underwent a remarkable expansion in the Santa Cruz. These
rodents of the Deseado stage are the most ancient yet dis-
covered in South America and represent only two families,
both belonging to the Hystricomorpha, or porcupine group.
If, as Dr. Schiosser and other European palaeontologists main-
tain, the Hystricomorpha were all derived from a family of
the European Eocene, this would necessitate a land-connection
between South America and the Old World independent of
North America, for the latter continent had no hystricomorph
rodents until the connection between the two Americas was
established.

The great bulk of the Deseado fauna is made up, so far as
individual abundance is concerned, of hoofed animals belong-
ing to the typically South American groups. The fToxodonta
were represented partly by genera which were the direct
ancestors of the common Santa Cruz genera tfPronesodon,
jProadinotherium) , and, more numerously, by a very peculiar
family, the fNotohippidae, which had highly complex, cement-
covered grinding teeth. Still a third family of this suborder,

SUCCESSIVE MAMMALIAN FAUNAS 263

the fLwmtiniicl86! wa8 highly characteristic of the Deseado
fauna and is not known from the Santa Cruz. These were
large animals, with a small horn on the tip of the nose and low-
crowned, comparatively simple grinding teeth. Even more
abundant were the tTypotheria, small forms which were

ancestral to the Santa Cruz genera, larger ones which died
out without leaving successors and one quite large animal (f#u-
trackytherw) which seems to have been the ancestor of the
Pliocene and Pleistocene ^Typotherium. This series is not
known to have been represented in the Santa Cruz and may
have withdrawn from Patagonia at the end of the Deseado stage.
The fEntelonychia, those strange toxodont-Iike animals
with claws instead of hoofs, were much more numerous and
varied than they were afterward in the Santa Cruz, when they

264 LAND MAMMALS IN THE WESTERN HEMISPHERE

were on the verge of extinction, and included both very small
and very large species. The fPyrotheria, a suborder which
is not met with in the Santa Cruz or later formations, likewise
included some very large forms. The typical genus, ^Pyro-
therium, included large, relatively short-legged and very mas-
sive animals; the upper incisors formed two pairs of short,
downwardly directed tusks, and in the lower jaw was a single
pair of horizontally directed tusks; the grinding teeth were
low-crowned and had each two simple, transverse crests.
These grinding teeth and the lower tusks so resemble those of
the ancestral Proboscidea in the Oligocene of Egypt, that
the tpyrotheres have actually been regarded as the beginnings
of the fniastodons and elephants, but this is undoubtedly an
error. The fAstrapotheria, another group which became ex-
tinct at or soon after the end of the Santa Cruz, were rel-
atively abundant in the Deseado and counted some very large
species. Finally, the fLitopterna were represented by the
same two families as continued through the Pliocene and one of
them far into the Pleistocene. The horse-like fproterotheres
were present, but not enough of them has been obtained to
show whether or not they were in a notably less advanced
stage of development than those of the Santa Cruz. The
fmacrauchenids were quite similar to those of the latter for-
mation, though considerably smaller. In addition, there
were a few genera, survivals from earlier times, which were not
referable to either of these families.

The large number of genera, especially among the ftoxo-
donts and ftyp°theres, which had high-crowned, cement-
covered teeth, may be taken as an indication that grazing
habits had already begun to be prevalent.

Of this wonderful assemblage of hoofed animals, divisible
into six separate groups, whether of ordinal or subordinal
rank, not a trace remains to-day. Not only are all the species,
genera and families extinct, but the suborders and orders also.
Further, this was a very strictly autochthonous fauna, so far

SUCCESSIVE MAMMALIAN FAUNAS 265

as the hoofed animals were concerned, and no member of any

of the six groups has ever been found outside of the Neotropical

region.

4. Eocene

North America. — In the western interior of North America
the Oligocene followed so gradually upon the Eocene, that there
is great difficulty in demarcating them and much difference
of opinion and practice obtains as to where the boundary line
should be drawn. Not to depart too widely from the scheme
used by Professor Osborn, the Uinta stage is here treated as
uppermost Eocene, though this is a debatable procedure.
For several reasons, the extraordinarily interesting and sig-
nificant Uinta fauna is far less completely known than that of
the preceding Bridger and succeeding White River stages. For
one thing, it has been much less thoroughly explored, and it
may be confidently expected that future exploration will
greatly enlarge our knowledge.

The smaller mammals of the Uinta are particularly ill-
known. No Insectivora have yet been found, though this
gap will assuredly be filled ; rodents are scanty in the collec-
tions and include only two families, one the fischyromyids,
which were still common in the White River, the other of
doubtful position, but not improbably to be considered as the
beginning of the pocket-gophers (Geomyidae). The archaic
flesh-eaters, or fCreodonta, were represented by two fami-
lies, one comprising smaller animals with somewhat cat-like,
shearing teeth ( fOxyaenidae) , the other, very large beasts
with crushing teeth (fMesonychidae), neither of which con-
tinued into the White River. As compared with the middle
and lower Eocene, the fcreodonts had greatly diminished and,
to replace them, the true Carnivora were beginning to come
in. As yet, however, only small and very primitive dog-like
forms are known and no trace of fsabre-tooths or mustelines
has been found. Indeed, it is very doubtful whether mem-
bers of these families ever will be found in the Uinta, for their

266 LAND MAMMALS IN THE WESTERN HEMISPHERE

presence in the succeeding White River was probably due to
immigration.

The Perissodactyla were the preponderant type of. hoofed
animals, and ancestral forms of most of the White River genera
have already been identified. The ftitanotheres (\Diplaeodony
\Protitanotherium) were much smaller and lighter than those
of the lower White River and had much shorter horns. The
fhyracodonts, the lightly built, cursorial rhinoceroses, were
represented by a genus (jTriplopus) which was smaller and
more slender than the White River form {\Hyracodon) and
its teeth were of distinctly more primitive character. The
heavy, massive and presumably aquatic famynodonts {\Amyn-
odon) were likewise smaller and less specialized than their
descendants of the Oligocene. No member of the true rhinoc-
eros series has yet been identified in the Uinta, but there is
some reason to think that they were nevertheless present.
Tapirs are distinctly indicated by certain fossils, but they are
still too incompletely known to make possible any statement
as to their degree of development. The horses (]Epihippus)>
like the other families mentioned, were much smaller and dis-
tinctly more primitive than their successors in the Oligocene.

The Artiodactyla were, for the first time in the history of
North America, as numerous and as varied as the perisso-
dactyls and, with the exception of the peccaries and fanthra-
cotheres, representatives of all the White River families are
known. The finding of the peccaries is merely a question of
further exploration, but the t&^hracotheres were migrants
from the Old World, and there is no likelihood that they will
be discovered in the Uinta at any future time. Fairly large,
pig-like animals, probably referable to the fgiant-pigs or fen-
telodonts, occurred, but nothing has yet been found which can
be considered as the direct ancestor of the White River genus.
As was true of the perissodactyls, the Uinta artiodactyls were
nearly all much smaller and more primitive than their Oligocene
descendants and the differences are most interesting from the

t

SUCCESSIVE MAMMALIAN FAUNAS 267

evolutionary point of view. The ancestral camel {\Protylojms)
was a little creature no bigger than a fox-terrier, though the
fhypertragulids ( ^Leptotragulus) were as large as ^Leptomeryx
and ^Hypertragulus of the White River. The most ancient
known members of the foreodonts (^Protoreodon) and the
t agriochoerids (^Protagriochcerus) are found in the Uinta.

The middle Eocene fauna, Bridger stage, though it passed
upward very gradually into that of the Uinta, was yet, on the
whole, very different from the latter. It was exclusively indig-
enous and so radically distinct from the mammals of corre-
sponding date in Europe as to preclude the possibility of a land-
bridge with that continent. In the lower Eocene, as will be
shown in a subsequent page, the communication between the
two continents was broadly open and the faunas of the two
continents were much more closely similar than they have
ever been since. It is really remarkable to see with what com-
parative rapidity the two regions, when severed, developed
different mammals under the operation of divergent evolution.
Had the separation continued throughout the Tertiary and
Quaternary periods, North America would now have been as
peculiar zoologically as South America is, a result which has
been prevented by the repeated renewal of the connection.

The characteristic features of the Bridger mammalian fauna
were chiefly due to the great expansion and diversification of
certain families, which began their career at an earlier stage,
and to the disappearance of many archaic groups which had
marked the more ancient faunas. Other archaic groups,
however, survived and even flourished in the Bridger, and of
these it is particularly difficult to convey a correct notion to
the reader, because they were so utterly unlike anything that
now lives. One of these orders, the fTseniodontia, which had
so many points of resemblance to the tground-sloths that
several writers have not hesitated to include them in the
Edentata, survived only into the older Bridger, but the equally
problematical jTillodontia then reached their culmination,

268 LAND MAMMALS IN THE WESTERN HEMISPHERE

though they were not very numerous. Though not at all
related to that group, the ftillodonts looked like huge rodents,
with their chisel-like incisor teeth. There was a remarkable
assemblage of Insectivora, more numerous and varied than in
any subsequent formation, no less than six families being known.
One of these somewhat doubtfully represented the moles and
two others modern Asiatic groups. The very unexpected
discovery of an armadillo in the Bridger has been reported,
but the propriety of referring this animal to the armadillos,
or even to the edentates, has not yet been proved, and it would
therefore be premature to discuss its significance. The only
marsupials were opossums.

So far as our information extends, there were no true Car-
nivora in the Bridger, all the beasts of prey of the time belonging
to the archaic fCreodonta, which then reached their maximum
development in numbers and diversity. One family (fOxy-
aenidae) included large and powerful flesh-eaters, with cat-like
dentition and short, rounded, lion-like heads, long bodies and
tails and short, heavy limbs, giving them the proportions
of otters. Another (the fHysenodontidse) comprised small,
long-headed, fox-like and weasel-like animals, which doubtless
preyed upon small mammals and birds. A third family
(fMesonychidae) was made up of moderate-sized, long- jawed
creatures, which must have resembled, rather upmotely, short-
legged and long-tailed wolves and hyenas. Their habits and
mode of life are somewhat problematical, for their grinding
teeth were blunt, not adapted to the shearing of flesh, and their
claws were broad, almost hoof-like. Such creatures could
hardly have subsisted by the pursuit of living prey and were
probably carrion-feeders and more or less omnivorous. The
fMiacidae, a family which connected the fcreodonts and true
carnivores and might almost equally well be placed in either
group, were externally much like the small fhyaenodonts, but
were more efficiently equipped for the capture and devouring
of prey.

SUCCESSIVE MAMMALIAN FAUNAS 269

Of the archaic and extinct orders of hoofed animals, the
only one which persisted from earlier times into the Bridger
and greatly flourished there was the fAmblypoda, one family
of which (tUintatheriidffi) was preeminently characteristic
of middle Eocene life, becoming very rare and then dying out
in the upper Eocene. The fuintatheres of the Bridger under-
went considerable modification in size and appearance within

the limits of the stage, the larger and stranger species appearing
toward the end of the time. Most of these great creatures
may fairly be called gigantic, for they equalled the largest
modern rhinoceroses and smaller elephants in size. The body,
limbs and feet were so elephantine in character that they
were once believed to be ancestral Proboscidea, .but the teeth
and the fantastic skull were so radically different that this
belief was long ago abandoned. The upper canine teeth were
converted, in the males, into formidable spear-like or scimitar-
like tusks, protected by great flange-shaped expansions of the

268 LAND MAMMALS IN THE WESTERN HEMISPHERE

though they were not very numerous. Though not at all
related to that group, the ftillodonts looked like huge rodents,
with their chisel-like incisor teeth. There was a remarkable
assemblage of Insectivora, more numerous and varied than in
any subsequent formation, no less than six families being known.
One of these somewhat doubtfully represented the moles and
two others modern Asiatic groups. The very unexpected
discovery of an armadillo in the Bridger has been reported,
but the propriety of referring this animal to the armadillos,
or even to the edentates, has not yet been proved, and it would
therefore be premature to discuss its significance. The only
marsupials were opossums.

So far as our information extends, there were no true Car-
nivora in the Bridger, all the beasts of prey of the time belonging
to the archaic fCreodonta, which then reached their maximum
development in numbers and diversity. One family (fOxy-
aenidae) included large and powerful flesh-eaters, with cat-like
dentition and short, rounded, lion-like heads, long bodies and
tails and short, heavy limbs, giving them the proportions
of otters. Another (the fHyaenodontidse) comprised small,
long-headed, fox-like and weasel-like animals, which doubtless
preyed upon small mammals and birds. A third family
(fMesonychidae) was made up of moderate-sized, long-jawed
creatures, which must have resembled, rather upmotely, short-
legged and long-tailed wolves and hyenas. Their habits and
mode of life are somewhat problematical, for their grinding
teeth were blunt, not adapted to the shearing of flesh, and their
claws were broad, almost hoof-like. Such creatures could
hardly have subsisted by the pursuit of living prey and were
probably carrion-feeders and more or less omnivorous. The
fMiacidae, a family which connected the fcreodonts and true
carnivores and might almost equally well be placed in either
group, were externally much like the small fhyaenodonts, but
were more efficiently equipped for the capture and devouring
of prey.

SUCCESSIVE MAMMALIAN FAUNAS 269

Of the archaic and extinct orders of hoofed animals, the
only one which persisted from earlier times into the Bridger
and greatly flourished there was the fAmblypoda, one family
of which (fUintatheriidffi) was preeminently characteristic
of middle Eocene life, becoming very rare and then dying out
in the upper Eocene. The fuintatheres of the Bridger under-
went considerable modification in size and appearance within

the limits of the stage, the larger and stranger species appearing
toward the end of the time. Most of these great creatures
may fairly be called gigantic, for they equalled the largest
modern rhinoceroses and smaller elephants in size. The body,
limbs and feet were so elephantine in character that they
were once believed to be ancestral Proboscidea, but the teeth
and the fantastic skull were so radically different that this
belief was long ago abandoned. The upper canine teeth were
converted, in the males, into formidable spear-like or scimitar-
like tusks, protected by great flange-shaped expansions of the

270 LAND MAMMALS IN THE WESTERN HEMISPHERE

lower jaw ; bony knobs on the end of the nose probably sup-
ported a pair of dermal horns like those of a rhinoceros and,
in addition, a pair of high, cylindrical, horn-like, bony pro-
tuberances arose above the eyes and another, more massive
pair, near the back of the head. It would be difficult to imagine
more extraordinary creatures than the fuintatheres, which
were the largest land-mammals of their time. The family
was entirely confined to North America, no trace of them having
been found in any other continent.

While the backward and archaic orders, most of which have
left no descendants in the modern world, had thus a stately
representation in Bridger times, they were outnumbered in
genera, species and individuals by the progressive orders,
which are still in more or less flourishing existence. The
Primates, whether lemurs or monkeys, were numerous, and
this, so far as is definitely known, was their last appearance
in extra-tropical North America. They may at any time be
found in the Uinta, but there is small probability that they
will ever turn up in the White River or later formations.
The many rodents all belonged to the fischyromyids, an extinct
family which, there is much reason to believe, was ancestral
to many families of the squirrel-like suborder of Sciuromorpha.
Most of them were species of a single genus (\Paramys) and
varied in size from a mouse to a beaver, or even larger.

The Perissodactyla may be said, in one sense, to have
reached their culmination in the Bridger; not that many of
them, such as the horses and rhinoceroses, did not advance
far beyond their state of development in the Eocene, but at no
subsequent time did the order as a whole possess such domi-
nating importance. There were five or six families of peris-
sodactyls in the Bridger, and their remains are much the most
abundant fossils found there. Individually, the commonest
perissodactyls of the time were the ftitanotheres, of which
there were several genera and many species, differing chiefly
in size and proportions, though the largest hardly exceeded

SUCCESSIVE MAMMALIAN FAUNAS

271

i!r

> J

Vk "-

-=!_

^AUK 1 V\ ^~ -i

Fig. 140. — Some characteristic mammals of the Bridger Eocene reduced to a uniform
scale, with a pointer dog, in frame, for comparison. 1. Primitive rhinoceros
(1 Hyrachj/us eximius). 2. t Tritemnodon agilis. 3. tPatriofelis feroz, and 4, IDro-
mocyon velox, tcreodonts. 5. Primitive rodent (IParamysdelicatior). 6. WJintathe-
rium aUiceps. 7. tTitanothere (\ Mesatirhinus superior).

a modern tapir in stature and was not dissimilar in appearance.
These Bridger ftitanotheres were considerably smaller than
those of the Uinta and therefore very much more so than the
White River forms; it was not till the latter stage that the
family lived up to its name of "titanic beasts.' ' By far the

272 LAND MAMMALS IN THE WESTERN HEMISPHERE

commonest of the genera in the middle and lower Bridger was
IfPalceosyops, which was hornless, while in the upper part of
the beds are found genera (e.g. ^Manteoceras and ]Dolicho-
rhinus) in which the horns were just beginning to appear.
Another extinct family, the fLophiodontidse, which was very-
abundant in the European Eocene, formed a very subordinate
element in this fauna and included a number of small tapiroid
genera (e.g. \Helaletes).

The horses (\Orohippus) were very small and primitive
creatures, no bigger than a fox, with four toes in the front foot
and three in the hind. So completely different in appearance
and proportions were these little animals from any of the
modern horses, that it requires an effort of the imagination
to think of them as belonging to the same family, and it is only
by employing the family to designate a genetic series that such
a classification can be justified. The fhyracodonts, or cursorial
rhinoceroses, were very abundantly represented by a number
of small and medium-sized animals (^Hyraehyus) which had
less specialized teeth, shorter neck and limbs than their upper
Eocene and Oligocene successors, and four toes in the front
foot ; one genus (]Colonoceras) had a pair of nasal horns,
but would seem to have died out without leaving descendants.
In the upper part of the beds is found the Uinta genus fTVtpZo-
pus, with three-toed fore foot ; and in the same division occurs
another Uinta genus, ^Amynodon, the most ancient known
species of the supposedly aquatic rhinoceroses. True rhi-
noceroses, that is animals which were directly ancestral to the
modern members of the family, have not been identified and
may not have been present in North America; that is still
an open question. Tapirs, all of them quite small, were rel-
atively common, but are still very incompletely known. The
earliest known members of the clawed fchalicotheres were of
Bridger date.

It is worth remarking that, except a single genus in the
upper and later portion of the stage (1[Triplopus)y all of the

SUCCESSIVE MAMMALIAN FAUNAS 273

Bridger perissodactyls had four toes in the front foot and three
in the hind, while in the White River beds above the lowest
substage the number three in both fore and hind feet was
almost equally universal.

One of the most radical and striking differences between
the Uinta and Bridger faunas was the rarity of Artiodactyla
in the latter, which is in almost equally strong contrast with
their abundance in the middle Eocene of Europe. Most
significant of these rare Bridger artiodactyls were the little
creatures {}Homaeodori), hardly so large as a domestic cat,
which may fairly be regarded as a very early stage, if not the
actual beginning, of the great camel family, which was destined
to play so conspicuous a part in the life of America, North
and South. Small pig-like animals (^Helohyus) which were
no doubt ancestral to the peccaries, were fairly common and
there were, in addition, relatively large animals (^Achamodon)
allied, but not ancestral, to the fgiant-pigs of the Oligocene ;
some of these were considerably larger than a full-grown Wild
Boar (Sus scrofa).

Among all the many hoofed mammals of the Uinta and
Bridger there was not a single one that had the high-crowned,
persistently growing teeth of the grazers ; all of them must have
had browsing habits and have fed upon such soft vegetable
tissue as did not rapidly abrade the teeth. The same state-
ment applies, d fortiori, to the stages antecedent to the Bridger
and therefore to the entire Eocene and Paleocene. From these
facts it may be inferred that the grasses had not yet taken
possession of wide areas. Concerning the Bridger fauna,
Professor Osborn, who has done so much to elucidate it, says :
"On the whole, it is a very imposing, diversified and well-
balanced fauna, with an equal distribution of arboreal, cur-
sorial, aquatic, fossorial, carnivorous and herbivorous types/ '

The lower Eocene is divisible into two stages, in descending
order, the Wind River and Wasatch, both extensively exposed
in central Wyoming. As would be expected from its strati-

274 LAND MAMMALS IN THE WESTERN HEMISPHERE

graphical position, the Wind River fauna was largely transi-
tional between that of the Bridger above and that of the
Wasatch below. Unfortunately, the fossils are far less numer-
ous than those of the Bridger and not so well preserved, and
therefore give us a less adequate conception of the life of that
time. The archaic, non-progressive orders were strongly
represented, but already the progressive groups were in a numer-
ical majority of species; most of these archaic orders may be
most advantageously described in connection with the Wasatch.
Opossums were almost certainly present, though the available
specimens are too fragmentary for assured determination.
The ftiUodonts, ftseniodonts and insectivores differed little
from the Wasatch representatives of these orders, except that
the Bridger ftseniodont, \Stylinodon, which had rootless,
persistently growing teeth, was associated with the Wasatch
genus ]Calamodon. On the other hand, the primitive flesh-
eaters, or fcreodonts, which were referable to Wasatch families,
were less numerous and varied and formed a mixture of Bridger
and Wasatch genera. The fOxyaenidae, the family with cat-
like teeth and head, had both the smaller Wasatch genus
\Oxycma and the very large Bridger 1[Patriofelis. Of the
blunt-toothed fMesonychidse, one very large animal (1[Pachy-
ama) survived from the Wasatch. The small forms of the
family fHyaenodontidse were common, and there were numerous
species of the progressive family fMiacidse.

Among the hoofed animals there were two of the antique
orders which became extinct before the end of the Eocene,
indeed, one of these groups, the fCondylarthra, made its
last appearance in the Wind River. This extremely primitive
group, which, in a sense, connected the hoofed with the clawed
mammals, will be described under the more ancient faunas.
The other order, the fAmblypoda, was represented by two
very different families, one of which, the f uintatheres, was
so flourishing in the Bridger, where it formed the most char-
acteristic and by far the most striking element of the fauna.

SUCCESSIVE MAMMALIAN FAUNAS 275

The Wind River genus (^Bathyopsis) was a very much smaller
animal than any of the Bridger forms and its horn-like pro-
tuberances were in an incipient state, while in various other
respects it was decidedly more primitive than its successors.
The second family was represented by the genus ^Coryphodon,
which did not survive into the Bridger, but was especially
characteristic of the Wasatch fauna, with which it will be
described.

Turning now to the progressive orders, we note that the
rodents, lemurs and monkeys were very similar to those of
the Bridger and belonged to the same families, but were
decidedly less numerous. This difference, however, may be
rather apparent than real and due to the much more favourable
conditions for the preservation of small mammals in the middle
Eocene. Among the Perissodactyla, the horses were inter-
mediate in size and structure between those of the Bridger
and those of the Wasatch, but were decidedly nearer to the latter.
The flophiodonts, so far as known, were represented by a single
genus (\Heptodori) which also occurred in the Wasatch. The
modest beginnings of the ftitanotheres, the family which be-
came so very conspicuous in the middle and upper Eocene
and lowest Oligocene, may be noted in the Wind River fauna,
in which there were two genera. One of these (\Eotitanops) ,
the very probable ancestor of all the subsequent genera, was
quite small, about two-thirds the size of a modern tapir, while
the other (^Lambdotherium) was a much smaller, lighter and
more slender animal and apparently belonged to an abortive,
short-lived phylum. Then, too, the first of the fhyracodonts,
or cursorial rhinoceroses, made their appearance here in the
genus ^Hyrachyus, which was afterward so common in the
Bridger.

No Artiodactyla have yet been found in the Wind River,
though there can be little doubt that they then inhabited North
America, as they did both before and afterward.

The Wind River fauna was of so much less peculiar and

!

276 LAND MAMMALS IN THE WESTERN HEMISPHERE

isolated character than that of the Bridger as to suggest
a connection with the eastern hemisphere, a suggestion which
is strengthened by the unheralded appearance of the ftitano-
theres and fhyracodonts, of which no forerunners have been
found in the Wasatch.

The lowest and most ancient of the Eocene faunas is that
of the Wasatch formation, which is extensively developed
in central and southern Wyoming, Utah and New Mexico.
The fauna of this stage is plainly divisible into two groups :

(1) those types which were the descendants of American
Paleocene mammals and were therefore indigenous, and

(2) the immigrants from other continents. The indigenous
mammals, which almost all belonged to orders now extinct,
few of which survived later than the Eocene, must have given
a very bizarre appearance to the assemblage, especially as
they were more numerous, varied and, for the most part,
larger and more conspicuous than the newcomers. Marsupials
have not yet been found, but the occurrence of opossums in the
Bridger and probably in the Wind River gives some reason to
believe that they were in North America during Wasatch
times also. The fTaeniodontia, which bore a certain resem-
blance to South American edentates, had one pair of incisor
teeth above and below enlarged and chisel-shaped, somewhat
like those of rodents. The fTillodontia were much smaller than
those of the Bridger, and their incisors were only beginning to
take on the chisel-like form. Insectivora were quite abundant,
and three, or perhaps four, families were represented in the
Wasatch ; some of these resembled the modern aquatic in-
sectivores of the west African rivers and others were more
like European hedgehogs.

The flesh-eaters all belonged to the fCreodonta, and,
though rather less diversified than those of the Bridger, were
yet relatively abundant. In size, they ranged from little
creatures not larger than a weasel up to truly enormous beasts,
and differed, no doubt, largely in habits and manner of life.

SUCCESSIVE MAMMALIAN FAUNAS 277

For the most part, the families were the same as those of the
Bridger fcreodonts, but the genera all were different. The
foxyaenids {^Oxycena) were much smaller and lighter than the
large and massive representatives found in the middle Eocene,
and their teeth were not so cat-like. Another group of pre-
daceous animals tfPalceonictis) which also inhabited Europe,
but did not survive the lower Eocene in either continent,
had short, broad and very cat-like heads. The fmesonychids
were far larger than those of the Bridger, a departure from the
ordinary rule, and the several species of the common Wasatch
genus (^Paehycena) had grotesquely large heads. A family
(fArctocyonidae), of very extensive geographical range and
great antiquity, had its last representatives here in a very
curious animal (IfAnacodori) which had the flat-crowned,
tuberculated grinding teeth of the bears and the enlarged,
scimitar-like upper canines of the fsabre-tooth cats. Such a
combination seems utterly incongruous and no one would
have ventured to predict it. The progressive family of fcre-
odonts (fMiacidse) was already quite numerously repre-
sented, but only by small forms, which must have preyed
upon small mammals, birds and lizards.

Two archaic orders of hoofed mammals were fairly numer-
ous. One, the fCondylarthra, comprised quite small, five-
toed animals, with long tails and short feet and extremely
primitive in structure. A genus (1[Phenacodus) of this order
was long regarded as being ancestral to most of the higher
orders of ungulates, but this belief has proved to be untenable.
More numerous were the fAmblypoda, one genus of which
(}Coryphodon)y though persisting into the Wind River, was
especially characteristic of the Wasatch. The fcoryphodonts
were the largest of lower Eocene mammals, and some of the
species equalled a tapir or small rhinoceros in length and height,
but had heavier limbs; as the skeleton conclusively shows,
these must have been heavy, clumsy and exceptionally ugly
brutes, with formidable tusks, large head, but relatively more

278 LAND MAMMALS IN THE WESTERN HEMISPHERE

SUCCESSIVE MAMMALIAN FAUNAS 279

slender body, short and massive limbs and elephantine feet.
In appearance, these strange beasts were not altogether unlike
the Hippopotamus and were perhaps more or less amphibious
in habits. The other family of tAmblypoda, the fuintatheres,

FlO- 142. — The commonest of Wasatch ungulates, the tamhlypod, Woryphodon testis.
Restored from a skeleton in the American Museum of Natural History.

have not yet been registered from the Wasatch, but they will
undoubtedly be found there, as they were unquestionably
present at that time.

All of the preceding groups were of the archaic, non-
progressive type and have long been extinct. With the sole
exception of one fcreodont family (fMiacidse) and perhaps
some of the insectivores, they have no descendants or repre-
sentatives in the modern world. All of them appear to have
been indigenous and derived from North American ancestors,
though it is possible that a few were immigrants. We now
turn to the orders which were more significant of the future,
because they had within them the potency of a far higher
development. These progressive groups were all immigrants,
coming to North America from some region which cannot yet

280 LAND MAMMALS IN THE WESTERN HEMISPHERE

be positively identified, but most probably was Asia. From
the same region and at a corresponding period of time Europe
received many of the same forms, and so many genera were at
that time common to the latter continent and North America that
a broad and easy way of intermigration must have been open.

One of these immigrant orders, the Rodentia, the most
ancient known members of which were these species from the
North American Wasatch, was represented by the same family
( flschyromyidse) and some of the same genera (\Paramys,
]Sciuravus) as throve also in the Bridger stage.

There were two orders of hoofed mammals, which were
newcomers to the western world, Perissodactyla and Arti-
odactyla. Of the former was a genus {\Eohipjms) of the most
ancient American horses. These most interesting little ani-
mals, no larger than small foxes and domestic cats, would
hardly be called horses, were it not for the long series of gradual
and successive modifications which led from \Eohippus up
to the modern horses. The graceful little creatures had a short
neck, curved back, and relatively short, slender limbs, with
four functional toes in the front foot and three in the hind ; and,
though they differed from existing horses in almost every detail
of teeth and skeleton, there was something unmistakably equine
about them. From the abundance of their remains it may be
inferred that herds of them swarmed in the forests and glades
of Wasatch times. The second perissodactyl family, the
fLophiodontidse, which comprised considerably larger animals,
never attained to importance in America, but flourished and
became greatly diversified in Europe. What are believed to
be the most ancient tapirs yet discovered (^Systemodon) were
individually very common in the Wasatch. This tapir was no
larger than a Coyote, had no proboscis and was so little like
a tapir in outward appearance that an observer might well
be pardoned for overlooking the relationship ; e 'en the skel-
eton is of so indifferent a character that the reference of this
genus to the tapirs cannot be positively made.

SUCCESSIVE MAMMALIAN FAUNAS 281

Of equal significance for the future was the arrival of the
Artiodactyla, of which there were members of three families
in the Wasatch, though individually they were much less
common than the horses. These were geologically the oldest
known artiodactyls, Europe having yielded none of this date,
and are still too imperfectly known to justify any very positive
statements about them. One genus, however (^Trigono-
lestes), tiny little creatures, like rabbits in size, would seem to
represent the beginnings of the great ruminant tribe, now so
very important a factor in the life of the world. A second
genus {\Eohyus)j considerably larger, is very doubtfully refer-
able to the pigs; while a third (^Parahyus), still larger, was
the first in the short-faced series of the fentelodonts, which
persisted in ever increasing size through the whole Eocene,
but could hardly have been ancestral to the true fentelodonts,
or fgiant-pigs, of the Oligocene, the place and time of whose
origin are unknown.

Another immigrant order of great interest, since we our-
selves belong to it, the Primates, made its first appearance in
North America in the Wasatch, but was not destined to long
life or great importance in this continent, where it did not
survive the Eocene. Several different kinds of small, lemur-
like and monkey-like creatures dwelt in the tree-tops of the
Wasatch forests. One genus {] Anaptomorphus) had a remark-
able likeness to the modern Tarsier (Tarsius spectrum) of the
Malay peninsula and islands.

South America. — The Eocene of South America, referred
by some writers to the upper Cretaceous, is very incompletely
and unsatisfactorily known. The Casa Mayor formation
(or Notostylops Beds), which has yielded a great variety of
mammals, for the most part very fragmentary, probably
contains not one but several successive faunas which have
not yet been fully discriminated, and that of the next succeed-
ing Astraponotus Beds is still but a scanty list. This list,
however, includes the most ancient fglyptodonts yet discovered

282 LAND MAMMALS IN THE WESTERN HEMISPHERE

and the most ancient fastrapotheres in the narrow sense of the
term. The Astraponotus Beds may be either Eocene or
Oligocene in date.

Taking the Casa Mayor faunas as a whole, they were a very
numerous and diversified assemblage of small mammals,
without a single large one among them. There were no
monkeys or rodents; otherwise, the orders were in almost
all cases the same as those which made up the Santa Cruz
fauna. The marsupials were represented by the opossums
and by several of the carnivorous kinds, the only beasts of
prey that South America had until the migrations from the
north brought in the true Carnivora, late in the Miocene or
very early in the Pliocene. There were also numerous small
marsupials of peculiar type, of which the last living survivor
is Coenolestes, of Ecuador. Throughout the stage, armadillos
were present in considerable variety, but are known only
from the bony plates of the carapace, and therefore little can
be determined as to their relationships to the modern families.
Only a single and very problematical genus of the fground-
sloths, which afterwards throve so mightily in the Miocene
and Pliocene, has been obtained and that in the later portion
of the stage.

The orders of hoofed mammals were represented by many
small animals, most of which are known only from the teeth,
which show these Casa Mayor genera to have been far more
primitive and less specialized than their descendants in the
Deseado and Santa Cruz stages. All of them had the low-
crowned grinding teeth of the browsers, and no grazers were
then in existence, so far as is known. No ftoxodonts, in the
more restricted sense of that term, have been found, but the
two allied suborders of the fTypotheria and fEntelonychia
were numerously represented. Of the former there were two
families and of the latter three, which is more than in the
Deseado or Santa Cruz formations. One of the families of
the fEntelonychia ( fNotostylopidse) consisted of very small,

SUCCESSIVE MAMMALIAN FAUNAS 283

rodent-like animals, with a pair of chisel-shaped incisors in
upper and lower jaw, and a second family (fHomalodonto-
theriidse) contained genera which would seem to have been
directly ancestral to those of the Santa Cruz, but were very
much smaller than their successors. The very large and
massive fPyrotheria of the Deseado stage were represented
by small animals, in which the grinding teeth had two pairs
of conical tubercles, not yet united into transverse crests. Two
families of the f&strapotheres, in the broad sense, were far
smaller than their Oligocene and Miocene descendants. To
the fLitopterna are referred a number of genera, in which the
grinding teeth were tuberculated and had very imperfectly
developed crests, so as strongly to suggest the teeth of the
fCondylarthra. However, until something is ascertained re-
garding the skeleton, especially the feet, of these animals, their
relationships will remain more or less doubtful.

It will be observed that these Casa Mayor faunas not only
were made up exclusively of small animals, but also that
they already were typically and characteristically South
American and bore the stamp which remained essentially
the same until the successive waves of migration from the
north so greatly modified the composition of the Neotropical
fauna. The absence of rodents and monkeys and the com-
parative unimportance of the Edentata gave a somewhat
different character to these ancient faunas from those of the
Santa Cruz and later formations.

5. Paleocene

North America. — A very important discovery is one lately
made by American Museum parties of a formation intermediate
between the Wasatch and Torre j on. The interesting fauna
of these beds has not yet been described, but it may be re-
marked that it contained none of the immigrant orders.

The vegetation of the Paleocene was already very mod-
ern in character, and nearly all of the common forest-trees

284 LAND MAMMALS IN THE WESTERN HEMISPHERE

were represented by species which differed but slightly from
those of the present. The grasses were already in existence,
but, there is good reason to believe, they had not attained
to much importance and did not cover the plains and open
spaces as they did in the Miocene and still continue to do.
As the grasses afford the principal food-supply of so many
grazing animals, the matter of their abundance and extension
is a very significant one in the history of mammalian develop-
ment, and, as we have already learned, eventually led to wide-
spread and profound modifications of structure, especially of
the teeth. While there is thus nothing very strange about
the plant-world of Paleocene times, the higher animal life was
almost totally different from that of modern times and made
up a most curious and bizarre assemblage, from which nearly
all the familiar Recent types were absent. The reptiles had
been greatly impoverished by the world-wide and, as yet, un-
explained destruction which overtook them at the end of the
Mesozoic era, but it is possible that in both North and South
America a few of the huge Dinosaurs survived the decimation
of the class. Very characteristic of the Paleocene in North
America and Europe were large, lizard-like reptiles, allied to
the New Zealand Tuatara, while crocodiles and tortoises
abounded; snakes were present, but do not appear to have
been very common.

It is the mammals which were the strangest element of
Paleocene life, and our imaginary observer would find no
creature that he had ever seen before. The difference from
modern mammalian life was not merely one of species, genera
or even families, but of orders, for only one, or at most two,
of the orders now living were then to be found in North America,
and both of these (marsupials and insectivores) were primitive
and archaic groups, which seem like belated survivals in the
modern world. There were no rodents, or true carnivores, no
lemurs, monkeys, artiodactyls, perissodactyls or proboscideans.

In the Torrejorty or upper Paleocene, there were many

SUCCESSIVE MAMMALIAN FAUNAS

285

herbivorous marsupials, with very complex grinding teeth and
chisel-like incisors, but no carnivorous or insectivorous mem-
bers of the order have been found. Insectivora were present.
Of the fcreodonts, or primitive flesh-eaters, there were no
less than five families ; the bear-like tArctocyonidse, which
died out in the Wasatch, were quite numerous, and the
problematical fMesonychidie were much smaller and more

primitive mammals than those of the Eocene. Passing over
two families which did not survive the Torrejon, we may note
the first of the fMiacidffi, the progressive family which led
eventually to the true Caraivora. The hoofed animals all
belonged to the archaic tCondylarthra and fAmblypoda;
of the former there were many genera and species referable
to three families, one of which contained the forerunners of
the Wasatch ^Phenacodus. The genus ^Pantolambda of the
Amblypoda may well have been ancestral to both the fcory-
phodonts and the fuintatheres of the Eocene.

286 LAND MAMMALS IN THE WESTERN HEMISPHERE

The Puerco fauna was much like that of the Torrejon, but
even less advanced and diversified. The herbivorous marsu-
pials were more abundant, and some of them (t Poly mastodon)
larger than those of the Torrejon ; Insectivora may have
been present, but this is doubtful. The fcreodonts, so far
as they have been discovered, were less numerous, varied and
specialized than those of the Torrejon and included but one

History .

of the families which passed over into the Eocene. The
fCondylarthra were much less common and the |Amblypoda
but doubtfully represented, but the edentate-like |Tseniodontia
were conspicuous.

Not only were the Paleocene faunas radically different
from the mammals of our time, but they could not have been
ancestral to the latter, being hardly more than an advanced
and diversified Mesozoic assemblage. It is true that some
of its elements, such as the fCondylarthra, fAmblypoda and
fCreodonta, developed greatly and played an important part

SUCCESSIVE MAMMALIAN FAUNAS 287

in the life of the Eocene, but of these only a few fcreodonts
continued into the Oligocene and all became extinct without
leaving any descendants behind them. Another curious fact
concerning the Paleocene mammalian faunas is that they were
made up entirely of small and very small animals ; not a single
mammal as large as a sheep has yet been found in these beds,
and the same is true of Europe.

That a land-connection with the Old World existed during
the Paleocene epoch, is indicated by the similarity of the faunas
of North America and Europe.

CHAPTER VIII

HISTORY OF THE PERISSODACTYLA

^| In attempting to trace the evolutionary history of the various

mammalian groups, it is necessary to bear in mind the inevitable
limitations of work of this kind. Speaking of plants, Dr.
D. H. Scott says : "Our ideas of the course of descent must of
necessity be diagrammatic; the process, as it actually went
on, during ages of inconceivable c>;\a+!3ri, was doubtless in-
finitely too complex for *' 6? Asp, even were the whole

evidence lying open befo se J n illustration, on a small

scale, of the complexity t1 xoblem, in the case of domesti-
cated forms, evolved urder Jie influence of man. Though
we know that our cultivated plants, for instance, have been
developed from wild species within the human period, and
often within quite recent years, yet nothing is more difficult
than to trace, in any given instance, the true history of a field-
crop or garden plant, or even, in many cases, to fix its origin
with certainty.' ' l With some mammalian groups the task,
though difficult enough, is not so hopeless, because of more
complete records, yet in dealing with mammals a very trouble-
some complication is introduced by the existence within the
families, and even within the genera, of two or more parallel
phyla, or genetic series. Without complete and perfect mate-
rial it is impossible to make sure that we are not confusing
the different phyla with one another and placing in one series
species and genera that properly belong in a different one.
Thus, Osborn distinguishes no less than seven such phyla

1 D. H. Scott, Studies in Fossil Botany, London, 1900, pp. 524-525.

288

HISTORY OF THE PER1SSODACTTLA

289

sr-^

among the true rhinoceroses of the Old and New Worlds,
which long followed parallel, but quite independent, courses
of development, and five phyla
among the American horses. While
these phyla add so much to the dif-
ficulty of working out the genealogi-
cal series, it is possible to simplify
the problem and treat it in a broad
and comprehensive manner that
will sufficiently establish the essen-
tial steps of change.

In external appearance and gen-
eral proportions the different fami-
lies of existing per1""' ' yls have
very little :- ...... a' -""«

and rhinoceroses she, be
is not surprising, but he jt

would seem to be as far rem, t.d
from both of the former as posai ji?.
Why, then, should they be included
in the same order ? A study of the
skeleton, however, reveals the com-
munity of structure which obtains
between the three families, a com-
munity which removes them widely
from all other hoofed mammals. In
all existing perissodactyls, though
not in most of the Eocene genera, all
the premolars, except the first, have
the size and pattern of the molars.
The foramina of the skull, or per-
forations by which blood-vessels and nerves enter and leave the
cranium, are arranged in a way characteristic of the order and
different from that seen in other hoofed mammals. The femur
always has the third trochanter. The number of digits in each

Fio. 145. — Left manus of Tapir
ITapirus terrains). S., scaph-
oid. L., lunar. Pi/., pyramidal.
Pis., pisiform. Til., trapezoid.
M., magnum. (/»., unciform.
The metacarpals are erroneously
numbered. Mc. I., second met-
acarpal. Mc. II., third do.
Mc. III., fourth do. Mc. IV.,
fifth do. Ph. 1, first phalanx.
Ph. X. second do. Ung., un-
gual phalaoi.

LAND MAMMALS IN THE WESTERN HEMISPHERE

foot is usually odd, 1, 3 or 5, but four-
toed forms occur, as the tapirs, which
have four toes in the front foot, three
in the hind ; the important character
is that the median plane of the foot
bisects the third digit, which is sym-
metrical. The third and fourth, each
asymmetrical, together form a sym-
metrical pair. Especially character-
istic is the form of the astragalus and
calcaneum (ankle and heel bones) ; the
astragalus has but a single, deeply
grooved and pulley-like surface, that
for the tibia, the lower end is nearly
flat and rests almost entirely upon the
navicular, covering but little of the cu-
boid (see Figs. 146, 148). The cal-
caneum does not articulate with the
fibula and its lower end is broad and
covers most of the cuboid.

While the foregoing list includes
the most important of the structural
features which are common to all
perissodactyls and differentiate them

Flu. 146 —Left pea of Tapir. , , , . ,

Col., ctticnneiuD. Ail, astrag- from other hoofed animals, there are
ahiB. n., navicular. Cn. i, many others which it is needless to

Cn. S, Cn. S, first, second and J

third cuneiforms. Mr. ii, 111, enumerate.

IV. aecond, third and fourth ^ subjoined table gives the

families and principal genera of the
American Perissodactyla ; extinct groups are marked f-

Suborder CHELODACTYLA. Normal Perissodactyls

I. Equid.e. Horses.

\Eokippus, low. Eoc. ^Orohippus, mid. Eoc. ^Epihippus, up. Eoc.
\Mesokippus, low. Oligo. \Miohippus, up. Oligo. fAnchitAe-
rium, up. OUgo. t Parahippus, low. Mioc. to low. Plioc. fZ>es-

motatarsals.

HISTORY OF THE PERISSODACTYLA 291

matippus, mid. Mioc. ^Hypohippus, mid. Mioc. to low. Plioc.

^Merychippus, mid. Mioc. to low. Plioc. t Prptohippus, up. Mioc.

t Pliohippus, up. Mioc. and low. Plioc. t Neohipparion, up. Mioc.

and low. Plioc. t Hipparion, Plioc. f Hippidion, Pleist., S. Amer.

^Hyperhippidium, Pleist., S. Am. Equus, Pleist., N. and S. Amer.
II. fTiTANOTHERHDiE. fTitanotheres.

t Lambdotherium, low. Eoc. t Eotitanops, low. Eoc. ^Palceosyops,

mid. Eoc. ^Telmatherium, mid. Eoc. ^Dolichorhinu*, up. Eoc.

^Diplacodon, up. Eoc. ^Titanotherium, low. Oligo.
III. Tapirimj. Tapirs.

^Systemodon, low. Eoc. tfsectolophus, mid. and up. Eoc. ^Pro-

tapims, Oligo. ^Tapiravus, mid. Mioc. Tapiru*, Pleist., N. Amer.,

Pleist. and Recent, S. Amer.

IV. tLoPHiODONTiD.B. tLophidonts.

t Heptodon, low. Eoc. ^Helaletes, mid. Eoc. t Colodon, low. Oligo.

V. RhinocerotiDjE. True Rhinoceroses.

^Trigonias, low. Oligo. ^Ccenopus, Oligo. and low. Mioc. ]Dxce-
ratherium, up. Oligo. and low. Mioc. ^Aphelops, mid. Mioc. to
low. Plioc. ]Teleocerasf mid. Mioc. to low. Plioc.
VI. fHYRACODONTiDiB. fHyracodonts and fAmynodonts, cursorial and
aquatic Rhinoceroses.
]Hyrachyusy low. and mid. Eoc. ^Triplopus} mid. and up. Eoc.
^Colonoceras, mid. Eoc. ]Hyracodon} low. Oligo. \Amynodan up.
Eoc. ^Metamynodon, low. Oligo.

Suborder tANCYLOPODA. tClawed Perissodactyls

VII. t CHALicoTHERiiDiB. Chalicotheres.

^Moropus, up. Oligo. and low. Mioc. ? ^Schizotheriumt low. Oligo.
"\Eomoropus, mid. Eoc.

The earliest perissodactyls of which we have any knowl-
edge are found in the older part of the lower Eocene (Wa-
satch stage) of Europe and North America, into which they
must have migrated from some other region yet unknown,
for no probable ancestors of the group are found in the Paleo-
cene of either continent.

I. Suborder Chelodactyla. Normal Perissodactyla.

1. Equidce. Horses

In order to make intelligible the evolutionary changes which
have led up to the modern horses, it will be necessary to say
something concerning the dental and skeletal features which

292

LAND MAMMALS IN THE WESTERN HEMISPHERE

characterize these animals. Using the term horses in a
broad sense to include all the existing members of the family
Equidze, true horses, asses, zebras and quaggas, we find a greater
uniformity in the skeleton and teeth than would be expected

—By permission of the

from the external appearance. The differences in appearance
are, however, largely due to colouring, growth of mane and
tail and the size of the ears, which leave no record in the skeleton.

The teeth (Figs. 45, p. 95 ; 154, p. 306) are extremely high-
crowned, or hypsodont, and do not form roots till an advanced
age; the incisors have a deep, enamel-lined pit, the "mark" in
the centre of the grinding surface ; the first premolar in each
jaw is very small and of no functional importance ; the other
premolars have the same pattern as the molars, which is
excessively complex in the arrangement of the enamel ridges
and the areas of dentine and cement.

The skull (Fig. 154, p. 306) is long, especially the facial por-
tion, the eye-socket (orbit) being shifted behind the teeth, which

HISTORY OP THE PERISSODACTYLA 293

otherwise, on account of their great height, would press upon
the eye itself ; the orbit is completely encircled in bone. The
lower jaw is deep vertically and the ascending ramus (see p. 66)
very high, on account of the hypsodont character of the teeth,
which thus necessitates a remodelling of the skull in several
respects. The neck is long, each of its seven vertebrae being
elongate; except in the atlas and axis, the anterior face of
each centrum is strongly convex and the posterior of all except
the atlas is deeply concave ; the odontoid process of the axis
(see p. 71) is spout-shaped, concave on the upper and convex
on the lower side, lodging and protecting the spinal cord. The
spines of the anterior dorsal vertebrae are very high, making
a low hump at the withers between the shoulder-blades ; the
trunk-vertebrae are so arranged as to make the back almost
straight and horizontal. The limbs and especially the feet
are very long. The two bones of the fore-arm, the ulna and
radius, are coossified into a single piece (Fig. 30, p. 81), but
the limits of each are still plainly to be seen, especially in a
young animal ; and it is evident that the ulna is greatly re-
duced in size and has lost its middle portion, while all the
weight is borne by the radius. Similarly, in the hind leg the
enlarged tibia, or shinbone, alone supports the weight ; and
only the two ends of the fibula are preserved (Fig. 38, p. 87),
and these are indistinguishably fused with the tibia in the
adult animal, but may be made out in the colt. The thigh-
bone has a very characteristic shape, which is difficult to de-
scribe without an undue use of technical terms, but the unusual
prominence of the great trochanter (Fig. 35, p. 85) and of the
rotular groove is an important factor in producing this ap-
pearance.

The very long and slender feet are so raised from the ground
that the animal walks upon the very tips of the toes, the
wrist being what horsemen call the "knee" and the heel is the
"hock," and the gait is thoroughly unguligrade. Each foot
has but a single functional toe, the third or middle one of the

294

LAND MAMMALS IN THE WESTERN HEMISPHERE

iCtfi

-MtW.

7k 1

MU*

5S.v .' ,

*9:

* • i

Fig. 148. — Left pes of
Horse. Cal.t cal-
caneum. As., as-
tragalus. N.t navic-
ular. Cn. S, third
cuneiform. Mt. Ill,
functional (third)
metatarsal. Mt. II
and Mt. IV, splints.

primitive five-toed foot ; and, as this toe has
to carry the whole weight supported by its
leg, it is necessarily much larger than in ani-
mals which distribute the weight among sev-
eral digits. The horses are therefore said to
be monodactyly or single-toed, but the term
is not strictly accurate, for on each side of
the functional digit is a rudimentary or ves-
tigial one, the 2d and 4th of the original five.
These rudimentary digits, which are not visi-
ble externally, have no phalanges and are
merely " splint-bones/ ' metapodials (see p.
90) which have very slender shafts and end
below in blunt
points. The sin-
gle functional
metapodial has
encircling its
lower articular
end a prominent
ridge or keel,
which fits into
a corresponding
groove on the up-
per end of the
first phalanx and

McW.

serves to prevent
lateral dislocation. In most mam-
mals this keel is merely a projec-
tion from the lower articular sur-
face and is confined to the pos-
terior side, so as not to be visible
from the front. The terminal or un-
gual phalanx is much enlarged to
carry the great weight which it sup-

McS

Fig. 149. — Left manus of Horse,
front side ; to the right, rear view
of the metacarpus. S. , scaphoid.
L., lunar. Py., pyramidal. Pis.,
pisiform. Td., trapezoid. M ,
magnum. U., unciform. Mc. II,
Mc. IV, rudimentary second and
fourth metacarpals, or splints.

HISTORY OP THE PERISSODACTYLA 295

ports and is enclosed in the characteristic hoof, unlike that of
any other mammal,

In brief, the whole structure of the horses is pre-eminently
adapted to swift running; they are admirable " cursorial
machines," as they have been called, and every part of the
skeleton has been modified and specialized to that end; the
narrow, rigid hoofs fit them for walking on firm ground and
they speedily are made helpless in quicksand or bog. Did we
know nothing of their mode of life, we might confidently infer
from their teeth that the horses were grazers, feeding prin-
cipally upon grass. A long-legged, grazing animal must needs
have a neck of sufficient length to enable the mouth to reach
the ground easily, unless a long proboscis is developed ; and so
we shall find in the history of the horses that the elongation
of the head and neck kept pace with the lengthening of the
legs and feet.

Though it can hardly be doubted that the horses passed
through most of their development in North America, yet the
immediate ancestry of all the existing species must be sought
in the Old World, none of the many Pleistocene species of the
western hemisphere having left any descendants. In North
America all of the known Pleistocene forms belonged to the
genus Equus, but the True Horse, E. caballus, was not among
them. The more abundant and important of these species
have been sufficiently described in Chapter VII (p. 199) ; it
need only be recalled that there were ten or more distinct
forms, ranging in size from the great E. ^giganteus of Texas
to the minute E. ^tau of Mexico, while the plains and forests
were the feeding grounds of moderate-sized species, about
14 hands high.

In the latest Pliocene, and no doubt earlier, species of the
modern genus Equus had already come into existence ; and in
association with these, at least in Florida, were the last sur-
vivors of the three-toed horses which were so characteristic of
the early Pliocene and the Miocene. However, little is known

296 LAND MAMMALS IN THE WESTERN HEMISPHERE

about those earliest recorded American species of Equus, for
the material so far obtained is very fragmentary. In the ab-
sence of any richly fossiliferous beds of the upper Pliocene
generally, there is a painfully felt hiatus in the genealogy of
the horses ; and it is impossible to say, from present knowledge,
whether all of the many species of horses which inhabited
North America in the Pleistocene were autochthonous, derived
from a purely American ancestry, or how large a proportion of
them were migrants from the Old World, coming in when so
many of the Pleistocene immigrants of other groups arrived.
It is even possible, though not in the least likely, that all of the
native American stocks became extinct in the upper Pliocene
and that the Pleistocene species were all immigrants from the
eastern hemisphere, or the slightly modified descendants of
such immigrants ; but, on the other hand, it is altogether prob-
able that some of these numerous species were intruders. Un-
fortunately we are in no position yet to distinguish the native
from the foreign stocks.

In the middle Pliocene, which also has preserved but a meagre
and scanty record of its mammalian life, we again meet with
horses in relative abundance, but of a far more primitive type.
They are still incompletely known, but it is clear that they
belonged to three parallel series, or phyla, of three-toed grazing
horses, with teeth which, though high-crowned, had not at-
tained to the extreme degree of hypsodontism seen in the
species of Equus and had a somewhat less complex pattern
of the grinding surface, though distinctly foreshadowing the
modern degree of complication. One of the genera (fPfto-
hippus) was not improbably the ancestor of a very peculiar
horse (^Hippidion) of the South American Pleistocene. These
middle Pliocene genera were much smaller animals than the
Pleistocene horses, aside from the pygmy species of the latter,
of light and more deer-like proportions, and with three func-
tional toes or digits. The median digit (3d of the original
five) was much the largest and carried most of the weight, on

HISTORY OP THE PERISSODACTYLA 297

hard ground practically all of it; the lateral digits (2d and
4th) which in existing horses are represented by the rudimen-
tary metapodials, or "splints," though much more slender
than the median digit, yet had the complete number of parts
and each carried a small hoof. Mere "dew-claws" as these
lateral toes were, they may have been of service in helping to
support the weight in mud or snow. In all parts of the skele-
ton there are little details which show that these species of the
middle Pliocene were not so advanced and differentiated as are
their modern successors, but it would be unprofitable to enumer-
ate these details, which are of interest only to the anatomist.
In the lower Pliocene the horses were very much more
numerous and varied than in the middle portion of the epoch.
The same three genera of grazing animals, represented by less
advanced and modernized species, are found ; and, in addition,
there was an interesting survival {^Merychipjma) from the
middle Miocene of an intermediate type, together with several
species of browsing horses {\Parahipjms and ^Hypohipjms) .
In these browsing forms the teeth were all low-crowned and
early formed their roots, and the crowns were either without
cement or with merely a thin film of it in the depressions of the
grinding surface. The pattern of the grinding surface is so
very much simpler than in the high-crowned, prismatic teeth
of the grazers that it requires close analysis to detect the
fundamental identity of plan. Such teeth imply that their
possessors must have fed habitually upon a softer and less
abrasive diet than grass, probably the leaves and soft shoots
of trees and bushes and other succulent vegetable substances,
very much in the fashion of existing deer, and must therefore
have been chiefly inhabitants of the woods and groves and
thickets along streams, as the grazing species were of the
plains and open spaces. "This assemblage of the progressive
and conservative types of horses was certainly one of the most
distinctive features of Lower Pliocene time in North America "
(Osborn).

298 LAND MAMMALS IN THE WESTERN HEMISPHERE

In the upper Miocene very much the same conditions pre-
vailed and, for the most part, the same genera of horses, with
different and somewhat less advanced species, were found as
in the lower Pliocene, so that no particular account of them is

needed. In the middle Miocene, however, there was a change,
the typically grazing horses being very rare or absent and those
with intermediate forms of teeth taking their place. Evi-
dently, it was about this time that the horses with more plastic
organization and capable of readjustment to radically different
conditions began to take to the grazing habit, while other
phyla, less capable of advance, retained the ancient, low-
crowned type of grinding teeth and, after persisting, as we have
seen, into the lower Pliocene, became extinct before the middle
of that epoch. It is of great interest to observe that in the
genus (^Merychippus) intermediate between the browsing and
grazing types, the milk-teeth retained the older and more prim-
itive character of low crowns without covering of cement,

HISTORY OP THE PERISSODACTYLA

299

while the permanent grinders had much higher, cement-covered
and complex crowns. In the lower Miocene, the variety of
horses was much diminished and all had the low-crowned,
cement-free, browsing type of teeth. Reversing the statement,
we see that in the middle and still more in the upper Miocene

Fig. 151. — Skeleton of \ Neohipparion whilneyi. American Museum.

the primitive and more or less distinctly homogeneous phylum
branched out into several series, like a tree, some of the branches
continuing and further subdividing through the Pliocene and
Pleistocene, while others, less progressive and less adaptable,
underwent but little change and had died out before the middle
Pliocene.

The Oligocene horses deserve more particular attention,
for they were almost the half-way stage of development in the
long backward ascent to the earliest known members of the
family in the lower Eocene. We may pass over the John Day
horses (■fMiokippus), which were somewhat larger than those
of the White River, but otherwise very like them, merely noting
the presence of a slightly different genus tfAnckitherium)

300

LAND MAMMALS IN THE WESTERN HEMISPHERE

which was the probable ancestor of ^Hypohippus and the other
non-progressive types of the Miocene and Pliocene. The genus
(jMesohippus) which characterizes the White River, or lower
Oligocene, was a group of species of different sizes, becoming
smaller as we go back in time, the commonest one being con-
siderably smaller than a sheep and differing more or less in all

its parts from the horses of the upper Miocene and all subse-
quent formations. The teeth were very low-crowned and
fitted only for the mastication of soft vegetable tissue ; but it is
of particular interest to observe the beginnings of the "mark"
in the upper incisors in the form of a low enamel-ridge arising
behind the cutting edge of the tooth ; the lower incisors still had
the simple chisel-like crowns of the more ancient genera ; all
the premolars, except the first, had already acquired the
molar-pattern.

The skull resembled that of a very small modern horse,
but with many differences of detail, the most obvious of which
is the shallowness of the jaws, for depth was not needed to

HISTORY OF THE PERISSODACTYLA 301

carry the very low-crowned teeth, and, for the same reason, the
ascending ramus of the lower jaw was short. The face was
relatively short and the eye-socket, which was incompletely
surrounded by bone, was directly above the hindmost teeth ;
the cranium was proportionately large and capacious and the
brain, as is shown by the cast, was richly convoluted. The
neck was relatively far shorter than in the Miocene genera,
the ball-and-socket joints between its successive vertebrae
were less elaborated and the odontoid process of the axis was
in the first stage of assuming the spout-like form, being semi-
cylindrical, with convex lower and flat upper surface. The
trunk was proportionately long and the back sloped forward,
owing to the greater length of the hind legs. The limbs and
feet were elongate and very slender, but the fore-arm bones
are only partially coossified, and the ulna, though greatly
attenuated, was still complete. The same is true of the bones
of the lower leg ; the shaft of the fibula was hardly more than
a thread of bone, but its full length was preserved. In the
fore foot there were three functional digits, the median one
enlarged and supporting most of the weight, but its hoof was
much thinner and flatter than in the corresponding digit in the
Miocene and subsequent genera ; the lateral digits touched the
ground and were not entirely functionless and, in addition,
there was a small splint, the rudiment of the fifth digit. The
hind foot was three-toed, without splint.

The little Uinta horse {^Epihippus) is still very incompletely
known, but gives us one point at least of greater primitiveness
than the White River genus in that only the last two premolars
had taken on the molar-pattern, the forward two being smaller
and simpler. The known species of the Uinta genus was very
much smaller than any of the White River forms and even
smaller than some of those of the preceding Bridger formation ;
but it should be remembered that the Uinta has been but par-
tially explored and much remains to be learned regarding its
fauna.

302 LAND MAMMALS IN THE WESTERN HEMISPHERE

The Bridger horses are fortunately much better known.
There are several species of the genus \Orohipjms, which form
a connected and progressive series ; and, though much smaller
than the smallest and oldest of the White River forms, they were
somewhat larger than the known representative of the Uinta,
\Epihippu8, but distinctly more primitive in all other respects.
The incisors were simple cutting teeth, with no trace of even
an incipient "mark," and only one premolar in each jaw, the
hindmost one, had taken on the molar-pattern. The orbit
was farther forward in the skull and less enclosed behind than
in ^Mesohippus, the cranium narrower and less capacious;
the neck was even shorter and the odontoid process of the
axis still retained the primitive peg-like form. The limbs and
feet were conspicuously shorter in proportion than those of
the White River genus ; the ulna and fibula were stouter and
less reduced and entirely separate from the radius and tibia
respectively. The front foot had four functional toes; the
fifth digit, which in \Mesohippus had been reduced to a splint,
was completely developed in the Bridger horses, but the hind
foot was three-toed.

Passing over, for lack of space, the transitional forms of
the Wind River, we come finally to the most ancient known
horses, the Wasatch species comprised in the genus \Eohippusy
the "Dawn Horse," as its name signifies; these were little
creatures ranging in size from a cat to a small fox. Despite
an unmistakably equine look in the skeletons of these di-
minutive animals, it is only the long intermediate series of
species and genera, together forming a closely linked chain,
which we have traced back from the Pleistocene to the lower
Eocene, that leads us to regard ^Eohippus as the ancestral
type of the horses. Were only the two ends of the chain
known, he would be a daring speculator who should venture
to connect them. In these little Wasatch horses we have
the evidence of a still more ancient form with five fully
developed toes in each foot, since the front foot had four

HISTORY OP THE PERISSODACTYLA

303

functional digits and indication of a splint, and splints,
as the whole history of the long series teaches, always are
found to be functional digits in the ancestor ; the hind foot had
three toes and perhaps two splints. This preceding form
is hardly to be looked for in America or Europe ; it will be
found, if ever, in the region whence the great migration came.

Fio. 153. — The

Restored from a

In all other respects, as well, ^Eohippus was what we should
expect the forerunner of the Wind River and Bridger horses to
be. The premolars were all smaller and simpler than the
molars and the latter in the upper jaw are particularly interest-
ing, for they had no crests and ridges of enamel, but four prin-
cipal conical cusps, arranged in two transverse pairs, and be-
tween the cusps of each pair was a tiny cuspule no bigger than
the head of a pin. These cuspules were the first step in the for-
mation of the transverse crests, which were destined to assume
such importance in the subsequent members of the series. The

304 LAND MAMMALS IN THE WESTERN HEMISPHERE

neck was very short, the body long, with curved or arched back,
the limbs and feet short, and the hind limb much longer than
the fore, making the relative proportions of the various parts of
the skeleton very different from what they afterwards became.
Reviewing this marvellous history of steady and long-con-
tinued change, beginning with the most ancient genus, ^Eohip-
pu8, the following modifications may be noted :

(1) There was a nearly constant, if somewhat fluctuating,
increase in size, leading by slow gradations from the diminutive
horses of the lower Eocene to the great animals of the Pleis-
tocene.

(2) The molar teeth, originally made up of conical cusps,
changed to a highly complex pattern of crests and ridges, and
the premolars, one by one, assumed the size and pattern of the
molars ; the low-crowned, rooted and cement-free teeth, fitted
only for browsing, became very high-crowned, prismatic and
cement-covered, admirably adapted to grazing. Beginning
in the upper incisors of the White River ^Mesohippus, the
"mark" became established as an enamel-lined pit, growing in
depth as the teeth increased their length.

(3) The face grew relatively longer, the eye-socket being
shifted behind the teeth and becoming completely encircled
in bone, and the jaws were greatly increased in depth to ac-
commodate the very long teeth.

(4) The short neck was greatly elongated and the individual
vertebrae modified so as to give flexibility with no loss of
strength. The primitive peg-like odontoid process of the
axis became first semicylindrical and then spout-shaped.

(5) The arched back was straightened and the neural spines,
especially of the anterior dorsals, elongated.

(6) The limbs grew relatively much longer ; the bones of the
fore-arm and lower leg were fused together, the one on the inner
side (radius and tibia) enlarging to carry the entire weight
and the external one (ulna and fibula) becoming more or less
atrophied.

HISTORY OP THE PERISSODACTYLA.

305

D

Fig. 154. — Series of horse skulls in ascending geological order. A., lEohippua, lower
Eocene (after Cope). £., t Mesohippus, lower and middle Oligocene. C.f iProto-
hivpua, upper Miocene (after Cope). D., Equus.

X

306

LAND MAMMALS IN THE WESTERN HEMISPHERE

(7) The feet were much elongated and the median (3d)
digit of each gradually enlarged until it carried the whole

Fia. 155. — Right man us and left pes of

Equus.

1

//

HiJ

\

Tfi**i

r'fl

i

vV\V

Fiq. 156. — Right manus and left pes of
t Protohippus.

weight, at the same time modifying the shape of the hoof so as
to fit it to be the sole support of the body. The other toes
gradually dwindled and became functionless, though often
retained as splints. The first digit (pollex and hallux) was first

HISTORY OF THE PERISSODACTYLA

307

lost, then the fifth, then the second and fourth were reduced
to dew-claws and finally to splints. Thus the pentadactyl
horses of the lower Eocene
were transformed into the
monodactyl species of the
Pliocene and Pleistocene.

In South America the
story of the horses was a brief
one, for they were among the
immigrants from the north
and did not reach the south-
ern continent till the Plio-
cene, probably late in that
epoch, for none of the three-
toed genera have been found
in South America. So far
as known, these southern
equines were small and me-
dium sized animals, with large heads, relatively short feet
and somewhat ass-like proportions. There were two well-
defined groups of these animals : (1) species of the genus
Equus, which thus, at one time or another, inhabited every
one of the continents, Australia excepted; (2) three gen-
era peculiar to South America and developed there from
northern ancestors, probably \Pliohippus. Two of these
genera (}Hippidion and \Onohippidium) displayed curious
modifications of the nasal bones, which were extremely slender
and attached to the skull only at their hinder ends, instead
of being, as is normally the case, supported for nearly their
whole length by lateral articulation with other bones. What
can have been the significance and function of these excessively
slender, splint-like nasals, it is difficult to conjecture. The
third genus (fHyperhippidium) was a small mountain-horse,
with extremely short feet, which were well adapted to climbing.

This is the merest outline sketch of a most wonderful series

Fig. 157. — Right Fia. 158. — Right
manus and left pes manus and pes of

of iMesohippus. \Eohippus.

308 LAND MAMMALS IN THE WESTERN HEMISPHERE

of gradual and progressive modifications, a sketch that might
readily be expanded into a volume, were all the details filled
in. While each set of organs, teeth, skull, neck, body, limbs
and feet, might appear to advance independently of the others,

Fig. 159, — Skeleton of a. Pampean horse (t Hippidion neogositm). National Museum,
Buenos Aires. For restoration, see Fig. 119, p. 214. Note the splint-like nasal bones
attached only at the hinder end .

in reality there was no such independence, for at every stage of
the progression all the parts must have been so coordinated
into a harmonious whole, that the animal could thrive and
hold its own in the stress of competition. Could we but dis-
cover all the facts of environment, on the one hand, and or-
ganization, on the other, we should doubtless learn that the
little \Eohippm was as exquisitely fitted to its place in the
Wasatch world, as are the horses, asses and zebras of the
present day to theirs. It was the response to changing needs,
whether of food, climate, disease or competition, that was
the main factor of development.

2. ^Titanolkeriidce. jTitanotheres
This family, all of whose members vanished from the earth
ages ago, was a comparatively short-lived group and nearly
the whole of its recorded history was enacted in North America ;

HISTORY OF THE PERISSODACTTLA

IC.

' i flirt
L 1 Iff

1 ' 1 1

|n

«?.

**

■ Bk *

la iuBi

Si

IW

310 LAND MAMMALS IN THE WESTERN HEMISPHERE

only a few belated stragglers reached the eastern hemisphere,
though the family may, nevertheless, have originated there.

In the lowest of the three substages of the White River
Oligocene the most conspicuous and abundant fossils are
the ftitanotheres, the latest members of which were huge
animals of almost elephantine proportions. They belonged to
four parallel, or rather slightly divergent, phyla, differing in
the development of the horns, in the shape of the head and in
the relative length and massiveness of the limbs. The teeth
were all low-crowned, or brachyodont, the canines much too
small to have been of any service as weapons and the incisors
had curious little, button-shaped crowns, which can have had
little or no functional importance, since they show hardly
any wear, even in old animals. With such front teeth, a
prehensile lip and long tongue would seem to have been neces-
sary for gathering and taking in food.

The ftitanotheres were one of two perissodactyl families in
which the premolars never became so large and complex as
the molars. The upper molars had a longitudinal outer wall,

Fiq. 161. — Second upper molar, lefl aide, oUTUanotherium. A., masticating surf ace ;
B., outer side of crown.

composed of two deeply concave cusps, and two internal
conical cusps, but no transverse ridges; the lower molars
were composed of two crescents, one behind the other, a
pattern which was very widely distributed among the early
and primitive artiodactyls and perissodactyls.

The so-called "horns" were not strictly such, but a pair

HISTORY OF THE PBRISSODACTYLA 311

of bony protuberances from the front of the skull and, from
their shape, could hardly have been sheathed in horn. The
long, immensely broad and massive head resembled that of
some fantastic rhinoceros, as did also the body and limbs.
The brain was quite absurdly small, the cavity for it, lost in
the huge skull, would hardly contain the fist of an ordinary
man ; these great beasts must have been incredibly dull and
stupid, surpassing even the modern rhinoceroses in this respect.
As is generally true in mammals which have horns, antlers,

Flo. 162. — Skull of t Ttianotherium datum. American Museum.

or similar weapons borne upon the skull, or very large tusks,
the bones of the brain-case were made enormously thick and
yet lightened by an intricate system of communicating cavities
or "sinuses," separated by many bony braces and supports
connecting the inner and outer denser layers, which form the
surfaces of the bones. In this way the skull is made strong
enough without any proportionate increase of weight to endure
the severe shock of impact, when the horns or tusks are made
use of. The principle is the same as the engineer employs
in designing a steel truss-bridge. The upper profile of the head
was deeply concave, just as it is in those rhinoceroses which
are armed with nasal horns.

312 LAND MAMMALS IN THE WESTERN HEMISPHERE

The neck was of moderate length and the body, as indicated
by the long, arched ribs and the greatly expanded hip-bones,
was extremely bulky and massive. The spines of the anterior
dorsal vertebrae were excessively long, forming a great hump
at the withers. The limbs and feet were columnar, like those
of an elephant; the feet were supported on a great pad,
while the hoofs were mere excrescences on the periphery of the
foot. The bones of the fore-arm were entirely separate and
the ulna was very stout ; in the lower leg also the bones were
not coossified, but the fibula was but moderately heavy.
This is a sharp contrast to the arrangement found in the horses
and in those hoofed animals generally which are swift runners
and have slender, elongate limbs and feet, such as deer, ante-
lopes, camels, etc. Heavy, slow-moving animals, like elephants,
tapirs, rhinoceroses, etc., almost always have separate fore-
arm and leg-bones and generally a heavy ulna. The number of
digits was four in the front foot and three in the hind. The
genera differed in the proportions of limbs and feet, one
having them longer and less ponderous than another, and,
no doubt, the former was of swifter gait.

At a certain level in the White River beds the ftitanotheres
abruptly cease, disappearing with what seems like startling
suddenness. In all probability, however, the extinction was
more gradual and its apparent abruptness was due, partly at
least, to the break in the deposition of the beds, which is very
obvious. Such a break, or " unconformity/ ' as geologists
call it, almost always implies an unrecorded lapse of time, which
may have been very long. However it came about, gradually
or suddenly, the extinction of these great animals is difficult
to explain ; no Carnivora of the time could have been formi-
dable enemies and they had no rivals in their own walk of life.
Their stupidity may have been a factor, but it seems more
likely that the onset of some new infectious disease, perhaps
imported by incoming migrants from the eastern hemisphere,
gave the coup de grace. In the lower substage, beneath the

HISTORY OF THE PERISSODACTYLA 313

unconformity, where the remains of ftitanotheres are so abun-
dant, successive changes may be observed. The species with
great "horns," rounded, flattened or triangular, are confined
to the upper levels ; in the middle section other species, some-
what smaller and with shorter "horns," are found, while in
the bottom levels the animals are much smaller and have still
smaller "horns." :

The Uinta ftitanotheres were much more numerous and
varied than those * of the White River; in the upper part of
these beds are found two genera tfDiplacodon and \Protitan-
otherium) which already had quite prominent bony protuber-
ances on the nose ; their canines were large enough to be of
value as weapons and the incisors were well developed and
functional. Evidently, there was a change here in the manner
of feeding, the front teeth were used for cropping and browsing,
a function which in the White River members of the family
must have been largely taken over by the lips and tongue, while
the growth of the horn-like protuberances on the skull rendered
the canines superfluous as weapons. This latter change is one
which recurs frequently in different phyla of the hoofed animals,
in which the earlier and more primitive members had canine
tusks, and the later, more advanced representatives developed
horns, the tusks diminishing as the horns increased. While this
rule is a general one, it is not entirely without exceptions.

In the lower Uinta and in the Bridger the ftitanotheres
were extremely abundant and numerically they are the com-
monest of all fossils in those beds ; no less than five series or
phyla may be distinguished, three of them being added in the
upper Bridger. The differences between the phyla, however,
principally concern the forms of the teeth and the shape of
the skull ; in some the head was short and broad, in others
long and narrow, and in others again of medium proportions ;
some had broad and extremely low-crowned grinding teeth,
which in others were higher and more erect. But these are
matters of minor detail, useful as they are in pointing the way

314 LAND MAMMALS IN THE WESTERN HEMISPHERE

to a proper arrangement of the various species ; in essentials,
the forms all agreed and constituted several series of closely

allied genera. Comparing these Bridger animals with the

great ftitanotheres of the lower White River, the first and

most obvious difference that strikes the observer is the very

much smaller size of the more ancient types.

With some variation in this respect, hardly

any of the Bridger species exceeded a modern

tapir in stature and very much resembled one

in proportions. The canine teeth were tusks

as large as those of a bear and must have been

very effective weapons ; the molar-pattern was

identical with that found in the great Oligocene

ltPah^°o>>^re Dea9ts, but the premolars were simpler and

relatively smaller.

The skull had a straight upper profile, though in several

of the phyla small bony protuberances were developed over

Fia. 164. — Second
upper molar, right
Bide of a Bridger

HISTORY OF THE PERISSODACTYLA 315

the eyes, and must clearly be regarded as incipient stages of
the " horns' ' which were subsequently to become so long and
prominent. Instead of being broad on top as it was in the
White River genera, the cranium carried a high ridge of bone,
the sagittal crest, which served for the attachment on each
side of the great temporal muscle, one of the most important
of the muscles of mastication. The trunk was less massive
and the limbs were lighter than in the Oligocene genera, but
the number of digits was the same, four in the front foot and
three in the hind, and the hoofs were much better developed,
serving actually to carry the weight and not being mere ex-
crescences upon the periphery of a pad. Aside from the pro-
boscis, which lends such a characteristic appearance to the
existing tapirs, the "ftitanotheres of the Bridger must have
looked much like tapirs, and in early days, when the mutual
relationships had not been satisfactorily determined, they were
frequently described as "tapiroid." The term is unobjection-
able in so far as it is understood that a merely superficial like-
ness is implied, not any real relationship other than that which
unites all the perissodactyl families.

As noted above, the phyla of the ftitanotheres were much
more numerous in the later than in the earlier part of the
Bridger stage, when they were reduced to two. In the still
older Wind River stage these two united into one. The Wind
River animals (^Eotitanops) were similar, but much smaller,
and occurred in incomparably less variety and abundance.
Indeed, one of the most striking differences between the Wind
River and the Bridger faunas consists in the great increase and
diversification of the ftitanotheres in the latter. There was,
it is true, a second phylum of the family in the Wind River,
represented by the genus ^Lambdotherium, but this was a short-
lived series, which left no descendants in the Bridger or sub-
sequent formations. These were the smallest known members
of the family and were light, slender-limbed animals, a very
notable difference from the others.

316 LAND MAMMALS IN THE WESTERN HEMISPHERE

With the Wind River the history of the ftitanotheres breaks
off short, and from present information, can be carried no
farther back. Possibly, there was a Wasatch ancestor, which
only awaits discovery, but it seems more likely that these
earliest known genera were belated immigrants from the same
as yet unknown region, whence came the modernized and pro-
gressive elements of the Wasatch fauna. Except for its ob-
scure beginning, the family was pre-eminently characteristic
of North America, and only two representatives of it have been
found outside of that continent, one in Hungary and one in
Bulgaria. No doubt others will yet be found in Asia.

Both in its resemblances and its differences, as compared
with the far longer and more complex story of the horses, the
history of the "ftitanotheres has instructive bearings upon
evolutionary theory.

(1) Starting with two phyla, one of which speedily died
out, the other ramified into four or five, which continued until
the disastrous end, pursuing a nearly parallel course of develop-
ment.

(2) There was a great increase in size and especially in bulk
and massiveness from species no bigger than a sheep in the
Wind River stage to those which rivalled small elephants in
the lower White River.

(3) The teeth underwent comparatively little change ; the
incisors dwindled and lost functional importance and the ca-
nines were reduced, horn-like growths taking their place as
weapons; the premolars grew larger and more complicated,
but never attained the full size and complexity of the molars,
as they did in other perissodactyl families.

(4) Horn-like, bony protuberances appeared first as small
humps and knobs over the eyes and steadily enlarged, at the
same time shifting their position forward, until they finally
attained great size and were on the nose.

(5) The skull was modified so as to support these weapons
and endure the shock of impact when they were put to use,

HISTORY OF THE PEHI880DACTTLA 317

(a) by making the upper profile strongly concave from before
backward ; (6) by greatly widening the top of the cranium,
where in the older and more primitive genera the high mid
thin sagittal crest was placed ; (c) by immensely increas-
ing the thickness of the cranial bones and at the same time
hollowing them by means
of an intricate system of

Fia. 165. — Series of beads of t titanotheres in ascending geologic a] order. A., t Pal-
aotyops, lower Bridger. B., 1 Manteoccrat, upper Bridger, C. , t Diplacodon, Uinta.
D.. t Titanotherium, extreme development of horns, White River. From models in
the American Museum and Princeton University.

cavities ; in this way sufficient strength was secured without un-
due increase in weight.

(6) The growth of the brain did not keep pace with the
increase in the size and weight of the body and head, and this
deficiency may have been a factor in determining the early
extinction of the family,

(7) To support the huge head, stout ligaments and power-
ful muscles were needed in the neck and trunk and these in
turn required large bony surfaces for their attachment. To
meet this need, the spines of the anterior trunk-vertebne were

318

LAND MAMMALS IN THE WESTERN HEMISPHERE

very much lengthened, so as to form a hump at the shoulders,
and this elongation of the spines went on in proportion to the
growing weight of the head.

(8) The limb-bones increased in thickness until they be-
came extremely massive, to carry the immense weight of the
body, and they eventually lost the marrow-cavities, which were
filled up with spongy bone, a great gain in strength. As is
generally, though not universally, true of the large and heavy
mammals, there was no coossification between the limb-bones
and no great increase in their proportionate length. The
thigh-bone, or femur, lost the cylindrical shape of the shaft,
becoming flattened and very broad, and acquiring something
of the appearance of the same bone in the elephants.

(9) There was no loss or coossification of elements in
wrist (carpus) or ankle (tarsus) and no reduction of digits within
the limits of the family. In the latest, largest and most special-
ized genera, as well as in the earliest, smallest and most prim-
itive, there were four toes in the front foot and three in the
hind. We have the most cogent reasons for assuming that all
mammals were derived from ancestors which had five toes in
each foot, neither more nor less. If this be true, then the most

HISTORY OF THE PERISSODACTYLA 319

ancient known ftitanotheres, which were small and light, had
already suffered the loss of the first digit in the fore foot and of
the first and fifth digits in the hind foot, but there reduction
ceased. With the growing body-weight, long, narrow and slen-
der feet would have been a detriment, whereas in swift-running
animals, like horses and deer, long and very slender feet are a
great advantage. The contrast is both striking and instructive,
showing the importance of a short, broad, polydactyl and pillar-
like foot to very large and heavy mammals, all of which have
feet of this character.

(10) The hoofs, as shown by the terminal bones (ungual
phalanges) which formed their bony cores, were reduced in
size until they became mere nail-like excrescences around the
border of the massive foot.

3, 4. Tapiridce and ^Lophiodontidce. Tapirs and \Lophiodonts

The history of the tapir family is not at all satisfactorily
known, partly because tapirs are comparatively rare as fossils
in all of the Tertiary formations, and still more for the reason
that the specimens so far collected are so fragmentary, not a
single half-complete skeleton among them. Had these animals
actually been as rare in North America as the fossils would seem
to indicate, they could not possibly have maintained them-
selves for so long a time, throughout nearly the whole of the
Tertiary and Quaternary periods. For some reason, probably
because they have always been forest-haunting animals, their
habits must have kept them in places remote from the areas
where the accumulation of sediments was in progress, and thus
only occasional stragglers were buried and preserved.

The rarity and incompleteness of the material render it
impossible to give any such full account of the tapirs as is
practicable for the horses and ftitanotheres, but the cir-
cumstance is less unfortunate in the case of the tapirs than in
that of many other families. This is because these creatures

320

LAND MAMMALS IN THE WESTERN HEMISPHERE

have been so conservative and unprogressive, that they have
undergone comparatively little change since their earliest re-
corded appearance. They have been aptly termed "living
fossils" and seem like belated survivors from some older world,
out of place in the modern order of things. Attention has
already been directed (p. 137) to the remarkable geographical
distribution of the tapirs at the present time; Central and
South America, southeastern Asia and the adjoining islands.

Fit). 167. — American Tapir (Tapirus terrains'). By perm
London.

The tapirs are all of moderate size, going back to very small
forms at the beginning of their history and never at any period
developing into large animals. The only striking and un-
usual feature about any of the existing members of the family
is the long proboscis, a flexible, dependent snout, and, were
they all extinct and nothing known of them but the skull,
this proboscis could have been confidently predicated of them
from the great shortening of the nasal bones. Small tusks,
not showing when the mouth is closed, are formed in an ex-

HISTORY OF THE PERISSODACTYLA

321

ceptional way by the enlarged external upper incisor and the
lower canine, the upper canine being much reduced and without
function. The grinding teeth have very low crowns, pre-
molars (except the first) and molars are all alike and of a very
simple pattern, which has been independently repeated in
several different orders of herbivorous mammals; in both
upper and lower teeth, there are two elevated, straight, trans-
verse crests.

Except for the modification of the skull which is conditioned
by the development of the proboscis, the skeleton might be-
long to any one of several
Eocene or Oligocene fami-
lies, and it is this general-
ized, indifferent character
which has led to the dub-
bing of many early peris-
sodactyls as "tapiroids."
The limbs are short and
moderately heavy, the
bones of the fore-arm and
lower leg all separate and
the number of toes is four

in the front foot and three in the hind. The toes end in well-
formed separate hoofs, but behind them is a pad, which carries
most of the weight. The body is covered with smooth, short
hair, which in the American species is of a uniform dark brown,
but in the Asiatic species the head, neck and limbs are black and
the body is white. In both, however, the young have longitudi-
nal, light-coloured stripes and spots on a dark ground (see Fig. 6,
p. 47) indicating what the colour-pattern of the ancestral
forms must have been. As might be inferred with certainty
from the low-crowned teeth, the tapirs are browsing, not graz-
ing, animals, feeding upon leaves and shoots and other soft
vegetable tissues. They are shy and solitary in habit and live
usually in thick forests and near water, which they frequently

Fig. 168. — Skull of American Tapir, right side.

322 LAND MAMMALS IN THE WESTERN HEMISPHERE

enter, both for bathing and as a place of refuge when pur-
sued. Under modern conditions, the only perissodactyls of
the western hemisphere are the tapirs of the Neotropical re-
gion, North America proper, which for ages was the principal
home of the order, not having a single representative now.

In the Pleistocene, tapirs were apparently more abundant
than in any of the Tertiary epochs, but this was probably due
to the fact that the Pleistocene of the forested regions is far more
fully recorded than is any Tertiary stage. One species, which
was hardly distinguishable from the Recent Central American
form, was common in the forested region east of the Mississippi
and in California, and a second species (Tapirus ^haysii) was
larger and heavier than the other. Except in Texas, none have
been found in the Great Plains area, nor are they likely to be,
for that region, then as now, appears to have been devoid of
forests. No doubt, these Pleistocene species had substantially
the same habits as the existing ones, but they were adapted to
a colder climate and a different vegetation, for, except the
Pinchaque Tapir (T. roulini) of the high Andes, all the modern
species are tropical in distribution.

Concerning the Pliocene and Miocene tapirs, but meagre
information has been obtained. Enough material has been
gathered by the collectors to demonstrate the continuous pres-
ence of the family in North America throughout those epochs,
but the broken and fragmentary specimens are insufficient to
show what the structural changes were. It should be remem-
bered, however, that it is only in the region of the Great Plains
and the Great Basin of Nevada that any considerable quantity
of Miocene and Pliocene mammals have been found, and in those
regions tapirs probably never were common. If the Peace Creek
formation of Florida is properly classified as latest Pliocene,
then at that time the American tapirs were essentially what
they are to-day, for the Florida species is hardly separable from
the modern T. terrestris.

Not till we reach the lower Oligocene, or White River beds,

HISTORY OF THE PERISSODACTYLA 323

do we get material which permits the making of definite state-
ments regarding the course of developmental changes. The
White River genus, f Protapirus, which is also found in the
middle Oligocene of Europe, was a much smaller animal than
any of the known Pleistocene or Recent species, barely more
than half the size, in fact. The teeth show that the small

Fig. 169. — Skull of White River tapir tfProtapirus validus) .left side. Princeton Uni-
versity Museum. N.B. This figure is much less reduced than Fig. 168.

tusks were canines, both above and below, and that the curious
substitution of the external upper incisor for the canine had not
yet taken place. The grinding teeth were identical in pattern
with those of the existing genus, but not all the premolars had
yet acquired the form and size of the molars. In the skull
the nasal bones had begun to shorten, but the change had not
yet made much progress, and the proboscis must have been in
merely an incipient stage of development. What little is
known of the skeleton other than the skull was like that of the
modern genus, but the bones were much smaller and propor-
tionately lighter.

The Eocene tapirs are still very imperfectly known ; all
that can be said of them is that they become successively
smaller as they are traced backward in time, and that in them
the premolar teeth were all smaller and simpler than the

324 LAND MAMMALS IN THE WESTERN HEMISPHERE

molars. The Wasatch genus ('\Systemodon) is the most ancient
member of the series yet discovered. Dating from the Eocene
immigration, the tapirs are to be regarded as a North American

family, for there is here a complete continuity from the lower
Eocene to the Pleistocene, while in Europe they first appeared,
probably by migration from North America, in the middle
Oligocene.

In South America the history of the tapirs is even shorter
and less eventful than that of the horses; the latter, as we
have seen, reached the southern continent in the Pliocene
and there gave rise to a number of peculiar and characteristic
genera, but the tapirs have been found only in the Pleistocene
of Argentina and Brazil and only the modern genus is repre-
sented.

Wofully broken and incomplete as the developmental his-
tory of the tapirs still is, the fragments are nevertheless suffi-
cient to show a mode of evolution differing in certain important

HISTORY OF THE PERISSODACTYLA

325

respects from that followed by the horses or ttit&n°theres.
Certain features are common to all three groups, such as the in-
crease in size and in proportionate stoutness from stage to stage

m t

Fxo. 171. — Upper teeth, left side, of tapirs, showing comparative sizes. A, \ Prota-
pirua validus, White River Oligocene. B, Tapirus terrestris, modern. iS, external
incisor, c, canine, m 1 , first molar.

and the gradual enlargement and complication of the pre-
molar teeth. On the other hand, the tapirs have been very
conservative, and they underwent far less radical changes
than did either of the other families. Aside from the pro-
boscis and the modifications of the skull which the develop-
ment of that organ necessitated, these animals remain to-day
very nearly what they were in Oligocene times. This, then,
is an example of development practically restricted to a few
organs, while all the other parts of the structure changed but
little.

The extinct flophiodonts, like the tapirs, of which they would
seem to have been near relatives, are known only from incom-
plete material, and comparatively little has been learned regard-
ing their history. While they were abundant and varied in
Europe, during the Eocene epoch, they never were a striking
or prominent element among the mammals of North America,
where they persisted one stage later, and they did not reach
South America. In North America they are found from the
Wasatch to the White River.

326 LAND MAMMALS IN THE WESTERN HEMISPHERE

The White River genus (^Colodori), which is fairly well
known, might almost be described as combining the characters
of horses and tapirs ; but such an expression is not to be inter-
preted as meaning that this genus is in any sense a connecting
link or transition between the two families, but merely that
in certain important respects its course of development ran
parallel with that followed by the horses. The teeth were
very tapir-like, especially those of the lower jaw, which,
indeed, are hardly distinguishable from those of a tapir, and
the premolars had the molar-pattern. The limbs were very
light and slender and the feet long and narrow ; the fore foot
retained a small fifth digit ; the feet, especially the hinder one,
had a resemblance to those of the contemporary horses (fAfeso-
hippus) , though the median digit was not so much enlarged,
nor the lateral ones so far reduced. It is highly probable that,
had this family persisted till the Pleistocene, instead of dying
out in the lower Oligocene, it would have eventually terminated
in monodactyl forms.

The flophiodonts of the Eocene are represented by very
fragmentary material; so far as that material goes, it does
not show much change from the White River genus, except
that the premolar teeth were smaller and simpler, the limbs and
feet retaining the same characteristics of length and slender-
ness. The Wasatch genus (^Heptodon) had a similar light-
ness of limb and narrowness of feet, these characters thus ap-
pearing at the very beginning of the family history, so far
as their North American career is concerned.

•

5. Rhinocerotidce. True Rhinoceroses

The history of the great group of rhinoceroses and rhinoc-
eros-like animals is a very long and complicated one, inferior
in its completeness only to that of the horses. The com-
plexity of the story arises from the large number of phyla
into which the families are divisible, and, despite the great

HISTORY OF THE PERISSODACTYLA 327

wealth of material and the admirable preservation of much
of it, it is extremely difficult to find a clew through the mazes
of this labyrinthine genealogy. From the standpoint of the
existing geographical distribution of animals, few mammals
could seem more foreign and exotic to North American life
than do the rhinoceroses, and yet for a very long time that
continent was one of the chief areas of their development,
so far, at least, as that development can be followed. It is
even probable, though not clearly demonstrable, that the
family originated here and subsequently spread to the Old
World, but not to South America, where no member of it
has ever been found. The later history of the rhinoceroses ran
its course in the Old World entirely, and the highest speciali-
zations within the family are to be found there; in North
America these animals are not known to have persisted beyond
the lower Pliocene, and if they did survive, it was only as a few
stragglers in out of the way places.

The modern rhinoceroses are restricted to Africa, southern
Asia and some of the larger Malay islands, Borneo, Sumatra
and Java, and within these wide geographical limits are to be
found the terminal representatives of at least three separate
and quite distinct phyla, the African, Indian and Sumatran
genera respectively (Opsiceros, Rhinoceros, Dicerorhinus) . It
will be advisable to begin the study of this peculiarly interesting
family with a brief examination of its modern members, even
though none of these are found in the western hemisphere.

All the existing rhinoceroses are large and massive animals,
ranging from four feet to six feet six inches in height at the
shoulder, and all have solid dermal horns, except in most
females of the Javan species1 (R. sondaicus). The Indian
and Javan species have a single horn on the nose, while those
of Africa and Sumatra have, in addition to the nasal horn, a
second one on the forehead. The horns, thus, do not form a

1 The names, Javan and Sumatran rhinoceroses, are somewhat misleading,
since both of these species are also found on the mainland of India.

328 LAND MAMMALS IN THE WESTERN HEMISPHERE

transverse pair, but are placed in the median line of the head,
one behind the other ; it should also be noted that these horns
are solid, dermal structures, made up of agglutinated fibres
or hairs and not having a bony core formed by outgrowths of

the skull, as do the horns of most ruminants, such as oxen,
sheep and antelopes, which are therefore called ' ' hollow-
horned" (Cavicornia). The skull, however, betrays the pres-
ence of horns by the extremely rough areas which serve for
their attachment and thus the presence or absence of these
weapons may be readily determined in the case of an extinct
species of which only the skeleton remains. The skin is very
thick and coarse, typically "pachydermatous," and is quite
naked in most of the species ; but in the Sumatran form there
is a sparse coat of hair, which is quite thick in the young
animal. In the Indian Rhinoceros unicornis the enormously
thick skin has conspicuous and regularly arranged folds, which
make the creature look as though encased in armour ; the ears
and tail are tufted with hair. In the African and Sumatran
genera the folds are obscurely marked and not definitely
arranged, giving the body a smoother appearance. All the
existing species, except one, are browsers and feed upon leaves

HISTORY OP THE PERISSODACTYLA 329

and twigs, and they frequent forests and marshes where their
food is abundant. Not that these and other browsing animals
do not occasionally eat grass, but it is not their principal diet.
The exception noted is the largest of all the living species, the
Broad-Lipped Rhinoceros (erroneously called "White") of
Africa, Opsiceros simusy which is strictly a grazing animal and
therefore frequents more open country than the other African
species, 0. bicornis.

There are considerable differences in proportions and
general appearance among the various species, but they all
have short necks, very long and massive bodies, short and heavy
limbs and short, columnar feet, which look much like those
of elephants, but have only three toes each. In all but two
of the living species the upper lip is prehensile and characteristi-
cally pointed and can be used to pick up very small objects,
like the "finger" on an elephant's trunk; in the Sumatran
species (Dicerorhinus sumatrensis) the lip, though pointed, is
horny and inflexible, while in the African 0. simus it is broad
and straight-edged.

The teeth of the modern rhinoceroses are extremely char-
acteristic and may always be recognized at a glance. In the
African genus (Opsiceros) there are no front teeth, all the incisors
and canines being lost; the other genera have on each side
a single large and trenchant upper incisor, in shape like a broad,
obliquely edged chisel, which shears against a still larger
elongate and tusk-like lower incisor, that is procumbent and
points directly forward. The Indian Rhinoceros (R. unicornis)
is said to use its tusks as weapons in very much the same fashion
as the Wild Boar. Between the large lower tusks there is a
pair of very small incisors, which can have little or no functional
value ; the third lower incisor has been suppressed, as have also
the canines of both jaws. The dental formula then is : i | or #,
ch p|, w|, x2 = 28 or 34 (see p. 93). The premolars,
except the first, though somewhat smaller than the molars,
have essentially the same pattern. The upper molars have

330 LAND MAMMALS IN THE WESTERN HEMISPHERE

moderately high crowns, yet they are purely brachyodont,
except in the grazing, broad-lipped African species (0. simus),
in which they may fairly be called hypsodont. The external
wall of the tooth is broad and nearly smooth, not divided into
cusps, as it is in the horses and tapirs, and the two transverse
crests, which in the tapirs are directly transverse, are very
oblique. In all the existing species additional complications
are given by the short spurs, which project inward from the
outer wall or from the transverse crests. The lower molars
are formed each of two crescents, one behind the other, but
their arms or horns are angulate, not curved as they are in
other perissodactyls which have crescentic lower teeth.

The upper surface of the skull is very concave in the antero-
posterior direction and very broad over the cranium, where
there is no sagittal crest. The nasal bones are immensely
thick and strongly arched, with the convexity upward ; both
this arching of the nasals and the fore-and-aft concavity of the
skull are devices for giving a strong and solid attachment to
the great nasal horn, for the attachment of which these bones
have an extremely rough surface, and in the two-horned species,
a second roughened area on the forehead marks the place
of attachment of the frontal horn. The bones of the cranium
are very thick, but lightened by the many chambers which
traverse them. The articulation of the lower jaw with the
skull is in some respects unique among mammals ; the post-
glenoid process is a long spike, which fits inside of a bony
lump (the postcotyloid process) behind the condyle of the lower
jaw, and the posterior margin of the latter is greatly thickened.
The neck is short and stout, the trunk very long, broad and
deep, the long and strongly arched ribs and the widely ex-
panded hip-bones providing space for the great mass of viscera.
The bones of the limbs are short and very massive ; the humerus
has a very prominent deltoid ridge and the femur an unusually
large third trochanter; the bones of the fore-arm and lower
leg are separate, as in the massive ungulates generally. The

HISTORY OF THE PERISSODACTYLA

331

foot-bones are likewise extremely short and heavy, and the
number of digits is three in each foot. Each of the five or
more existing species has its skeletal pecu-
liarities, every portion of the bony structure
showing characteristic features ; but these
are only minor modifications of the general
plan and may be neglected in any compre-
hensive account of the living representa-
tives of the family.

In order to find any American members
of this family, it is necessary to go back
to the lower Pliocene, where a great abun-
dance of them is encountered, representing,
according to Osborn's view, four or five
phyla; and just as in the case of the
horses of the same formation, they were n°- I73-"

, . of Indian Rhinoceros

an assemblage curiously made up of pro- (r. untcomw).
gressive and old-fashioned, conservative
genera, — some were persistent native stocks, others the de-
scendants of immigrants from the Old World, which reached
America in the middle Miocene. There was great variety of
form, size and proportions among these animals, North America
at that time having a larger number of genera and species than
Africa and Asia combined have now. Some were quite smalt,
some large, though none equalled the larger modern species.
Some of the genera had relatively long legs, but in one genus,
t Teleoceras (Fig. 125, p. 230), an Old World type, they were most
grotesquely short, the belly almost touching the ground, as in
a hippopotamus. Most of these rhinoceroses were hornless,
but ^Teleoceras had a small horn on the very tip of the nose.
In consequence of the lack of horns, the nasal bones were thin
and weak, in marked contrast to the massive, convex nasals
of the modern species, and, for the same reason, the upper
profile of the skull was nearly straight. Except for minor
details, the dentition was in very nearly the modern stage

332 LAND MAMMALS IN THE WESTERN HEMISPHERE

of development; there was a single trenchant upper incisor
on each side, a procumbent lower tusk and between the tusks
a pair of small incisors ; the other incisors and the canines
were already lost. One genus (^Peraceras) had lost all the
upper front teeth. The grinding teeth had the same character
as in the existing species, but were somewhat simpler, owing
to less development of the accessory spurs. In the more pro-
gressive types the teeth were rather high-crowned, though in
none were they actually hypsodont; while the persistent
ancient genera had teeth with much lower crowns.

Aside from the differences in the skull, which are obviously
to be correlated with the absence or very small size of the
horn, the skeleton in these Pliocene genera differed but little
from the type common to the existing rhinoceroses, and in
all the species the feet were three-toed. In short, the denti-
tion and skeleton, except the skull, had already attained to
substantially the modern conditions. While the Old World at
that time had both horned and hornless rhinoceroses in abun-
dance, none of the genera with large and fully developed horns
ever migrated to the western hemisphere. This is the more
remarkable in that the great f Woolly Rhinoceros (Opsiceros
^antiquitatis) of the Pleistocene, which had two very large
horns, inhabited Siberia with the fMammoth (Elephas 1[primi-
genius). The latter extended its range through Alaska and
the northern United States, but the rhinoceros, for some
unknown reason, did not accompany it in its eastward
wanderings.

The rhinoceroses of the upper Miocene did not differ suffi-
ciently from those of the lower Pliocene to call for particular
attention. Needless to say, there were differences between
the species of the two epochs, but in such a sketch as this only
the broader and more obvious changes can be taken into account.
Even in the middle Miocene the only feature which calls for
notice was the first appearance in North America of the Old
World genus fTeleoceras, which became so abundant in the

HISTORY OP THE PERISSODACTYLA 333

upper Miocene and lower Pliocene. The middle Miocene
species (fT. medicornutus) would seem to have been descended
from ]T. aurelianensis of the lower Miocene of France ; the
two species agreed not only in having a small horn on the tip
of the nose, but also in the presence of a still smaller one on
the forehead.

In the lower Miocene but two phyla of rhinoceroses have
been found, both of which were the comparatively little changed
descendants of Oligocene ancestors ; and there was thus a notable
difference from the rhinoceroses of the middle Miocene and sub-
sequent stages, which were decidedly more modern in character.
One of these phyla was constituted by those rhinoceroses
(t Dicer atherium, Fig. 129, p. 239) which had a transversely placed
pair of horns on the nose, not one behind the other, as in all
of the subsequent two-horned species, of which North America
had but the one middle Miocene form (]T. medicornutus)
mentioned above. The lower Miocene species of fDicera-
therium was a very small animal, and smaller than any mem-
ber of the family from later formations. The fdiceratheres
originated in North America, and the stages of their develop-
ment may be clearly made out ; they also migrated to the east-
ern hemisphere and have been found in France, though it is
possible that the genus was not truly monophyletic and arose
independently in both hemispheres.

The second phylum is that of the hornless forms tfCoenopus)
which were so abundantly represented in the Oligocene and
persisted with little change into the Pliocene.

In the upper Oligocene, or John Day, the fdiceratheres
are the only rhinoceroses certainly yet obtained, and of these
there were several species, large and small. The hornless
forms may have been present in Oregon, but this has not been
clearly demonstrated. That they continued to exist some-
where during that stage is hardly open to question, for they
reappeared in the lower Miocene.

From the White River, or lower Oligocene, many well-

334 LAND MAMMALS IN THE WESTERN HEMISPHERE

preserved rhinoceroses, including complete skeletons, have been
gathered in the various collections and display very interesting
differences in the three substages of the White River beds.
In the uppermost substage is found the apparent beginning
of the fdicerathere phylum, though it may be traced back
to the middle substage; the nasal bones had become much
thickened so as to serve as a support for the horns, and these
are indicated by a small, but very rough, area on the outer
side of each nasal. Comparing this White River species with
those of the upper Oligocene and lower Miocene, two dif-
ferences may be observed : in the later species the horn-
supports were well defined bony knobs or prominences, and
these knobs were close to the anterior ends of the nasals ; while
in the White River animal the places for the attachment of
the horns were mere roughened areas, and these were well
behind the tips of the nasals. Tbk is not an in^equent sort
of change, that horns sho* ^»rward

or that the portion of the nas^ nlH

be shortened. Parallel ch°
otheres.

In the middle White Rivr.r c, . miu,.. ..^^ ^rn-

less, but the same two phyla may oe distinguished ; the actual
starting point of the fdiceratheres had no indication of the nasal
horns, but may be identified as such by their close resemblance
in other respects to the species of the upper substage in which
the incipient horns appeared. Much commoner were the mem-
bers of the typical hornless line (see Fig. 135, p. 256), which,
though true and unmistakable rhinoceroses, were yet far re-
moved in many details of structure from the progressive genera
of the middle and upper Miocene. There are several species in
this phylum, which constitute a series of diminishing size al-
most in proportion to their increasing antiquity. The dentition
was already thoroughly and characteristically rhinoceros-like,
but a more primitive feature was the presence of a second
upper incisor, a small tooth placed behind the trenchant one,

HISTORY OF THE PERISSODACTYLA

making the incisor formula \ ; the third incisor and the canines
of both jaws were already lost. The assumption of the molar-

- (t Canopat tridactyltta) ; middle White River

~*»' iH much in degree of complete-

s. molars, while having all
,an of struc-
ture, iiau a „oii lesL Co .ex 'appearance
than in the Recent genera, because of the ab-
sence of the accessory spurs; and all the
grinding teeth were very low-crowned, in
strong contrast to the high-crowned (yet not
properly hypsodont) teeth of the middle Mio-
cene and subsequent genera.

As already mentioned, there was much
variation in size among the species, but
none was as large as those of the Miocene and Pliocene
genera, not to mention the enormous animals of the Pleis-
tocene and Recent epochs in the Old World. The com-
moner species of the middle White River substage (iCceno-
pus occidentalis) was an animal nearly equalling in size the
American Tapir (T. terreslris) and quite like that species in

FlO. 175.— Second up-
per molar, left side,
of t Canopus, show-
ing the masticating

336 LAND MAMMALS IN THE WESTERN HEMISPHERE

its proportions, the limbs being relatively longer and less heavy
and the feet narrower than in the rhinoceroses of the subse-
quent geological epochs. The skull, being hornless, had thin,
pointed and nearly flat nasal bones, an almost straight and
horizontal upper profile, and a short and low, but distinct,
sagittal crest ; the cranial bones were quite thin, there being
no extensive development of sinuses within them. The artic-
ulation of the lower jaw with the skull was only beginning to
take on the characteristic peculiarities seen in the later genera,
and the hinder margin of the lower jaw was not much thickened.
Thus, many of the features which distinguish the skull in all
Recent and Pleistocene and most Pliocene, and upper and mid-
dle Miocene rhinoceroses were entirely lacking in 1[Camopus9
yet no anatomist could doubt that the White River animal
was a genuine rhinoceros.

The neck was short, but not very heavy, the trunk elongate,
but not massive, the ribs not being inordinately long nor
strongly arched, and the hip-bones so little expanded that
they were tapiroid rather than rhinocerotic in appearance.
The limb-bones were relatively much more slender than in any
existing species, and, although every one of them was char-
acteristically that of a rhinoceros, yet the comparative light-
ness of body and sienderness of limb gave to these bones a cer-
tain resemblance to those of tapirs. The feet, which were
moderately elongate and rather narrow, were three-toed, as in
all subsequent North American species and in all existing
members of the family.

The most ancient and primitive representative of the true
rhinoceroses so far discovered occurs in the lowest division of
the White River beds and is of particular interest as throwing
light upon the origin of the family. The genus (fTrigonias)
differed from that tfCamopus) which was so abundant in the
middle White River substage in several highly significant
particulars, though on a merely casual inspection one might
easily be misled into thinking that the two animals were nearly

HISTORY OP THE PERISSODACTYLA 337

identical, for ^Trigonias was an undoubted rhinoceros. Such
an identification, however, would be a great mistake, for the

Fio. 178. — Skull of t Trigoniat otbomi, lower White River. (After Hatcher.)

differences, though not striking, are very important. In the
upper jaw the first or anterior incisor had already assumed the
characteristic trenchant, chisel-like shape, but two other
incisors were present also, thus bringing the number up to
the original three, common to all early perissodactyls ; even
more interesting is the presence of a small upper canine. The
lower jaw likewise had
three incisors on each
side, the first and third
small, the second en-
larged and tusk-like, but
the canine had already
been suppressed, and
thus the dental formula
was: if, c^,p|,mg, X2 =
42, or 14 more than the
formula of the existing

African species. The premolars were smaller and less complex
than the molars.

From this ancient genus may readily be inferred the steps

Fio. 177. — Anterior end of right upper jaw i
t Trigoniat oaborni (after Lucas). c, caaiai
i 3, external incisor, i S, middle incisor, i)

338

LAND MAMMALS IN THE WESTERN HEMISPHERE

by which the peculiar characters of the anterior teeth in the
true rhinoceroses were attained. The first stage was undoubt-
edly an animal in
which, as in all
other Eocene peris-
sodactyls, there
were three well-de-
veloped incisors on
each side of both
jaws, 12 in all, and
moderately promi-
nent canine tusks ;
all these teeth were
erect. The second
stage was the en-
largement of the
first upper and sec-
ond lower incisors,
the latter becoming
less erect and begin-
ning to assume the recumbent position ; at the same time the
other incisors and the canines were reduced in size and were so
little used that they lost their functional importance. The
third stage, in which the first and second lower incisors were
horizontal and pointed directly forward, and the first upper and
second lower teeth were still further enlarged, the non-func-
tional teeth reduced in size and the lower canine suppressed,
was realized in the genus 1[Trigonias. There were thus but
two hypothetical stages between this lo\ver White Region genus
and the tapir-like forms of the middle Eocene, so far, at least,
as the anterior teeth are concerned.

The skeleton of \Trigonias was, on the whole, very much
like that of the succeeding genus, ^Camopus, of the middle
substage of the White River, but with the important exception
that the front foot had four digits instead of three. The

A Ti.

Fig. 178. — Anterior end of left upper jaw of t Ccenopus, A,
adult; B, immature animal (after Osborn). II, first
incisor ; / 2, second incisor ; C, canine.

HISTORY OF THE PERISSODACTYLA

339

pollex, or first of the original five, almost always the first to
disappear, had been suppressed, the third or median digit was
already the largest of the series, both in length and breadth ;
the second and fourth, some-
what shorter together made a
symmetrical pair, while the
fifth, though much the most
slender of all, was still func-
tional and had retained all of
its parts. In the hind foot
the digits had been reduced
to three. This arrangement,
four toes in the manus and
three in the pes, is the same as
is found in the existing tapirs
and in the Eocene perissodac-
tyls generally, with only two or
three known exceptions. In
the Oligocene, on the other FlQ" *' ~
hand, all the genera except the
ftitanotheres, tapirs, f'ophiodonts and famynodonts were tri-
dactyl both before and behind.

With \Trigonias the definitely known history of the true
rhinoceroses breaks off abruptly, and it is possible that that
genus was an immigrant, though it is perhaps more likely that
its ancestors existed in the upper and middle Eocene (Uinta
and Bridger stages) of North America. Some fragmentary
specimens from the Uinta beds, too imperfect for any definitive
identification, are an encouragement to hope that the fore-
runner and direct ancestor of ^Trigonias may yet be dis-
covered in that formation. It is also quite possible that one of
the larger species of the genus \Hyrachyus, so abundant in the
Bridger and going back to the Wind River, may take its
place in the same series.

340 LAND MAMMALS IN THE WESTERN HEMISPHERE

6. ^Hyracodontidoe. \Cwr8orial and ^Aquatic Rhinoceroses

The luxuriant diversification of the rhinoceros-stem was
not exhausted by the many phyla of what we have called the
true rhinoceroses. Two other series, very distinctly marked
and rather distantly connected with the first, are yet to be
considered. These two series, the fhyracodonts (in the narrow
sense) and the f&niynodonts, ran courses which, in certain
respects, were singularly alike ; both were of North American
origin and one, the fhyracodonts, was entirely confined to
that continent, while the other sent out late migrants, which
entered Europe, no doubt through Asia, and both ended their
careers before the close of the White River time. Their history
was thus a brief one when compared with that of the true
rhinoceroses, three phyla of which persist to the present day,
though their geographical range is greatly restricted in com-
parison with what it was in the Miocene and Pliocene, when
they ranged over every continent except Australia and South
America.

Just how to classify these three series of rhinoceroses and
rhinoceros-like animals, so as most accurately to express their
mutual relationships, is a question that has received several
answers. One method suggested is to include them all in a
single family and to make a subfamily for each of the three
well-distinguished series; this is the arrangement which
personally I should prefer. A second plan is to accord family
rank to each of the three groups; while the most elaborate
scheme, that of Professor Osborn, is as follows : for the rhi-
noceroses, in the broader sense, he makes two families, the
Rhinocerotidae and the fHyracodontidae, and divides the former
into four subfamilies, which include all of the true rhinoceroses,
living and extinct, of the Old and New Worlds, and the latter
into two subfamilies, the fHyracodontinae and fAmynodontinae.
It is not a matter of very great moment as to which of these
three schemes is followed, and I shall therefore adopt the one

HISTORY OF THE PERISSODACTYLA

341

proposed by Professor Osbom, in order to avoid, so far as
possible, the confusing effect of different methods of classi-
fication.

As before mentioned, the subfamily of the fhyracodonts
(fHyracodontiiue) became extinct in White River times, during

most of which it was represented by the single genus jHyra-
codtm, whence are derived the names for the family and sub-
family. The series was purely North American, and no mem-
ber of it has ever been found in any other continent. The
species of \Hyracodon were altogether different in appearance
and proportions from the true rhinoceroses, being lightly
built, slender, cursorial creatures, suggestive rather of horses
than of rhinoceroses, to which they bore much the same rela-
tion as the slender-limbed, narrow-footed flophiodonts did to
the tapirs (see p. 326) ; in size, they were somewhat taller and
considerably heavier than a sheep.

The low-crowned grinding teeth had the unmistakable
rhinoceros-pattern, and between them and the teeth of the

342 LAND MAMMALS IN THE WESTERN HEMISPHERE

contemporary fCcenopus the difference was merely one of
size, except for one small, but not insignificant feature. The
last upper molar had not perfectly acquired the triangular
form characteristic of all the true rhinoceroses, caused by the
complete fusion of the outer wall with the posterior crest, but
the wall projected a little behind the crest, as in perissodactyls
generally. Premolars (except the first) and molars were alike
in structure and of nearly the same size. While the grinding
teeth were thus hardly to be distinguished from those of the
true rhinoceroses, the anterior teeth, incisors and canines,
were totally different ; they were very small and had simple,
pointed and slightly recurved crowns, and were all very much
alike in size and form. Thus, there were in the front of the
mouth eight small, hook-like teeth, above and below, which
were obviously quite useless as weapons; and as the skull
had no horn, the animal was defenceless, and must have de-
pended entirely upon speed for its safety from the attacks of
the larger and more powerful beasts of prey.

The skull was short, deep and thick, and the head must
have been heavy and clumsy, quite out of keeping with the
body and limbs. The neck was surprisingly long, longer in-
deed proportionately than in the contemporary genus of horses
{]Mesohippus), but the neck- vertebrae were relatively stout
and strong, as was required for the muscles to move and control
the heavy head. The body was rather elongate, but not deep
or massive, and the limbs were proportionately much longer
than in any of the known rhinoceroses. The limb-bones, one
and all, despite their length and slenderness, bore an unques-
tionable likeness to those of the true rhinoceroses. In this
elongation of the limbs the fore-arm and thigh were the parts
most affected, and the slenderness, though in notable contrast
to the proportions both of the true rhinoceroses and the famyno-
donts, was yet much less marked than in the middle Eocene
representatives of the fhyracodonts themselves. The feet
were long and narrow, approximating, though not actually

HISTORY OF THE PERIS SOD ACTY LA

343

attaining the proportions of the feet in the White River horses
(^Mesohippus). There were three digits in each foot, and the
median toe (third of the original five) was so much enlarged
and the lateral toes (second and fourth) so reduced, though
still functional, as strongly to suggest a monodactyl foot as the
outcome of this course of development, had not the early
extinction of the subfamily put an end to it. It is interesting
to reflect that, had the t'ophiodonts and fhyracodonts con-
tinued their existence to the present time and had persisted in
advancing along their particular lines of specialization, we
should, in all probability, have had monodactyl tapirs and
rhinoceroses, as well as horses.

As in the case of so many other mammalian series, the
fhyracodonts of the but partially explored Uinta formation
are still very imper-
fectly known. Al-
most all that can be
positively stated
about them is that
they were smaller
than their White
River successors and
that the assumption
of the molar-pattern
by the premolars was
incomplete. In the
upper Bridger beds
also not very much
is known regarding
the then representa-
tives of the series,
( f Triplopus) . So
much is clear, how-
ever, that they were still smaller and lighter animals, that
the limbs were very light, and that the number of digits in

1 Triplop*

, uppi-r BriiJgiT.

?A4

L.KSO MAMMALS IX THE WESTEBX HEMISPHERE

iht; Vit-. foot had already been reduced lo three, the only known
Bri'lger peri-rola/nyl of which this is true, all the other? having
four dija'.- in ihe man us and three in the pes.

In th* middle arid lower Bridger. and even in the Wind River,
wzw. a genu* iH'jTorKyu*' which contained a large number
of *peHe«, rarifdrig in size from a full-grown modern tapir to
creature* no larger than foxes. It is among these smaller
»r*ecies that the most ancient member of the thyracodont
fine it to he sought, though it is not yet practicable to select
any particular one. tHyrachjut. indeed, may very possibly
have contained among its many species the ancestors of all
three lines of the rhinoceroses and rhinoceros-like animals,
and thus formed the starting point from which they developed

in diverging series. It is always a very significant fact when
two or more groups approach one another the more closely,
the farther back in time they are traced, because that can only
be interpreted to mean that ultimately they converged into

HISTORY OP THE PERISSODACTYLA 345

a common term, even though that common ancestor should
elude discovery.

\Hyrachyus may be described as a generalized, relatively
undifferentiated perissodactyl, from which almost any other
family of the order, except the horses and the ftitanotheres,
might have been derived. The incisors, present in undi-
minished number, were well developed and functional, but not
large, and the canines were moderately enlarged, forming
small tusks. The premolars were all smaller and less complex
than the molars, which had a strong resemblance to those
of the tapirs ; in the lower jaw they were identical with the
latter, but in the upper jaw there was more than a suggestion
of likeness to the rhinoceroses. The skull was long, narrow

Fig. 183. —Skull of t Hyrachyxts. (After Oabom.)

and low, hornless, and with thin, slender nasals and straight,
horizontal upper contour. The neck was short, the body
very long and the limbs of medium length and weight ; though
relatively stouter than in \Triphpus of the upper Bridger and
Uinta beds, they cannot be called heavy. The feet were not
especially elongate and rather slender ; the manus had four
toes and the pes three.

A brief and short-lived branch of this stock existed in the

346 LAND MAMMALS IN THE WESTERN HEMISPHERE

Bridger stage, but was not, so far as is known, represented
in any of the subsequent stages, and was made up of a single
genus i^Cohnoceras) which had a small pair of dermal horns
upon the nasal bones. In other respects, it was like }Hyra-
chyus. It is surprising to find that the horned series should
have so speedily died out, while the defenceless forms not only
persisted, but actually became more defenceless through the
reduction of the canine tusks. A priori, one would have ex-
pected the opposite result, but the key to the enigma is
probably to be found in the more perfect adaptation of the
surviving kinds to swift running.

The second subdivision (fAmynodontinae) of this family
contains a series of animals which developed in a very divergent
fashion and went to quite the opposite extreme from the
cursorial fhyracodonts, resembling the latter (aside from the
fundamental characteristics common to all rhinoceroses, in
the broadest sense of that term) only in the pattern of the molar
teeth and in the absence of horns. The terminal member of
the famynodont series was a White River genus tfMetamyno-
dori) of which the remains have been found almost exclusively
in the consolidated and cemented sands filling the old river-
channels of the middle substage of the White River beds.
This fact, together with certain structural features of the skull
and skeleton, leads at once to the suggestion that these ani-
mals were chiefly aquatic in their habits and somewhat like
hippopotamuses in mode of life. ^Meiamynodon was quite
a large animal, the heaviest and most massive creature of its
time, after the disappearance of the giant ftitanotheres, but
was low and short-legged.

The true rhinoceroses, save those which, like the existing
African species, have lost all the front teeth, all agree in the
peculiar differentiation of the incisors, which was fully de-
scribed in the preceding section of this chapter. The fhyra-
codonts had a second scheme, the incisors and canines being
all similar in shape, small, pointed and recurved, while still

HISTORY OF THE PERISSODACTYLA

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348 LAND MAMMALS IN THE WESTERN HEMISPHERE

a third mode of development was exemplified by the famyno-
donts, in which the canines became large and formidable tusks,
a very notable difference from all other rhinoceroses whatever.

In ^Metamynodon the incisors were not enlarged, but were
unreduced and functional; the upper canine was a short,
heavy tusk, obliquely truncated by the abrasion of the lower
tusk, which was very large. Another striking difference from
all the other groups of rhinoceroses was the reduction of the
premolar teeth, which, instead of equalling the molars in size,
were much smaller and were diminished to three in the upper,
two in the lower jaw. The molars were of the characteristic
rhinoceros-pattern, but were very narrow, especially the inferior
ones, in which the enamel did not surround the whole crown, as
it normally does, but was lacking along vertical bands, where
the dentine formed the surface. The skull was extremely pecul-
iar and, with its very long and high sagittal crest and immensely
expanded and heavy zygomatic arches, had a surprising like-
ness to the skull of some great beast of prey. The face was
very much shortened and the skull depressed, so that the
head was remarkably low, broad and flat, proportions which
did not recur in any other group of rhinoceroses. The neck
was short, the body very long and very massive, as is shown
by the long and strongly arched ribs. The limbs were short
and stout and the feet quite primitive in character, the front
foot retaining four fully developed and functional digits.
No other perissodactyls of the middle White River beds,
except the flophiodonts and tapirs, had more than three digits
in the manus, and thus ^Meiamyodon was a belated exception
to the general rule.

The Uinta member of this series was 1[A mynodon, a similar
but smaller and lighter animal. The canine tusks were of
more moderate size and none of the premolars had been lost,
but were considerably smaller than the molars, and the last
two had assumed the molar-pattern. The face was not conspic-
uously shortened and the zygomatic arches of the skull were

HISTORY OF THE FERISSODACTYLA 349

not so heavy or so widely expanded as in the White River
genus, and the skeleton was less massive.

The genus \Amynodon is also represented in the upper
Bridger beds, but by a species different from that of the Uinta
stage. This more ancient species was a smaller animal than
its upper Eocene successor and had less enlarged canine tusks,
but it already possessed the typical rhinoceros molar teeth, the
only Bridger mammal of which this is true. Beyond this
species the line, as at present understood, cannot be traced,
though probably some species of ^Hyrachyus, or an allied
genus, will prove to be the ancestor sought ; but the connecting
link has not yet been brought to light.

The history of the rhinoceroses and rhinoceros-like animals,
of which a very much simplified sketch has just been given,
is a highly complex one, much more so than that of the horses,
ftitanotheres, or tapirs, and is less fully recorded, the earlier
chapters of the story being still missing. However, in the
progress of discovery these chapters will almost certainly
be recovered, and it is already possible to draw close inferences
as to what they will reveal. The complexity of the history
is chiefly due to the fact that, as compared with the other
perissodactyl groups, the rhinoceros stem ramified more widely
and gave rise to more divergent and diversified forms. At one
extreme, we find huge, massive, slow-moving types ; and, at
the other, light, slender, cursorial creatures, almost horse-like
in appearance, with intermediate forms of moderate size.
Some were long and others short legged, mostly adapted to
terrestrial life, but some with aquatic habits. The three very
different sorts of modification which the anterior teeth (incisors
and canines) underwent in the three principal series may be
taken as an illustration of this divergent development, and
to these may be added a fourth, the complete suppression of
all the incisors and canines above and below, as is exemplified
by the modern African species.

Of the three rhinoceros groups, whatever rank be assigned

350 LAND MAMMALS IN THE WESTERN HEMISPHERE

them, family or subfamily, much the most prolific in diver-
gent forms was that of the true rhinoceroses (Rhinocerotidae)
of which seven or more phyla have been distinguished, three
of them surviving to the present time. Only in this series
were horns frequently present, the brief experiment, as it
might be called, of the Bridger genus ]Colonoceras} being the
only known instances of horns among the fhyracodonts, and
the famynodonts were all hornless. In making the comparison
as to degree of ramification among the three series, it should
be borne in mind that the true rhinoceroses were the only
long-lived group, the other two dying out before or at the end
of the White River stage. Within the series or family of the
true rhinoceroses, there was no great divergence of type, and
all the members were much alike, heavy and slow animals,
but with very great variety in the details of structure. Take,
for instance, the matter of horns ; we find both hornless and
horned genera, the former preceding the latter in time, but,
so far as North America is concerned, continuing in associa-
tion with them till the end. Among the horned genera, the
horn may be single, double in a transverse pair (}Dicera-
therium) or arranged one behind the other in the median line
of the head {Dicer orhinus, Opsiceros, etc.). The single horn
may be on the nose or the forehead ; if on the nose, it may be
on the upper side of the nasal bones (Rhinoceros) or on
the extreme tip and pointing obliquely forward (^Teleoceras).
The single frontal horn was much less common, but in the ex-
traordinary ^[Elasmotherium, of the European and Siberian
Pleistocene, the horn was of gigantic size and the surface for
its attachment an enormous, dome-like boss on the forehead.

All three of the series had their most ancient known repre-
sentatives in North America, and it seems probable, though
by no means certain, that they all originated here by diver-
gence from a common stock, which was represented more or
less closely by the genus ^Hyrachyus of the Bridger and Wind
River stages of the Eocene. However that may be, true rhinoc-

HISTORY OF THE PERISSODACTYLA 351

eroses flourished exceedingly in the Old World from the
upper Oligocene to the Pleistocene, the events of the latter
epoch restricting them to their present range. The signifi-
cance of the American genera for the ancestry of the modern
types can be found only in the most ancient forms, flYi-
gonias and ^Ccenopus ; the subsequent development which led
up to the existing species of Asia and Africa went on entirely
in the eastern hemisphere. The fhyracodont subfamily
had no known representatives outside of North America,
but the faray^odonts sent out emigrants, which appeared
for a brief time in the Oligocene of Europe.

In the varied history of the rhinoceroses, the principles
of evolutionary change which may be deduced from the recorded
development of the horses, tapirs and ftit&notheres are found
to be applicable.

(1) There was the same gradual increase in size from the
earlier to the later geological stages. Not that all the phyla
kept equal pace in this respect, and even within the same
phylum it was the rule rather than the exception to find
larger and smaller contemporary species.

(2) In all of the early forms, up to the middle Miocene,
the teeth were low-crowned ; after that time there was a
decided increase in the height of the teeth, though only in
^Elasmotherium was the fully hypsodont, cement-covered
crown attained. In the existing African Broad-Lipped Rhi-
noceros (Opsiceros simus), which is a grazing animal, the high,
cement-covered teeth may also fairly be called hypsodont.

(3) In all of the lines, as in the other perissodactyl families,
the premolars gradually took on the pattern of the molars;
only in the f&mynodonts were the premolars notably reduced
in number and size.

(4) The three different modes of development of the anterior
teeth, exemplified by the true rhinoceroses, the fhyracodonts
and famynodonts respectively, need not be recapitulated
here. It is sufficient to call attention to the fact that the three

344

LAND MAMMALS IN THE WESTERN HEMISPHERE

the fore foot had already been reduced to three, the only known
Bridger perissodactyl of which this is true, all the others having
four digits in the manus and three in the pes.

In the middle and lower Bridger, and even in the Wind River,
occurs a genus (^Hyrackyus) which contained a large number
of species, ranging in size from a full-grown modern tapir to
creatures no larger than foxes. It is among these smaller
species that the most ancient member of the fhyracodont
line is to be sought, though it is not yet practicable to select
any particular one. ^Hyrachyw, indeed, may very possibly
have contained among its many species the ancestors of all
three lines of the rhinoceroses and rhinoceros-like animals,
and thus formed the starting point from which they developed

in diverging series. It is always a very significant fact when
two or more groups approach one another the more closely,
the farther back in time they are traced, because that can only
be interpreted to mean that ultimately they converged into

HISTOBY OF THE PERIBSODACTYLA 345

a common term, even though that common ancestor should
elude discovery.

\Hyrachyus may be described as a generalized, relatively
undifferentiated perissodactyl, from which almost any other
family of the order, except the horses and the ftitanotheres,
might have been derived. The incisors, present in undi-
minished number, were well developed and functional, but not
large, and the canines were moderately enlarged, forming
small tusks. The premolars were all smaller and less complex
than the molars, which had a strong resemblance to those
of the tapirs ; in the lower jaw they were identical with the
latter, but in the upper jaw there was more than a suggestion
of likeness to the rhinoceroses. The skull was long, narrow

— Skldl of t Hyrachyua.

and low, hornless, and with thin, slender nasals and straight,
horizontal upper contour. The neck was short, the body
very long and the limbs of medium length and weight ; though
relatively stouter than in ^Triplopus of the upper Bridger and
Uinta beds, they cannot be called heavy. The feet were not
especially elongate and rather slender ; the manus had four
toes and the pes three.

A brief and short-lived branch of this stock existed in the

346 LAND MAMMALS IN THE WESTERN HEMISPHERE

Bridger stage, but was not, so far as is known, represented
in any of the subsequent stages, and was made up of a single
genus (^Colonoceras) which had a small pair of dermal horns
upon the nasal bones. In other respects, it was like \Hyra-
chyus. It is surprising to find that the horned series should
have so speedily died out, while the defenceless forms not only
persisted, but actually became more defenceless through the
reduction of the canine tusks. A priori, one would have ex-
pected the opposite result, but the key to the enigma is
probably to be found in the more perfect adaptation of the
surviving kinds to swift running.

The second subdivision (tAmynodontinae) of this family
contains a series of animals which developed in a very divergent
fashion and went to quite the opposite extreme from the
cursorial fhyracodonts, resembling the latter (aside from the
fundamental characteristics common to all rhinoceroses, in
the broadest sense of that term) only in the pattern of the molar
teeth and in the absence of horns. The terminal member of
the famynodont series was a White River genus {^Metamyno-
don) of which the remains have been found almost exclusively
in the consolidated and cemented sands filling the old river-
channels of the middle substage of the White River beds.
This fact, together with certain structural features of the skull
and skeleton, leads at once to the suggestion that these ani-
mals were chiefly aquatic in their habits and somewhat like
hippopotamuses in mode of life. ^Metamynodon was quite
a large animal, the heaviest and most massive creature of its
time, after the disappearance of the giant ttitanotheres, but
was low and short-legged.

The true rhinoceroses, save those which, like the existing
African species, have lost all the front teeth, all agree in the
peculiar differentiation of the incisors, which was fully de-
scribed in the preceding section of this chapter. The fhyra-
codonts had a second scheme, the incisors and canines being
all similar in shape, small, pointed and recurved, while still

HISTORY OF THE PERIBSODACTYLA

348 LAND MAMMALS IN THE WESTERN HEMISPHERE

a third mode of development was exemplified by the tamyno-
donts, in which the canines became large and formidable tusks,
a very notable difference from all other rhinoceroses whatever.

In ^Metamynodon the incisors were not enlarged, but were
unreduced and functional; the upper canine was a short,
heavy tusk, obliquely truncated by the abrasion of the lower
tusk, which was very large. Another striking difference from
all the other groups of rhinoceroses was the reduction of the
premolar teeth, which, instead of equalling the molars in size,
were much smaller and were diminished to three in the upper,
two in the lower jaw. The molars were of the characteristic
rhinoceros-pattern, but were very narrow, especially the inferior
ones, in which the enamel did not surround the whole crown, as
it normally does, but was lacking along vertical bands, where
the dentine formed the surface. The skull was extremely pecul-
iar and, with its very long and high sagittal crest and immensely
expanded and heavy zygomatic arches, had a surprising like-
ness to the skull of some great beast of prey. The face was
very much shortened and the skull depressed, so that the
head was remarkably low, broad and flat, proportions which
did not recur in any other group of rhinoceroses. The neck
was short, the body very long and very massive, as is shown
by the long and strongly arched ribs. The limbs were short
and stout and the feet quite primitive in character, the front
foot retaining four fully developed and functional digits.
No other perissodactyls of the middle White River beds,
except the flophiodonts and tapirs, had more than three digits
in the manus, and thus ^Metamyodon was a belated exception
to the general rule.

The Uinta member of this series was fi4 mynodon, a similar
but smaller and lighter animal. The canine tusks were of
more moderate size and none of the premolars had been lost,
but were considerably smaller than the molars, and the last
two had assumed the molar-pattern. The face was not conspic-
uously shortened and the zygomatic arches of the skull were

HISTORY OF THE PERISSODACTYLA 349

not so heavy or so widely expanded as in the White River
genus, and the skeleton was less massive.

The genus \Amynodxm is also represented in the upper
Bridger beds, but by a species different from that of the Uinta
stage. This more ancient species was a smaller animal than
its upper Eocene successor and had less enlarged canine tusks,
but it already possessed the typical rhinoceros molar teeth, the
only Bridger mammal of which this is true. Beyond this
species the line, as at present understood, cannot be traced,
though probably some species of ^Hyrachyus, or an allied
genus, will prove to be the ancestor sought ; but the connecting
link has not yet been brought to light.

The history of the rhinoceroses and rhinoceros-like animals,
of which a very much simplified sketch has just been given,
is a highly complex one, much more so than that of the horses,
ftitanotheres, or tapirs, and is less fully recorded, the earlier
chapters of the story being still missing. However, in the
progress of discovery these chapters will almost certainly
be recovered, and it is already possible to draw close inferences
as to what they will reveal. The complexity of the history
is chiefly due to the fact that, as compared with the other
perissodactyl groups, the rhinoceros stem ramified more widely
and gave rise to more divergent and diversified forms. At one
extreme, we find huge, massive, slow-moving types ; and, at
the other, light, slender, cursorial creatures, almost horse-like
in appearance, with intermediate forms of moderate size.
Some were long and others short legged, mostly adapted to
terrestrial life, but some with aquatic habits. The three very
different sorts of modification which the anterior teeth (incisors
and canines) underwent in the three principal series may be
taken as an illustration of this divergent development, and
to these may be added a fourth, the complete suppression of
all the incisors and canines above and below, as is exemplified
by the modern African species.

Of the three rhinoceros groups, whatever rank be assigned

350 LAND MAMMALS IN THE WESTERN HEMISPHERE

them, family or subfamily, much the most prolific in diver-
gent forms was that of the true rhinoceroses (Rhinocerotidae)
of which seven or more phyla have been distinguished, three
of them surviving to the present time. Only in this series
were horns frequently present, the brief experiment, as it
might be called, of the Bridger genus }Colonoceras> being the
only known instances of horns among the fhyracodonts, and
the famynodonts were all hornless. In making the comparison
as to degree of ramification among the three series, it should
be borne in mind that the true rhinoceroses were the only
long-lived group, the other two dying out before or at the end
of the White River stage. Within the series or family of the
true rhinoceroses, there was no great divergence of type, and
all the members were much alike, heavy and slow animals,
but with very great variety in the details of structure. Take,
for instance, the matter of horns ; we find both hornless and
horned genera, the former preceding the latter in time, but,
so far as North America is concerned, continuing in associa-
tion with them till the end. Among the horned genera, the
horn may be single, double in a transverse pair (fZH'cera-
therium) or arranged one behind the other in the median line
of the head (Dicer or hinus, Opsiceros, etc.). The single horn
may be on the nose or the forehead ; if on the nose, it may be
on the upper side of the nasal bones (Rhinoceros) or on
the extreme tip and pointing obliquely forward (IfTeleoceras).
The single frontal horn was much less common, but in the ex-
traordinary ^[Elasmotherium, of the European and Siberian
Pleistocene, the horn was of gigantic size and the surface for
its attachment an enormous, dome-like boss on the forehead.

All three of the series had their most ancient known repre-
sentatives in North America, and it seems probable, though
by no means certain, that they all originated here by diver-
gence from a common stock, which was represented more or
less closely by the genus IfHyrachyus of the Bridger and Wind
River stages of the Eocene. However that may be, true rhinoc-

HISTORY OF THE PERISSODACTYLA 351

eroses flourished exceedingly in the Old World from the
upper Oligocene to the Pleistocene, the events of the latter
epoch restricting them to their present range. The signifi-
cance of the American genera for the ancestry of the modern
types can be found only in the most ancient forms, fTri-
gonias and ^Caenopus; the subsequent development which led
up to the existing species of Asia and Africa went on entirely
in the eastern hemisphere. The fhyracodont subfamily
had no known representatives outside of North America,
but the t&mynodonts sent out emigrants, which appeared
for a brief time in the Oligocene of Europe.

In the varied history of the rhinoceroses, the principles
of evolutionary change which may be deduced from the recorded
development of the horses, tapirs and ftitanotheres are found
to be applicable.

(1) There was the same gradual increase in size from the
earlier to the later geological stages. Not that all the phyla
kept equal pace in this respect, and even within the same
phylum it was the rule rather than the exception to find
larger and smaller contemporary species.

(2) In all of the early forms, up to the middle Miocene,
the teeth were low-crowned; after that time there was a
decided increase in the height of the teeth, though only in
^Elasmotherium was the fully hypsodont, cement-covered
crown attained. In the existing African Broad-Lipped Rhi-
noceros (Opsiceros simus), which is a grazing animal, the high,
cement-covered teeth may also fairly be called hypsodont.

(3) In all of the lines, as in the other perissodactyl families,
the premolars gradually took on the pattern of the molars;
only in the t&mynodonts were the premolars notably reduced
in number and size.

(4) The three different modes of development of the anterior
teeth, exemplified by the true rhinoceroses, the fhyracodonts
and f&mynodonts respectively, need not be recapitulated
here. It is sufficient to call attention to the fact that the three

352 LAND MAMMALS IN THE WESTERN HEMISPHERE

kinds of modification diverged from a common starting-point
such as may be seen in the middle Eocene perissodactyls
generally, and that in each series the transformation was
gradual.

(5) The modification of the skull followed several different
courses, as designated by the major and minor subdivisions
of families, subfamilies and phyla. The development of horns,
whether single or double, in transverse or longitudinal pairs,
was the most important single influence in transforming the
skull, as determined by the mechanical adjustment necessary
to make these weapons effective, but even in the hornless
forms changes went on, and in all the phyla the skull departed
more and more widely from the primitive Eocene type in
each succeeding geological stage. The most aberrant form
of skull was that of the hornless and presumably aquatic
^Metamynodon, in which the greatly shortened face, high
sagittal crest and extremely wide zygomatic arches were alto-
gether exceptional.

(6) When the history of any horned phylum is at all com-
plete, the development of the horns may be followed step by
step from the marks which they left upon the skull. As a rule,
the story was one of gradual enlargement, but, in one case at
least, an incipient horn apparently failed to enlarge and was
eventually lost.

(7) In the light, slender and cursorial fhyracodonts the
mode of development resembled that of the horses, as appears
in the elongation of the neck, limbs and feet, in the enlarge-
ment of the median toe and concomitant reduction of the
lateral digits. Also, as in the horses, the elongation of the
limbs began to be noteworthy while the body-weight was small
and was consequently accompanied by great slenderness; as
the body-weight increased, the limbs became stouter, to yield
the necessary support.

(8) In the phyla composed of massive animals the principle
of change agreed with that exemplified by the ftit&notheres,

HISTORY OF THE PERISSODACTYLA 353

increasing body-weight being the determining factor in both
cases. When this increase began to be decided, the reduction
of digits ceased at the point which had already been reached
in any particular series, three in both manus and pes in the
true rhinoceroses, four in the manus and three in the pes
in the f&mynodonts. Very heavy animals require broad,
columnar feet to support them, and hence the similarity of
appearance in such widely separated groups as elephants,
rhinoceroses and hippopotamuses, not to mention several
extinct orders and families. Among the larger and heavier
rhinoceroses, as in those of the present time, there was great
variety in the proportionate lengths of the limbs, body and
feet.

In brief, the great complexity of the history of the rhinoc-
eroses is due to the many divergent and parallel phyla into
which these animals may be grouped. Broadly speaking,
they may be subdivided into the slender, cursorial types and
the heavy, slow-moving types, the former developing in a man-
ner similar to that shown by the horses, while the latter were
modified after the fashion of the ftitanotheres. Obviously
the load to be supported by the legs and feet was a very impor-
tant factor in determining the character of evolutionary
change.

II. fANCYLOPODA. tCLAWED PERISSODACTYLS

The very extraordinary and aberrant animals which are
referable to this suborder have been understood only since
the year 1888, for, as was shown in an earlier chapter (p. 41)
their scattered parts had been assigned to two different mam-
malian orders, the skull to the perissodactyls and the feet to
the pangolins, or scaly anteaters (Pholidota) of the Old World,
since it occurred to no one that the same animal could have
such a skull and teeth in combination with such feet.

The history of the Ancylopoda is still very incomplete,
only four genera, of the lower Pliocene, middle and lower

2a

354 LAND MAMMALS IN THE WESTERN HEMISPHERE

Miocene, and the middle Eocene respectively, being at all
adequately known, but even in this imperfect form the story
is worth telling. The suborder was probably of American
origin and its most ancient known member existed in the middle
Eocene. Both in 'Europe and North America the group per-
sisted into the lower Pliocene and it is believed, though not
clearly demonstrated, that in eastern Asia it continued even
into the Pleistocene. All the genera of the suborder may be
included in a single family.

7. fChcdicotheriidce. ^Chalicoiheres

The specimens which so far have been found in the Ameri-
can middle and upper Miocene and lower Pliocene are very
fragmentary, consisting of little more than teeth, and give
no information other than to demonstrate the presence of the
family in North America during that period of time. On the
other hand, the European genera of the middle Miocene and
lower Pliocene are well known and may or may not have
been closely similar to their American contemporaries, though
they were undoubtedly larger. In these most peculiar and gro-
tesque animals (^Macrotherium and ^Chalicotherium) the head
was relatively small, the teeth were very low-crowned and
adapted only to a diet of soft vegetable substances and the
mode of feeding must have been that of browsing upon leaves
and shoots of trees and bushes ; the premolars had not acquired
the molar-pattern, which was very exceptional for perisso-
dactyls of so late a time, such a difference between the two
classes of teeth being characteristic of the Eocene members
of the order ; the incisors and canines were reduced, but the
formula is not definitely known.

The neck was of moderate length, the body very long, and
the limbs were also elongate, especially the anterior pair, in
consequence of which the back sloped downward from the
shoulders to the rump; the two fore-arm bones were fused

HISTORY OF THE PERISSODACTYLA 355

together, and these, with the thigh-bones, were the longest
segments of the limbs. The special peculiarity of these ani-
mals was in the character of the feet, which had three toes,
each armed with a huge claw, instead of terminating in a hoof,
as it does in all normal perissodactyls. The external digit,
which, in the absence of the fifth, was the fourth, was the largest
of the series and apparently bore the most of the weight, a
notable departure from the normal perissodactyl symmetry,
in which the third or median toe is the largest. The hind
feet were considerably smaller than the fore, but had similar
claws.

Many suggestions have been offered as to the manner in
which these great claws were employed. The teeth demon-
strate that these animals could not have had predaceous habits,
but must have been inoffensive plant-feeders. As no such
herbivorous creatures are living now, it is impossible to reach
a definitive solution of the problem, which is further compli-
cated by the fact that in two other orders of hoofed mammals,
Artiodactyla and fToxodontia, a more or less similar trans-
formation of hoofs into claws took place, and among the eden-
tates the large, herbivorous fground-sloths (fGravigrada) had
enormous claws. It is inadmissible to suppose that these
great fchalicotheres could have been burrowers, or tree-
climbers, or that they pursued and slaughtered prey of any
kind, for, aside from the character of the teeth, such heavy and
slow-moving beasts would have been utterly inefficient at
work of that sort. No doubt, the claws were used, to some
extent, as weapons of defence, as the existing South American
Ant-Bear (Myrmecophaga jubata) uses his formidable claws ;
probably also some, if not all, of these clawed ungulates would
employ the fore feet in digging for roots and tubers, as is done
by the bears generally. Many years ago, the late Sir Richard
Owen suggested with reference to the fground-sloths that the
principal use of the fore feet, other than that of locomotion,
was to draw down within reach of the long tongue and pre-

356

LAND MAMMALS IN THE WESTERN HEMISPHERE

hensile upper lip the branches upon which they browsed.
This explanation may perhaps be applicable to all of these
aberrant and exceptional groups of hoofed animals.

In the lower Miocene (Arikaree stage) of North America
well-nigh complete skeletons of a large fchalicothere (fJVforo-
pus, Fig. 130, p. 240) have been obtained, an animal which
considerably exceeded a large horse in bulk and stature. In
structure this genus had departed less widely from the normal
perissodactyl type than the genera of the European Miocene
and Pliocene above described and was in many respects more
primitive. It could not, however, have been directly ancestral
to the European forms, though indicating in a general sort of
way what the ancestral
type must have been.
\M oropus had a relatively
small, slender and pointed
head, a long neck, much
longer than in the Euro-
pean genera, and long fore
legs ; the shorter hind legs
...y gave the back a steep in-
clination from the shoul-
ders to the rump. The pro-
portions of the head, neck
and limbs suggest those of
a giraffe, in less exaggerated
form, but the likeness is
more marked in the skele-
ton than in the restoration
and is at best a distant one.
The feet were armed with
the great claws characteristic of the suborder, but the fore foot,
in addition to the three functional toes, had a long splint,
representing the rudimentary fifth digit ; of the first, or pollex,
no trace remained. The perissodactyl plan of symmetry had

(After Peterson.)

HISTORY OF THE PEMSSODACTYLA 357

«

not yet been lost, the third or median digit being the longest
of the series. In the hind foot, which had only three toes, the
departure from the perissodactyl arrangement had already
begun, and the third and fourth digits (i.e. of the original five)
were of nearly equal size, both in length and thickness, while
the second was smaller.

The family is represented in the John Day, or upper Oligo-
cene, by specimens which are sufficiently characteristic to
prove that they are properly referable to this group. They
have been assigned to the same genus as that of the lower
Miocene, but whether the identification is justified remains
to be determined.

In the lower White River beds of Canada is found a much
smaller animal of this family, but the material is too fragmen-
tary for generic identification. Something more is known of
a genus tfSchizotherium) from the European Oligocene, like-
wise much smaller than the Miocene and Pliocene forms,
which had four, or possibly even five, functional digits, in the
manus, but it has not been ascertained whether the trans-
formation of hoofs into claws had already taken place.

It is not yet practicable to determine the relationships of
the European and American fchalicotheres to one another,
because of the imperfect nature of most of the material.

The molar teeth of the fchalicotheres were suggestively
like those of the ftitanotheres, and, were the teeth alone to be
taken into account, no one could hesitate to regard the two
families as closely related.

The most ancient known member of the family is the genus
^Eomoropus, from the Bridger Eocene, which will be described
by Professor Osborn in a paper soon to appear. ^Eomoropus
was much nearer to the normal perissodactyls than were the
genera from the Oligocene and Miocene above described.

CHAPTER IX

HISTORY OF THE ARTIODACTYLA

The artiodactyls are and for a very long time have been
a very much larger and more variegated group than the peris-
sodactyls, and the Old World has been and still is their head-
quarters and area of special development, where they are
represented in far greater number and variety than in the
New ; the perissodactyls, on the other hand, flourished espe-
cially in North America, as was shown in the preceding chapter.
At the present time the artiodactyls are the dominant ungulate
order, far outnumbering all the others combined, and include
an assemblage of varied types, which, when superficially
examined, appear to be an arbitrary and unnatural group.
What could seem more unlike than a dainty little mouse-deer,
no larger than a hare, a stag, a camel, a giraffe, a bison and
a hippopotamus? Yet, in spite of this wonderful diversity
of size, proportions, appearance and habits, there is a genuine
unity of structure throughout the order, which makes their
association in a single group altogether natural and proper,
especially as these structural characters are not found united
in any other group.

It would be superfluous to enumerate all of the diagnostic
characters which, on the one hand, unite all the living and
extinct artiodactyls and, on the other, distinguish them from
all other hoofed animals, and it will suffice to mention a few
of the more significant of these features.

As the name implies, the artiodactyls typically have an
even number of toes in each foot, four or two; though this
rule may be departed from and we find members of the order

358

HISTORY OP THE ARTIODACTYLA

359

with five digits or three, just as the tapirs

and nearly all the Eocene genera of perisso-

dactyls had four toes in the manus. Much

more important is the fact that the plane of

symmetry, which in the perissodactyls bisects

the third digit and is therefore said to be

mesaxonic, passes between the third and

fourth digit and is paraxonic. The third

and fourth digits always form an equal and

symmetrical pair and are the "irreducible

minimum," beyond which the number of toes

cannot be diminished. A single-toed artio-

dactyl would seem to be an anatomical im-
possibility ; at all events, such a monstrosity

was never known. Hence the term "cloven"

or "divided" hoof, which seems to take the Fro. iss.— -Leftfon-
solid hoof of the horse £„£*„? £
as the norm ; but " cloven **>/*). a., radius.

,. . , , ,, , ., [/..ulna. oi.,olecra-

or divided, while ex- j^^
pressing the appearance
of the foot with sufficient accuracy, is
erroneous, if taken to mean the splitting
of what was once continuous.

Especially characteristic of the order
is the structure of the ankle, or "hock-
joint" of the hind limb. The ankle-bone,
or astragalus, has a double pulley, the
upper and lower ends being of quite similar
shape; its lower end is almost equally
divided between the cuboid and navic-
ular, which are made concave to receive
it. This type of astragalus is altogether
peculiar to the artiodactyls, all of which
possess it ; it is unlike that of any other
mammal whatever and may be recognized

Fio. 187.-
of Pig.

L, lunar. I'y..
da]. Pit., pisiform. Td„
trapesoid. M., mag-

Mc. I. sw^nd. Mc. II,
third. Mc. Ill, fourth,
Mc. IV, fifth, meta-

360 LAND MAMMALS IN THE WESTERN HEMISPHERE

at a glance. The calcaneum, or heel-bone, has a large convex
facet, by means of which it articulates with the fibula, or exter-
nal leg-bone ; there is no such articula-
tion in the perissodactyls. The lower
end of the calcaneum is narrow and fits
into a step cut in the cuboid, which
is thus every whit as peculiar and char-
acteristic as the calcaneum and astrag-
alus. The femur never has the third
trochanter, which is always present in
the perissodactyls. Another respect in
which the artiodactyls differ from all
perissodactyls except the horses is in
the much more complex mode of articu-
lation between the vertebra of the lum-
bar and posterior dorsal regions, which
the former display, and even the horses
have no such elaborate arrangement.
Finally, another very marked difference

Via. 188— Left pes of Pig.
Cai , cajcaneum. At., as-
tragalus. .V.. navicular,
Cb., cuboid. Cn. 8, Cn. 3,
second and third cunei-
forms. Mt. II-V. second
to fifth metatarsals.

Flo. 189. — Bunodont
upper molar of pec-
cary (Tagaasu).

FlQ. 190. — Selenodont
upper molar of deer

(OdocoUeut).

from the perissodactyls is in the teeth, for the premolars and
molars are never alike, and only in very rare instances does
the last premolar assume the molar-pattern. Of this pattern,
there are two principal kinds, one exemplified by the pec-
caries, in which the crown supports a series, fundamentally
two pairs, of conical cusps, and called bunodont, and the
other, to be seen in all the ruminating animals, in which the
crown is composed of two pairs of crescents and is therefore
said to be selenodont. The bunodont was the primitive type,

HISTORY OF THE ARTIODACTYLA 361

whence the other was derived, and many transitional forms
are known.

The classification of the immense horde of living and extinct
genera and species which are referable to the artiodactyls
is an extremely difficult problem, which has found no thoroughly
satisfactory solution and will not until much more is learned
concerning the history of the order and conflicting opinions
can be reconciled. The most important American families
and genera are given below, though the arrangement is but
tentative.

Suborder A. ARTIODACTYLA fPRIMITIVA. (Extinct genera of

doubtful affinities)

I. fTRIGONOLESTIDiE.

^Trigonolestes, low. Eoc.

II. tLEPTOCHOSRIDiE.

t Leptochcerus, low. Oligo. ^Stibarua, low. Oligo.
III. fDiCHOBUNiDjE. ^ Homacodon, mid. Eoc. ^Bunomeryx, up. Eoc.

IV. tANTHRACOTHERIIDiE.

^Anihracotheriumj low. Oligo. ^Bothriodon, do. ^Arretotherium,
do.

V. ? fOREODONTIDiB.

t Protoreodon, up. Eoc. ^Merycoidodon, low. Oligo. ^Eporeodon,
up. Oligo. f Promerycochcerus, up. Oligo. to up. Mioc. \Mery-
cochcerus, Mioc. and low. Plioc. f Pronomotherium, up. Mioc.
^Mesoreodon, low. Mioc. ^Merychyus, low. Mioc. to low. Plioc.
t Leptauchenia, low. Oligo. to low. Mioc. \Cydvpidiu8, mid.
Mioc.

VI. fAORIOCHCERIDiE.

^ProtagriochcBruSf up. Eoc. t Agriochoerus, Oligo.

Suborder B. SUINA. Swine-like Animals

VII. TagassuidjE, Peccaries.

^Heiohyus, mid. Eoc. ^Perchcerus, low. Oligo. ^Thinohyus, up.
Oligo. ^Desmathyus, low. Mioc. t Prosthennops, up. Mioc. and
low. Plioc. ^Platygonus, mid. Plioc. to Pleist. Tagassu, Recent,
Pleist. in S. A.
VIII. fENTELODONTiD/E. fGiant Pigs-

^Parahyus, low. Eoc. t Achcenodon, mid. and up. Eoc. \Archceothe-
rium, low. Oligo. t Boochoerns, up. Oligo. \Dinohyust low Mioc.

362 LAND MAMMALS IN THE WESTERN HEMISPHERE

Suborder C. TYLOPODA. Camels and Llamas

IX. Camelid,e.

t Protylopu8, up. Eoc. ^Eotylopus, low. Oligo. f Poebrotherium,
Oligo. f Pseudolabw, low. Oligo. t Protomeryz, up. Oligo. and
low. Mioc. ^Oxydactylus, low. Mioc. \Miolabis, mid. Mioc.
^Protolabis, mid. and up. Mioc. ^AUicamelus, mid. Mioc. to
low. Plioc. ^Stenomylus, low. Mioc. t Procamelns, up. Mioc.
and low. Plioc. t Pliauchenia, up. Mioc. to mid. Plioc. Camelus,
Pleist. Lama, Plioc. to Recent, S. A.

X. fHYPERTRAGULIDiE.

t Leptotragidus, up. Eoc. t Leptoreodon, up. Eoc. ^Leptomeryx,
low. Oligo. t Hypertragvlus, Oligo. ^Hypisodus, low. Oligo.
^Protoceras, low. Oligo. ^Syndyoceras, low. Mioc.

Suborder D. PECORA. True Ruminants

XI. CervidjE. Deer.

] Blastomeryx, low. Mioc. to low. Plioc. Cervus, Pleist. and Rec.
Rangifer, Pleist. and Rec. A Ice, Pleist. and Rec. ^Cervalces,
Pleist. Odocoileus, Pleist. and Rec, N. and S. A. Mamma,
Pleist. to Rec, S. A.
XII. fMERYCODONTiDiE. fDeer-Antelopes.

^Merycodus, mid. Mioc. to low. Plioc. ^Capromeryx, Pleist.

XIII. AntilocapridjE. Prong-Bucks.

Antilocapra, Pleist. and Rec. ? fDromomeryx, mid. and up. Mioc.

XIV. Boviafi. Antelopes, Sheep, Goats, Oxen, etc.

\Neotragocerus, ^Ilingoceros, ^Sphenophalus, low. Plioc. f Preptoceras,
iEuceratherium,]Syrnbo8,Fleist. Ovibos, Pleist. and Rec. Bison,
Pleist. and Rec.

This list of families and genera, portentous as it is, would
be greatly increased by the addition of the Old World forms,
which outnumber those of the western hemisphere.

Suborder Suina. Swine-like Animals

The history of the American types of pig-like forms is,
in one sense, very full and complete in that the successive
genera may be traced back to the Eocene, but, in another
sense, the story is exasperatingly imperfect, because so much of
the material is fragmentary. Of most of the genera, nothing
is known but teeth and jaws, and these, though sufficient for

HISTORY OF THE ARTIODACTYLA 363

identification, tell but little of the structural changes which it
is desirable to know. It is merely a question of time, when
more adequate material will be obtained.

1. Tagassuidce. Peccaries

The peccaries, or American swine, are now chiefly of Neo-
tropical distribution, extending into the Sonoran region only
as far as Arkansas ; but this has been true only since the Pleis-
tocene, for nearly the entire history of the family has been
enacted in North America. In many points of structure the
peccaries of the present day are more advanced and specialized
than the far more varied and diversified true swine of the Old
World, for it is a singular fact that such a long-lived and per-
sistent stock as the peccaries should have given rise to so few
variants and side-branches. Existing peccaries all belong to a
single genus (Tagassu) and are relatively small animals, of
unmistakably pig-like character and appearance, but far
smaller than the Wild Boar (Sus scrofa) of Europe, or the Wart
Hog (Phacochcerus cethiopicus) of Africa, to mention only two
of the Old World swine.

One characteristic and thoroughgoing difference between
the peccaries and the swine is the shape of the canine tusks.
In the former, the tusks, though
very effective weapons, are not
very large and are straight and
have a vertical direction, while in
all the true swine the upper tusk is
curved upward and outward, pro- Fl° i9i. -Dentition of the Coi-

lared Peccary {Tagansu tajacu) left
jecting Strongly from the Side Of side. % 3, external inciHor. c,

the jaw, and the great, curved ™ / *- 8or,mid !™,ar (the

* 7 . first is lost), m/, first molar.

lower tusk wears against its an-
terior side. The peccaries further have smaller and simpler
molars, each with four principal, conical cusps (quadrituber-
culate pattern) arranged in two transverse pairs, with
numerous very small cuspules around and between them,

364 LAND MAMMALS IN THE WESTERN HEMISPHERE

obscuring the plan. In the true swine the teeth are much
larger and covered with innumerable wart-like cusps, large
and small, seldom arranged according to any definite
plan.

In the following particulars the modern peccaries show
advance over the Old World swine : (1) the last lower premolar
has taken on the molar-pattern, a very exceptional feature
among the artiodactyls ; (2) the ulna and radius are coossified ;
(3) there are but two functional digits in each foot ; the fore
foot has, in addition, two complete, but very reduced and slender,
lateral digits and the hind foot only one, whereas in all the pigs
of the eastern hemisphere there are four functional toes in each
foot ; (4) in the hind foot the two functional metatarsals, the
third and fourth, have coalesced to form a " cannon-bone/ '
a structure which is not found in any other family of the sub-
order; (5) the stomach is complex, approximating that of
a ruminant.

In the North American Pleistocene the predominating kind
of peccary was a genus (fPlatygonus) which was more ad-
vanced than the existing form (Tagassu), and, to all seeming,
better fitted to survive, though for some inexplicable reason it
failed to do so. It was a considerably larger animal, with
proportionately longer and heavier legs. Its molar teeth are
of special interest because they reproduced a type which has
been so often repeated and independently acquired in so many
different groups of mammals. In this molar the two conical
cusps of each pair were fused into a high, transverse ridge or
crest. Precisely the same modification took place among the
true swine in the genus fListriodon of the French middle
Miocene. ]Platygonus first appeared in the middle Pliocene,
and its predecessor in the lower Pliocene and upper Miocene
showed the crests of the molars in process of formation. In the
latter stage it was accompanied by a true peccary with tuber-
culated teeth, which differed from the modern species in the
simplicity of the hindmost premolar, which had not taken on

HISTORY OF THE ARTIODACTYLA 365

the molar-pattern. If the feet and limbs of this upper Miocene
peccary were known, they would doubtless prove to be much
more primitive than those of Tagassu, but they still await dis-
covery.

Little can be said of the peccaries of the middle and lower
Miocene other than to record the fact of their presence in those
formations, but those of the upper Oligocene (John Day) are,
however, represented by well-preserved skulls, which show that
more than one phylum of the family had arisen, though there
was no great difference between them ; they were considerably
smaller animals than those of the Pliocene and Pleistocene.
Still smaller was the White River genus (fPerchcerus) of which
some fragmentary skeletons have been obtained. Although
an undoubted peccary, this animal was not far from what the
common progenitor of the peccaries and the true swine might
be expected to resemble. The molars were quadrituberculate
without the numerous accessory cuspules of the modern genus ;
the bones of the fore-arm were separate and the feet had four
functional digits each, while there was no cannon-bone in the
pes, the metatarsals remaining free.

No peccaries have yet been found in the Uinta, but prob-
ably this is a mere accident of collecting. It is, however,
possible that the White River genus was not of American deri-
vation, but an immigrant from the Old World. In the middle
Eocene, or Bridger stage, this series is known only from teeth
and jaws and a very few scattered foot-bones, and these,
though probably referable to the family, cannot be definitively
assigned to it without more complete material. Several species,
larger and smaller, of the genus ^Helohyus occurred in the Bridger,
where they were not uncommon, considering the general rarity
of artiodactyls in that stage. Thus, the peccaries, though
none of them were large, followed the usual law of mammalian
development, and, beginning with very small forms, increased
in size with each succeeding geological stage down to the
Pleistocene.

366 LAND MAMMALS IN THE WESTERN HEMISPHERE

2. fEntelodontidce. f Giant Pigs

The fgiant pigs, a most remarkable group of swine-like
forms and of as yet unknown origin, appeared for the last time
in North America in the lower Miocene, where the genus of that
date (}Dinohyus) was the largest of known suilline animals,
the hippopotamuses excepted. In nearly every part of the
skeleton these great beasts displayed an unusual and aberrant
kind of development. The incisors were long and pointed, and
the canines formed stout and heavy, though not very long,
tusks, which in shape were more like those of a bear than those
of either peccaries or swine. The premolars were very simple,
of compressed conical and trenchant shape, and occupied a
very long space in the jaws, while the molars were relatively
small and quadrituberculate, the crowns covered with very
thick, coarsely wrinkled enamel. The skull was immensely
elongate, especially the facial region in front of the eyes, while
the brain-case was so absurdly small as to give the skull a
reptilian aspect, when viewed from above. Evidently, these
great pigs were profoundly stupid, in this respect rivalling
the ftitanotheres of the White River (p. 311). Beneath
each eye-socket was a long, descending, bony flap, or process,
and on the under side of the lower jaw were two pairs of prom-
inent knobs, the function of which, as of the flaps beneath the
eyes, is quite problematical. The eye-sockets themselves were
completely encircled in bone, a rare character in the suborder.

The neck was short, as in the pigs generally, the body not
very elongate and the tail of moderate length ; at the shoulders,
the spines of the dorsal vertebrae were very long, making a
decided hump, and in the lumbar and posterior dorsal region the
processes for articulation between the vertebrae were extremely
elaborate. For one of the pigs, the limbs were very long and
gave quite a stilted look to the animal. As in the modern pec-
caries, the fore-arm bones were indistinguishably fused together
and the feet had only two toes each, the only members of the

HISTORY OF THE ARTIODACTTLA

367

suborder in which digital reduction had pro-
ceeded so far, though the existing peccaries
approximate this condition. There were,
however, nodular vestiges of two other digits,
which prove the derivation of this form from jf
at least a four-toed type ; no cannon-bone
was formed. In view of the size of the
animal, the hoofs were surprisingly small,
which suggests that the weight was chiefly
borne upon a pad. ^Dinohyus was a very
large animal, six feet or more in height at the
shoulder.

In the upper Oligocene were very large
species of another, but closely similar, genus
( fBodchcerm) though somewhat smaller than
those of ]Dinohyu$, and the species of the
upper White River beds (t Archtsotherium)
were little, if at all, smaller than those of the
John Day. A number of specimens in the
museum of Princeton University throw a wel-
come light upon the habits of these strange
creatures. In one, the external, or third,
upper incisor tooth has a deep, triangular notch worn in its

[Q. Ifl2. — Right
manun of trnU'lo-
dont (t Archiruthe-
rium ingtni) from
lower White River
beds. Princeton
Univereity Mu-

368 LAND MAMMALS IN THE WESTERN HEMISPHERE

posteroexternal face, and the lower canine has a well-defined
groove worn on the posterior side at the base of the crown ;
other individuals show less distinct marks of similar kind.
{See Fig. 194.) It is out of the' question to suppose that
these grooves and notches could have been produced by
abrasion with other teeth, for no other teeth could reach
the worn areas, and it is altogether probable that they were
made in digging up roots. The root, held firmly in the ground
at both ends and looped over the teeth which pulled until it
^ broke, and being covered with

abrasive grit, would wear just
such marks as the teeth actually
display. ' While the tentelo-
donts were thus rooters, they
were doubtless omnivorous, like
other pigs, and did not disdain
a meal of carrion when they
could get it. It is likely that
Fio. iM. —Specimen ahowing charac- tne heavy canine tusks were

teriatic grooves of wear in the interior

teeth of tentelodont (t Archaoiherium) alSO Used 88 WeapODS, both in

from upperWhite Riverbed.. Prince- defence agfa^ the attacks of
ton University Museum, °

carnivores and in fighting be-
tween the males of the same species. It must have been in
some such encounter that the animal represented by a com-
plete skeleton in the Princeton Museum received its broken
rib ; that the fracture was made during life is demonstrated
by the large callus growths on the broken ends, but the pieces
did not knit.

In the middle and lower substages of the White River the
genus (^ArchcEotherium) was the same as in the upper substage
of these beds, but the species were all smaller and some of them
very much so, not exceeding an ordinary pig in size. Through-
out the series, as we now have it, from the lower Oligocene into

1 This plausible and no doubt correct explanation was suggested to me by
my colleague, Professor C. F. Brackett.

HISTORY OF THE ARTIODACTYLA

369

the lower Miocene, there is very little change except in size,
all the essential features of structure remaining the same;
the genera are therefore distinguished by modifications of very
secondary importance, and it is a question whether all the
species should not be included in a single genus. The European
genus \Entelodony which gives its name to the family, is so like
the American forms that by most writers the White River
species are referred to it. It is of interest to note that the
tgiant pigs have also been found in the marine Miocene of
New Jersey, one of the few records of the Tertiary land mam-
mals of the Atlantic seaboard.

At present, the fentelodonts proper cannot be traced back
of the lower White River beds, nor are they found in any more
ancient formations in Europe. It is, therefore, probable that
they were immigrants in both of these continents, presumably
from Asia.

The whole Eocene of North America had a series of pig-like
animals, called the fachaenodonts or fshort-faced pigs, which
seem to have
been related to

the fentelo-
donts. They
ended their
career in the
Uinta just be-
fore the appear-
ance of the fen-
telodonts, and
it would be nat-
ural to suppose

that the latter Fl°* 195# — Sku11 °* tshort-faced pig tfAchanodon robustus)

from the Bridger Eocene. Princeton University Museum.

were descended

from them. If, however, the principle that an organ or
structure once lost can never be regained, is valid, then there
can be no relation of ancestor and descendant between the

2b

370 LAND MAMMALS IN THE WESTERN HEMISPHERE

two groups, for of the fachaenodonts, even their most ancient
representatives had lost the first premolar, giving the formula
pf , while in the f entelodonts it is constantly pf . The fachae-
nodonts, which are much less fully known than the fentelo-
donts, had teeth very similar in form to those of the latter ;
and their most conspicuous feature was the shortness of the
face and jaws, as contrasted with the extreme elongation of
these parts in the fentelodonts, nor did they have the bony
flaps under the eyes or the knobs on the lower jaw which gave
such a fantastic appearance to the f entelodont skull. Little
is known of the skeleton except that there were four functional
digits in the manus. The Uinta and Bridger genus {} Achat-
nodori) was larger than the Wasatch form (\Parahyus), which
was an immigrant, probably from the same region as after-
wards sent out the fentelodonts to America and Europe ; this
would account for the similarity and probable relationship of
the two subfamilies.

Suborder Artiodactyla fPRiMmvA. fPRiMrnvE

Artiodactyls

No doubt, this suborder is an artificial assemblage of unre-
lated families, a sort of waste-basket, into which are thrown
the groups of which no other disposition can be made in the
present state of knowledge. As information becomes more
complete, the various families will be redistributed among
the groups with which they had a genuine relationship.

3. 1[Anthracotheriidce. fAnthracotheres

This family was abundantly represented in Europe from
the middle Eocene through the Oligocene, in Asia persisting
even into the Pliocene, and were abundant in the Oligocene of
Egypt. Migrants from the Old World reached America in
White River times, but speedily died out, as they did not sur-
vive into the upper Oligocene. The most fully known of these
animals is an American species of a European genus }Bothri-

HISTORY OF THE ARTIODACTTLA 371

odon. Almost complete skeletons of this genus have been
obtained in the channel sandstones of the upper White River
eubstage. In size and proportions, \Bothriodon was not
unlike a domestic pig, but had a very long head with slender,
pointed snout ; it had also a short neck, long body, short
limbs and feet. The primitive character of this genus is made
clear by many features of its structure ; the molar teeth were
extremely low-crowned and their cusps were so imperfectly

crescentic in form as to be called buno-selenodont, as indicating
their transitional nature, and the upper molars had five cusps
instead of four, a very primitive feature. Another very sig-
nificant character was the five-toed manus ; the first digit,
or pollex, was much smaller than the others.

The second genus of the family which had American rep-
resentatives was ^Anthracotherium, which was much like
^Bothriodan, but even more archaic in character ; the molars
could hardly be called selenodont at all.

372 LAND MAMMALS IN THE WESTERN HEMISPHERE

4. ^Oreodontidce. f Oreodonts

This was one of the most characteristic of North American
artiodactyl families, and its members were exceedingly abun-
dant throughout the upper Eocene, the whole Oligocene and
Miocene, ending their long career in the lower Pliocene. In
distribution the family was exclusively North American, and
no trace of it has been found in any other continent. In the
course of their long history the f oreodonts underwent many
transformations and branched out into several distinct phyla,
yet through all these changes they remained singularly con-
servative, for the transformations, some of them sufficiently
bizarre, affected chiefly the teeth and skull, the remainder of
the skeleton changing but little. The foreodonts were all
small or of moderate size, none of them surpassing the Wild
Boar in stature, nor was there any decided increase in size
from stage to stage. One and all, they were strange beasts.
Dr. Leidy, who first described and named most of the genera,
spoke of them as combining the characters of camel, deer and
pig, and called them " ruminating hogs," a conception expressed
in the names which he gave to some of them, such as }Merychyy&
and 1[Merycochcerus7 both of which mean ruminant swine.

The general proportions of most of the species were quite
as in the peccaries, though, for the most part, with much longer
tails ; they had a short neck, elongate body, short limbs and
feet. In one genus (fMesoreodori) of the lower Miocene a
rudimentary collar-bone has been found, and probably all of
the more ancient genera possessed it, but only by an unusually
lucky chance would so small and loosely attached a bone be
preserved in place. As the collar-bone is superfluous in hoofed
animals, in which the limbs are used only for locomotion and
move in planes parallel with that of the backbone, it is almost
universally absent in them, and in only one other group of
ungulates, the extinct fTypotheria of South America, has its
presence been demonstrated. In all of the foreodonts the

HISTORY OF THE ARTIODACTYLA 373

bones of the fore-arm and lower leg remained separate. The
teeth were in continuous series, and there was a peculiar feature
in the dentition common to nearly every one of the genera.
On casual examination, one would say that the animals had
four lower incisors on each side and that the lower canine closed
behind the upper one, a most exceptional arrangement. More
careful study shows that the apparent fourth incisor was the
canine, a transformation which has also taken place in all of the

ruminants except the camels, and the tooth which had as-
sumed the form and function of the lower canine was really
the first lower premolar ; this latter change is not found among
the ruminants, but was repeated in a few other extinct families.
Only two genera of tore°donts (\Merychyus and \Mery-
cochasrus) survived into the lower Pliocene. Both had the
proportions common throughout the family, but ]Merychyus
was much more slender and lightly built, its lateral digits were
reduced in size and very thin and it had hypsodont grinding
teeth ; while fMerycochcerus was of larger size (about that of a

374 LAND MAMMALS IN THE WESTERN HEMISPHERE

large domestic pig) and stouter build and had low-crowned
teeth; its head, however, had a very different appearance,
given by the possession of a short proboscis, the presence of
which is indicated by the greatly reduced nasal bones; the
jaws and face were also much shortened. The eye-sockets
presented obliquely forward and upward, intead of laterally,
as is usual among mammals, and were placed high in the head.
This position of the eyes and of the entrance to the ear renders
it probable that }Merycochcerus was largely aquatic in its habits.
Both genera had short, four-toed feet, as was general through-
out the family and in no genus did the reduction of digits proceed
beyond the loss of the first of the original five, the pollex and
hallux.

The two genera above described, representatives of two
distinct phyla within the family, held over, as it were, from the
upper Miocene without essential change. The phylum of the
hypsodont and slender }Merychyus went back, with only minor
modifications, into the upper substage of the lower Miocene,
but cannot as yet be traced to an Oligocene ancestry ; it is
therefore still impossible to say just where and when it branched
off from the main stem of the family. Future discoveries in
the Oligocene will no doubt clear up this problem. The real
terminal and most highly specialized member of the \Mery-
cochcerus phylum and the most extraordinary member of the
entire family was confined to the upper Miocene. The extreme
peculiarity of this genus ( t Pronomotherium) was displayed only
in the head, which was an exaggeration of the \Meryco-
chcerus type, the face being excessively shortened and the nasals
so reduced as to show that the proboscis was much better
developed than in the parent genus. The shortening of the face
and the great vertical height of the skull and lower jaw gave
a decided likeness to the skull of a great ape, though the probos-
cis would mask any such resemblance in the living head.
^Merycochoerus itself went back to the upper division of the
lower Miocene, but in the lower division it was replaced by an

HISTORY OF THE ARTIODACTYLA 375

ancestral genus, ^pTomerycochaems, which had an elongate
face and jaws and no proboscis; but in other characteristic
features, such as the extreme thickness and roughness of the
zygomatic arches, it was like its descendant. fPromeryco-
chcerus contained the largest known species of foreodonts,
some of them equalling a Wild Boar in stature, and its remains

Restored from a

are found so abundantly in the middle and lower Miocene and
upper Oligocene, that there must have been great herds of these
animals over the plains. Probably it was itself derived from
some of the larger species of \Eporeodon of the- upper White
River beds, but there is a gap in the history, due to the fact
that the lower part of the John Day is almost barren of fossils
and the connecting link has not been recovered.

It is an interesting and significant fact that ancestral and

376 LAND MAMMALS IN THE WESTERN HEMISPHERE

derivative genera may continue to live side by side in the same
region. \Pr ornery cockcerus, it is believed, gave rise to ^Mery-
cockarus, but survived with it into the middle Miocene.
\Merycockcerus, in its turn, produced ^Pronomotkerium, and,
so far from being replaced by the latter, actually outlived it and
persisted into the lower Pliocene.

A third phylum of the fareodonts, which appeared for the
last time in the middle Miocene (genus ^Cyclopidius), was a

series of small and very small species, of which the skull was
almost as peculiar as that of \Pronomotherium, but in a dif-
ferent fashion. The face was very much shortened and on
each side a great vacuity reduced the nasal bones to mere
splints ; the elevated position of the eye-sockets, which pro-
jected above the forehead, and of the tubular entrance to the
ear is an evidence of an aquatic or amphibious mode of life,
such as is illustrated by the hippopotamuses, which can float
almost completely submerged, with only the ears, eyes and

HISTORY OF THE ARTIODACTYLA

377

nostrils above the surface of the water. The tympanic bullae
(see p, 66) or bony chambers into which the ear-tubes opened,
were of relatively enormous size and added much to the unusual
appearance of the skull. The incisors were very small and the
grinding teeth narrow and completely hypsodont, this and
the ^Merychyus series being the only two phyla of the family
in which the hypsodont molar was fully acquired. The re-
mainder of the
skeleton differed
but little from
the type common
to the whole
family, except
for a somewhat
shorter tail.

The animals
of this series were
common in the
middle and lower
Miocene and in
the upper sub-
stage of the

White River, but have not been found in the intermediate
John Day. This may have been a matter of geographical dis-
tribution, these creatures not extending west of the main
ranges of the Rocky Mountains. In the upper White River
the genus ]Leptauchenia is extremely common, but below that
level they suddenly and completely vanish and, as in the case
of the ^Merychyus phylum, it is not yet practicable to deter-
mine the point in time or space of their branching off from the
main stem of the family. Were the foreodonts not entirely
confined to North America, we should, as a matter of course,
explain the seemingly sudden appearance of 1[Leptauchenia as
due to immigration, and it is entirely possible that the series
did actually originate in some part of North America which

Fia. 200.

Skull of t Leptauchenia nitida, upper White
River.

378 LAND MAMMALS IN THE WESTERN HEMISPHERE

has left no record of its Eocene or Oligocene terrestrial life.
On the other hand, no one can imagine that everything that
can be known of the mammals of the middle and lower White
River has already been learned, and at any time the sought-
for ancestor of fLephxuchenia may be found in those beds.

The fourth phylum may be regarded as the main or central
stem of (he family and was the one which underwent the least
change, though it probably gave rise to all the other phyla,

tara&rd cS fcv*n ii si vsri^ nagev in its history.

row :=•— .;r,s:<v: in ihc r.-.w.;> Mi.wne and comprised
prom. &i: very r.aA siifcc, :a the lower j-tAjres of that
i>»«iV«jrart» + .V,*w,V% d:>?kyed a very

i~r5- iw^iarlty tf «r.!,i^ :r. the ossScaiion of the

irrf^rf «" lJ* krvr.v »>.:,->. «vr.-* to point to »be pos-
:c ^^'"-"^ v.vsi yiowre*. I: ^ impossible to say

■r :J.?> fiiiT-r*- »** iw.r.rsv; to :hc si^5f penus, or was

HISTORY OF THE ARTIODACTYLA

379

tremely delicate a structure be preserved. In the John Day
_ the genus \Eporeodon, which was very abundant, was the repre-
sentative of this phylum, and the same, or a closely similar,
genus lived in the latter part of the White River stage.

In the middle and lower White River substages foreodonts
are the commonest of fossils, so that the collector soon wearies
of them (see Fig. 136, p. 259) ; they must have lived in great
herds in the forests and along the streams. There were several
species, varying principally in size, the largest about as long
as a wolf, but with shorter legs, and the smallest not so much
as half of that size.
All belonged to a single
genus, for which the
rigid law of priority
compels i4s to use ^
most cut jrous nair *
tfMeryc dodon), '
wide! ,ed te^

fOreot ing a s>

v
nym. xtus-gemu,

the central stock 6.

family, from wL

most, if not all, the others were directly or indirectly derived,

though, as previously pointed out, we cannot in all cases trace

the connection. In these White River animals the grinding

teeth were very low-crowned and had considerable resemblance

to those of a deer ; the molars were typically selenodont and

made up of two pairs of crescentic cusps. The skull differed

little from that of the succeeding genera of this phylum ; the

neck was short, body and tail long. An especially interesting

fact is that the fore foot had five digits, the first, or pollex,

very small and of no functional value, but complete in all its

parts ; the hind foot was four-toed. In all of the subsequent

genera of the family the number of digits was uniformly four

in both manus and pes.

— Skull of ]Merycoidodon culbertsoni, middle
White River. (After Leidy.)

380 LAND MAMMALS IN THE WESTERN HEMISPHERE

In the Uinta stage of the upper Eocene lived the most
ancient and primitive member of the family yet discovered,
the genus ]Protoreodony which is in every respect what the
ancestor of the White River genus should be. The functional
transformation of the lower canine into a fourth incisor and
the replacement of the canine by the first lower premolar had
already taken place, but the molars were much more primitive
than those of the White River and succeeding genera; the
crescents were thicker and less complete, plainly indicating
their derivation from conical cusps, and a small fifth cusp was
present between the anterior pair of the upper molars, as in

the f&nthracotheres
and other European
families of the Artio-
dactyla fPrimitiva.
Before the discovery

&

../.i>y« W^^^^^^^^^^uJaa» °f 1[Protoreodon, the
U _ "# - — ^e^—j^ character of its

molars was predicted

Fig. 203. — Skull of \Protoreodon parvus, Uinta Eocene, by Dr. SchloSSer, of
Princeton University Museum. N.B. This skull is Munich. The skull
actually much smaller than that shown in Fig. 202.

resembled that of the
White River genera, except that the eye-socket was open
behind, and there was no glandular pit in front of the eye. The
skeleton is but partially known, but it has been ascertained that
there were five toes in the manus and probably also in the pes.
Nothing has yet been discovered in formations older than
the upper Eocene which can be regarded as ancestral to the
foreodonts, and this is not surprising in view of the extremely
meagre and unsatisfactory nature of our information regarding
the artiodactyls of the Bridger. On the whole, however, it
seems rather more probable that the Uinta genus was an immi-
grant (whence, we cannot say) than that the Bridger will ever
yield the desired ancestral forms. So long as the early Tertiary
mammals of northern and central Asia remain unknown, this

HISTORY OF THE ARTIODACTYLA 381

and many similar problems can find no definitive solution.
The question of relationship with other families is bound up
with that of the origin of the foreodonts; many characters
point to a connection with the t&nthracotheres and, from
the standpoint of present knowledge, that appears to be the
most probable affinity; but, on the other hand, there are
structural features which suggest relationship with the primi-
tive camels. Between these and other alternatives, only the
recovery of the middle and lower Eocene forms can finally
decide.

Reviewing the long history of the oreodont family from the
evolutionary point of view, we find a course of development
which differs in several respects from that exemplified by most
of the families previously considered :

(1) There was a general increase in size, though it was far
from steady, and almost every genus had larger and smaller
species, and in some of the phyla the species were far larger than
in others. The members of the f Leptauchenia phylum were
very small and no member of the family ever attained to more
than moderate size.

(2) The upper molars early lost the fifth cusp, and after
that there was little change in the dentition, except that in
the ]Merychyus and ^Leptauchenia phyla the grinding teeth
became hypsodont.

(3) There was great variety in the modifications of the
skull, each phylum having its own peculiarities. The orbit,
which was open behind in the Uinta ^Protoreodon, was closed
in the White River and all succeeding genera. In the \Mery-
cochcerus series, the skull first enlarged, with little change in
proportions, then elongated the facial region, then shortened
the face and so reduced the nasals as to indicate the presence of
a proboscis, culminating in the grotesque, ape-like skull of
^Pronomotherium. In the ^Leptauchenia phylum the skull
became depressed and flattened and the face was invaded by
great openings, or vacuities; the tympanic bullae were enor-

382 LAND MAMMALS IN THE WESTERN HEMISPHERE

mously inflated and the orbits and ear-openings raised, pre-
sumably in adaptation to an amphibious mode of life. These
were the extremes of change within the family ; the other phyla
need not be considered.

(4) At an early stage the digits were reduced from five to
four, first in the pes and then in the manus, and there reduction
ceased ; though in ^Merychyus, especially in the upper Miocene
species, the lateral
digits were very
slender and, had
this series survived,
it would probably
have led to didactyl
forms.

In other respects
there was very little
difference in the
skeletons of the vari-
ous phyla and herein
lies the peculiarity
a, mervcoido- in the history of the

\Merycocharut , ., . . ,

family, great variety
in the form of the
skull, and, relatively speaking, hardly any change in the body,
limbs or feet. In the horses, rhinoceroses and ftitanotheres
the modifications of the successive genera affected all parts of
the structure, but in the foreodonts, except for the loss of one
digit in manus and pes and variations in the length of the tail,
the skeletons of the latest genera did not differ in any impor-
tant respect from those of the earliest. Such a combination
of mutability and plasticity in the skull with extreme conserva-
tism in the remainder of the bony structure is an exception to
the usual mode of development, though something of the same
sort has already been pointed out in the case of the tapirs
(p. 325) and will recur in that of the elephants (Chap. X).

Fig. 204. — Left manus of toreodonta.
don culbertmni, White River. i
propriut, upper Miocene.

HISTORY OF THE ARTIODACTYLA

383

5. ^Agriochceridce. ^Agriochcerids

This family, one of the strangest and most aberrant of
ungulate groups, was very closely allied to the foreodonts and
by many authorities is included in the same family. The his-
tory of the successive steps of discovery, by which the struc-
ture of these extraordinary animals was gradually made plain,
is much the same as in the case of the even more peculiar
perissodactyl family of the fchalicotheres (p. 356). The
various parts, found scattered and at long intervals of time,
had been referred to no less than three different mammalian

Fig. 205. — Skull of t Agriochcerua lali/rons, White River. (After Wortman.)

orders ! for, until the discovery of f chalicothere skeletons gave
the clue, no one imagined that such discordant parts could
belong to the same animal.

The f agriochoerids had a very much shorter career than the
allied family of the foreodonts, extending only through the
upper Eocene and the Oligocene (Uinta to John Day, inclusive) ;
and only two genera of the family are yet known, f Agriochcerus
of the John Day and White River, and ]Protagriochosrus of the
Uinta. In the former the teeth were not in a continuous,
closely crowded series, but there were open spaces behind the
upper canine and first lower premolar ; the same exceptional
character of the lower teeth which was found in the foreodonts
was repeated in the present family, the canine assuming the

384 LAND MAMMALS IN THE WESTERN HEMISPHERE

form and functions of an incisor and the first premolar those
of the canine ; the upper incisors were extremely small and were
shed in the adult, just as in the true ruminants. The molars
had the selenodont pattern, but the upper molars were
very different in shape from those of the foreodonts, resem-
bling rather those of the fanthracothere ^Botkriodon (see p. 370).
Another difference from the foreodont dentition was that the

last lower premolar had acquired the molar form and the last
upper one nearly so, a very unusual feature among the artio-
dactyls. The skull was almost exactly like that of the White
River foreodonts, save in a few details ; the face was somewhat
longer, the orbit was open behind and there was no glandular
pit on the face in front of the eye. The neck was short and the
body long, and the backbone in the region of the loins very
stout, the vertebra of this region having much resemblance to
those of the great cats, as though \Agriocherus were an agile

HISTORY OF THE ARTIODACTYLA

385

and powerful leaper. Another likeness to the cats was in the
very long and heavy tail, which was much longer than in the
foreodonts, and its vertebrse were hardly distinguishable from
those of a Leopard. The limbs were relatively longer than
those of the foreodonts and the separate bones had a suggestive
likeness to those of carnivores, and, more specifically, of cats.
The feet, save in one particular, were not only artiodactyl,
but also characteristically foreodont in structure and, as in
the earlier members of that family, there were five toes in the
manus and four in the pes. The excep-
tion was that, instead of narrow and
slender hoofs, the feet were armed with
sharp, though not very large claws, which
were not comparable in relative size to
the great claws of the fchalicotheres.

Altogether, a strange jumble of in-
congruous characters was united in this
skeleton. Were only the skeleton known
without the skull, one would be tempted
to call it that of a carnivorous artio-
dactyl, but the teeth make such a sugges- j
tion absurd, since they could have been
used only for masticating a diet of soft
vegetable substances. No flesh-eater
has, or ever had, teeth in the remotest degree like these, which
were of characteristically herbivorous type. How such a
creature lived and what were its habits, are questions to
which no satisfactory answer has been found.

^Protagriochcerus of the upper Eocene is, unfortunately,
known only from very imperfect and fragmentary specimens,
which, however, are sufficient to determine some significant
points. These remains show that, while the two families of
the f agriochcerids and the foreodonts were already distinct in
the Uinta, they were decidedly nearer together than they
became in the Oligocene. In other words, it is clear that the

— Right man
of ^Agriockarus latifroi
White River. (Aft
Wortman.)

386 LAND MAMMALS IN THE WESTERN HEMISPHERE

two groups were converging back to a common ancestry. This
may be discovered in the Bridger, but it seems more probable
that these forms were immigrants. Another fact concerning
the Uinta genus, which is important, is that the upper molars
possessed the fifth or unpaired cusp which also occurred in the
contemporary foreodonts, as well as in the f&nthracotheres
and other Old World families.

Suborder Tylopoda. Camels and Camel-like Animals

Existing Tylopoda are all included in a single family, the
Camelidae, and by several authorities no other family, even of
extinct forms, is admitted to the suborder. My own prefer-
ence, however, is to refer the problematical little fhypertrag-
ulids to this group, as will be shown subsequently.

6. Camelidce. Camels and Llamas

Under modern conditions, no mammals could seem more
completely foreign to North America than those of the camel
family, which, now restricted to two well-defined genera, in-
habit central Asia and the colder parts of South America.
Yet, as a matter of fact, this family passed through nearly
the whole of its development in North America and did not
emigrate to the other continents before the late Miocene or
early Pliocene, and it is this North American origin of the
family which explains its otherwise inexplicable distribution
at the present time. To all appearances, the whole family
had completely disappeared from this continent in the later
Pleistocene, but in the middle and earlier portions of that
epoch both true camels and large llama-like animals were very
abundant on the Great Plains and in California, while they
seem to have avoided the forested regions.

In order to appreciate the changes through which the
camels and llamas have passed, it will be necessary to consider
briefly the skeletal and dental structure which characterizes

HISTORY OF THE ARTIODACTYLA 387

the modern genera. In the true camels (Camelus) the first
and second upper incisors have been lost, but the third re-
mains as a large, sharp-pointed tooth, as are also the upper
canine and first premolar ; thus there are three pointed, spike-
like teeth in a row, with spaces between them, constituting
with the lower canine a very effective lacerating apparatus.
Behind the first premolar is a long gap, the second being sup-
pressed ; the third and fourth are grinding teeth, but unusually
small. The molars are selenodont and high-crowned, though
not extremely hypsodont. The lower incisors are large and
shovel-shaped, the canine large and erect and there are but two
lower premolars. The dental formula thus is : i £, c \, p § , m f .
The skull is long, with the facial region much and abruptly
narrowed, which gives a triangular appearance to the head when
seen from above ; the orbit is completely encircled with bone
and the sagittal and occipital crests are very prominent. The
tympanic bullae are large and filled with spongy bone. The
condyle of the lower jaw is hemispherical and not, as it is in
most ungulates, semicylindrical, and a curious, hook-like
angulation is on the posterior border of the bone. The neck
is very long, and the vertebrae have the exceptional peculiarity
that the canal for the vertebral artery runs through the side of
the neural arch, instead of perforating the transverse process,
and thus is invisible externally ; the odontoid process of the
axis is spout-like. The legs and feet are very long; the
humerus has a double bicipital groove and the fore-arm bones
are coossified, and the ulna is so reduced that the radius carries
the whole weight ; in the lower hind leg the tibia supports the
weight, and of the fibula only the lower end remains as the
malleolar bone. There are but two digits in each foot, the
third and fourth, the metapodials of which have coalesced
to form a cannon-bone, which differs from that of the true
ruminants, or Pecora, in the curious way in which the lower
ends, separated by a A-shaped notch, diverge from each other,
and by the fact that the keels of the lower articular surfaces

388 LAND MAMMALS IN THE WESTERN HEMISPHERE

are confined to the posterior side, not visible from the front.
The ungual phalanges are small and nodular, and the hoofs,
which carry no part of the weight, are hardly more than nails.
Under the other phalanges is a broad pad of elastic tissue, upon
which the weight rests, and the separation of the toes is very
partial. The peculiar external appearance of the camels is
largely due to structures which leave no trace in the skeleton,
and especially to the great humps, one or two according to the
species, which are accumulations of fat; the ears are short
and rounded and the hair is not woolly, but almost straight.

The teeth and skeleton of the llamas (Lama) are closely
similar to those of the camels, but the absence of humps, the
long, pointed ears, the woolly hair and the much smaller size
and lighter build give to the living animals a more marked
difference of appearance from the camels than one would expect
from a comparison of the skeletons alone. The dental formula
is : i I, c |, p |, m § . The remaining upper incisor, the third, is
recurved, as is also the canine, but the spike-shaped first pre-
molar of the camels is absent and the other premolars are
much smaller than in the latter. In the skull the brain-case
is larger, and the sagittal and occipital crests are much less prom-
inent. The skeleton differs hardly at all from that of the
camels, except for its smaller size and more slender proportions.
The toes are more distinctly separated, each having its own
pad. Thus, among the existing representatives of the family
are two very well-defined phyla, each characteristic of a differ-
ent continent.

The Blanco stage of the middle Pliocene, which has pre-
served but a meagre representation of the life of its time, has
yielded a number of very large, llama-like species, not, however,
ancestral to the modern species, for they had but one premolar
in each jaw. From the lower Pliocene we have fuller infor-
mation. In the Snake Creek stage the separation of the two
modern phyla was complete, and there was a third one, now ex-
tinct, that of the browsing or " tgiraffe"camels " (\Alticamelus)

HISTORY OF THE AHTIODACTYLA 389

(see Fig. 127, p. 236), a term which must not be taken as implying
any relationship with the giraffes, but merely a resemblance to
them in proportions. These browsing camels were very large
animals, but with relatively small heads and low-crowned teeth
not suited for grazing ; the neck was extremely long, made so by

the great elongation of five of the vertebrae (second to sixth,
inclusive), and the legs were also very long, fitting their pos-
sessors to browse upon trees. Much of the description of the
appearance and habits of the Giraffe given by Flower and
Lydekker would no doubt be applicable to these extinct camels.
"To produce the extremely elongated neck the seven cervical

390 LAND MAMMALS IN THE WESTERN HEMISPHERE

vertebrae are proportionately long, which gives a somewhat
stiff and awkward motion to the neck. . . . The Giraffe
feeds almost exclusively on the foliage of trees ... for brows-
ing on which its prehensile tongue and large free lips are specially
adapted." 1

In teeth and skeleton the phyla of the true camels and of
the llamas in the lower Pliocene did not differ very strongly
from the living forms ; the upper incisors were already reduced
to one, but the premolars were not so small; the ulna and
radius had coalesced and of the fibula only the lower end re-
mained ; the cannon-bones were completely formed, and that
the pads of the feet had already been developed is shown by
the phalanges, especially the irregular, nodular unguals.

The most ancient known camels of the Old World are found
in the Pliocene of India, and the first llamas recorded in South
America are also Pliocene. Since both camels and llamas
existed together in North America, it may reasonably be asked
why only one phylum migrated to Asia and only the other to
South America. Why did not each continent receive migrants
of both kinds? Without knowing more than we are ever
likely to learn about the details of these migrations, it will not
be possible to answer these questions, though plausible solu-
tions of the problem suggest themselves. It is to be noted, in
the first place, that a migration from the central portion of
North America to Asia was by way of the far north and thus
involved very different climatic conditions from those which
must have been encountered in passing through the tropics to
South America. It is perfectly possible that animals which
lived together in temperate North America should have had
very different powers of adaptation to heat and cold respec-
tively, and the northern route may have been impassable to
one and the southern route to the other. To this it might
perhaps be objected that the llamas are cold-country animals,
but this is true only of the existing species, for fossil forms are

1 Flower and Lydekker, Mammals Laving and Extinct, p. 332.

HISTORY OF THE ARTIODACTYLA 391

found abundantly in the Pleistocene of Ecuador, Brazil and
Argentina. Another possibility is that both phyla did actually
migrate to both continents and that only the camels succeeded
in permanently establishing themselves in Asia and only the
llamas in South America, though for this solution the fossils
afford no evidence.

The camels of the upper Miocene did not differ sufficiently
from those of the lower Pliocene to call for special notice other
than to remark that the two phyla of the true camels and the
llamas were hardly distinguishable and one genus (f-Pro-
camelus) may have been ancestral to both. In the middle
Miocene the browsing camels (t Alticamelus) reached the
acme of their importance and made no great progress subse-
quently. The generalized stock, from which the upper Mio-
cene and lower Pliocene \Procamelus descended, was repre-
sented by ^Protolabis and ^Miolabis, smaller animals, which
had a full set of upper incisors and premolars and the grinding
teeth were not so high-crowned. In most of the species the
metapodials had not fused to form cannon-bones and probably
there were no pads on the feet, though } Alticamelus, the
tGiraffe-Camel, had already developed both cannon-bones
and pads.

In the lower Miocene the tgiraflFe-camels were represented
by the genus ^Oxydactylus, which was a considerably smaller
animal than its successor f Alticamelus , of the middle Miocene
and later formations, and had shorter neck and legs. The
teeth, though brachyodont, were not very low-crowned. There
was no cannon-bone, the two metapodials of each foot remain-
ing separate. An especially noteworthy feature in this genus
is to be observed in the character of the hoofs, which, as the
ungual phalanges demonstrate, were narrow and pointed,
like those of antelope and deer, and carried most of the weight.
The member of the grazing series tfProtomeryx) was smaller
in every way than its contemporary (\Oxydactylus) of the
browsing line and had shorter neck and legs, though these were

LAND MAMMALS IN THE WESTERN HEMISPHERE

-a

I

vm ?iSKiv '

M

•c -1

I-

HISTORY OF THE ARTIODACTYLA

393

already long. The teeth were present in undiminished number,
and the grinders, while not properly to be called hypsodont,
showed a decided tendency to assume that character. The
feet were in the same stage of development as in fOxydactylus,
that is to say, with two free digits and pointed, deer-like hoofs.
We have thus the remarkable and most significant fact that,
while the grazing and browsing camels of the lower Miocene

were already distinctly separated, neither had yet attained to
the type of foot-structure which both of them afterwards in-
dependently acquired. This is a very instructive example of
parallel evolution in closely related series.

Of still another phylum of the camel family, the lower Mio-
cene contains the only representatives yet discovered, the little
"tgazelle-camels," as they may be called. The single known
genus tfStenomylus, Fig. 131, p. 242) of this series was quite a
small animal, much smaller than its contemporaries of the graz-
ing or browsing series. ^Stenomylus was an extremely slender,

394 LAND MAMMALS IN THE WESTERN HEMISPHERE

cursorial creature and had a very exceptional feature in its
dentition in the apparent presence of ten lower incisors, five on
each side, the canine and first premolar having assumed the form
and functions of the incisors; the molars were low-crowned.
The head was rather small and rounded, the neck long and light,
the limbs and feet elongate and excessively slender. The feet
had two digits each, which were separate, not forming a cannon-
bone, and the hoofs were narrow, pointed and deer-like. These
delicate and graceful little animals had but a brief career, which
seems to have reached its close in the lower Miocene. Perhaps
their complete defencelessness made it impossible for them to
maintain themselves against their enemies, despite their evi-
dent capacity for swift running.

The camels of the upper Oligocene (John Day) are still
incompletely known, but appear all to have belonged to the
series of grazers which led up to the modern genera. Future
discovery may bring to light in the John Day earlier members
of the fgiraffe-camel series, of which a possible member is
found in the uppermost substage of the White River, or perhaps
both phyla united in the upper Oligocene, a question which
remains to be determined. At all events, in the middle sub-
stage of the White River, or lower Oligocene, there is no evi-
dence of more than a single phylum, from which the others
were almost certainly derived, branching off from the main
stem at different levels. First was given off the branch of the
fgiraffe-camels, then (or perhaps even earlier) that of the
little fgazelle-camels, and, finally, the main stem bifurcated
into the two phyla of the llamas and the true camels. The
point of origin of the fgazelle-camels is still uncertain.

The typical White River genus (fPoebrotherium) included
a series of species which increased in size from the earlier to the
later portions of the stage, but showed no such structural changes
as to call for special notice. The larger of these species was
somewhat taller than a sheep, but of much lighter proportions,
with small, pointed head, long neck and body and long, very

HISTORY OF THE ABTIODACTYLA

396 LAND MAMMALS IN THE WESTERN HEMISPHERE

slender limbs and feet. The teeth were present in undiminished
number, 44 in all ; the lower incisors were small, simple, nearly
erect and chisel-shaped, very different from the large, pro-
cumbent and shovel-like teeth of the modern genera, and the
trenchant canines were much smaller than in the latter. The
first premolar had an isolated position, the second and third
were trenchant and much extended antero-posteriorly, quite
as in many other groups of primitive artiodactyls. The
molars, which were typically selenodont, were low-crowned in
the upper jaw, but in the lower showed an incipient tendency
to hypsodontism. The skull, by its shape and the characteris-
tic narrowing of the face, immediately suggests the modern
type, but differed in many details of structure, the most ob-
vious of which were the incompletely closed orbits, the shallow
and slender jaws, and the very large, hook-like process from the
angle of the lower jaw, which, in greatly reduced form, is pres-
ent in both of the Recent genera. The neck was relatively
long, though by no means so long proportionately as it sub-
sequently became, and the vertebrae had already acquired the
peculiarity found in all the succeeding camels, of the exceptional
position of the canal for the vertebral artery, save in the sixth
vertebra, where it pierced the transverse process, as in mam-
mals generally; the odontoid process of the axis was neither
spout-like nor peg-like, but of intermediate form, convex
below and flat above. The body was long and light* and the
ribs were much more slender than in the Recent genera. The
fore and hind limbs, which were of nearly equal length, were
very slender ; the humerus had a single bicipital groove ; the
fore-arm bones were fully coossified and in the lower leg only
the two ends of the fibula remained. The feet were already in
the stage of development which persisted through the lower
Miocene in all of the phyla, with two separate digits and nodular
remnants of two others, and deer-like hoofs.

It would be of interest to compare this little White River
camel with its contemporary genus of horses, \Mesohippus>

HISTORY OF THE ARTIODACTYLA 397

and to observe in how many respects they have followed a
parallel course, and how nearly ^Po&brotherium occupied the
same position with reference to the modern camels and llamas
as ^Mesohippus did to the Recent horses; but such a com-
parison would involve too many technicalities to be profitably
undertaken here. Suffice it to say that in many details there
was a genuine parallelism in the progress of these two widely
separated families from a polydactyl ancestry towards an ex-
treme of digital reduction, ending in the horses in the single-
toed and in the camels in the two-toed foot. The members of
the two series kept nearly equal pace in their slow progress,
with the camels a little in advance, since they were the first
to attain the modern state of development in the height of the
teeth and the structure of the feet, though eventually the horses
surpassed them in both respects.

In the upper Eocene (Uinta stage) there were at least two
kinds of camels, the time-relations of which to each other are
not known, that is, whether they were contemporary or suc-
cessive. The best-known genus, \Protylopus, may perhaps
not be in the direct line of camel descent, but it so nearly
represents the proper ancestral stage that, for all practical
purposes, it will serve nearly as well. It was a much smaller
animal than the smallest of the White River species, and was
hardly larger than a " jack-rabbit.' ' The teeth of each jaw
were in continuous series and the canines were but slightly
longer than the incisors; the premolars had less anteropos-
terior extension than in \Poebrotherium, and all the molars
above and below were very low-crowned. The skull was
almost a miniature copy of that of \Poebrotherium, but more
primitive in a number of details, the most important of which
was that the tympanic bullae were much smaller and hollow,
not filled with spongy bone. The neck, concerning which it
would be very desirable to have information, is almost the
only part of the skeleton that is not known. The fore limb
was considerably shorter than the hind, making the back slope

398 LAND MAMMALS IN THE WESTERN HEMISPHERE

downward from the rump to the shoulders; in the fore-arm
the two bones were entirely separate and in the lower leg the
fibula, though very slender, was still complete. In the manus
there were four functional digits, the laterals not very much
smaller than the median pair; but in the pes the lateral
metatarsals were reduced to mere bony threads, to which small
phalanges, in full complement, were attached, making tiny
dew-claws.

With \Protylopus ends the genealogy of the camels so far
as it can be definitively traced, but in the middle of the Bridger
stage is found a genus, }Homacodon (family fDichobunidae) ,
which is a probable member of the series. However, until
the connecting link can be found in the upper Bridger, this
conclusion cannot be demonstrated and ^Homacodon itself is
incompletely known. It was a very small animal, even less
in size than ^Protylopus, and had not yet acquired the seleno-
dont molars. These teeth were quadritubercular, i.e. with
four principal cusps arranged, in the upper molars, in a square,
and with a minute cuspuie between each transverse pair, while
the lower molars were narrower and had only the four prin-
cipal cusps. The cusps were not conical, as they are in the
pigs, but angular and pyramidal, the first step toward the
assumption of the selenodont form. The skull was not
specifically cameline in appearance, but rather indifferent,
as though almost any kind of an artiodactyl might have been
derived from it. The feet were decidedly more primitive than
those of the Uinta genus, having four functional digits each,
perhaps five in the manus. While it cannot be positively
stated that \Homacodon was the actual ancestor of \Protylo-
pus7 it nearly represents what we should expect that ancestor
to be.

In the lower Eocene (Wasatch stage) lived a tiny creature,
\Trigonolestes (family fTrigonolestidae), smaller even than fffom-
acodon of the Bridger, and one of the most ancient and primitive
of known artiodactyls, but, unfortunately, still represented only

Fio. 212. — Diagram to illustrate the development of the skull and molar teeth in the
came] tribe, in ascending geological order. A, fProtj/loput peterioni, Uinta Eocene.
B, iPiXbrotheriumwilaoni, White River. (After Wortman.) C, IProcamelua gmcilit.
Upper Miocene. (After Cope.) D, Lama huanacua, the modern Guanaco.

400

LAND MAMMALS IN THE WESTERN HEMISPHERE

by very imperfect specimens, so that much which it would
be highly desirable to learn must await the finding of better
material. The upper molars were triangular and tritubercular,
i.e. with three principal cusps arranged in a triangle, and are
hardly to be distinguished from those of other early mam-
malian orders. From the teeth alone the artiodactyl nature
of the animal would not have been
suspected, and, in fact, they were,
when first discovered, referred to primi-
tive monkeys. The feet probably had
five toes each, but this is not certain,
and the femur had the third tro-
chanter, the only known artiodactyl
of which this is true. As this little
Wasatch genus is so imperfectly known,
it would be premature to claim it as
the starting point of the
camel family, and yet it
may very well have been
so. Better material of
this genus and
toj the links of the
A |H chain which be-
|l\ long in the upper
Jmw Bridger and the
Wind River re-
spectively must

White River. C, IProcameliu, upper fe recovered be-
Miocene. (After Cope.) D, Recent Gunnaco.

fore this earliest
portion of the family history can be written in more than
tentative fashion.

The mode of evolution displayed by the camels does not
differ in any significant respect from that seen in the horses.
There was the same increase in bodily stature and in the rel-
ative lengths of the limbs and feet, the same kind of diminu-

l, iPratyloput, Uint

HISTORY OF THE ABTIODACTYLA

401

tion in the number of digits from the original five, the same
reduction of the ulna and its coalescence with the radius and
the lose of the fibula save for its two ends. There was also a

Fto. 214. —Right pen of camels. A, \Protylopua. B, I Potbrolhtrium.
C, tProcamttua. (After Cope.) D, Guanaco.

similar development of the high-crowned, or hypsodont, grind-
ing teeth, from the low-crowned, or brachyodont, type. In
still another respect there was a similarity in the mode of de-
velopment of the two families, namely, in the way in which
the several phyla of each originated. For the earlier portion
of their history there was in each but a single distinguishable

402 LAND MAMMALS IN THE WESTERN HEMISPHERE

series, though it is very possible that fuller knowledge and
more complete material would enable us to distinguish more
than one. This monophyletic condition continued through
the Eocene and most of the Oligocene, but in the upper por-
tion of the latter and, more markedly in the lower Miocene,
the two families branched out, each in its own fashion.

Of course, there were differences in the development of
the camels and horses, some conditioned by the fundamental
distinction between artiodactyl and perissodactyi, such as the
didactyl foot as the possible minimum and the formation of
cannon-bones in the camels. Other differences are character-
istic of the latter family, such as the great elongation of the
neck and the peculiar structure of its vertebrae, the formation
of pads on the feet and concomitant reduction of the hoofs.
In a general way, the two families kept quite an even pace in
their advance from the more primitive to the more specialized
condition and, though the camels were the first to acquire
certain modifications, the horses ultimately surpassed them.

Even more close was the parallelism in evolution between
the camels and the true ruminants (suborder Pecora) , and this
case is of particular importance as clearly demonstrating the
development, in two independent but related lines, of similar
structures not derived from a common ancestry. This com-
parison must naturally await the description of the Pecora.

7. ^Hypertragulidce. ^Hypertragulids

This was a very peculiar family, of exclusively North
American distribution and of doubtful systematic position, the
known history of which extended from the upper Eocene into
the lowest Miocene and then abruptly terminated. None of
its members attained to considerable size, the largest hardly
surpassing a sheep, and some were extremely small. In view
of its comparatively brief career, this family was surprisingly
ramified, and no less than four phyla may be distinguished
within its limits.

HISTORY OF THE AHTIODACTYLA

404 LAND MAMMALS IN THE WESTERN HEMISPHERE

One of the phyla which persisted into the lower Miocene was
there represented by a most fantastic creature (^Syndyoceras)
with four horn-like outgrowths from the skull, one pair arising
from the anterior part of the face and curving outward away
from each other, and the hinder pair, which were placed over
the eyes, curved toward each other at the tips and were shaped
much like a cow's horns in miniature. The shape of these
bony protuberances makes it unlikely that they were sheathed
in horn and probably they were merely covered with skin like
the horns of the giraffes. This description applies only to the
skull of the male ; that of the female is not yet known, but there
is good reason to believe that in that sex the horns were much
smaller or wanting, as in nearly all existing deer. The skull was
long, narrow and low; the orbits were small, completely en-
closed in bone and unusually prominent ; the nasal bones were
exceedingly short, as though indicating the existence of a
proboscis, but this can hardly have been the case, for the nasal
opening was divided into anterior and posterior portions by
the bony bridge which united the bases of the forward pair of
horns. In no other known mammal does such a division of the
nasal opening occur. The upper incisors had aH disappeared,
but there was a small upper canine tusk and another formed by
the first lower premolar, while the real lower canine had gone
over to the incisor series. This exceptional arrangement is a
point of resemblance to the foreodonts (see p. 372). The
grinding teeth were brachyodont. The fore limb is not known,
but the hind limb has been completely recovered ; it was stout
and not very long in proportion to the length of the head.
The fibula was completely reduced, only the ends remain-
ing, and the pes was didactyl, the two metatarsals uniting
in a cannon-bone; the hoofs were like those of deer and
antelopes.

No representative of this series has yet been found in the
upper Oligocene ; and it is not yet possible to say whether their
absence from the John Day beds, as in several other cases

HISTORY OF THE ARTIODACTYLA

406 LAND MAMMALS IN THE WESTERN HEMISPHERE

already referred to, was due to an actual geographical differ-
ence in contemporary faunas, or whether it is merely one of the
accidents of preservation and collecting. In the upper White
River, however, was another most curious animal (tProtoceras) ,
a forerunner, if not a direct ancestor, of fSyndyoceras. The
exact relationship between the two forms can hardly be de-
termined, until the genera, one or more, which once connected
them shall have been recovered, though it is obvious that they
belonged to the same series. ^Protoceras was a smaller ani-
mal and, if anything, an even more bizarre-looking object, for

Fio. 217. — IProtectrat cder, skull of male. (After Osborn and Wortman.)

the anterior protuberances were broad, prominent and everted
plates of bone, not even suggesting horns in their form, and
the posterior pair were short and club-shaped ; in the female
neither pair was more than indicated. The dentition was very
similar to that of ^Syndyoceras, except that the upper tusk
was considerably larger and scimitar-shaped ; the female had
no tusks. In the fore-arm the two bones were just beginning
to coalesce, but in the lower leg the fibula was completely
reduced. The manus had four complete and functional digits,
the laterals not very much shorter and thinner than the median
pair ; but the pes was already didactyl, though the metatarsals
were separate, not fused into a cannon-bone ; two long and

HISTORY OF THE ARTIODACTYLA 407

pointed splints were the vestigial remnants of the second and
fifth digits.

It is not yet possible to trace this phylum below the level
of the uppermost White River beds, yet that will very probably
be accomplished by future exploration.

The second phylum of the family was represented in the
lowest Miocene by }Hypertragulusy a genus of much smaller
animals than those of the preceding series, which went back
to White River times without essential change, and was abun-
dant in the John Day stage. Despite this fact, the structure
of the genus is still incompletely known and much remains
to be learned, but enough has already been ascertained to
justify the association of this phylum with the 1[Protoceras-
^Syndyoceras series in one family as reasonable. The num-
ber of upper incisors in \Hypertragulus has not been ascer-
tained, but the canines were enlarged and tusk-like, the lower
one not having gone over to the incisors, as it had in the pre-
ceding group. The skull had much resemblance to that of
the contemporary camels, the sudden narrowing of the facial
region giving it a very llama-like appearance ; the orbit was
open and on the face in front of it was a conspicuous vacuity.
The ulna and radius were coossified and there were four digits
in the manus, two in the
pes, but no cannon-bone
was formed.

The third phylum, that
of ^Leptomeryx, had about
the same range in time as
the preceding one, though

it has not yet been found Fl°- 218.— Skullof t Leptomeryx evansi, White
. , T , t^ . . . River. (After Matthew.)

in the John Day, and the

genus is assuredly known only from the White River beds,
in which it is not uncommon. ^Leptomeryx comprised a
number of species, all very small animals, and none larger
than a jack-rabbit. (See Fig. 277, p. 563.) In size, propor-

408 LAND MAMMALS IN THE WESTERN HEMISPHERE

tions and appearance, these dainty little creatures must have
been very like the existing chevrotains or " mouse-deer ' ' of
Asia and the Malay islands, and by many writers they have
been classed in the same suborder, the Tragulina. The upper
incisors had been suppressed and the upper canine reduced to
very small size, while the lower canine had become functionally
one of the incisors. The skull had a very long and slender facial
region, but had a less llama-like appearance than in \Hy-pertra-
gulus. The neck was short and the fore limbs much shorter than
the hind, so that the back sloped downward from the rump to
the shoulders, as in the chevrotains. There was a remarkable,
indeed quite unparalleled, difference between the fore and hind
limbs and feet, the hinder extremity being not only much longer,
but also much more specialized, while the anterior one retained
in very large degree its primitive characteristics. Thus, in the
fore-arm the ulna was complete and separate from the radius,
but in the lower leg the fibula was reduced to its minimum. In
the manus there were four entire and functional digits, in the
pes only two, which were joined in a cannon-bone.

Finally, there was a fourth phylum, that of \Hyjrisodus, which
was confined to the White River stage and is still incompletely
known. This was a tiny creature, much smaller than any of
the preceding ones, and is the only known White River un-
gulate with fully hypsodont grinding teeth. Another very ex-
ceptional peculiarity of its dentition was that in the lower jaw
it had ten incisor-like teeth ; not only the canine, but the first
premolar as well, had assumed the character of the incisors.
This same peculiarity is found in the lower Miocene fgazelle-
camel, ]Slenomylus (see p. 394), but in no other mammal.

A considerable assemblage of genera belonging to this family
occurs in the upper Eocene, but the material yet obtained is too
fragmentary to permit the assignment of these forms to the
different phyla, though it is very probable that among them are
to be found ancestors of all the White River and subsequent
genera.

HISTORY OF THE ARTIODACTYLA 409

While there is little difference of opinion as to the propriety
of including in the family fHypertragulidae the four phyla de-
scribed in the foregoing pages, the systematic position and the
relationships of that family as a whole are matters of debate
and likely long to remain so. Dr. Matthew refers the entire
group to the suborder Tragulina and regards \Leptomeryx as
being closely related to the direct ancestry of the American deer,
a view which is accepted by Professor Osborn, but in which I
am unable to concur. My own belief is that the family was an
early offshoot from the cameline stock and therefore referable
to the Tylopoda, in which suborder they are here included. It
would be out of place to enter upon a discussion of this per-
plexing problem, which can hardly receive a definitive solution
until the artiodactyls of the Uinta stage are thoroughly under-
stood. As in so many other series, the key of the mystery lies
hidden in the Uinta fauna, which is still so inadequately known.

Suborder Pecora. True Ruminants

This is the most advanced, specialized and diversified group
of the artiodactyls, though the ruminating habit is shared by
both Tylopoda and Tragulina. In this multitude of forms,
giraffes, deer, antelopes, sheep, goats, oxen, buffaloes, bisons,
etc., it is difficult to find a clue to a natural arrangement or
classification. As a whole, the suborder is a well-defined group,
and many structural characters, not all of which is it needful
to enumerate here, are common to all of its members. The
upper incisors are invariably absent, and, save in a few of the
deer, the upper canine also, while the lower canine has become
incisiform ; the premolars are always three in number in each
jaw and the molar-pattern is selenodont throughout. The
odontoid process of the axis is spout-shaped. Except in a few
deer, the Pecora all have bony outgrowths of the skull in the
form of antlers or horns, at least in the males, many females
being hornless. The ulna is coossified with the radius and the

410

LAND MAMMALS IN THE WESTERN HEMISPHERE

fibula is lost, except the lower end, which is a
separate malleolar bone. There is always, in
both fore and hind feet, a cannon-bone, the
lower ends of which are
parallel, not divergent, as
they are in the Tylopoda,
and each articular surface
is encircled all around by a
prominent median keel, as
in the horses, which in the
other suborders, as in mam-
mals generally, is confined
to the posterior side and
not visible from the front.
(Cf. Figs. 220 and 214, p.
401.) In no existing mem-
ber of the Pecora are there
complete lateral digits, and
in several modern genera
they have been completely
suppressed ; but in most
there is, behind the func-
tional pair of digits, a pair
of "dew-claws," the bones
, , of which are more or less

in. 219. — Left manus

at Patagooiftn Deer completely reduced, often

%rTZ.$£. t° -°™ ""doles. The

l„ lunar. Py., py- stomach, which in the Tylo-

ramidal. Td., M., eo- j . m ■■ i ,•
ossified trapezoid and P°da and Tragullna IS three-
magnum. Un„ unci- chambered, is in the Pecora
form. Mc. II and V, ,..,,. , ,.
rudimentary second divided into four distinct
and fifth metacarpals, nortg
Mc. Ill and IV, can- F

non-bone. Ph. i, s. As already intimated, the
first and second pha- subdivision of the Pecora

lanj?ca. brig., ungual

phaiam. into smaller groups is far

Fio. 220. — Lett pes
of Patagonian
Deer. Cal., calca-

alua. JV..' Cb.. co-
ossified navicular
and cuboid. Ml.
Ill, IV, cannon-
bone. Other let-
ters aa in Fig. 219.

HISTORY OF THE ARTIODACTYLA 411

from easy. "The great difficulty which all zoologists have
felt in subdividing them into natural minor groups arises
from the fact that the changes in different organs (feet, skull,
frontal appendages, teeth, cutaneous glands, etc.) have pro-
ceeded with such apparent irregularity and absence of correla-
tion that the different modifications of these parts are most
variously combined in different members of the group.' ' *
Two main sections of the suborder are, however, sufficiently
well defined, (1) the Cervicornia and (2) the Cavicornia.

SECTION CERVICORNIA. DEER AND GIRAFFES

This section includes two families, the giraffes and the deer.
Inasmuch as the former have not now and never did have any
representatives in the western hemisphere, for the purposes of
this book the section becomes identical with the deer family.

8. Cervidae. Deer

In most of the deer now existing the male has antlers. The
antler is a bony outgrowth from the frontal bone of the skull
and is annually shed and replaced, increasing, as a rule, in
size and in the number of branches with each renewal. During
the period of growth the antler is richly supplied with blood-
vessels and covered with skin and is then said to be "in the
velvet," which dries and peels off when growth is complete;
after the rutting season a layer of bone at the base of the antler
is resorbed, loosening the antler, which is then shed. There
is, however, a permanent, cylindrical process, of greater or
less length, from each frontal, the "pedicle," from which the
antler is annually reproduced, and around the base of the antler
and shed with it is a roughened ring, the "burr" Among
the different genera of deer there is great variety in the form
and size of the antler, from a single spike to the immense and
complicated appendages of the Wapiti (Cervus canadensis).
As a rule, the "beam" or main stem of the antler and its

1 Flower and Lydekker, op. cit., pp. 307-308.

412 LAND MAMMALS IN THE WESTERN HEMISPHERE

branches or "tines" are cylindrical and tapering; but in some
cases, as in the Moose (Alee) and the Fallow Deer (Dama), the
antler is very broad and flat and is then said to be "palmated"
Except in the Reindeer and Caribou (Rangifer) the female is
without antlers.

In the skeleton there is little difference between the deer
and the Cavicornia, but there are some differences in the teeth.
In the males of those deer which have no antlers, such as the
Musk-Deer (Moschus moschiferus) and the Chinese Water-
Deer (Hydropotes inermis) , as well as in certain forms with very
small antlers, like the muntjacs of Asia (Cervvlus and Elapho-
dus) , the upper canine is a long, thin, recurved and sabre-like
tusk, a very effective weapon. Speaking of the Indian Munt-
jac or "Barking Deer" (Cervulus muntjac) , Flower and Lydek-
ker say, "When attacked by dogs the males use their sharp
canine teeth with great vigour, inflicting upon their opponents
deep and even dangerous wounds." In other forms of deer
the upper canines are small or absent. The grinding teeth are
brachyodont, but in the existing genera they have higher
crowns than in the Tertiary progenitors of the family, and in
the Axis and Hog Deer of India (Axis axis and A. porcinus)
the molars are quite hypsodont.

As was shown in Chapter V, the existing deer of North
America are of two kinds : (1) the northern, which are plainly
of Old World origin and so closely similar to Old World species
that many naturalists deny the necessity of making distinct
species for the American forms. The best known of these
are the Wapiti (Cervus canadensis) , the Caribou (Rangifer
caribou) and the Moose (A Ice americanus) . (2) The southern
deer, of which the common Virginia Deer (Odocoileus virgin-
ianus) is a familiar example, though overlapping in their
range that of the northern genera, are peculiar to the Americas,
and, though not exactly autochthonous, they must have had
a long American ancestry. In the Pleistocene we find the
same genera and mostly the same species, their distribution

HISTORY OF THE ARTIODACTYLA 413

over the continent shifting in accordance with the many cli-
matic changes of that epoch. There was, however, at least one
Pleistocene genus (\Cervalces) different from any now living
and different from any known in the eastern hemisphere. The
most complete specimen of this animal is a skeleton in the
museum of Princeton University, found beneath a bog in
northern New Jersey, though other bones, collected in Ken-
tucky and elsewhere, are very probably referable to it. \Cer-
valces was very nearly related to the Moose, the neck, body,
limbs and feet being almost identical in the two genera, but
the skull 9&d antlers were notably different ; the nasal bones
were not nearly so much shortened as in the Moose, indicating
that the proboscis-like snout was not so large or inflated as in
the latter. The antlers were quite unique ; though in general
like those of the Moose, they were much less palmated and they
had, in addition, a great trumpet-like plate of bone on the lower
side of each antler (see Fig. 117, p. 209), such as occurs in no
other known member of the family. Although \Cervalces has
not been found in the Old World, it was almost certainly an
immigrant from eastern Asia.

The Moose, Caribou and Wapiti were unquestionably im-
migrants and came in not earlier than the Pleistocene. Noth-
ing is known in the Pliocene or more ancient Tertiary epochs
of North America which could be twisted into forms ancestral
to these typically Old World genera. With the southern deer
(OdocoileuSy etc.) the matter stands differently, for these have a
probable American ancestry extending back to the lower
Miocene and possibly much farther. On the other hand, it is
not altogether certain that these may not have been Pliocene
immigrants, for their genealogy is still in an extremely frag-
mentary and unsatisfactory condition. The North American
genus, Odocoileus, extended back to the Pliocene with very
little change. The annoying, unrecorded gap of the upper
Pliocene and the meagre representation of the middle Pliocene
mammals given by the Blanco leave us without information

414

LAND MAMMALS IN THE WESTERN HEMISPHERE

regarding the deer of that time. In the lower Pliocene and
through the whole Miocene we meet with frequent remains of
a genus {\Blaatomeryx) which was quite probably the ancestor
of the American types of deer. It was considerably smaller
than any of the existing North American species and had no
antlers, but possessed the sabre-like, upper canine tusks, which
characterize the muntjacs and hornless deer of Asia. The
limb-bones had already attained nearly their present state of

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development, as regards the reduction of ulna and radius, for-
mation of cannon-bones, etc. \Blostomeryx probably en-
tered North America in the lower Miocene, but, as was men-
tioned previously (p. 409), Dr. Matthew and Professor Osborn
regard the genus as autochthonous and descended from the
fHypertragulidie.

In the middle Miocene \Blostomeryx gave rise to an ab-
errant genus (t Merycodus) which has been made the type of a
distinct family (fMerycodontidse, see table, p. 362), but this

HISTORY OF THE AHTIODACTYLA

415

is perhaps unnecessary. ^Merycodus had deer-like antlers,
but completely hypsodont teeth such as no known member
of the Cervicue possesses. The middle Miocene species {^M.
osborni) was a little creature, not more than eighteen or twenty
inches high at the shoulder, and had a branched antler of three
tines, which was considerably longer than the skull, while in
the species of the upper Miocene (fAf. furcatns) the antler
was shorter and simply forked. From the number of speci-

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furcatus, upper Miocene). Restored frnm •nwimmi

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mens of these animals found in which the burr is incomplete
or absent, it may be inferred that the antler was not always
deciduous. The legs were long and very slender, and appar-
ently there was no trace of the lateral digits, even in the fore
foot. These peculiar hypsodont deer persisted even in the
older Pleistocene.

Deer are the only members of the Pecora which inhabit
South America, where there are several genera of them, all
much more nearly allied to North American than to Old World

416 LAND MAMMALS IN THE WESTERN HEMISPHERE

forms. No record of the presence of the family in the southern
continent has been found in beds older than the Pleistocene,
but in view of the degree of specialization which they have
there undergone, it is probable that the immigration took place
in the Pliocene.

SECTION CAVICORNIA. HOLLOW-HORNED RUMINANTS

In the animals of this second and far larger section of the
Pecora there are bony outgrowths of the skull, from the frontal
bones, outgrowths which are permanent and non-deciduous;
these are the horn-cores, which are tapering and unbranched.
The horn-core is, in turn, covered with a sheath of horn, like-
wise unbranched and permanent, but growing from year to
year until the maximum size is attained, a process which is
familiarly illustrated in the growth of a calf. Among Recent
Cavicornia there is but one exception to the rule that the
horny sheath is non-deciduous and unbranched and that one is
the Prong Buck (Antilocapra americana) . In the Cavicornia it
is the very general rule that both sexes are horned, though the
females commonly have smaller horns and in several genera
of antelopes the does are hornless. There is almost as great
variety in the shape and size of the horn as of the antler ; we
find small, medium-sized and enormously large horns, which
may be straight, simply curved, complexly curved, spiral,
lyrate or twisted. The antelopes have many types of horns,
as have the sheep and goats, the oxen, buffaloes and bisons ;
but only a few of them are exemplified in the western hemi-
sphere, which now, as in the preceding geological periods, is
singularly poor in representatives of the Pecora.

9, 10. Antilopidce and Antilocapridce. Antelopes

Two very different kinds of antelopes are found in North
America at the present time; one of them, the erroneously
named Rocky Mountain Goat (Oreamnos montanus), is evi-
dently a late immigrant from the Old World, and fossil remains

HISTORY OF THE ARTIODACTYLA 417

of it have been found in the Pleistocene cave-deposits of Cali-
fornia. This animal is a member of the true antelope family
(Antilopidae) and belongs to the chamois group of mountain-
antelopes; it has no near relatives among other American
mammals, living or extinct.

The Prong Buck, or Prong-horned Antelope (Antilocapra
americana) , occupies a very isolated position, so much so that a
distinct family, the Antilocapridae, has been created for its
reception. It differs from all other Cavicornia in having a
branched horn, though the bony core is simple, and in an-
nually shedding and renewing the horny sheath ; the horn is
directly over the eye ; there are no dew-claws and all traces of
the bones of the lateral digits have completely disappeared.
The grinding teeth are thoroughly hypsodont. The genus
occurred in the older Pleistocene, where it was associated with
the last of the fdeer-antelope, or \Merycodus series (fCapro-
meryx), and which, so far as it is known, would seem to con-
nect the two families, though this is doubtful. A middle
Miocene genus (\Dromomeryx Fig. 128, p. 237) would be a more
probable ancestor of the Prong Buck, if it were not for the long,
unfilled gap of the upper Miocene and the whole Pliocene.
^Dromomeryx had erect horn-cores placed directly above the
eyes as in the modern genus, but low-crowned grinding teeth ;
it was the most ancient American cavicorn yet known. It
remains to be determined by future exploration, whether this
middle Miocene genus was actually the ancestor of Antilocapray
or merely an anticipation of it.

In the lower Pliocene have been found the remains, very
incomplete, of several antelopes, which appear to have been
immigrants from the Old World, but are too imperfectly known
for any definitive reference. One resembles the flat-horned, or
goat-horned, antelopes of the European Miocene and Pliocene.
Others had spirally twisted horns like those of the Recent
strepsicerine, or twisted-horn antelopes of Africa and Asia, but
may, nevertheless, be referable to the Antilocapridae.

2s

418 LAND MAMMALS IN THE WESTERN HEMISPHERE

Antelopes even penetrated to South America, and three
genera of them have been reported from the Pleistocene of the
Brazilian caverns and the Argentine pampas, but they were less
successful in establishing a foothold than were the deer, and form
no part of the modern Neotropical fauna.

11. Bovidce. Sheep, Bisons, Oxen, etc.

A series of genera, of disputed systematic position, is rep-
resented to-day by the so-called Musk-Ox (Ovibos moschatus),
which is now exclusively North American, but in the Pleistocene
ranged over northern Asia and Europe as far west as Great
Britain. The Musk-Ox, which is at present found only in the
extreme north, is a heavy, short-legged animal, three and a half
to four feet high, and six feet or more in length ; the body is
covered with a dense coat of woolly hair overlaid by a thatch of
long, straight hair, which gives the animal a very shaggy ap-
pearance. The horns are broad at the base, especially so in old
males, in which they meet in the middle line and cover much of
the head as with a horny casque ; they curve downward and then
upward and forward, with the tips directed toward the front ; in
the females and young males the horns are very much smaller.

This series cannot be traced back of the Pleistocene, in
which epoch it was not only far more widely distributed, but
also very much more diversified, no less than three extinct
genera, in addition to the existing one, having been found in
the North American Pleistocene. One of these ( ^Symbos) , which
extended from Alaska to Arkansas, had horns which were
smaller and shorter than in the modern genus, and, even when
fully developed, did not meet in the middle line of the head.
The other two genera, from California {^Euceratherium and
\Preptoceras Fig. 116, p. 203), are of great interest as showing
affinities to the Musk-Ox and also to sheep and to certain ante-
lopes, such as the Takin (Budorcas) of northern India and Tibet.
They serve to connect the musk-oxen with other Cavicornia,
but the origin of all these animals is to be sought in Asia.

HISTORY OF THE ARTIODACTYLA 419

In Recent North America there are four or five species of
sheep (Ovis) which are confined to the mountainous and broken
areas of the western part of the continent and extend from
Alaska to Mexico. The " Bighorn' ' or Rocky Mountain
Sheep (Ovis canadensis) is characterized by great, spirally coiled
horns in the rams, in the ewes the horns are very much smaller
and nearly straight ; the other species differ but slightly from
this type. The species 0. canadensis has been found in the
Pleistocene, but nothing further is known of its history.
Evidently, the sheep were late immigrants.

' ' The geographical distribution of wild sheep is interesting.
The immense mountain ranges of Central Asia, the Pamir and
Thian Shan of Turkestan, may be looked on as the centre of
their habitat.' ' "Sheep are essentially inhabitants of the
high mountainous parts of the world, for dwelling among
which their wonderful powers of climbing and leaping give
them special advantages. No species frequent by choice either
level deserts, open plains, dense forests or swamps. By far
the greater number of species are inhabitants of the continent
of Asia, one extending into North America [should read, four
or five] one into Southern Europe and one into North Africa.
. . . No remains that can be with certainty referred to the
genus [Ovis] have been met with in the hitherto explored true
Tertiary beds, which have yielded such abundant modifications
of Antelopes and Deer." *

The only other division of the family which is represented
in North America is that of the bisons, of which the fast vanish-
ing remnant of a single species 2 (Bison bison) is all that is left
of what was once an extensive and varied assemblage. The
bisons differ from the true oxen in the form and structure of
the skull, in the shoulder-hump, which is produced by the very
long spines of the dorsal vertebrae and in consequence of which
the back slopes downward from the shoulders to the croup.

1 Flower and Lydekker, op. cit., pp. 355 and 357.

* The Woodland Bison of Canada is now regarded as a distinct species.

420 LAND MAMMALS IN THE WESTERN HEMISPHERE

They differ further in the character of the hair, which is short
and woolly on the body and hind quarters, very long and shaggy
on the head and neck. In the Pleistocene of North America
there were at least seven recognizable species of bisons, which
ranged over the continent from Alaska to Florida, though it
is not probable that they were all contemporary. One of the
earliest and by far the largest of these was the gigantic B.
^latifrons, a specimen of which in the American Museum of
Natural History measures sixieet across the horns in a straight
line ; this was a Mississippi Valley species and extended from
Ohio to the Gulf of Mexico and westward to Kansas and Texas.
Another gigantic species (B. \crassicornis) lived in Alaska in
association with a second and smaller species (B. \occidentalis)
which ranged as far south as Kansas. B. IfocddentaliSy though
smaller than the preceding species, was larger than the existing
one and was remarkable for the great size of the hump. The
bisons were migrants from the Old World and are the only
members of the great ox-tribe that ever reached America. At
present the Old World has but a single species of Bison {B.
bonasus) , which has been saved from extermination only by the
most rigid protection.

Neither sheep nor bison extended their range to South
America ; both are and have been essentially northern groups
and seem to have been unable to cross the tropics.

From the foregoing account, confused as it unavoidably is,
one thing at least stands out clearly, that North America
played a very insignificant r61e in the evolution of the Pecora,
and has only two peculiar groups, the Prong Buck and the
American types of deer, and of these, the probable American
ancestry does not extend back of the lower Miocene and per-
haps not so far. Even in the Old World the story, so far as it
has been deciphered, is by no means clear and consistent, which
is no doubt due to the fact that the regions from which Tertiary
mammals have been obtained are so small in comparison with

HISTORY OF THE ARTIODACTYLA 421

those that have yielded nothing. Certain broad outlines of the
history may, nevertheless, be discerned.

The suborder Pecora at an early date became divided into
the two great branches of the Cervicornia and Cavicornia,
the former giving off the giraffe series, which in the Miocene
and Pliocene ramified and extended through Asia and southern
Europe, though now confined to Africa. In the lower Miocene
of Europe the muntjac-like deer and the antelopes, the first
of the Cavicornia, were already well distinguished. From the
primitive antelopes arose not only the wonderful assemblage
of modern antelopes, but also the goats and sheep and the great
and varied ox-tribe. From the middle Oligocene. forms it
may obviously be inferred that both Cervicornia and Cavi-
cornia united in a single trunk, or, traced in the other direction,
diverged from a common stock, to which also the suborder of
the Tragulina goes back.

On the other hand, it is equally obvious that the camels
and llamas have been separated from the Pecora at least since
the middle Eocene, and, consequently, the many points of
agreement between the two suborders, other than those shared
with all artiodactyls, are not due to inheritance from a common
ancestry, but have been independently acquired in the two
series. It will be instructive to note some of the more im-
portant of these independent similarities : (1) the selenodont
and more or less hypsodont character of the grinding teeth ;
(2) the spout-shaped odontoid process of the axis ; (3) the
great reduction of the ulna and its coossification with the
radius ; (4) the loss of the fibula, except for its lower end, which
persists as a separate malleolar bone ; (5) the formation of
cannon-bones by the fusion of the third and fourth metapodials ;
(6) the development of a complex, many-chambered stomach.
Other points of likeness might be cited, but those already given
will suffice to show how very important this parallel mode of
evolution often proves itself to be.

CHAPTER X

HISTORY OF THE PROBOSCIDEA

Utterly foreign as the elephant-tribe appears to be to
present-day North America, it was a very conspicuous element
in the fauna of that continent from the middle Miocene to the
end of the Pleistocene, and in the latter epoch it spread over
South America also. Like so many others of the mammals
which have, from time to time, flourished in the Americas, the
elephants and their allies, the tm&stodons, were immigrants
from the Old World, and, until comparatively lately, the region
of their origin was a complete mystery. They appeared sud-
denly and unheralded and at approximately the same time in
Europe and North America and nothing is known from pre-
ceding geological formations of either continent which could
with any plausibility be regarded as ancestral to them. The
mystery was dispelled by the discoveries of Dr. C. W. Andrews
in Egypt, which demonstrated that these strange and huge
beasts had originated in Africa and had migrated thence through
Asia to Europe, on the one side, and to North America on the
other.

The proboscideans occupy a very isolated position among the
hoofed mammals, and in structure they display a curious min-
gling of high specialization with an extreme conservatism of
primitive characters, the specialization being exemplified in
the teeth and head and the conservatism in the body and limbs,
very much as in the foreodont family of artiodactyls (p. 382).
The most conspicuous of the external features in the order is
the long trunk, or proboscis, which gives its name to the group,
and is a great prolongation of the nose, with the nostrils at the

422

HISTORY OF THE PROBOSCIDEA

423

end and a finger-like tip, which can be used to pick up minute
objects.

In the true elephants the dental formula is : i J, c g, p £, m f ,
X 2= 14, though this formula is misleading, to the extent that
the milk premolars, three in number in each jaw, take the place
and perform the functions of the premolars, thus adding 12 to
the effective number of teeth. The single upper incisor on
each side grows into an immense tusk, which has enamel only
on the tip, where it is speedily worn away ; the lower jaw is
without incisors and there
are no canines above or
below. The grinding teeth
are very large and have a
highly complex structure
and a most exceptional
method of eruption on
coming into use. They
are thoroughly hypsodont
and each is composed of a
large number of high, broad
and thin plates of dentine
covered with enamel and
the spaces between the
enamel ridges are filled
with cement (see Fig. 47,
p. 97) ; indeed, the whole tooth is so thickly covered with
cement that, when unworn, it looks like a mere lump, with
no ridges showing on the surface. The teeth increase in size
and in the number of component ridges from before back-
ward, and in the Indian species (Elephas maximus) the
number of ridges in the six grinding teeth, including the
milk premolars, is : 4, 8, 12, 12, 16, 24. In the African Ele-
phant {Loxodonta africanus) the teeth are not so high and
have fewer and thicker plates, the formula being : 3, 6, 7, 7,
8, 10. The teeth do not succeed one another vertically in the

Fia. 223. — Molar of the African Elephant
(Loxodonta africanus) showing the oblique
mode of wear. Heavy black lines indicate
enamel, enclosing areas of dentine, cement
covering the whole tooth.

424 LAND MAMMALS IN THE WESTERN HEMISPHERE

normal mammalian fashion, but come in successively from
behind and the series moves forward, so that the foremost tooth
is pushed out, when it is so worn down as to be of no further
service. As these teeth are very large and the jaws are rela-
tively short, only one tooth on each side, above and below, is in
use at the same time, though part of a second may also be in-
volved. The movement of the successive teeth is not directly
forward, but oblique, an upper tooth coining forward and down-
ward and a lower tooth forward and upward. In consequence
of this arrangement the teeth are abraded obliquely, the anterior
part first coining into use, and, by the time a tooth is fully in
place, the front portion is worn down to less than half the
height of the hinder part. All of these peculiarities in the
dental system imply a very high degree of specialization and a
notable difference from other mammals.

The skull is equally specialized, as is indeed required by
the character of the teeth and the development of the long
and heavy proboscis. The premaxillae are converted into
sheaths for the great tusks ; the nasals are extremely abbreviated
and the anterior nasal opening is shifted to the top, directly
above the posterior opening, so that the nasal canal passes
vertically downward through the skull. All of the bones
forming the cranium are enormously thickened and at the same
time lightened by the formation of an extensive system of
communicating sinuses, and thus the brain-chamber is, as it
were, hidden away in the middle of the huge mass of the skull.
This explains the difficulty of killing an elephant by shooting
it in the head ; the shot must be so directed as to reach the
brain, which requires knowledge and skill.

The neck is short, the body long and extremely massive,
the tail of moderate length. The shoulder-blade is very large
and has a prominent metacromion given off from the spine ;
the hip-bones are immensely expanded in correlation with the
breadth of the thorax and abdomen. The limbs are long,
massive and columnar, their upper segments, especially the

HISTORY OF THE PBOB08CIDEA

425

thigh, are very long, so that the knee-joint is brought below
the body and free from it to the position of the hock-joint
in the Horse ; hence, the hind leg appears to bend in the op-
posite direction from the bend in the legs of ordinary quad-
rupeds, in which the true knee-joint is concealed. The fore-
arm bones are separate and, for most of its length, the ulna
is far heavier than the radius, a wide departure from the pro-
portions usual in hoofed
animals. The femur
has no pit in its head
for the round ligament
and no third trochanter ;
the shaft is broad and
much flattened, having
quite lost the normal
cylindrical shape. The
bones of the lower leg
are also separate, but
the fibula, though stout,
is very much more
slender than the ulna.
The long bones have
no marrow-cavities, but
are filled with spongy
bone. The feet are ex-
tremely short and broad
and of columnar shape,

the weight resting upon a pad of elastic tissue and the small,
nail-like hoofs are mere excrescences upon the periphery.
There are five digits in manus and pes, but not all of them
have hoofs ; in the Indian and West African species the
number of hoofs is five in the fore foot and four in the hind,
in the East African four and three respectively. In the adult
the skin is quite hairless, though the young calf has a consider-
able quantity of hair.

of the Indian Elephant

426 LAND MAMMALS IN THE WESTERN HEMISPHERE

At present, the Proboscidea are restricted to the warmer
parts of Asia and Africa, where five species, four of them
African, are recognized. This is a very great reduction in the
number of species and in the area inhabited during the Pleis-
tocene epoch, when they ranged through every continent,
except Australia, and were adapted to every climate from the
tropics to the shores of the Arctic Sea. Four distinct species
of proboscideans existed in Pleistocene North America, three
elephants and a {mastodon, though not all in
the same areas, nor probably alt at the same
time, their ranges both in time and space
overlapping to a greater or less degree, but
not exactly coinciding in either respect.

The first species was an immigrant, the
northern fMammoth (Elephas jprimigertius) ,
which extended over the greater part of the
Pio. 225. — Vertical northern hemisphere, both in the Old World

section through anJ j„ jjjg pjew -pnjs jg fae SpeCie9 0f which
the manus of the - , , , .

iodian Eicphaot. complete carcasses with hide and hair have
u lower end of been found m the frozen gravels of northern

ulna. L. lunar.

m. magnum. Siberia, its structure and appearance being
cf£aithird /TT ^us a^most M weU known as those of any
phalange, e, pad modern elephant. That the fMammoth was
(After M.weber) perfectly adapted to life in a climate of severe
cold is shown not only by the contents of the
stomach, which are comminuted fragments of present-day
Siberian vegetation, but also by the dense coat of woolly hair,
covered by long, coarse outer hair, which afforded full protec-
tion against the cold. The tusks, with considerable variation
of form, had a tendency to spiral curvature, curving first
downward and outward, then upward and inward ; the grind-
ing teeth were characterized by their relative breadth and the
numerous thin enamel-ridges which traversed them. The
number of these ridges was very variable in different indi-
viduals, but may be expressed for the six successive teeth as

HISTORY OF THE PROBOSCIDEA 427

follows: 3-4, 6-9, 9-12, 9-15, 14-16, 18-27. The skeleton
was more like that of the Indian Elephant than of the other
species, though with a number of small differences in the skull.
In size, the fMammoth was comparatively small, standing
about nine feet six inches at the shoulders. In North America
its range was from Alaska southeastward across the continent
to New England.

The second species, the fColumbian Elephant (E. ^columbi
Fig. 114, p. 198), was eighteen inches or more taller than the
fMammoth and rivalled the largest existing elephants in
stature ; its huge tusks curved first^downward and then upward
and inward, their tips crossing when full-grown. The grinding
teeth had fewer and thicker enamel- plates than those of the
fMammoth. The; range of the fColumbian Elephant over-
lapped the southern border of that of the fMammoth, but was,
on the whole, much more southern ; it crossed the continent
from ocean to ocean and covered nearly the whole of the United
States, extending down to the southern end of the Mexican
plateau. The two species were very closely related and in some
cases are so intergraded that it is difficult to distinguish them j
the fMammoth was an undoubted immigrant and the fColum-
bian Elephant was probably a local North American variant of
it, adapted to a somewhat warmer climate. Nothing is known
of the skin or hair in the latter animal, but, from the fact that
it was not a tropical species and was exposed to very cold
winters, it may be inferred that it had a hairy covering of
some sort.

The third species of elephant (E. \imperator) was older
geologically than the others, as it was more characteristic of
the lower Pleistocene and uppermost Pliocene; its range
coincided with the western half of the region covered by E.
^columbi, extending far into Mexico, but not occurring east
of the Mississippi River. It was an enormous creature, the
largest of known elephants, with an estimated height of thirteen
and a half feet at the shoulder (Osborn). The grinding teeth

428 LAND MAMMALS IN THE WESTERN HEMISPHERE

HISTORY OF THE PROBOSCIDEA

429

had thicker and more crumpled enamel plates than in either
of the other species.

The fourth of the Pleistocene proboscideans of North
America was a member of a different and much more ancient
genus, ^Mastodon, which in the Old World became extinct
before the end of the Pliocene. The American fMastodon
(fiW. americanus) was thus a belated survival of an ancient
type, seemingly out of place even in the strange Pleistocene
world, which had so many bizarre creatures. The distinguish-
ing characteristic of the genus was in the simple, low-crowned
and comparatively small grinding
teeth, which had three or four
prominent transverse ridges, cov-
ered with heavy enamel, and,
usually, with no cement on the
crowns. As these teeth were so
much smaller than those of the
elephants, as many as three on
each side of each jaw might be
in simultaneous use. In this
species there was no vertical suc-
cession of teeth, but in some of
the Tertiary fmastodons such
succession has been observed. The long tusks were directed
nearly straight forward and were almost parallel, with but
slight curvature, the convexity downward. In the males
there was a short single tusk or, less commonly, a pair of such
tusks, in the lower jaw, which were probably not visible ex-
ternally ; these were the vanishing remnants of an earlier
stage of development, when the fmastodons had a fully
developed pair of lower tusks, nearly as large as the superior
pair.

The skull, while essentially proboscidean, was yet much
lower and flatter and less dome-like than in the elephants ;
the thickening of the cranial bones was less extreme. The

430 LAND MAMMALS IN THE WESTERN HEMISPHERE

remainder of the skeleton differed so little from that of the
elephants as to require no description. In size, this species
about equalled the f Mammoth, the larger individuals measur-
ing nine feet six inches at the shoulder. Remains have been
found which prove that the American fMastodon had a cover-
ing of long, coarse hair, and that it fed upon the leaves, shoots
and small branches of trees, ©specially of conifers. There is
much reason to believe that the species outlived the elephants
in this continent and persisted until after the establishment
here of the American Indian, and it may well have been human
agency which finally extinguished the dwindling race. The
range of the species nearly coincided with that of the fColum-
bian Elephant, but did not extend so far into Mexico, and in
the central part of the continent reached much farther north,
even into Alaska.

In the Pliocene of Texas, Nebraska and Idaho lived the
American representatives of a genus ("\Stegodon) which was a
connecting link between the elephants and the fmastodons, and
which was especially characteristic of the Pliocene of India.
The tusks, which were confined to the upper jaw, had lost
their enamel and the last molar, above and below, had five or
six enamel ridges, but the crowns, which in the Asiatic species
were buried in cement, had but a small amount of this
material. Several species of ^Mastodon occur in the same beds,
but only isolated teeth have been found.

The fniastodons, in a broad sense of the term, have been
divided into several genera and subgenera in accordance with
different schemes ; the simplest perhaps is to group into a
second genus those species which had fully developed lower
tusks. This four-tusked genus has received several names,
of which \Tetrabelodon is most commonly used in this country,
but the term \Gomphotherium is much older and, according
to the law of priority, must therefore be employed. The lower
Pliocene species of 1[Gomphotherium had a pair of large lower
tusks, of cylindrical shape, and both upper and lower tusks

HISTORY OF THE PROBOSCIDEA 431

had longitudinal bands of enamel, and in order to support the
weight of these great tusks the symphyseal, or chin, region of

Fio. 228. — Head of upper Miocene tmastodon UOomphtXhcrium produclum) showing
the chisel-like lower tusks. Restored from a skull in the American Museum of Natu-
ral History.

the lower jaw was greatly elongated ; the molars had four

In the upper Miocene is found another and more primitive
stage of proboscidean development. In these species the grind-
ing teeth were three-ridged ; the upper tusks were quite short
and curved downward, diverging somewhat from each other,
and they had enamel bands. The lower tusks were still
shorter and of depressed, flattened and somewhat chisel-like

432 LAND MAMMALS IN THE WESTERN HEMISPHERE

form and so worn as to show that they were regularly employed
in cropping and browsing. The skull was low and broad and
the symphysis of the lower jaw was greatly prolonged to carry
the tusks.

A very important fact concerning these early fmastodons
is that they had the normal method of tooth-succession, per-
manent premolars forming beneath (in the lower jaw, above
in the upper) the milk-teeth and pushing them out at maturity.

Of the middle Miocene proboscideans not much is known
beyond the mere fact of their presence in North America
at that time and indeed little of the skeleton, other than the
skull, has yet been found in the American Miocene ; but well-
nigh complete skeletons have been obtained from the middle
Miocene of Europe, and these bring out the surprising fact that
the body and limbs of these species did not differ in any note-
worthy manner from those of the existing elephants; the
modern skeletal structure of these animals had been attained
at a time when the dentition and skull were still in a far less
advanced stage of development. In size, however, there was
a decided difference, the species of the American Miocene
rarely attaining a height of six feet.

Proboscidea have been reported from the lower Miocene
of the Great Plains, but the material is insufficient for a defin-
itive judgment. There is no doubt as to their presence in
Europe at that time, but in neither continent can the history
be traced any farther and we must turn to Africa for a back-
ward continuation of the story. In the lower Oligocene of
the FayAm, southwest of Cairo in Egypt, occurs the highly
interesting genus 1[Palceomastodon, which was much more
primitive than any of the genera described above, though it
was an unmistakable member of the order and even of the
family Elephantidae. The dentition was already much re-
duced, giving the formula : i \, c #, p f , m f . The upper tusks
were short, compressed, directed downward, and slightly diver-
gent, and had a broad band of enamel on the outer side ; the

HISTORY OF THE PROBOSCIDEA 433

lower tusks were still shorter and procumbent, pointing straight
forward, and were covered with enamel, which was very thick
on the lower side and thin or wanting on the upper. All of
the grinding teeth were in place and function at the same time,
which was not true of any of the genera previously considered,
and each of the premolars had its predecessor in the milk-series,
which it succeeded and displaced in the normal vertical manner.
The premolars were smaller and simpler than the molars,
which were made up of three pairs of conical tubercles arranged
to form a three-crested crown. The skull, as compared with
that of the elephants, was long and narrow, the premaxillaries
extending into a long snout; the nasals were shortened,
though not so much as in the succeeding genera, and there was

4

probably rather a long and flexible snout than a true proboscis.
The skull had a long and well-defined sagittal crest, which
none of the later genera had, and the development of sinuses
in the cranial bones, though considerable, was much less than
in the elephants. The occiput was relatively high and the
thickened parietals did not tower above it to any such degree
as they do in the elephants. The symphysis of the lower jaw
was greatly prolonged, extending out beyond the ends of the
upper tusks, and this implies that the lower lip had a corre-
sponding prolongation.

The skeleton is still incompletely known, though it may be
said that the neck was probably longer than in the subsequent
genera of the family. The limb-bones were already proboscid-
ean in character, differing only in details from those of the
more typical members of the order, but the animal was more
lightly built and had less massive limbs. The presence of the
third trochanter on the femur, which is lacking in all of the
succeeding forms, is an interesting approximation to other and
still more primitive groups of ungulates. The several species
of ^PaUeomastodon represent a considerable range in size,
from animals which were not much larger than a tapir to those
which equalled a half-grown Indian Elephant.

2p

434 LAND MAMMALS IN THE WESTERN HEMISPHERE

It is possible to take another and very long step back from
1[Palceomastodon} so long, indeed, as to make it apparent that
one or more links in the chain are still missing. The genus
\Mcxritherium is found together with IfPalceomastodon in the
lower Oligocene, but also occurs separately in the upper Eocene.
It seems likely that it is a persistent middle Eocene type and
that the known species of it were somewhat aside from the
main line of descent, but that it very closely represents, never-
theless, a very early stage in the elephant genealogy. These
known species were quite small animals, about the size of a
tapir, and therefore not much less than the smaller members of
IfPalceomastodon. The dental formula of 1[Mceritherium was :
ih ch Vh mh X 2 = 36. The first or median upper incisor
was a relatively small and simple tooth, but the second was
quite a large, downwardly directed tusk, which was much
smaller and less curved than in f Palceomastodon, and was not
capable of indefinite growth. The third incisor and the canine
were small, spike-like teeth of no functional importance, but
their presence is significant as approximating the primitive,
unreduced dentition of the ungulates. The lower incisors
were nearly procumbent, with a slight upward inclination;
the first one was long and the second a thick, enamel-covered
tusk, with a chisel-like edge, which was produced by wear.
The premolars were smaller and simpler than the molars, which
were quadritubercular, the four conical cusps arranged so as
to form two transverse crests, giving a pattern like that of the
early pigs and peccaries and of precisely the kind that might
have been predicted from the teeth of 1[Palceomastodon.

The skull had an utterly different appearance from that
of \Palceomastodon, the difference being much greater than
between the latter and the Miocene \Gomphotherium. It was
long and narrow, and, except for the very prominent zygomatic
arches, of nearly uniform, tubular shape, the brain-case being
of small capacity, though, as compared with other Eocene
mammals, the brain was proportionately large. "It is possible

HISTORY OF THE PROBOSCIDEA 435

that the early tendency toward a considerable cerebral devel-
opment shown in these primitive Proboscidea is one of the
causes why the group has survived and flourished through so
long a period " (Andrews). The cranium was very long and
the facial region extremely short, the premaxillaries not being
prolonged into a snout, as they were in ^Palceomasiodon ; the
occipital bones formed nearly the entire posterior surface of
the cranium and even encroached slightly upon the roof. There
was a long, but not very prominent, sagittal crest, and some of
the cranial bones were much thickened; in one species the
hinder part of the cranial walls was distinctly inflated, a begin-
ning of the enormous thickening which has culminated in the
true elephants. The nasal bones were already much shortened,
though they were twice as long as those of IfPalceomasto-
don, and the animal would appear to have had an incipient
proboscis.

The neck was of moderate length and the body very long,
with at least twenty pairs of ribs, and there was probably
a long tail. The hip-bone differed remarkably in its extreme
narrowness from that of the later Proboscidea and the limb-
bones were much more slender, though not dissimilar in shape.

At a very early period the order became divided into two
main branches, one of which includes all the forms so far
considered, and the other the very strange ^Dinotherium. The
fdinotheres entered Europe together with the fmastodons
in the lower Miocene and continued into the Pliocene without
much change and then died out, leaving no descendants.
They never invaded North America, probably because they
were of more or less aquatic habit, like the hippopotamuses,
and therefore less likely to find suitable conditions in the
narrow and unstable land-bridges which connected the Old
World with the New, than were animals of purely terrestrial
habitat. The fdinotheres were of huge size, equalling the
larger elephants in this respect and closely resembling them in
the skeleton of the body and limbs. As usual in this order,

436 LAND MAMMALS IN THE WESTERN HEMISPHERE

the generic peculiarities were to be found in the teeth and skull.
There were no superior tusks, all the upper incisors and canines
being lost, but there was a pair of large lower tusks, which
were directed downward, with a strong backward curvature.
The dental formula then was : i\, c#, pf, mf , X 2 = 22. The
grinding teeth were relatively quite small and had, except the
first molar, two transverse crests, giving a pattern singularly
like that seen in the tapirs. The skull was remarkably long,
low and flat, and no doubt these animals had a proboscis of
some sort. That the fdinotheres were derived from the same
ancestral stock as the fmastodons and elephants is perfectly
obvious and is not questioned by any one, but it is not yet
possible to trace the connection.

The proboscideans were late immigrants into South
America, being known there only in the Pleistocene and late
Pliocene times, and only the fmastodons entered the southern
continent, where they gave rise to several peculiar local species
in Argentina, Bolivia, Chili and Brazil; one of these (\ Mas-
todon andium) had a deposit of cement on the crowns of the
grinding teeth. Why the elephants, which extended to the
northern border of the Neotropical region, should have failed
to reach South America and maintain themselves there, is but
one of many similar questions to which no assured answer can
be given.

The evolution of the Proboscidea was, in a certain sense,
very similar to that of the foreodont family (p. 381) among the
Artiodactyla, in that the developmental changes affected
chiefly the dentition and the skull, the skeleton of the body
and limbs having very early acquired a character which was
afterward but little modified. Were the skull and teeth of the
lower Miocene ^Gomphotherium not known, we should hardly
hesitate to refer the skeleton to the genus Elephas, and even
in the Oligocene t Palceomastodon all the bones of the skeleton,
other than the skull, were characteristically and unmistakably
proboscidean. On the other hand, the transformations of the

£/e/>Aas /b

Sfeoocfon fa

Mastodon fa

RECENT

PLEISTOCENE

f Elephas

(short chin).

UPPER PLIOCENE)]

LQMR PLIOCENE \Gomf>horAer/um
UPPER MIOCENf J <**"%£<

Steoodon
(phortchin).

7etrabelodori fa

MIDDLE MIOCENE

Miyrothn into
North America

LOVER MIOCENE

Chin)

I Gomphotherium
' Qnoustidens
{hno chin^

UPPER OLIGOCENE

IOW£ROUGOCENE\

Poloeomastodon '/¥ UPPER EOCENE

rbfoeomashdoh
(kuf/Mnino chlri

A/oeri/lberivm

M/OOLE EOCENE I (sto***)

Moeritherium /?

? L OMIf/i £OC£Aff (ancestor unknown). %

Fig. 229. — Evolution of the Proboscidea : on the right, a series of skulls ; on the left,
last lower molar. (After Lull, modified by Sinclair.) N.B. \Tetrabdodon should
read t Gomphotherium.

(437)

438 LAND MAMMALS IN THE WESTERN HEMISPHERE

teeth and skull were very profound and far-reaching, very
much more so than those which took place in the foreodonts.

In the dentition we may consider separately the develop-
ment of the tusks and of the grinding teeth. The first step
in the known series, as exemplified by \M(Britheriumy was the
enlargement of the second incisor in each jaw to form a tusk
which, though actually quite long, was very small when judged
by the proboscidean standard. The upper tusk was directed
vertically downward and the lower one was procumbent, point-
ing almost directly forward ; the third incisor and the canine
were small and in the lower jaw already lost. In the next known
stage, ^Pal&omastodon, all of the anterior teeth, except the
tusks, had been suppressed; the upper tusks were longer
and more curved and of an oval cross-section ; they extended
less directly downward and more forward, while the enamel
was restricted to the outer side of the tusk ; the lower tusks
were more fully procumbent than in the preceding genus. The
third stage, that of the lower Miocene \Gomphotherium, showed
the upper tusks greatly elongated and directed more forward
than downward, while the lower tusks were but little larger
than before. From the middle Miocene two phyla may be
distinguished by the tusks alone ; in one, which was not destined
to long life, the lower pair increased greatly both in length and
in diameter, while in the other series they rapidly diminished
and eventually disappeared. Even in the Pleistocene, how-
ever, the American fMastodon had remnants of these tusks
in the males. In the later tmastodons, the fstegodonts, and
true elephants, the upper tusks, which alone remained, lost
the enamel bands and attained enormous proportions, differing
in the various genera and species in the extent and direction
of curvature. An aberrant mode of tusk development was
to be seen in the fdinotheres, in which the upper pair was sup-
pressed and the lower pair enlarged and so curved that the
points were directed backward.

The grinding teeth underwent much more radical and

HISTORY OF THE PROBOSCIDEA 439

striking changes. At first {\Mceritherium) they were small,
very low-crowned and of simple pig-like or quadritubercular
pattern, making two interrupted cross-crests ; all were in use
simultaneously and the succession of milk-teeth and premolars
was by vertical replacement, as in normal mammals generally.
In 1[Palceomastodon there were three pairs of tubercles on the
molars and in ^Gomphotherium these coalesced into ridges, but
in all the fmastodons there was more or less distinctness of the
conical tubercles. In one or more phyla the three-ridged plan
persisted for a long time, one such phylum terminating in the
Pleistocene ^Mastodon americanus. In the other series the
number of ridges increased, first to four, then to five, six and
more {\Stegodon) ; the crowns of the teeth became much
larger and higher, and the ridges, as their number increased,
became much thinner, and the valleys between them were filled
with cement, and finally, in the true elephants, with their
fully hypsodont, many-crested teeth, were thickly covered all
over with cement. The vertical succession of milk-teeth and
premolars was retained in \Gomphotherium, at least in some
species, but the large molars, which could not find room to be
exposed while the premolars were in place, came in successively
from behind. This horizontal mode of succession is the only
one to be seen in the true elephants, in which but one tooth,
or parts of two, on each side of each jaw are in simultaneous
use and the premolars have entirely disappeared, but the milk-
teeth are retained.

The changes in the skull, which amounted to a recon-
struction, were very largely conditioned by the great increase
in the length and consequent weight of the tusks, in the size
of the grinding teeth and the development of the proboscis. In
the earliest known type (IfMceritherium) the skull had little
about it that would, at first sight, suggest proboscidean affin-
ities ; it was long and narrow, with sagittal crest and occiput
of normal type, very long cranial and very short facial region.
The nasal opening was directed forward and the nasal canal

440 LAND MAMMALS IN THE WESTERN HEMISPHERE

was relatively long and horizontal in direction, but the nasal
bones were already much shortened, indicating that the pro-
boscis was probably in an incipient stage. The symphysis
of the lower jaw was procumbent and somewhat elongated, but
to only a comparatively slight degree.

While the skull of IfMceriiherium was not obviously pro-
boscidean, that of its successor, ^Pakeomastodon, was unmis-
takably so, yet retained several primitive features, which were
lost in all of the subsequent genera, such as the sagittal crest,
the relatively low cranium and moderate thickening of the
cranial bones, the forward direction of the nasal opening, etc. ;
the symphysis of the lower jaw was very greatly prolonged.

As the tusks enlarged and the proboscis grew longer, the
weight of the head and its appendages necessitated a largely
increased area of attachment for the neck-muscles, and this
was attained by a very great ''thickening of the cranial roof,
the occiput not increasing proportionately ; at the same time,
the thickened bones were honeycombed with sinuses, so as to
reduce their weight without sacrifice of strength. In those
species of the Miocene \Gomphotherium which had large and
heavy tusks, this thickening was not very much less than in
the true elephants. The enlargement of the tusks had other
consequences, as, for example, in lengthening and broadening
the premaxillaries and, in the elephants, in their downward
bending, so as to shorten still further the facial region of the
skull. With the development of the proboscis, the nasal
bones were reduced to a minimum and the anterior nasal
opening was no longer directed forward, but obliquely upward,
while the nasal passage lost its horizontal direction and became
almost vertical. The lower jaw continued to elongate the
symphysis, reaching a maximum in certain species of fGom-
photherium ; but the reverse process of shortening this anterior
region of the jaw began with the reduction of the lower tusks,
and, when these had disappeared, nothing remained of the
immensely elongated symphysis, except the short spout of the

HISTORY OF THE PROBOSCIDEA 441

elephant's jaw. As the grinding teeth increased in height,
there was a concomitant increase in the vertical depth of the
jaws for their lodgment.

It was an obvious advantage in the mechanical problem
of supporting the enormous weight of head, tusks and trunk
to shorten the neck and thus bring the weight nearer to the
point of support at the withers, the lengthening proboscis
rendering it unnecessary for the mouth to reach the ground
in feeding or drinking. The other parts of the skeleton under-
went comparatively little change, the degree of modification
being greatest between ^Mceritherium and ^Palceomastodon.
Throughout the series the bones of the fore-arm and lower
leg remained separate, and the feet very short and five-toed.
In size also the great stature and massiveness were attained
early. After the great migration of the Proboscidea to the
northern continents, we find considerable differences of size
between the various phyla, though all were very large, and
even as early as the lower Miocene of France, there were
species which rivalled the modern elephants in bulk. It was
this rapid attainment of great size and weight which appears
to have been the determining factor in the conservatism of the
skeleton. After the skeleton had become fully adjusted to
the mechanical necessities imposed by immense weight, and
that adjustment, as we have seen, was effected at a com-
paratively early period in the history of the order, then no
further modification of importance would seem to have been
called for. No doubt the habits and mode of life of these
massive, sedate and slow-moving animals underwent but little
change from the lower Oligocene onward. There is reason to
think that ^Mceritherium was semi-aquatic and a haunter of
marshes and streams, but, if so, the change to a life on dry
ground was complete in the lower Oligocene, for the structure
of ^Palceomastodon gives no reason for supposing that it was
anything but a dweller on solid land and a denizen of forests.

Although this book does not undertake to deal with the

442 LAND MAMMALS IN THE WESTERN HEMISPHERE

obscure problems connected with the marine mammals, it may
be noted in passing that one of these problems has been brought
near to solution, if not actually solved, by the discoveries in
Egypt and that is the question concerning the origin of the
Sirenia. The order includes the existing Manatee or Sea-
Cow (Manatus) of the coast of Florida, northeastern South
America and western Africa, and the Dugong (Halicore) of the
Indian Ocean. These are mammals which are adapted to a
strictly marine habitat and are incapable of existence on land,
having lost the hind limbs and converted the fore limbs into
swimming paddles. Unlike the whales, porpoises and other
Cetacea, the Sirenia are herbivorous and feed upon seaweed
and eel-grass and the aquatic plants of large rivers. The
Egyptian discoveries tend very strongly to the conclusion that
the Sirenia and Proboscidea were both derived from a common
stock and that the genus ^Mceritherium was not very far removed
from the probable ancestor from which both of the orders
descended.

CHAPTER XI

HISTORY OF THE fAMBLYPODA AND f CONDYLARTHRA

These are two orders of hoofed animals which long ago
vanished from the earth and no member of either is known to
have survived later than the Eocene epoch ; both were of great
antiquity, dating back to the Paleocene, perhaps even to the
Cretaceous. The last of the f Amblypoda are found in the
lowest Uinta or highest Bridger, but they were relatively
abundant in all the more ancient beds. The following table
gives the more important American forms :

Order fAMBLYPODA. fShort-Footed Ungulates
Suborder f Taugrada

I. fPERIPTYCHIDiE.

t Periptychns, Paleoc.

II. fPANTOLAMBDIDiE.

^Paritolambda, Paleoc.

Suborder fPANTODONTA

III. fCoRYPHODONTIDiE.

^Coryphodon, Wasatch and Wind River.

Suborder fDiNOCERATA

IV. fUlNTATHERIIDiE.

t Bathyopsis, Wind River. fElaehoceras, Bridger. ^Uintatherium,
do. ^EobasileuSj do.

As is shown in the table, the suborder f Taligrada is entirely
Paleocene in distribution, the fPantodonta are lower Eocene
and the fDinocerata chiefly middle Eocene, though persisting
into the upper. The fDinocerata were the most striking and
characteristic of Bridger mammals, and two or three phyla
of them may be distinguished, though for our purposes this

443

444 LAND MAMMALS IN THE WESTERN HEMISPHERE

is hardly necessary, for these strange and bizarre creatures
were all very much alike. From the commonest and best-
known genus (^Uintatherium) they are called fumt&theres.
They were large and ponderous animals, the veritable giants
of their time, far exceeding any of their contemporaries. In
appearance they were among the most fantastic of the many
curious beasts which the fossils have revealed.

The skull carried three pairs of bony protuberances, or
horn-like outgrowths; one pair on the nasal bones suggest
by their shape and character that they formed the support of
dermal horns like those of the paired-horn rhinoceroses (f-Dicer-
atherium) of the Oligocene and lower Miocene. (See p. 239.)
The second pair, which were moderately high and thick prom-
inences, almost cylindrical in shape and tapering but slightly
to their bluntly rounded ends, were chiefly outgrowths of the
maxillaries, or upper jaw-bones. From their shape, it is likely
that these were not sheathed in horn, but were merely covered
with skin, as were also the third pair, which arose from the
parietals. These were massive, club-shaped prominences,
eight or ten inches high and broadening to the free ends, a
shape which makes it impossible to suppose that these were
true horn-cores covered with horny sheaths. A high crest
of bone, representing the occipital crest, enclosed the top and
back of the cranium, connecting the posterior pair of " horns"
and dying away in front of them. The top of the cranium
had thus a deep, basin-like character, such as is to be found
in no mammal outside of this suborder and was one of the
most peculiar features of this extraordinary skull. The brain-
cavity was absurdly small, the growth of the brain not having
kept pace with that of the body ; the cavity is hidden away in
the postero-inferior portion of the skull, the immense thickness
of the cranial walls being somewhat lightened by the formation
of sinuses, but these were much less extensive and pervasive
than in other very large, horned or tusk-bearing mammals,
such as elephants, rhinoceroses, etc. Probably, as in the case of

HISTORY OF THE fAMBLYPODA

445

the ftitanotheres and fentelodonts, this deficiency of brain-de-
velopment was at least one of the factors which led to the early
extinction of the group. The premaxillaries were slender and
rod-like bones, which did not meet in the middle line and carried
no teeth. The long and massive nasal bones and the position of
the nasal opening show that these animals cannot have had
a proboscis of any kind. The lower jaw was remarkable for
the great bony flange which, in the males, descended on each

Fig. 230. — Skull of tuintathere (t Uintatherium alticcpa), lower jaw supplied from another
species. Princeton University Museum. For restoration, see Fig. 231, p. 447.

side from the lower border, near the anterior end, and served
to protect the great canine tusks from fracture.

The female skull differed in two respects from that of the
male : (1) the horn-like protuberances were much more slen-
der and less prominent ; (2) as the upper canine did not form
a tusk, the lower jaw had no flanges. The skull of the artio-
dactyl fProtoceras (p. 406) was remarkably similar to that of
the fuintatheres.

The dental formula was : i §, c \, p f , m J, X 2 = 34. The
upper incisors were completely lost and the lower ones had the

446 LAND MAMMALS IN THE WESTERN HEMISPHERE

very unusual peculiarity of being bilobate, or having the crown
separated into two well-defined cusps. The upper canines in the
males were very large, relatively thin, recurved and sabre-like
tusks, with acute points and sharp edges, which must have been
terrible weapons, though it is difficult to see how they were
used ; probably the mouth was widely opened, so as to clear
the points of the tusks, and the animal then struck with them,
as a snake does with its fangs. The lower canine was very small
and was included in the incisor series, the shape and function
of which it had assumed. Thus, the fuintatheres, with their
toothless premaxillaries and, to all appearances, eight lower
incisors, formed a curious parallel to the true ruminants
(Pecora), and, as in the latter, they must have had a firm
elastic pad on the premaxillaries, against which the lower
incisors could effectively bite, when cropping the soft plants
which formed the diet of theff •" *t V?sts. The grinding
teeth were low-crowned and y small in com-

parison with the size of tf ' he premolars and

molars were nearly alike ant or more transverse

crests.

Aside from the altogether excep *al character of the skull,
the skeleton was quite strikingly elephantine in appearance,
so much so, in fact, that these animals have repeatedly been
referred to the Proboscidea and some writers are still of the
opinion that the two orders were related. There is, however,
no sufficient ground for this view ; the undeniable likenesses are
much more probably to be ascribed to the operation of con-
vergent development.

The neck was of moderate length, sufficiently long to enable
the animal to reach the ground with the lips, a necessity in the
absence of a proboscis. The body was very long and, as is
shown by the length and curvature of the ribs and the great
breadth of the hip-bones, extremely bulky. The limbs were
very massive, and the long bones had lost the marrow-cavities,
being filled with spongy bone, as in the elephants, ftitanotheres

HISTORY OF THE t^MBLYPODA

448 LAND MAMMALS IN THE WESTERN HEMISPHERE

and most other very heavy mammals. The bones of the fore-
arm and lower leg were separate. The hip- and thigh-bones
and shin-bones were remarkably elephantine in character and,
if found isolated, might readily be referred to some unknown
proboscidean, but the bones of the fore limb were quite different
from those of the elephants. The feet likewise had a very
proboscidean appearance, notwithstanding important and
significant deviations in structure ; they had the same short-
ness and massiveness and a similar reduction in the size of
the hoofs, and the presence of all five digits added to the resem-
blance. Undoubtedly, the feet had the same columnar shape
and arrangement of elastic pads. The living animal must
have had an appearance quite similar to that of a rather small
elephant, not exceeding six or seven feet in height at the
shoulders and therefore not surpassing the largest modern
rhinoceroses, the broad-lipped species of Africa (Opsiceros
simus). Of course, the head must be excepted from the com-
parison, as that was totally unlike the head of any existing
creature; with its long and narrow shape, its fantastic pro-
tuberances and its lack of a proboscis, it had no suggestion of
likeness to any proboscidean. Whether the great body was
naked, or clothed with hair, it is of course impossible to deter-
mine with confidence, but, all things considered, it seems un-
likely that the hair should have been completely lost in any
terrestrial mammal at so early a period. As we have seen in
the preceding chapters, hairy elephants and rhinoceroses con-
tinued into and through the Pleistocene, not only in the cold
regions of the north, as is shown by the hair of the American
t Mastodon. In the tropics conditions were different, and in
that uniformly warm climate the loss of hair by the very large
mammals probably took place long before the Pleistocene.
At all events, it is a significant fact that no hairless land
mammals are now known in any region which has severe
winters. It is true that the middle Eocene climate over most
of North America was warm-temperate or subtropical, and

HISTORY OF THE fAMBLYPODA 449

the fumtatheres may, in consequence, have been hairless,
but there is no evidence of this.

Within the limits of the fuintathere family, considerable
modification and change may be traced, which, as in the case
of the Proboscidea, principally affected the skull and the gen-
eral stature. It is hardly worth while to deal separately with
the two or more phyla which may be distinguished, for the
differences between them are relatively unimportant. In the
uppermost part of the Bridger stage almost the latest repre-
sentatives of the family are found and the genus (^Eobasileus)
was of the largest size. These animals had remarkably long

Fig. 232. — Skull of \Elachoceras parvum (lower jaw restored).
Princeton University Museum.

and narrow heads and very large, shovel-shaped nasal protu-
berances ; in the males the upper canine tusks were very long
and curved back nearly in a semicircle. In the middle portion
of the stage the species of ^Uintatherium were somewhat
smaller and had shorter, wider and higher heads, the tusks,
though well developed, were not quite so long, nor so strongly
recurved; in some species they were nearly straight, with
" hastate' ' or spear-head point. In the same horizon is found
a third genus (fElachoceras) which was probably a survival
persisting from the lower Bridger, in which none of these ani-
mals and little of anything else has yet been found. }Elacho-
ceras was hardly half as large as the common species of f Uinta-
2a

450 LAND MAMMALS IN THE WESTERN HEMISPHERE

therium and its skull might be described as a preliminary sketch
for that of the latter ; the nasal horns were extremely small, or,
more probably, entirely absent; the median pair were mere
low knobs, hardly an inch in height, and the posterior pair
were simply thickenings of the crest which enclosed the top of
the cranium on three sides, scarcely rising above it. This
crest itself was much less prominent than in ^Uintatherium

•

and the basin-like top of the skull, in consequence, very much
shallower. The upper incisors and the first premolar had
already been lost and the upper canine enlarged into a sabre-
like tusk, which, however, was relatively smaller than in the
succeeding genera. The grinding teeth were quite the same
as in the latter. Unfortunately, the skull of \Elachoceras
is the only part of the animal which is known, but, so far as
that is concerned, it is precisely what we should expect the
forerunner of f Uintatherium to be ; an ancestor made to order
could hardly be more diagrammatic. It might, of course, be
objected that no such relation as that of ancestor and de-
scendant could obtain between these two genera, because they
were contemporaries, but the case is like that of the ancestral
elephants described in the preceding chapter. \Mceritherium
and ^Palceomastodon are found together in the Egyptian
Oligocene, the former surviving for a considerable time after
it had given rise to the latter, and in the upper Eocene only
^Moeritherium occurs. Many similar instances might be
given, just as grandfathers often live long with their grand-
children.

In the Wind River stage, or upper division of the lower
Eocene, lived the still incompletely known ^Bathyopsis, of
which, however, sufficient material has been obtained to show
that it was much less specialized than any of the Bridger genera.
This genus comprised animals much smaller than its successor,
\Elachoceras of the middle Eocene, being smaller than a tapir ;
it stood in much the same relation to ^Elachoceras as the latter
did to ^Uintatherium. In the American Museum of Natural

HISTORY OF THE fAMBLYPODA 451

History is a highly interesting skull of \Bathyopsis, which will
shortly be described by Professor Osborn. The premaxillaries
have not been preserved, and it is therefore impossible to say
whether the upper incisors had already been suppressed or not,
and though the upper canine has not been found, there can be
no reasonable doubt that it was a tusk. The lower canine had
not yet gone over to the incisor series, but was a thin though large
tusk. There was one more lower premolar, four in all, than
^Uintatherium possessed, and all the premolars were some-
what smaller and simpler than the molars. The small skull
had a broad and somewhat concave cranial roof, with slightly
raised enclosing crest, and the horn-like protuberances of the
posterior and median pairs were present in an incipient stage.
Whether those of the nasal pair were also indicated is not
known, but probably they were not. The lower jaw was of
very peculiar shape ; the flange of the inferior border was not
so well defined as in f Uintatherium, but had no hinder margin
and rose very gradually backward.

The series of genera in descending order, 1[Eobasileus,
^Uintatherium, ^Elachoceras and ^Bathyopsis, immediately
impresses the observer as being a natural phylogenetic series
of successive ancestors and descendants. Unfortunately,
only the skull is known in the two last named, but there is no
ground for supposing that the discovery of the skeletons would
require any alteration in the series as we now have it. No
member of this series has yet been found in the Wasatch, but
there can be no doubt that it was represented in that stage, for
a recent expedition from the American Museum has collected
teeth of a t BathyopsisAike form in still older beds.

SUBORDER fPANTODONTA

During the older part of the lower Eocene the f uintatheres
must have been a rare and unimportant element of the fauna,
at least in those parts of the continent whose history we know.
Their place was taken by another suborder, the fPantodonta,

452 LAND MAMMALS IN THE WESTERN HEMISPHERE

which was not ancestral to them, but collaterally related and
descended from a common ancestry. The largest and most
dominating of Wasatch mammals was the genus ^Coryphodon,
which also occurred in the lower Eocene of Europe, and the
species of which ranged in stature from a tapir to an ox, though
of much heavier form than the latter. The latest surviving
species lived in the Wind River stage as a contemporary
of ^Bathyopsis, but then the suborder gave way to the
fuintatheres.

In ^Coryphodon (see Fig. 142, p. 279) the number of teeth was
unreduced, a fact which is recorded in the name of the suborder,
the dental formula typical of all the primitive ungulates being
applicable to the genus. This formula was : if, c\y p%, m £ ,
X 2 = 44. The upper incisors were rather small, but functional,
and the canines of both jaws were formidable tusks, though not
rivalling in size the great sabres of the fuintatheres ; the pre-
molars had a simpler structure than the molars, which resembled
those of the fuintatheres in a general way, but not closely. The
skull differed greatly from that of the fuintatheres in having
no horn-like protuberances, and was relatively large and heavy,
the cranium having a broad, flat roof and no sagittal crest, and
the lower jaw had no descending flange from the inferior border ;
in every way this skull was more normal and less bizarre-
looking. The neck was proportionately longer than in the
fuintatheres, the body long and the tail of medium length;
the trunk-vertebrae had surprisingly small and weak spines,
perhaps an indication of aquatic habits. The limbs were
quite short and very heavy, and the bones, in comparison with
those of the fuintatheres, were less proboscidean and more
perissodactyl in character. For example, the femur retained
the third trochanter and the long bones had marrow-cavities.
The feet, on the contrary, were very like those of the fuin-
tatheres, being extremely short and five-toed and with reduced,
nodular hoof-bones ; even in the details of the wrist and ankle
joints there was no important difference between the two groups.

HISTORY OF THE fAMBLYPODA 453

SUBORDER tTALIGRADA

None of the ungulate series considered in the foregoing
chapters can be traced back to a time earlier than the Wasatch,
and many of them not so far, but in the case of the f Amblypoda
the line may be carried down through the Paleocene. In the
upper stage of that epoch (Torrej on) the order was represented by
^Pantolambda (Fig. 143, p. 285), a member of the third suborder,
fTaligrada. The best-known species of the genus was an animal
with head and body somewhat smaller than those of a sheep
and much shorter legs. The teeth were present in unreduced
number, 44 in all ; the canines were tusk-like, but very much
smaller proportionately than those of \Coryphodon; the
premolars were smaller and simpler than the molars, which
closely represent the common starting point, whence the curious
tooth-patterns found in the subsequent genera of the various
families were derived. The skull was long and narrow and had
a prominent sagittal crest ; the neck was of ordinary length,
about equal to that of the head ; the body was long and the
tail very long, much as in the great cats. The hip-bones were
narrow and slender and not bent outward, having no such
breadth as in ^Coryphodon. The limbs were short and relatively
heavy, and the various bones were of such primitive character
that, if found isolated and not in association with teeth or
foot-bones, one would hardly venture to consider them as be-
longing to any hoofed animal ; the humerus had a very promi-
nent deltoid crest and an epicondylar foramen, and the femur
had the third trochanter. The five-toed feet were very short,
and the digits were arranged in a spreading manner and were
relatively much more slender than in ^Coryphodon. Each
digit terminated in a flat, pointed, well-developed hoof; evi-
dently there was no elastic pad to bear the weight, such as
recurs in nearly all very heavy ungulates. The gait of the
animal was probably semi-plantigrade, the hoofs being the
principal points of support.

454 LAND MAMMALS IN THE WESTERN HEMISPHERE

While ^Pantolambda was an undoubted ungulate and a
member of the fAmblypoda, there were many structural
features in its skeleton which point to a relationship with the
primitive flesh-eaters. In the lower stage of the Paleocene,
the Puerco, the genus \Periptychus would seem to be the most
ancient known member of the order, but it is still very im-
perfectly understood.

In the mode of evolution of the fAmblypoda, so far as that
is recorded by the fossils, there is much to recall the develop-
ment of the Proboscidea, though the story began and ended
at far earlier dates and may be traced back to a much more
primitive stage.

(1) There was a rapid increase of stature, especially of
bulk, in the fcoryphodonts, but decidedly more gradual
in the tuurtatheres, which eventually attained a far larger
size.

(2) The upper incisors were suppressed and the canines
grew into formidable tusks, at first straight, then the superior
one, enlarging still farther, acquired a curved, scimitar-like
shape, while the inferior one dwindled and became functionally
one of the incisors.

(3) The grinding teeth remained low-crowned throughout,
but acquired a more complex pattern, and the premolars became
almost like the molars.

(4) The skull underwent a most remarkable transformation.
Beginning with a form that might have belonged to almost
any of the ancient mammals, hoofed or clawed, having very
prominent sagittal and occipital crests, long cranium and
short face, it became in ^Coryphodon flat-roofed, with mod-
erately elongated face, while in the fuintatheres the top of the
cranium gradually took on a deeply concave basin-shape and,
with equal gradualness, three pairs of horn-like protuberances ;
the lower jaw developed a great bony flange for the protection
of the upper tusks. These peculiarities grew more and more

HISTORY OF THE fAMBLYPODA 455

exaggerated and were most striking in the terminal genus of
the series, \Eobasileu&.

(4) Unfortunately, nothing is yet known of the skeleton
of ^Bathyopsis and \Elaehoceras, so that it is not practicable
to follow out all the stages of skeletal modification, though the
general course of development is sufficiently plain. The neck
did not change greatly, except to become very strong and heavy
and to grow shorter proportionately as the skull was lengthened.
The body remained long throughout the series, but gained
greatly in bulk, as the stature of the animal increased.

(5) The limb-bones lost their primitive character, such as
the epicondylar foramen of the humerus and the third tro-
chanter of the femur, and then, with the great increase of the
weight to be supported, the marrow-cavities were filled with
spongy bone and the hip-bones increased enormously in width ;
the femur lost its cylindrical shape and was flattened antero-
posteriorly, which gave it a very elephantine appearance.
None of the limb-bones was suppressed or greatly reduced in
size, nor was there any coossification between them.

(6) The feet early gained their definitive character; at
no time was there any loss of digits, but the originally divided
toes were, in the genera of the Wasatch and subsequent stages,
united into the columnar foot, and the hoofs were reduced from
their primitively pointed shape to nodular form.

As in the Proboscidea, therefore, there was comparatively
little change in the skeleton after the massive and bulky pro-
portions had been acquired, but great and continual modifica-
tion of the skull. At the time when the fAmblypoda finally
disappeared, no ungulate had acquired the hypsodont dentition.
Had the group survived till the middle Miocene, a time when
the spread of grassy plains so profoundly affected the feeding
habits of many herbivorous mammals, the high-crowned teeth
might have been developed in them also, and this, in turn,
would have produced other changes in the skull, making closer
the parallel with the Proboscidea.

456 LAND MAMMALS IN THE WESTERN HEMISPHERE

In conclusion, a few words may be said concerning the geo-
graphical distribution of the fAmblypoda. In the Paleocene
the only known representatives of the order were those of
North America, but the fcoryphodonts of the lower Eocene
migrated to the Old World; indeed, the genus ^Coryphodon
was first described and named from English specimens, but
there were no such abundance and variety of these animals
in Europe as there were in the western United States. The
fuintatheres were strictly North American in distribution and
no member of the suborder has ever been found outside of this
continent. Animals referred to the fAmblypoda by some
authorities have been obtained in the Oligocene and Miocene
of South America, but the assignment has been made upon
insufficient evidence. (See p. 508.)

Order fCoNDYLARTHRA

The fCondylarthra were a group of exceedingly primitive
ungulates, which served to connect the hoofed and clawed
mammals in quite an intimate manner. So few indeed were
the distinctively ungulate characters which they had acquired,
that it is still premature to make any positive statements re-
garding their geographical distribution, because unusually
well-preserved specimens are required to make sure of their
presence in any particular region. Concerning North America
there is no room for question, and there is hardly any doubt
that they existed in the Paleocene of Europe. The South
American remains which have been referred to this order may
very well prove eventually to belong to it properly, but until
both feet and skulls have been obtained in unequivocal associa-
tion, the reference can be only tentative. In North America
they ranged through the Paleocene and lower Eocene, but are
not known from any subsequent formation, and even in the
Wind River only a few stragglers survived.

The principal American families and genera are as follows :

HISTORY OF THE tCONDYLARTHRA

457

I. fMENISCOTHKRIlDjB.

^Meniacotherium, Wasatch and Wind River.

II. tl'HENACODONTIU.E.

t Protogonodon, Puerco. \ Euprotogonia, Torrejon. j Phenaeodus,
Wasatch and Wind River.

1. \Phenacodontid(B
The typical Wasatch germs \Phenacodus, which is very fully
known from nearly complete skeletons, included species which
varied in size from a fox to a small sheep ; the same genus
occurred in the Wind River, but not later. 'fPhenacoduB
had the unreduced dental formula : i $ , c \, p \, m J, x 2 = 44.

The incisors were small and simple, the canines tusk-like,
but of no very great size, the premolars smaller and simpler than
the molars. The latter were of the quadrituberculate pattern,
of four simple, conical cusps arranged in two pairs, a pattern
which is common to the earlier and less specialized members of
many ungulate groups. The skull was long, narrow and low,
with long and well-defined sagittal crest. As in primitive
skulls generally, the cranial region was long and the face short,
the eyes being very far forward ; this does not imply large
brain-capacity, indeed, the brain was very small, but merely
that the portion of the skull behind the eyes was relatively
long. The jaws were short and shallow, in accordance with the

458 LAND MAMMALS IN THE WESTERN HEMISPHERE

small and low-crowned teeth which they carried. The neck was
of medium length, but the body was elongate and the tail was
very long and stout. The hip-bones were narrow and slender,
as in primitive ungulates generally. The limbs were short
and stout and retained many very primitive characteristics.
The humerus had a prominent deltoid crest and an epicondylar
foramen ; the fore-arm bones were separate and the ulna quite
unreduced, being almost as stout as the radius. The femur
had the third trochanter and the leg-bones were distinct,
though the fibula was slender. The feet, which were short, had
five digits each, but the third toe was enlarged, while the first
and fifth were shortened, as though preparing to disappear
and thus give rise to a three-toed perissodactyl foot. The
ankle-bone (astragalus) had a rounded, convex lower end,
fitting into the navicular, so that it might readily be taken for
that of a clawed mammal.

2. ^MeniscotheriidcB

A second family of Condylarthra was represented in the
lower Eocene by the genus ^Meniscotherium and was in some
respects considerably more advanced than the fphenacodonts.
These were small animals, in which the molars had acquired
a crescentic pattern, recalling that seen in the early horses and
in the ftitanotheres and fchalicotheres, and other perisso-
dactyl families. In the upper molars the two external cusps
had been so extended as to form a continuous outer wall, each
of the cusps having a concave external face and the two unit-
ing in a prominent median ridge. The lower molars had two
crescents, one behind the other, as in several families of both
perissodactyls and artiodactyls. The body and tail were long,
the limbs relatively longer and lighter than those of fPhena-
codus and the five-toed feet were so like those of the modern
conies, or klipdasses, of Africa and Asia Minor, that by some
investigators the family has been referred to the same order, the
Hyracoidea, but the suggestion is not a probable one. It is

HISTORY OF THE tcONDYLARTHRA 459

much more likely that these problematical little tmeniscotheres
were merely a short-lived branch of the fCondylarthra.

The fcondylarths were quite abundantly represented in
the Paleocene, where the genus ^Euprotogonia was the fore-
runner of the Wasatch ^Phenacodus, but had an even more
primitive type of dentition. The upper molars were not
quadritubercular, but tritubercular, the three cusps arranged
in a triangle, the two outer ones forming the base and the single

inner one the apex. This type of upper molar was, or is still,
common to the primitive and unspecialized members of a great
many mammalian orders, marsupials, insectivores, rodents,
carnivores, lemurs, artiodactyls, etc., and there is strong reason
to believe that the tritubercular molar was the common start-
ing point for almost all types of mammalian dentition. How-
ever that may be, ^Euprotogonia is of great interest as materi-
ally helping to close the gap between the clawed and the
hoofed mammals, belonging, as it did, to the latter and yet

460 LAND MAMMALS IN THE WESTERN HEMISPHERE

retaining in dentition, limbs and feet so many characteristics
of the former.

fCondylarthra were probably present in the lowest
Paleocene (Puerco stage), but the material so far obtained is
so fragmentary that there can be no certainty on this point.

It is not at all probable that any of the North American
fCondylarthra should be regarded as ancestral to any of the
more advanced ungulate groups ; on the contrary, they would
appear to have come to an end in the Wind River, leaving no
descendants behind them. It is further true, as was men-
tioned above, that the presence of fCondylarthra in other
continents, while very probable, cannot be positively asserted,
because the evidence is incomplete. Yet it would be a great
mistake to assume, for this reason, that these most primitive
of ungulates were devoid of evolutionary importance and
interest. As is so often the case, where, in the absence of the
direct ancestry, the collateral relations afford very valuable
information as to the course of descent and modification, the
fCondylarthra throw useful light upon the origin of the
ungulate groups. It is extremely probable that the f condy-
larths, or some very similar series of primitive hoofed mam-
mals, had a very wide and perhaps cosmopolitan range at the
end of the Cretaceous and beginning of the Tertiary period, and
that, in the still unidentified region, where the artiodactyls and
perissodactyls arose, it was from a condylarthrous ancestry.
Possibly, all the other ungulate orders may yet be traced back
to the same stock, but it is rather more likely that the ungulates
include several series of quite independent origin. At all
events, it is quite certain that the clawed mammals long ante-
dated the hoofed types and that the latter arose, either once or
at several separate times, from the former. The fCondy-
larthra show how one, at least, of these transitions was effected,
and thus, in principle, how all were accomplished.

CHAPTER XII

HISTORY OF THE fTOXODONTIA (OR fNOTOUNGULATA)

It is a regrettable circumstance that, while the successive
Tertiary faunas are very fully represented in South America,
approximately complete skeletons have, as yet, been obtained
from only a few of the various stages ; from the others the
known material is very fragmentary and largely made up of
teeth and jaws. No doubt, the history of fossil-collecting in
North America will, in due course of time, be repeated in the
southern continent and more and more complete and satis-
factory specimens be obtained. At present, however, it is not
possible to trace the modifications of structure in any given
series with such detail as in those which were developed within
the limits of Arctogaea. No such story as that of the horses,
the rhinoceroses or the camels, can yet be told of the South
American groups, whatever future exploration may teach us.
Nevertheless, much has already been learned concerning the
strange creatures that once inhabited the Neotropical region
and long ago vanished completely, leaving no trace in the
modern world.

As was mentioned in Chapter VI, on the present geographi-
cal distribution of mammals, South America is to-day the
richest and, after Australia, the most peculiar zoologically of
all the regions. All of the modern hoofed animals found in
that continent at present, the tapirs, peccaries, llamas and
deer, are immigrants derived at a comparatively late date
from the north, but throughout the Tertiary and the Pleisto-
cene there were several indigenous types of ungulates, and of
these the largest and most varied assemblage was that included

461

462 LAND MAMMALS IN THE WESTERN HEMISPHERE

in the order tToxodontia. The most important and best
known of the families and genera are listed in the table :

Suborder fTOXODONTA. fToxodonts Proper

I. tToXODONTID<E.

^Toxodon, up. Plio. and Pamp. ^Xotodon, do. ^Trigodon, Monte
Hermoso. ^Nesodon, Santa Cruz, t Adinotherium, do. ^Pro-
nesodon, Deseado. f Proadinotherium, do.

II. fNOTOHIPPIDiB.

^Notohippns, Patagonian. ^Rhynchippus, Deseado. \Morphip-
ptis, do.

III. fLEONTINIIDiE.

\Leontiniay Deseado. ^Colpodon, Patagonian.

Suborder fTYPOTHERIA. fTypothcres

I. fTYPOTHERIID.E.

^Typotherium, Plioc. and Pleist. f Eutrachytherus, Deseado.

II. flNTERATHERIID^.

^Interatherium, Santa Cruz. ^ Proty pother ium, do.

III. fHEGETOTHERIIDiE.

^Hegetotherium, Santa Cruz, t Pachyrukhos, Santa Cruz to Pam-
pean.

IV. f^OTOPITHECID^E.

^Notojrithecus, Casa Mayor. ^Adpithecus, do.

V. tARCH<EOPITHECID,E.

^Henricosbornia, Casa Mayor.

VI. tARCH^EOHYRACIDiE.

^Archceohyrax, Deseado.

Suborder fENTELONYCHIA. fHomalodotheres

I. fNoTOSTYLOPID^E.

^Notostylops, Casa Mayor.

II. flsOTEMNIDiE.

1[Isotemnas, Casa Mayor, f Pleurocododony Deseado.

III. tHOMALODONTOTHERIID,E.

^Homalodontotherium, Santa Cruz. ^Asmadeu*, Deseado. ^Pro-
asnwdens, Astraponbtus Beds. ^Thoma$h\ixUya< Casa Mayor.

Suborder fPYROTHERIA. fPyrotheres

fPYROTHERIIDAE.

t Pyrotherium, Deseado. t Propyrotherhim, Astraponotus Beds.
iCarolozitlellia, Casa Mayor, f Paulogervaisia, do.

HISTORY OF THE JTOXODONTIA 463

Suborder fToxoDONTA. IToxodonts Proper

Among the remarkable animals which Charles Darwin
found in the Pampean deposits of Argentina and took with him
to England, was a skull of one which Sir Richard Owen named
^Toxodon, or " Bow-Tooth/ ' from the strongly curved grind-
ing teeth, those of the opposite sides almost meeting in the
median line above the hard palate. For many years ^Toxodon,
of which hardly anything was known, save the skull and teeth,
was a zoological puzzle and no one was able to reach any satis-
factory conclusion as to its systematic position and relation-
ships, as all the attempts made to force it into one of the known
ungulate groups were obvious failures. The discovery of
complete skeletons, two of which are mounted in the La Plata
Museum, showed the necessity of making a new group for its
reception, as Owen had originally proposed. Through the
exploration of Argentina and its Patagonian provinces, the
history of the suborder was followed far back into the Tertiary
period and its indigenous character demonstrated. This and
all the other subdivisions of the fToxodontia were exclusively
Neotropical in distribution, and none have been found farther
north than Nicaragua and there only in the Pleistocene.

The suborder was represented in the Pampean beds by
several genera, which differed in size and in the complexity of
the grinding teeth, but only of ]Toxodon is the skeleton at
all fully known. The Pampean species of this genus were
massive, elephantine creatures, rivalling the largest rhinoceroses
in bulk, but not equalling them in height. The teeth were all
thoroughly hypsodont and apparently continued to grow
throughout life without forming roots ; the dental formula
was : i#|, c #, p f , m $ , X 2 = 34. The first upper incisor was
broad and chisel-shaped, the second more tusk-like, but in some
species these proportions were reversed ; the lower incisors
were procumbent, pointing straight forward, and of these the
third was the largest. The canines were lost and there was a

464 LAND MAMMALS IN THE WESTERN HEMISPHERE

long, toothless gap behind the incisors. The premolars were
smaller and simpler than the molars, and the anterior ones were
very small and were frequently shed at an early stage, making
the number of these teeth variable in different specimens. The
upper molars also were of quite simple pattern ; the broad and
. smooth external wall showed no distinct signs of a division
into cusps, and from it arose two oblique transverse ridges ; the
deep cleft or valley which separated these ridges was divided
and made Y-shaped on the grinding surface by a prominent
spur from the outer wall between the two principal crests.
The lower molars were composed of two crescents, one behind
the other, of which the posterior one was very much longer,
and both were very narrow transversely.

The skull had shortened nasal bones, an indication that
some sort of a proboscis or prehensile upper lip was present.
There was no trace of a horn, and the general aspect of the
skull was not unlike that of one of the hornless rhinoceroses,
except for its great vertical depth ; the sagittal crest was very
short and had almost disappeared. The auditory apparatus
was very extraordinary, though it can hardly be described
without an undue employment of anatomical terms ; suffice it
to say that in addition to the usual outer ear-chamber, formed
by the inflated tympanic bone, there was a second chamber in
the rear wall of the skull, communicating with the first by a
canal. This arrangement would seem to imply an unusual
keenness in the sense of hearing. The external entrance to the
ear was placed very high up on the side of the head, as in the
pigs and in many aquatic mammals, suggesting that \Toxodon
was more or less amphibious. The anterior, or symphyseal,
region of the lower jaw was very broad, flattened and shovel-like,
hardly projecting at all below the plane of the lower incisors.

The neck was short and stout, the body long and extremely
bulky, having an immense, almost hippopotamus-like girth ;
the spines of the anterior dorsal vertebrae were very long, mak-
ing a high hump at the shoulders. The limbs were short and

HISTORY OF THE fTOXODONTIA 465

very heavy, the bones very massive and with large projections
for muscular attachments. The fore leg was much shorter
than the hind, depressing the neck and head in very curious
fashion. The shoulder-blade was rather narrow, the spine
without acromion or distinct metacromion; the hip-bones
were greatly expanded and turned outward, quite in elephantr
like fashion, a character which almost invariably accompanies
great increase in bodily mass. The thigh-bone was also very
elephantine in appearance, a likeness due to its shape and pro-
portions, to the loss of the third trochanter and the flattening
of the shaft, so that the width much exceeded the antero-
posterior thickness. All of these characters are, as a rule, asso-
ciated with greatly augmented weight and have been independ-
ently acquired in several series of large and massive animals,
elephants, fuintatheres, ftitanotheres, and to this list should be
added the ftoxodonts. In the fore-arm the bones were sep-
arate and the ulna was quite unreduced and very stout, but in
the lower leg, which was very short in comparison with the
thigh, the tibia and fibula were coossified at the upper end,
but not at the lower, a most exceptional arrangement. The
feet were surprisingly small and had but three digits, the reduc-
tion from the original five having proceeded to that extent
before the process was arrested by augmenting weight. The
heel-bone (calcaneum) was so articulated with the other bones
of the tarsus as to project almost straight backward, nearly
at a right angle to the position normal in a digitigrade foot,
a feature which is not known to occur in any other mammal.
The hoof-bones were so small and nodular that the foot must
have been of the columnar type, the weight resting upon the
usual elastic pad.

The restoration (Fig. 121, p. 217) shows \Toxodon as a very
heavy, slow-moving, water-loving animal ; the aquatic habits
are, of course, conjectural, but the general proportions are
accurately given by the skeleton.

From the Pleistocene, \Toxodon may be followed back

2h

466

LAND MAMMALS IN THE WESTERN HEMISPHERE

without notable change to the Pliocene, but there it was in
association with the last of a curious phylum, the genus
\Trigodon (Fig. 138, p. 263), as yet known only from the skull.
In these animals a very prominent bony knob or boss on the
forehead clearly demonstrates the former presence of a large,
rhinoceros-like, frontal horn. But very few of the indigenous
South American ungulates possessed horns, or horn-like pro-
tuberances of the skull, and all of these so far discovered

Fio. 235. — Skull of \Toxodon, Pampean formation, the upper molars much broken.

La Plata Museum.

belonged to the suborder fToxodonta. \Trigodon was, from
present knowledge, the only horned creature of its time and
region, for the deer and antelopes which had probably arrived
in South America had not advanced so far south as Argentina.
Another very peculiar feature of this genus was that the lower
incisors were present in uneven number, two on each side
and one in the middle. Nothing has been found of the
skeleton, but it was doubtless that of a smaller and somewhat
lighter \Toxodon.

HISTORY OF THE JTOXODONTIA 467

The material from the lower Pliocene adds nothing to our
knowledge of the suborder, but in the Santa Cruz time of
Patagonia, which was Miocene, it was very abundantly repre-
sented and preponderatingly by the genus ^Nesodon, which
was the first discovered member of the marvellous Santa Cruz
fauna, named nearly 70 years ago by Sir Richard Owen.
It so chanced that Owen's specimen was the imperfect lower
jaw of a young animal with the milk-teeth, which were mis-
taken for the permanent dentition, and when the latter was
found long afterwards, it was naturally supposed to belong to
a different animal and received a different generic name. Nor
was this all ; the changes which took place in the appearance
and relative size of the permanent
teeth within the life-time of the in-
dividual were so remarkable, that
the successive stages of development
were by several investigators sup-
posed to be distinct genera and
species and named accordingly. In
this way nearly 30 different names Fig. 236.— skull of Santa Cm*

i_ , .. xi_ t_ ttoxodont, ^Nesodon ; same scale

have, at one time or another, been of reduction M Kg. 235.
assigned to the common species,

]N. imbricatus; and it was not until the late Dr. Ameghino
had brought together a complete series of skulls and jaws
illustrating these changes, and showing the gradual transition
from one to the other, that the confusion could be cleared up.

There was a long hiatus in time between fToxodon and
fNesodon and so great was the structural difference between
them, that there is much doubt whether the latter was directly
ancestral to the former; in any event, ^Nesodon so nearly
represents what the desired ancestor must have been, as to
serve for all practical purposes of the study.

All the species of this Santa Cruz genus were much smaller
animals than the species of ^Toxodon, ]N. imbricatus being
no longer than a tapir, with considerably shorter legs, and of

468 LAND MAMMALS IN THE WESTERN HEMISPHERE

much slighter and more slender build than \Toxodony though
every tooth and every bone proclaims its relationship to the
latter.

In \Nesodon the dental formula was unreduced; if, c\,
V\y w§, X 2 = 44, though several of the teeth were much
reduced in size, so as to have lost their functional impor-
tance, and frequently individuals are found in which one or more
of these insignificant teeth are lacking. The first upper incisor
was a broad, chisel-shaped tooth, which continued to grow for
a period, then formed its root, and growth ceased ; the second
incisor was a pointed, triangular tusk, which grew throughout
life, becoming longer with advancing age ; while the third, which
was lost in \Toxodon, was small and unimportant. In the
lower jaw the first and second incisors were chisel-like and had
a limited growth ; being rather narrow, they both bit against
the broad first upper incisor ; the third incisor was a persist-
ently growing tusk, not so large as the upper one, against the
posterior face of which it impinged and was obliquely trun-
cated by wear, so that its length was limited, while the upper
tusk continued to elongate and was made narrower and sharper
by wear. All the lower incisors were far less procumbent than
in fToxodon, and were directed obliquely upward and forward.
The remarkable changes of appearance which, as mentioned
above, took place within the life-time of the individual, were
largely due to the differential growth of the incisors. The
milk-incisors were all nearly alike and formed no tusks ; when
the permanent incisors were first protruded, the first upper
and the first and second lower were large and the tusks were
not visible, and, when the latter did appear, they were for some
time smaller than the other incisors. These, however, formed
roots and ceased to grow, actually becoming smaller with
advancing age, for the crowns narrowed to the roots and, the
more they were worn down, the smaller they became. The
tusks, on the other hand, grew throughout life and became
larger as the other incisors were reduced by wear, and thus the

HISTORY OF THE fTOXODONTIA 469

whole appearance of the anterior part of the jaw was totally
changed.

This mode of forming the tusks by the enlargement of the
second upper and third lower incisor is an unusual one, though
it was repeated in another South American ungulate order, the
fLitopterna, and nearly so in the Proboscidea, in which both
upper and lower tusks were the second of the three original
incisors.

In both jaws, the canines of fNesodon were insignificant and
sometimes absent. The premolars, which were smaller and
simpler than the molars, had quite high crowns, but early
ceased to grow and formed long roots. The molars were truly
hypsodont and formed no roots till late in life ; they were con-
structed on the same plan as those of fToxodon, but were de-
cidedly more complex, the upper ones having several spurs
and crests given off inward from the external wall, in addition
to the two principal transverse crests, and they had a certain
superficial likeness to the teeth of a rhinoceros. As in ]Toxo-
don> these upper molars were curved inward, so as almost to
meet those of the opposite side above the palate. The lower
molars had the same bicrescentic plan as in fToxodon, but
were more complicated, and in the concavity of the hinder
crescent was a vertical pillar, which was well-nigh universal
among the indigenous South American ungulates.

If fNesodon was really the ancestor of fToxodon, then the
development of the grinding teeth must have been a process
of completing the hypsodontism, until the teeth grew per-
sistently, never forming roots, and, at the same time, of sim-
plifying the pattern. This is contrary to the usual course of
evolution, in which the pattern grew more complex in the suc-
cessive stages ; but such steadily increasing complexity was not
invariable, and several instances of undoubted simplification
are known among mammals, though not yet in other ungulates.
Only the recovery of the intermediate genera will enable us to
determine whether \Nesodon was the actual ancestor of

470 LAND MAMMALS IN THE WESTERN HEMISPHERE

HISTORY OF THE fTOX0DONTIA 471

fToxodon, or whether it was merely one of a short-lived branch
from the main stem, in which the teeth had acquired an un-
usual degree of complexity.

A few years ago Dr. Ameghino announced the very sur-
prising discovery that, instead of having merely the normal
arrangement of two dentitions, the milk and the permanent,
^Nesodon developed three successive dentitions, one preceding
the milk-series, and therefore called pre-lacteal. In certain
other mammals traces of a pre-lacteal series had already been
found, in the shape of tooth-germs, which never attain full
development or even cut the gum ; and quite recently Dr.
Ameghino has shown that in the tapir at least one functional
pre-lacteal premolar is formed. The significance of this fully
developed pre-lacteal dentition in ^Nesodon is not yet clear,
though it seems reasonable to suppose that it was the almost
uniquely late retention of a primitive character.

The skull was closely similar to that of ^Toxodon, on a
smaller scale, but there were several minor differences, which
were, in part, conditioned by the larger and much more com-
pletely hypsodont teeth of the Pampean genus, as well as by its
generally increased size and bulk. In \Nesodon the sagittal
and occipital crests were much more prominent and the former
was much longer, while the thickening of the cranial bones
was in only an incipient stage.- The nasal bones were consider-
ably longer. The jaws were lower and shallower, in correla-
tion with the less perfectly hypsodont teeth, and in the lower
jaw the chin was much more erect and rounded. The entire
head of this curious Santa Cruz animal had something
remarkably rodent-like in its appearance, though it is
quite inadmissible to suppose that the likeness was due to
relationship.

The skeleton was far smaller and lighter and otherwise
differently proportioned from that of jToxodon, but there was,
nevertheless, a close agreement between the two genera. The
neck was of moderate length and thickness, the body long and

472

LAND MAMMALS IN THE WESTERN HEMISPHERE

heavy, but with no such relative bulk as in the Pampean genus.
The hump at the shoulders, as indicated by the spines of the
anterior dorsal vertebrae, though already well defined, was less
prominent. The shoulder-blade (scapula) was relatively
broader than in \Toxodon, its spine had a distinct acromion
and two very long and conspicuous processes given off backward
from the spine, only one of which, and that a mere vestige,

is indicated in ]Toxodon. The
hip-bones were almost parallel
with the backbone and were
not nearly so broad or so
everted as in the latter, a differ-
ence which is amply accounted
for by the great discrepancy in
girth.

The limbs were of nearly
equal length and there was no
such shortening of the fore-arm
or elongation of the thigh as in
\Toxodon, and so the descent
of the backbone forward, which
gave such grotesqueness to the
skeleton of the latter, was far

Fig. 238. -Left pes of Woxodon. La leSS pronounced. The limb-
Plata Museum. Cai., caicaneum. bones were rather slender, in

As., astragalus. N.t navicular. . , . .._

Cn. 1 and 2, coossified internal and Size and proportions not Unlike

middle cuneiforms. Cn. 8, external those of a tapir, but in StrUC-
cuneiform. Cb., cuboid.

ture very like the very much
larger and more massive ones of \Toxodon. The bones of the
fore-arm were separate, but those of the lower leg were coossi-
fied in the same exceptional manner as in the Pampean genus,
that is, the upper ends, but not the lower, were fused together.
The thigh-bone was not flattened, but had the normal cylin-
drical shaft and a conspicuous third trochanter. The feet,
in which the digits were already reduced to three, were ex-

HISTORY OF THE fTOXODONTIA

473

treraely small in comparison with the size of the animal ; in
structure, they were almost identical with those of \Toxodon,
but were far narrower and more slender. The heel-bone (cal-
caneum) articulated with the other bones of the tarsus in a
normal manner. The digits were well separated and the hoof-
bones quite strongly developed, indicating that the hoofs were
functional, supporting most of the weight. In short, the
difference in the external appearance of the feet between
the two genera was much the same as between
the tapirs and rhinoceroses.

The species of f-Vesodon, of which many
have been named on very questionable grounds,
differed but little in size and were of such vari-
able and fluctuating character that a proper
discrimination of them is exceedingly difficult.
One of these species {^N. cornutus) gives in-
dications of having possessed a small dermal
horn on the forehead and was thus a possible
ancestor of \Trigodon.

A second phylum of the suborder was
represented in the Santa Cruz stage by the
genus \Adinotherium, the species of which,
not equalling a sheep in size, were very much
smaller animals than those of fNesodon, but
closely like them in other respects. The denti-
tion, including the pre-lacteal series, and the
skull were almost identical in the two genera,
with the exception that a large proportion of the individuals
of \Adinotherium had the small frontal horn, while others had
no trace of it. While it is quite possible that the presence or
absence of the horn, which was always inconspicuous, may
have been a matter of specific distinction, a more probable
explanation is that it was a sexual character, the males horned
and the females hornless. Much the same thing is to be
observed in the modern Javan Rhinoceros <R. sondaicus) in

[«. 239. — Left pes of
t.Vworfon, Prince-
ton University
Museum. Letters
as iu Fig. 238 and
Scale of reduction

474

LAND MAMMALS IN THE WESTERN HEMISPHERE

which the females have a very small horn, or none at all, and
the males a large one.

In the skeleton also there were few differences, other than
those of size, between ^Adinotherium and \Neaodon; the for-
mer was not only smaller, but also lighter and more slender
proportionately, and there was no hump at the shoulders,
the spines of the dorsal and lumbar vertebrae all reaching the
same level, so that the back must have been nearly straight in

F.«. 240. — ^Adiaotheriun,
Htorcd from a skcletoo i
horn on the forehead.

the living animal. From the more general and constant pres-
ence of the frontal horn, \Adinolherium was more probably
the ancestor of the horned \Trigodon than was ^Nesodon, but
until the intermediate forms shall have been recovered, no
definite decision can be made.

The same or very nearly the same genera of the family
fToxodontidie lived in the Patagonian and Deseado stages,
but there the record breaks off and can, for the present at least,
be followed no farther. It remains to be determined whether

HISTOBY OF THE fTOXODONTIA 475

the series originated in regions farther to the north, or whether
the ancestral types will he found in Patagonia.

The other two families are still very incompletely known,
but sufficiently to justify their inclusion in the present suborder.
In the fLeontiniidffi, which are known only from the Deseado
stage (\Leonlinia) , we have a curious variant of the ftoxodont
type. The tusks were decidedly smaller than in the Santa
Cruz members of the preceding family, the grinding teeth with
lower crowns and simpler structure. The skull was much like
that of fNesodon, but the anterior nasal opening was of quite

a different shape, being carried much farther back on the sides,
so that the nasal bones had a far longer portion which was
freely projecting and unsupported; these bones were shorter
and much thicker than in the Santa Cruz genera and, to all
appearances, supported a small, median horn on their anterior
ends. The feet, so far as they have been recovered, did not
differ in any significant manner from those of the preceding
family.

Another imperfectly known family, that of the fNotohip-
pidae, occurred in the Patagonian stage, but was most abun-
dant in the Deseado, where several genera of it have been found.

476 LAND MAMMALS IN THE WESTERN HEMISPHERE

These animals had mostly hypsodont teeth, forming roots in
old age, and the teeth were in closed series, but there was no
tusk-like enlargement of the incisors. In the later genera,
those of the Patagonian stage (\Notohippusy t Argyrohippus) ,
the crowns of the grinding teeth had a thick covering of cement,
and those of the lower jaw had some resemblance, though not
at all a close one, to the teeth of horses. The skull also had a
certain suggestion of likeness to the horses and Dr. Ameghino
was persuaded that these animals were ancestors of the horses.
The family went back to the Astraponotus stage, but can be
traced no farther.

Suborder fTYPOTHERiA. fTYPOTHERES

This suborder was composed of much smaller animals than
the fToxodonta and contained no large forms ; some, indeed,
were exceedingly small, no larger than rabbits. It was much
the most diversified of the suborders, as is made evident by the
table of families and genera. Two of these families, the
fTypotheriidae and the fHegetotheriidse, continued into the
older Pleistocene. Of the former there was the genus first
named and described, \Typotheriumy which has given its name
to the family and suborder, and the species of which were much
the largest of the entire group, almost equalling a large pig in
size. At the first glance this genus might easily be mistaken
for a large rodent, and indeed it has actually been referred to
that order, but the resemblance was a purely superficial one
and involved no relationship.

In \Typotherium the teeth were considerably reduced in
number, the formula being : i £, c #, p \ , m |, X 2 = 24. The
first incisor in each jaw was a broad, scalpriform, persist-
ently growing tooth, which much resembled the corresponding
tooth in the rodents, but was not, as it is in the latter, worn to
a sharp chisel-edge by attrition, but was abruptly truncated.
There was a second similar, but much smaller, tooth in the lower
jaw ; the other incisors and all the canines had been lost and

HISTORY OF THE fTOXODONTIA 477

the premolars reduced to two in the upper and one in the lower
jaw. The molars were large, persistently growing and thor-
oughly hypsodont ; in pattern they were very similar to those of
^Toxodon. The skull without the lower jaw was low and the
cranial portion broad and flattened, but retaining a long sagit-
tal crest. The eye-sockets were nearly, but not quite, closed
behind by the very long and slender post-orbital processes of
the frontal bones. In front of the eyes the face was suddenly
constricted into a long, narrow rostrum, and it is this shape of
the skull which, together with the persistently growing, scal-
priform incisors, gave such a rodent-like appearance to the
head. The auditory region had the same remarkable struc-
ture as in the fToxodonta. The lower jaw had a short hori-
zontal portion and very high vertical portion, which gave the
head great vertical depth.

The skeleton, so far as it is known, was decidedly more primi-
tive than that of the contemporary ]Toxodon, as is shown by the
presence of collar-bones (clavicles) and by the larger number
of digits, five in the front foot and four in the hind. The hoof-
bones, or ungual phalanges, were narrow, pointed and nail-like,
though in the hind foot they were broader and more hoof-like.

Little can be done as yet in tracing back the history of this
family, the Santa Cruz beds having yielded no member of it.
In the Deseado stage, the genus ^Evlrachytherus differed
surprisingly little from \Typotherium) in view of the long hiatus
in time between them. The Deseado genus already had
thoroughly hypsodont and rootless teeth, and the molar pattern
was quite the same as in 1[Typotherium, but the teeth were much
more numerous, the formula being : i § , c \} p \y m §, X 2 = 42.
Nothing is known of the skeleton. The family arose probably
from one of the Eocene families (fArchaeopithecidae or fAcce-
lodidse) with low-crowned teeth, but the connection cannot be
made out. Presumably, the development of this family ran
its chief course in some part of South America far to the north
of the fossil-beds of Patagonia.

478 LAND MAMMALS IN THE WESTERN HEMISPHERE

The second family which was represented in Pampean times
was that of the fHegetotheriidae, and the sole genus of it which
survived so late was \Pachyrukhos, a little creature no larger
than a rabbit. The genus went back without any noteworthy
change to the Santa Cruz stage of the Miocene, from which
complete skeletons have been obtained. The dental formula
was nearly as in \Typotherium : i \, c §, p § , m f , X 2 = 30, and
the enlarged, rootless and scalpriform incisors were similar.
The grinding teeth were thoroughly hypsodont and had a thin
coating of cement ; the molar-pattern was fundamentally
like that of IfNesodon, in simpler form, but can be seen only in
freshly erupted and unworn teeth.

The skull was very rodent-like in appearance, its flat top
and narrow, tapering facial region, and the gnawing incisors
adding much to the resemblance. The very large eye-sockets
and the enormously developed auditory region suggest noc-
turnal habits, and, no doubt, the timid, defenceless little crea-
tures hid themselves by day, perhaps in burrows. The en-
largement of the accessory auditory chambers, which all of
the fToxodontia possessed, reached its maximum in \Pachy-
rukhos, and the chambers formed great, inflated protuberances
at the postero-external angles of the skull. The neck was
short, the body long and the tail very short, much like that of a
rabbit. Collar-bones were present, as they probably were in
all of the other members of the suborder fTypotheria, though
this has not been definitely ascertained in all cases. The limbs
were relatively long, especially the hind legs, and very slender ;
the bones of the fore-arm were separate, but those of the lower
leg were coossified at both ends. The feet, which had four
digits each, were of unequal size, the posterior pair being much
longer than the anterior, and the hoofs were long, slender and
pointed, almost claw-like. The entire skeleton suggests a
leaping gait and its proportions and general appearance were
remarkably like those of a rabbit-skeleton. In the restoration
(Fig. 300, p. 639) Mr. Knight has followed these indications

HISTORY OF THE tTOxODONTIA 479

and drawn an animal which might readily be mistaken for
a curious, short-eared rabbit ; and there is every justification
for doing this, though the character of the fur and the form
of the ears are, of course, merely conjectural. Perhaps the
ears are too small.

Associated with ^Pachyrukhos in the Santa Cruz stage was
another genus of the family, \Hegetotheriumf which, though it
cannot possibly have been ancestral to the former, yet serves
to indicate, in general terms, what the ancestor must have been.
This is another example of the long-continued survival of the
more primitive together with the more advanced and special-
ized form. 1[Hegetotherium persisted into the Pliocene, but
is not known from the Pleistocene. In this genus one upper
and two lower incisors were already enlarged, rootless and
scalpriform, but none of the teeth had been lost ; it is interesting
to note, however, that the teeth which were lacking in \Pachy-
rukhos were all very small and ready to disappear. The Santa
Cruz species of ^Hegetotherium were considerably larger and
more robust animals than those of ]Pachyrukhos.

Both of these genera were preceded by very similar, almost
identical forms in the Patagonian, Deseado and Astraponotus
stages, but the family cannot be definitely traced farther back
than the lower Oligocene, but it very probably arose from some
one of the groups, with low-crowned teeth, of the Casa Mayor
stage.

The family flnteratheriidse was, in most respects, more
conservative and underwent less change than either of the pre-
ceding groups. A persistently primitive type was the genus
\Protypotherium, which appeared for the last time in the Plio-
cene of Monte Hermoso, but was much more abundant and
better preserved in the Santa Cruz. The animal was small
and had the full complement of teeth, which were arranged
in each jaw in a continuous series, and were fully hypsodont and
rootless, except incisors and canine, which were rooted. None
of the incisors was specially enlarged, but there was a gradual

480 LAND MAMMALS IN THE WESTERN HEMISPHERE

HISTORY OF THE tTOXODONTIA 481

transition of increasing size and complexity from the incisors
to the molars. A remarkable feature of this genus was the
deeply cleft form of the lower incisors, giving them a fork-
like shape, somewhat as in the modern Hyracoidea. The
ulna and radius in the fore-arm and the tibia and fibula in the
lower leg were separate, but the digits were already reduced to
four in each foot. This was one of the few Santa Cruz un-
gulates which possessed a long and heavy tail. The limbs
were relatively long and the feet were armed with such slender
hoofs that they looked almost like claws. The restoration
shows the animal to have had, like nearly all of the fTypo-
theria, a very rodent-like appearance, a likeness which may,
perhaps, be unduly increased by the form given to the ears.

In the allied genus, \Interatherium, from which the family
is named, the head was short, broad and deep, almost bullet-
like ; the first incisor was enlarged and chisel-shaped, and the
other incisors and the canines were much reduced in size. It
is an interesting fact, observed as yet only in this genus, but
probably true also of all the smaller members of the suborder
which had hypsodont teeth, that the milk-premolars were
rooted and comparatively low-crowned, while their permanent
successors were completely hypsodont and rootless. The
limbs were considerably shorter than those of \Proly-potherium
and the tail long and thick, except for which, the general
appearance of the skeleton suggests that of the modern "co-
nies" or "klipdases" (Hyracoidea) of Africa and Syria, a sug-
gestion which Mr. Knight has followed in the drawing (Fig.
297, p. 636).

This family was represented in the Deseado stage by a
genus (IfPlagiarthrus) in which the teeth developed roots in
old age, but is not known from more ancient formations.
Their probable ancestors of the Eocene were very small ani-
mals, with brachyodont teeth, the premolars smaller and of
simpler pattern than the molars. The upper molars had a
continuous external wall, with indication of separate cusps,
2i

482 LAND MAMMALS IN THE WESTERN HEMISPHERE

and two transverse crests, as in the fToxodonta, and the lower
molars were composed of two incomplete crescents. The
teeth were present in undiminished number and the anterior
incisors were but little enlarged. Nothing is known of the
skeleton.

SUBORDER fENTELONYCHIA. fHOMALODOTHERES

This third suborder of the fToxodontia was in some respects
the most peculiar of all ; no representatives of it have been
found in formations later than the Santa Cruz, and the group
attained its culmination in the still older Deseado stage, in
which there were very large members of it. These most extraor-
dinary beasts are still incompletely known, and little can be
done as yet in the way of following out the steps of change
which led up to their exceptional characters, though the sub-
order itself may be traced back to the Eocene by means of
jaws and teeth alone.

The Santa Cruz genus labours under the portentous name of
1[Homalodontotherium9 which may be shortened to the ver-
nacular form of fhomaiodothere. In this genus the dentition
was unreduced in number, and the teeth, though having rather
high crowns, were all rooted and placed in continuous series,
with a gradual transition in shape from the incisors to the
molars. The canines were tusks of very moderate size, which
projected but little above and below the plane of the other
teeth ; the premolars, except the last, which was nearly mo-
lariform, were smaller and simpler than the molars, which had
a pattern fundamentally the same as in the fToxodonta.
Those of the upper jaw were, however, less complicated by
spurs and accessory crests, and they had a somewhat stronger
resemblance to the rhinoceros pattern, though the resemblance
is demonstrably superficial and not indicative of relationship.

The skull was very like that of the Santa Cruz ftoxodonts,
1[Nesodon, etc., and had the same unusual structure of the audi-
tory region as was found throughout the order, but differed in

HISTORY OF THE "JTOXODONTIA 483

many details, which it is not worth while to enumerate, though
it may be said that the nasal bones were so much shortened
that some kind of a proboscis or prehensile upper lip was prob-
ably present. The head was quite small in proportion to the
size of the animal as a whole. Such of the vertebra as are
known were quite similar to those of ^Nesodon, but the limbs
were far longer and quite stout, though not massive. The
humerus was remarkable for the great development of the
ridges for the attachment of the deltoid and supinator muscles
and for the prominence of the epicondyles, all of which gave
to the bone the appearance of the humerus of a huge burrower,
yet it is impossible to believe that so large an animal could have
had burrowing habits. The fore-arm bones were separate
and very long, the ulna almost as heavy as the radius; the
latter is not known from a complete specimen, but there would
appear to have been some power of rotation, a power which is
conditioned by the shape of the upper end of the radius, and
its mode of articulation with the humerus in the elbow-joint.
The thigh-bone was long and heavy and its shaft was much
flattened, having lost the normal cylindrical shape, but re-
tained a small third trochanter. The bones of the lower leg
were separate and relatively short, and the fibula was un-
commonly heavy.

So far, there was nothing very unusual, save in the shape of
the humerus, about the skeletal structure of the fEntelonychia,
the remarkable characters having been confined to the feet.
Were it not for these, the group might be included in the sub-
order fToxodonta without difficulty. The feet, which were
five-toed, differed notably in size, the manus being more than
twice as long as the pes. In the former the metacarpals
were very long and, though actually stout, were slender in
proportion to their length ; there was also a very unusual
feature in an ungulate foot, that the heaviest of the digits was
the fifth, or external one. The mode of articulation of the
metacarpals with the first row of phalanges was very excep-

484 LAND MAMMALS IN THE WESTERN HEMISPHERE

tional, indicating an extraordinary mobility of the toes, and the
hoofs had been transformed into large, bluntly pointed claws,
somewhat like those of the fchalicotheres, those aberrant
perissodactyls (see p. 354), but not so large or so sharp. In
the pes, the ankle-bone had hardly any groove for the tibia,
and its lower end was hemispherical, as in the fCondylarthra
and the clawed mammals generally. The toes were quite
grotesquely short in comparison with those of the fore foot,
and, as in the latter, the fifth was the heaviest of the series.
The hind foot was apparently plantigrade, the heel-bone and
the entire sole being applied to the ground in walking, while
the fore foot was probably digitigrade, the wrist being raised
and the metacarpals vertical. The weight was carried upon
the metacarpals and one or more pads under the phalanges,
as in the digitigrade carnivores, such as dogs and cats. In
describing the fchalicotheres, it was pointed out that it was
uncertain whether each foot had a single large pad, or whether
there was a separate one under the phalanges of each digit,
and a larger one, the "ball of the foot," under thetmetacarpals
collectively. The same doubt applies to the manus of the
fhomalodotheres.

This is the third instance to be cited of the acquisition of
claws by a hoofed mammal and, as in the other two cases, the
fchalicotheres and t&griochcerids (p. 383), we are con-
fronted by the seemingly incompatible association of teeth
which could have masticated only soft vegetable tissues with
feet like those of a beast of prey. As in the other two groups,
the problem as to the habits and mode of life of the fhomalodo-
theres is an unsolved one, chiefly because no mammal now
living is at all like these extraordinary creatures and one can
therefore form but vague conjectures as to the use of such feet
to herbivorous animals. Possibly they subsisted largely
upon roots and tubers and used the great claws for digging up
food, the principal employment that bears now make of their
claws. This remarkable transformation of hoofs into claws

HISTORY OF THE tTOXODONTIA 485

took place in three unrelated groups of hoofed animals and
must have occurred independently among the Artiodactyla,
the Perissodactyla and the fToxodontia. By no possibility,
so far as we are able to comprehend the course of evolutionary
change, could this common characteristic have been due to
inheritance from a common ancestry.

The fhomalodotheres were among the largest of Santa Cruz
mammals, but they were then already approaching extinction,
while in the Deseado stage they were more numerous and varied
and some of them very much larger. This is an exception
to the more common rule, according to which the successive
members of a phylum increased in stature until the maximum
was reached and this, in many cases, was followed by extinction.
The rule is, however, by no means without exceptions and
several have already been referred to. The largest of American
proboscideans was the flniperial Elephant (Elephas fim-
perator) of the upper Pliocene and Pleistocene and in many
other phyla the Pleistocene species were much larger than
the Recent. So with the fhomalodotheres; they reached
their culmination in size and importance in the Deseado stage,
fewer and smaller forms surviving into the Santa Cruz, after
which the entire suborder vanished. The family may be traced
back to the Eocene, where it is represented chiefly by a genus
{^Thomashuxleya) which had larger canine tusks and much
more brachyodont teeth, but there is no way of determining
when the transformation of the hoofs took place. The other
two families (fNotostylopidae, flsotemnidae) flourished chiefly
or exclusively in the Eocene and were small animals still very
imperfectly understood.

Suborder fPYROTHERiA. tPYROTHEREs

This suborder was a remarkable group, still incompletely
known, of elephant-like animals, which reached their culmina-
tion and died out in the Oligocene, their last appearance being
in the Deseado stage. The genus \Pyrotherium from the

486 LAND MAMMALS IN THE WESTERN HEMISPHERE

Deseado {also called the Pyrotherium Beds) was the latest,
largest and best known of the suborder. The dentition was
much reduced as is shown by the formula: i{, c#, pi, mf,x2
= 28. The upper incisors were two downwardly directed
tusks, the first quite small, the second considerably larger ;
the single lower incisor of each side was a stout, but not very
long, horizontally directed tusk, with the enamel confined to a

Fm. 243. — Head of 1Pi/rotherium, showing the two pairs of upper tusks. Restored
[mm a skull in the museum of Amherst College.

longitudinal band ; the other incisors and the canines had dis-
appeared. The premolars, except the foremost one, had the
molar-pattern, which very rarely occurred among the indig-
enous South American ungulates. The grinding teeth were
similar above and below and each had two elevated, transverse
crests, which, when quite unworn, carried a row of bead-Uke
tubercles. These teeth are decidedly reminiscent of the den-
tition of the aberrant proboscidean ^Dinotherium, from the
Miocene and Pliocene of Europe (p. 435) , and this resemblance,
together with the form of the tusks, has led to the reference of

HISTORY OF THE fTOXODONTIA 487

this group to the Proboscidea, but the assignment is un-
doubtedly erroneous, as is shown by the character of the skull
and skeleton.

The skull, hitherto unknown, was obtained by the Amherst
College Expedition to Patagonia and its description by Pro-
fessor F. B. Loomis is anxiously awaited. In advance of that,
he has published a brief account, with a figure. This skull
was long and narrow, with very short facial region and nasal
bones so shortened that the nasal canal passed almost vertically
down through the head, as in the elephants, and there must
have been a considerable proboscis. Despite this great modi-
fication, the skull was plainly of the ftoxodont and not of the
proboscidean type. The legs were extremely massive and
the fore legs were considerably shorter than the hind, with
such a difference in length that the head must have been carried
low, as in the Pampean ^Toxodon. The upper arm and thigh
were much longer than the fore-arm and lower leg respectively.
The humerus was immensely broadened, especially the lower
end, and the processes for muscular attachment were extremely
prominent. The femur was long, with broad and flattened
shaft, and had no trace of the third trochanter, quite strongly
resembling the thigh-bone of an elephant, which, as we have
repeatedly seen, is the type more or less closely approximated
by all of the very heavy ungulates. In the standing posi-
tion, the femur was in nearly the same vertical line as the tibia
and the whole leg must have been almost perfectly straight,
with the knee-joint free from the body. The short and massive
fore-arm bones were coossified, at least in some individuals,
as were the equally heavy bones of the lower leg, the fibula
being exceptionally stout. Little is known of the feet, but that
little renders probable the inference that they were short,
columnar and five-toed.

The Eocene representatives of the Pyrotheria are known
only from very fragmentary material. 1[Propyrotherium, of
the Astraponotus Beds, was smaller than the Deseado genus

488 LAND MAMMALS IN THE WESTERN HEMISPHERE

and still smaller was ]Carolozittellia of the Casa Mayor, which
was not so large as a tapir. In the latter the molars were of the
same type as in the succeeding forms and small tusks had al-
ready begun to develop. The older Eocene genus \PavXo-
gervaisia was probably a member of this suborder; if so, it
shows that the molars with transverse crests were derived from
quadritubercular teeth, just as happened in the Proboscidea
and several other ungulate groups.

CHAPTER XIII

HISTORY OF THE fLITOPTERNA AND t^STRAPOTHERIA

Besides the four well-defined groups which make up the
fToxodontia (or fNotoungulata) there are two other extinct
orders of indigenous South American ungulates, which remain
to be considered. These did not have the exceptional develop-
ment of the auditory region of the skull which characterized
the fToxodontia. The best known and most important genera
of the fLitopterna are listed in the following table :

fLITOPTERNA. fLitopterna

I. fMACRAUCHENIDA!.

^Macrauchenia, Plioc. and Pleist. iScalibrinitherium, Parand.
^Theosodon, Santa Cruz. ^Cramauchenia, Patagonian. ]Pro-
theosodon, Deseado.

II. PrOTEROTHERIIDjE.

iEpitherium, Monte Hermoso. ^Diadiaphorus, Santa Cruz and
ParanA. f Proterotherium, do. ^Thoatherium, Santa Cruz.
^Devterotherium, Deseado. f Prothoatherium, do.
III. Didolodidje.

]Didolodu8, Casa Mayor, f Lambdaconns, do. f Notoprogonia, do.
t Proectocion, do., etc., etc.

Only one of the families of this suborder survived into the
Pampean stage, where it was represented by a single genus,
^Macrauchenia. Like all the other large Pampean mammals
of distinctly South American type, this was a grotesque crea-
ture, from the modern point of view. The genus was first dis-
covered by Darwin, who says of it: "At Port St. Julian, in
some red mud capping the gravel on the 90-foot plain, I found
half the skeleton of the Macrauchenia Patachonica, a remark-
able quadruped, full as large as a camel. It belongs to the

489

490 LAND MAMMALS IN THE WESTERN HEMISPHERE

same division of the Pachydermata with the rhinoceros, tapir,
and palseotherium ; but in the structure of the bones of its
long neck it shows a clear relation to the camel, or rather to
the guanaco and llama." l The views upon classification and
relationship here expressed have been superseded, but the
passage is an important one in the history of scientific opinion.

\Macrauchenia (Fig. 120, p. 216), as Darwin says, was as
large as a camel ; it had an unreduced dentition of 44 teeth and
in each jaw the teeth were arranged in continuous series and
were quite decidedly hypsodont. Both in the upper and the
lower jaws the incisors formed a nearly straight transverse
row and have a "mark," or enamel pit, like that seen in the
horses ; the canines were but little larger than the incisors and
did not form tusks. The premolars were smaller and simpler
than the molars. The upper molars had two concave and
crescentic external cusps, connected by a median ridge, as in
several families of perissodactyls ; two transverse crests and
several accessory spurs and enamel-pockets gave to the grinding
surface, when somewhat worn, the appearance of considerable
complexity. The lower molars had the two crescents, one
behind the other, which recurred in almost all the South Ameri-
can types of ungulates ; the vertical pillar which so generally
in these types arose in the inner concavity of the posterior
crescent was wanting in the permanent teeth of fMacrau-
chenia, but present in the milk-premolars.

No part of this remarkable animal was more curious than
the skull, which was quite small in proportion to the rest of the
skeleton. It was long, narrow and low, sloping and tapering
forward to a blunt point at the end of the muzzle, though there
was a slight broadening here to accommodate the transverse
row of incisors. The sagittal crest was replaced by a short,
narrow and flat area ; the cranium was shortened and the face
elongated, the orbits, which were completely encircled in bone,
having been shifted behind the line of the teeth, as in the

1 Darwin, Voyage of a Naturalist, p. 172.

HISTORY OF THE fLITOPTERNA 491

modern horses. The nasal bones were reduced to a minimum,
a mere vestige of their original length, the anterior nasal
opening being directly over the posterior, making the nasal
passage vertical. Such an arrangement is an almost positive
proof that in life the animal had a flexible proboscis, a con-
clusion which is confirmed by the presence, on the top of the
head and behind the nasal opening, of deep pits for the attach-
ment of the proboscis-muscles. A very curious feature of this
skull was that the bones of the upper jaw, the maxillaries and
premaxillaries of the opposite sides, united in the median line,
making a long, solid, bony rostrum in front of the nasal open-
ing, a character not found in other land mammals.

The neck was almost as long as in a camel and its vertebrae
agreed with those of the latter in the very exceptional character
of having the canal for the vertebral artery passing longitu-
dinally through the neural arch, instead of perforating the
transverse process. As Darwin says in the passage quoted
above, "it shows a clear relation to the . . . guanaco and
llama/ ' but this is founded on the postulate that such a like-
ness must, of necessity, imply relationship. As was shown in
the chapters on the Artiodactyla and Perissodactyla, it is the
general rule among long-necked ungulates that the odontoid
process of the axis assumes a spout-like shape, but ^Macrau-
chenia was an exception and had an odontoid which retained
its primitive and peg-like shape; it was, however, relatively
very short and in cross-section was no longer circular, but
oval. This may be regarded as a step toward the assumption
of the spout-like form, but the extinction of the family put an
end to further changes in that direction.

The body was rather short and the limbs very long, giving
the animal a stilted appearance, while the feet were relatively
short. The proportionate lengths of the different limb-seg-
ments was unusual ; the upper arm was short, the fore-arm
very long, the thigh long and the lower leg quite short. The
humerus was very heavy ; the ulna and radius, which were

4*12 IAXO MAMMALS IN THE WESTERN HEMISPHERE

tirmly v\H>ssifiec!f formed a very long compound bone, which
*-%> broad transversely and thin antero-posteriorly. The long
tonmr had only a small and inconspicuous third trochanter
and tho shaft was broad and thin, being flattened, or "com-
wvsscd" antero-posteriorly. The tibia and fibula were united
a I both ends ; the former was very heavy at the upper end, but
diminished downward in width and thickness, and the fibula
articulated with the calcaneum, as in the artiodactyls. The
foot were tridactyl and had mesaxonic symmetry; that is to
saw the median digit, or third of the original five, was sym-
metrical in itself and was bisected by the middle line of the foot,
while the lateral toes (second and fourth), each of which was
asymmetrical, formed a symmetrical pair. It is this perisso-
dactyl character of the foot to which Darwin refers when he
says that ^Macrauchenia "belongs to the same division of
the Pachydermata with the rhinoceros, tapir and palaeothe-
rium." On the other hand, the very significant structure of the
ankle-joint was radically different from that of the Perisso-
dactyla; not only did the calcaneum have a special facet for
articulation with the fibula, but the lower end of the astragalus
was a convex "head," resting only on the navicular, as in the
fToxodontia, fCondylarthra, Hyracoidea and other very
primitive groups of hoofed animals and in clawed mammals
generally. Such a combination of characters is not known in
any of the perissodactyls and precludes the reference of the
fLitopterna to that order, though such a reference is strongly
maintained by several authorities. The ungual phalanges
were small and appear to suggest the presence of pads on the
feet.

The appearance of ^Macrauchenia in life must have been
sufficiently strange. The small head with its proboscis and the
long neck and legs should probably be regarded as indicative
of browsing habits, though the hypsodont teeth show that
grazing was at least an occasional mode of feeding. The long
limbs and short feet gave to the extremities an appearance un-

HISTORY OF THE JXITOPTERNA 493

like that of any existing hoofed animal. The form and size
of the ears and the character of the hairy coat are, of course,
conjectural.

In the later Pliocene the family was represented by forms
which differed so little from the Pampean ^Macravchenia as
to call for no particular notice, but in the presumably lower
Pliocene of the Parand stage, occurred several genera, all un-
fortunately but imperfectly known, which are of interest as
being less specialized than fMacrauchenia and as showing
the way in which some of the peculiarities of the latter were
acquired. In ^Scalibrinitherium, which may be taken as an
example of these genera, the teeth were brachyodont ; the
upper molars were rather less complex than those of \Mac-
rauchenia, while the lower molars had the pillar in the con-
cavity of the posterior crescent, which the Pampean genus
retained only in the milk-teeth. As we have repeatedly
found, the milk-dentition is often conservative and retains
primitive or archaic features which have been lost in the per-
manent teeth, and ^Macrauchenia is another illustration of the
same principle. In the skull of ^Scalibrinitherium the nasal
bones, though very short, had not suffered such extreme ab-
breviation as in the succeeding genus, the nasal opening was
farther forward and the maxillaries united in the superior
median line for only a short distance, while the premaxillaries
were fused together for their whole length. The orbit had not
been shifted entirely behind the teeth, but was above the third
upper molar.

Next in the ascending series, to use the genealogists term,
came the genus fTheosodon of the Santa Cruz, of which al-
most all the skeletal parts are known and thus make possible
a full comparison with \Macratxhenia, which assuredly was
its direct descendant. In view of the great lapse of time in-
volved, the differences between the two genera were less than
might have been expected, though the more ancient animal
was in all respects the more primitive. ]Theosodon was, in

494 LAND MAMMALS IN THE WESTERN HEMISPHERE

HISTORY OF THE fUTOPTERNA 495

the first place, considerably smaller, not much exceeding a
llama in size ; the teeth had lower crowns than even those of
^Scalibrinitherium and the incisors were arranged in line with
the grinding teeth, not in a transverse row, but curving inward
slightly, so that those of the opposite sides nearly met in
front. The incisors, canine and first premolar were simple,
sharply pointed, conical teeth, which gave an almost reptilian
expression to the anterior part of the skull. The upper molars
were on the same fundamental plan as those of ^Macrauchenia,
but in a less advanced stage of development, the transverse crests
being incomplete and the internal cusps had a certain degree
of separateness from the crests and from each other. It is evi-
dent that the upper molars were derived from the quadrituber-
cular type. The lower molars had the vertical pillar in the
concavity of the posterior crescent very prominently developed.
The resemblance of the skull to that of ^Macrauchmia is
obvious at the first glance, but it was less specialized and de-
parted less from the ordinary ungulate type. The cranium
was longer and the face shorter, the orbit, which was incom-
pletely closed behind, extending over the second molar. There
was a sagittal crest, the length of which differed much in the
various species; the nasal bones were already very short,
though decidedly longer than in the subsequent genus fScali-
brinitheriumy and the anterior nasal opening was extended
forward as a long, narrow slit, because the maxillaries did not
come into contact with each other in the superior median line,
and the premaxillaries touched each other, but were not co-
ossified. The nasal canal, though very short, was horizontal,
not vertical. The skulls of the three genera thus displayed
three successive stages in the backward shifting of the orbit
and of the anterior nasal opening, in the shortening of the
nasal bones and in the formation of a solid rostrum by the
fusion of the upper jaw-bones. No doubt also the living ani-
mals exhibited a corresponding gradation in the development of
the proboscis.

496

LAND MAMMALS IN THE WESTERN HEMISPHERE

The neck of fTheosodon was even longer proportionately
than in \Macravchenia and the transference of the canal for
the vetebral artery from the transverse processes to the neural

Fig. 245. — Development of the skull in the fMacrauchenictae, side views. A, \Thco-
sodon, Santa Cruz. B, ^ScaHbrinitherium% Parana. (After Ameghino.) C, fMacrau-
chenia, Pampean. (After Burmeister.) n.f nasal bones.

arch had already taken place, except in the first, sixth and
seventh vertebrae, and was thus less complete than in the
Pampean genus, in which all the vertebrae of the neck, save the
seventh, had the canal in its exceptional position. The odon-

HISTORY OF THE tLlTOPTERNA 497

toid process of the axis was less modified than in the latter,
being relatively longer and more conical. The body was

rather short, and the spines of the trunk-vertebrse were pro-
portionally higher and more prominent. No caudal vertebra

498

LAND MAMMALS IN THE WESTERN HEMISPHERE

have been found, but, from the shape of the sacrum, it is evi-
dent that the tail was short.

The limbs were long, but more slender and less elongate
than in ^Macrauchenia, in which the growth of the neck did

not keep pace with that of the limbs, the
lengthening of the proboscis probably
compensating for this. The shoulder-
blade had two conspicuous metacromia,
very much as in the contemporary ftoxo-
dont, ^Nesodon, but shorter and more
widely separated. The humerus was
short and quite slender and the fore-arm
bones, which were much longer, did not
coossify. The femur had a more slender
and rounded shaft than in ^Macrauchenia
and a much larger third trochanter ; the
leg-bones were also separate from each
other. The tridactyl feet were so like
those of the Pampean genus, that no
particular account of them is necessary,
and the proportions of the limb segments
were similar in both genera, short upper
arm and lower leg, very long fore-arm
and thigh, and short feet.

The appearance of the living animal,

as shown in the restoration, was no doubt

pyramidal. Tm., trape- somewhat like that of ^Macrauchenia,

sium. Td., trapezoid. , , , u . mi . Av x v

m, magnum, u., un- but kss bizarre. That there must have
ciform. v., rudimen- been some sort of a proboscis or pre-

tary fifth metacarpal. .. .. . .. . . .

hensile upper lip, is indicated by the
greatly shortened nasal bones, but this may not have been
longer than in the existing Moose or Saiga Antelope. The
long neck, short body and tail and long limbs suggest an
animal not unlike a Guanaco, but larger and heavier. The
hair may or may not have had the woolly character given

M

Fiq. 247. Left manus of
^Theosodon. S., scaph-
oid. L., lunar. Py.,

HISTORY OF THE fLITOPTERNA 499

to it in the drawing; upon such a point there can be no
certainty.

In the older formations preceding the Santa Cruz, the
fmacrauchenids are known only from fragmentary material,
though something of their history may be made out even from
these fragments. ^Protheo&odon, of the Deseado stage, was
considerably smaller than the Santa Cruz genus and had more
primitive upper molars, in that the internal cusps and inter-
mediate cuspules were isolated and conical, not forming trans-
verse crests. Still smaller were the several genera (]Lamb-
daconus, etc.) related to the fmacrauchenids found in the Casa
Mayor Eocene, which have been referred, perhaps correctly,
to the f Condylarthra. In these the formation of the external
wall of the almost bunodont upper molars was in progress, by
the fore-and-aft extension and transverse thinning of the ex-
ternal cusps ; the internal pair of cusps and the cuspules were
separate and conical. With much confidence, it may be in-
ferred that in these little animals the skull was normal, the
nasal bones were long and that the feet were five-toed, but
demonstration is lacking.

The second family of the fLitopterna, the f Proterotheriidae,
were remarkable for their many deceptive resemblances to the
horses. Even though those who contend that the fLitopterna
should be included in the Perissodactyla should prove to be
in the right, there can be no doubt that the fproterotheres
were not closely related to the horses, but formed a most strik-
ing illustration of the independent acquisition of similar char-
acters through parallel or convergent development. The
family was not represented in the Pleistocene, having died out
before that epoch, and the latest known members of it lived
in the upper Pliocene of Monte Hermoso. In the still older
Parand formation more numerous and varied forms occurred,
but only from the Santa Cruz have materials been obtained of
sufficient completeness to furnish a full account of the struc-

492 LAND MAMMALS IN THE WESTERN HEMISPHERE

firmly coossified, formed a very long compound bone, which
was broad transversely and thin antero-posteriorly. The long
femur had only a small and inconspicuous third trochanter
and the shaft was broad and thin, being flattened, or "com-
pressed" antero-posteriorly. The tibia and fibula were united
at both ends ; the former was very heavy at the upper end, but
diminished downward in width and thickness, and the fibula
articulated with the calcaneum, as in the artiodactyls. The
feet were tridactyl and had mesaxonic symmetry; that is to
say, the median digit, or third of the original five, was sym-
metrical in itself and was bisected by the middle line of the foot,
while the lateral toes (second and fourth), each of which was
asymmetrical, formed a symmetrical pair. It is this perisso-
dactyl character of the foot to which Darwin refers when he
says that ^Macrauchenia "belongs to the same division of
the Pachydermata with the rhinoceros, tapir and palaeothe-
rium." On the other hand, the very significant structure of the
ankle-joint was radically different from that of the Perisso-
dactyla; not only did the calcaneum have a special facet for
articulation with the fibula, but the lower end of the astragalus
was a convex "head," resting only on the navicular, as in the
fToxodontia, fCondylarthra, Hyracoidea and other very
primitive groups of hoofed animals and in clawed mammals
generally. Such a combination of characters is not known in
any of the perissodactyls and precludes the reference of the
fLitopterna to that order, though such a reference is strongly
maintained by several authorities. The ungual phalanges
were small and appear to suggest the presence of pads on the
feet.

The appearance of ^Macrauchenia in life must have been
sufficiently strange. The small head with its proboscis and the
long neck and legs should probably be regarded as indicative
of browsing habits, though the hypsodont teeth show that
grazing was at least an occasional mode of feeding. The long
limbs and short feet gave to the extremities an appearance un-

HISTORY OF THE fLITOPTERNA 493

like that of any existing hoofed animal. The form and size
of the ears and the character of the hairy coat are, of course,
conjectural.

In the later Pliocene the family was represented by forms
which differed so little from the Pampean ^Macrauchenia as
to call for no particular notice, but in the presumably lower
Pliocene of the Parand stage, occurred several genera, all un-
fortunately but imperfectly known, which are of interest as
being less specialized than ^Macrauchenia and as showing
the way in which some of the peculiarities of the latter were
acquired. In \Scalibrinitherium, which may be taken as an
example of these genera, the teeth were brachyodont ; the
upper molars were rather less complex than those of }Mac-
rauchenia, while the lower molars had the pillar in the con-
cavity of the posterior crescent, which the Pampean genus
retained only in the milk-teeth. As we have repeatedly
found, the milk-dentition is often conservative and retains
primitive or archaic features which have been lost in the per-
manent teeth, and }Macrauchenia is another illustration of the
same principle. In the skull of ^Scalibrinitherium the nasal
bones, though very short, had not suffered such extreme ab-
breviation as in the succeeding genus, the nasal opening was
farther forward and the maxillaries united in the superior
median line for only a short distance, while the premaxillaries
were fused together for their whole length. The orbit had not
been shifted entirely behind the teeth, but was above the third
upper molar.

Next in the ascending series, to use the genealogist's term,
came the genus \Theosodon of the Santa Cruz, of which al-
most all the skeletal parts are known and thus make possible
a full comparison with }Macrauchenia, which assuredly was
its direct descendant. In view of the great lapse of time in-
volved, the differences between the two genera were less than
might have been expected, though the more ancient animal
was in all respects the more primitive. ^Theosodon was, in

502 LAND MAMMALS IN THE WESTERN HEMISPHERE

HISTORY OF THE fLITOPTERNA 495

the first place, considerably smaller, not much exceeding a
llama in size ; the teeth had lower crowns than even those of
^Scalibrinitherium and the incisors were arranged in line with
the grinding teeth, not in a transverse row, but curving inward
slightly, so that those of the opposite sides nearly met in
front. The incisors, canine and first premolar were simple,
sharply pointed, conical teeth, which gave an almost reptilian
expression to the anterior part of the skull. The upper molars
were on the same fundamental plan as those of ^Macrauchenia,
but in a less advanced stage of development, the transverse crests
being incomplete and the internal cusps had a certain degree
of separateness from the crests and from each other. It is evi-
dent that the upper molars were derived from the quadrituber-
cular type. The lower molars had the vertical pillar in the
concavity of the posterior crescent very prominently developed.
The resemblance of the skull to that of fMacrauchenia is
obvious at the first glance, but it was less specialized and de-
parted less from the ordinary ungulate type. The cranium
was longer and the face shorter, the orbit, which was incom-
pletely closed behind, extending over the second molar. There
was a sagittal crest, the length of which differed much in the
various species; the nasal bones were already very short,
though decidedly longer than in the subsequent genus ^Scali-
brinitherium, and the anterior nasal opening was extended
forward as a long, narrow slit, because the maxillaries did not
come into contact with each other in the superior median line,
and the premaxillaries touched each other, but were not co-
ossified. The nasal canal, though very short, was horizontal,
not vertical. The skulls of the three genera thus displayed
three successive stages in the backward shifting of the orbit
and of the anterior nasal opening, in the shortening of the
nasal bones and in the formation of a solid rostrum by the
fusion of the upper jaw-bones. No doubt also the living ani-
mals exhibited a corresponding gradation in the development of
the proboscis.

504 LAND MAMMALS IN THE WESTERN HEMISPHERE

In still another respect the feet of ^Diadiaphorus deviated
markedly from those of the horses, viz. in the great proportion-
ate length of the phalanges, especially of the first one, and the
shortness of the metapodials, the three phalanges of the
median digit together exceeding in length the metacarpal or
metatarsal, while in the horses this proportion is reversed. The
skull of this genus was short, deep and with an anterior taper ;
it had a long sagittal crest, but a brain-chamber of good capac-
ity, considering its geological date. The nasals were quite
short, though the degree of shortening was not such as to sug-
gest the existence of a proboscis. In general appearance the
skull recalls that of one of the larger foreodonts (p. 372) of
the North American Oligocene.

To the genus fProterotherium, the type of the family, be-
longed a great number of Santa Cruz species, for at that time
the genus was in a state of most vigorous development and the
species were so variable that satisfactory discrimination of
them is exceedingly difficult. They were all much smaller and
slighter animals than the species of ^Diadiaphorus, but did not
differ from them in any important structural character. The
skull in this genus closely resembled that of the one last named,
save for its smaller size and lighter and more slender propor-
tions ; the nasal bones were considerably longer and the occiput
was somewhat wider.

A more isolated position was held by the genus }Thoa-
therium, which was very clearly demarcated from all of the
other genera of the family. Its species were the smallest of the
commoner Santa Cruz members of the order and were of very
light and graceful form. The dental formula was the same as
in the other genera, but there were no tusks ; the single upper
and two lower incisors were of nearly the same size and simple,
chisel-like form. The upper molars had the same elements
as in the preceding genera, but somewhat differently con-
nected, the two internal cusps and the anterior intermediate
cuspule being united into a nearly longitudinal ridge. The

HISTORY OF THE fLITOPTERNA 505

skull was light, slender and pointed ; the nasals were shortened,
though less than in 1[Diadiaphorus ; the sagittal crest was
shorter than in the latter and the occiput was far narrower.
The neck was short, the body of moderate length and the tail
short. The limbs and especially the feet were proportionately
more elongate and slender than in any other known genus of
the family, giving quite a stilted appearance to the skeleton.
The fore-arm bones were not coossified, but the ulna was much
more reduced than in any of the other genera of the family,
and the same is true of the fibula, which, though very slender,

Fio. 251. — Skull of IThoatherium, Santa Crui. Princeton University Museum.

showed no tendency to unite with the tibia. The limb-bones,
especially the femur, had a decided resemblance to those of
^Mesohippus, the lower Oligocene tridactyl horse of North
America, with the smaller species of which, ]M. bairdi, \Thoa-
therium agreed well in size. Most remarkable of all were the
feet, which were more strictly monodactyl than those of any other
known mammal. The single functional digit, the third, had
on each side of its upper end a very small, scale-like nodule of
bone, the last vestiges of the lateral digits, corresponding to
the immensely larger splints of the horse. Despite the un-
rivalled completeness of digital reduction which \Thoatherium
displayed, the mode of reduction was inadaptive and the
rudimentary metapodials retained the same carpal and tarsal

506 LAND MAMMALS IN THE WESTERN HEMISPHERE

HISTORY OF THE fLITOPTERNA

507

connections that they originally had in the
pentadactyl manus, a very great difference
from the horses. The ankle-joint also was of
the same -primitive character as in the other
fLitopterna. The feet were relatively longer
and more slender than in the other tPr°-
terotheres and the metapodial of the single
functional digit longer in proportion to the
phalanges.

The appearance of the living animal, aside
from the character of the hair, colour-pattern, jf
etc., may be closely inferred from the skeleton.
It was a much smaller and more graceful ani-
mal than its contemporary and relative fZH'a-
diaphorus, as light and agile as a gazelle. The
head had some resemblance to that of a small
horse, but the neck was much shorter than in
the horses ; the body also was shorter than in
the latter, and the proportions of the trunk
and limbs were quite as in the smaller ante-
lopes. But these likenesses to horses and an-
telopes were, it must again be emphasized,
superficial ; the fundamental characteristics
of structure were more primitive than in the
most ancient known artiodactyls and perisso-
dactyls.

With the aid of the fragmentary material
which alone represents the fproterotheres in
the formations preceding and following the
Santa Cruz in time, it is not practicable to
trace the development of the various phyla in
a satisfactory manner. Two of the Santa Cruz Fia- 253.— Left pea

. of iThoatherium.

genera, \Diadiaphorus and jProterothenum, Princeton Uni-
continued into the lower Pliocene (Parand), ?**!* Muae"m-

' Letters as in Fig.

and two additional ones have been named, 250.

t

I

508 LAND MAMMALS IN THE WESTERN HEMISPHERE

but little is known about them. The latest known member of
the family so far discovered is a genus (IfEpitherium) from the
upper Pliocene of Monte Hermoso, a tridactyl form like fZH'a-
diaphorus. It is a noteworthy fact that the most advanced
and specialized genus of the entire family ended with the
Santa Cruz, while the less differentiated types survived till a
considerably later period. Possibly, it was the incoming of
the highly efficient Carnivora from North America that led
to the extermination of the last fproterotheres.

Turning backward from the Santa Cruz, the family may be
traced without any question to the Deseado stage of the Oligo-
cene, though nothing but teeth has yet been obtained, while
in the Eocene it would appear to have become merged in the
same group of small, fCondylarthra-like animals with quad-
ritubercular molars, as those which are regarded as the probable
ancestors of the fmacrauchenids. Howev >r likely this con-
elusion may seem to be, its confirmation t* ait the dis-

covery of much more complete specimens * now avail-

able.

Order fAsTRAPOTHERiA. jAstrapotheres

In the Santa Cruz another group of peculiar South American
ungulates, the fAstrapotheria, made its last recorded appear-
ance. Though not at all uncommon in that formation, no
complete or even partial skeleton has yet been found, but
merely the skull and a few bones of the limbs and feet. For
this reason there is much doubt as to the systematic position
and relationships of these animals, which were among the most
curious of the many strange mammals which made up the
Santa Cruz fauna. They were mentioned in connection with
the fAmblypoda (p. 456) as possible representatives of that
order in South America, but, as will be seen later, this is an
improbable conclusion, and the group appears to have been
indigenous in the southern continent, in which, at all events,

HISTORY OF THE fASTRAPOTHERIA 509

it had a very long history. It has not been found in any for-
mation later than the Santa Cruz, unless the Friasian fauna,
which contains it, should be removed from that stage, of which
it apparently forms the latest division.

I. tASTRAPOTHERIIOfi.

^Astrapotherium, Santa Cruz and Patagonian. ^Astrapothericulus,
Patagonian. f Parastrapotherium, Deseado. ^Astraponotus, Astra-
ponotus Beds, t Albertogaudrya, Casa Mayor.

II. tTRIGONOSTYLOPID^J.

t Trigonostylops, Casa Mayor, f Edvardocopeia. Astraponotus Beds.

The genus fAstrapotherium, which was the only well-de-
fined representative of its family and order in the Santa Cruz
stage, contained several species, some of them the largest
animals of their time, as well as the most grotesque in appear-
ance. The dentition differed in some important respects from
that of all the oth^ South American ungulates, the formula
being : i $, <q > |, X 2 = 28. The upper incisors had com-

pletely disaj but the lower ones were large and, what

was an excej haracter, they were partially divided into

two lobes, s i' as in the Eocene fuintatheres of North

America (p. ^j. The canines were very large and formi-
dable tusks, which grew throughout life and apparently formed
no root ; the upper tusk was nearly straight and was obliquely
truncated by the strongly curved and sharp-pointed lower
tusk. This arrangement was very unusual among South
American hoofed mammals, many of which had no tusks at all ;
and in those which possessed them, such as the ftoxodonts
(p. 468), they were mostly incisors. Only in the fastrapotheres
and fhomalodotheres were there canine tusks, and in the latter
group they were small and of limited growth. All the teeth,
except the canines, were brachyodont and, though rather high-
crowned, formed roots before coming into use. The pre-
molars were small and greatly reduced in number (f), and in
pattern were simpler than the molars. The upper molars were
constructed on essentially the same plan as in the fToxodonta ;

510

LAND MAMMALS IN THE WESTERN HEMISPHERE

indeed, the first specimen of this genus collected was referred
to a large species of \Nesodon by Owen. On the other hand,
the resemblance to the rhinoceros teeth is very decided, and
has led several writers to postulate a relationship between the
tastrapotheres and the rhinoceroses. The lower molars were

of the bicrescentic pattern so frequently met with already ;
these teeth were very narrow in proportion to their length
and strongly suggest those of \Metamynodon, the supposedly
aquatic rhinoceros of the North American Oligocene (p.
346). It may be confidently inferred that so small a number
of premolars was due to reduction from a full series, and this is
confirmed by the milk-dentition, in which the premolars were J.

HISTORY OF THE fASTRAPOTHERIA 511

The skull was extremely peculiar, more so than in any other
of the contemporary genera of hoofed animals. The toothless
premaxillaries were quite small, but thick, and must have sup-
ported an elastic pad, against which the lower incisors could
effectively bite in cropping herbage. The nasal bones were
extremely short and there must have been a proboscis or greatly
inflated snout, probably the former; the immense develop-
ment of sinuses in the frontal bones elevated the whole fore-
head into a great, dome-like convexity, a feature which is not
equalled in any other known mammal. The orbits were open
behind and the brain chamber was small, so that the sagittal
and occipital crests were very high and strong, to afford suffi-
cient surface for the attachment of the great temporal muscles.
The horizontal portion of the lower jaw was shallow vertically,
but very thick and massive, and the symphyses! region was
broad and depressed.

Unfortunately, the skeleton is still very incompletely
known. Of the vertebrae, only the atlas and axis have been
recovered, and these resembled those of the Santa Cruz ftoxo-
dont ^Nesodon, on a larger scale. The scapula had a very
thick spine, without the projections which were found in most
of the Santa Cruz ungulates. The limb-bones were long and
comparatively slender, and the processes for muscular attach-
ment were singularly small and weak ; the bones of the fore-
arm and lower leg did not coossify and were proportionately
elongate, the tibia being but little shorter than the femur.
The latter had the flattened shaft which recurs in nearly all of
the very heavy ungulates, but retained a remnant of the third
trochanter. If the feet found isolated in the Santa Cruz and
Deseado stages have been correctly referred to this order, then
the genus was five-toed and the feet were broad, short and
heavy, quite elephantine in appearance, especially the fore
foot. The ankle-joint was very peculiar and the calcaneum had
no articulation with the fibula, which it had in all the other
indigenous South American ungulates.

512 LAND MAMMALS IN THE WESTERN HEMISPHERE

Incomplete as the material is, it is yet possible to form
some general conception of this extraordinary animal when in
life. The head was short, broad and deep, rounded and very
probably furnished with a proboscis ; the neck was of moder-
ate length, so that the mouth could not reach the ground
without a straddling of the fore legs. The body was no doubt
long, the limbs long and rather slender, giving the animal a
stilted appearance, the feet very short, broad and columnar.
Several species of the genus are known, which differed much in
size, the largest (fA. giganteum) probably exceeding any modern
rhinoceros in height and length, and the smallest (}A. nanum)
not much larger than a Wild Boar.

^Asfrapothtriculiis, of the Patagonian stage, was smaller
than the average species of the Santa Cruz genus, and had
teeth of the same number, but the canines were not capable
of indefinite growth, and the lower molars had the pillar in the
posterior crescent so characteristic of the South American
hoofed animals. In the Deseado stage, on the contrary, the
fastrapotheres were of larger size, and in the commonest genus,
1[Parastrapotherium} the grinding teeth had lower crowns and
the premolars were more numerous, at least f . In the still
more ancient ^Astraponotus, which gives its name to the upper
Eocene (or lower Oligocene) of Patagonia, the premolars were
present in full series. In the Casa Mayor the order was abun-
dantly represented by still more primitive genera, which as-
suredly had an undiminished number of teeth, though this
has not been proved. One of these genera, \Albertogaudrya,
was the largest animal of its time and the highly probable
ancestor of the series leading to the Santa Cruz ^Astrapothe-
rium.

The second family of the order, the "(Trigonostylopidse,
did not survive beyond the Eocene and is so imperfectly known
that any account of it would be to small profit.

As stated above, the fAstrapotheria were an isolated group
and their relationships are problematical and are likely to re-

HISTORY OF THE fASTRAPOTHERIA 513

main so pending the discovery of much more complete speci-
mens of the various genera which made up the series. I am
inclined to the opinion, however, that all of the indigenous
groups of South American ungulates, which inhabited that
continent before the great immigration from the north, were
derivatives of the same stock and more nearly related to one
another than to any of the orders which lived in other regions.

In looking over the labyrinth of ungulate history, as re-
corded by the fossils, certain facts stand out clearly, while
others are still very obscure. It is like trying to trace the
plan of vast and complicated ruins, which here are deeply
buried in their own debris, there are fully exposed and in
another place are swept away so completely that hardly a
trace remains. But the problem is far more complex than any
which can be presented by buildings, for the factor of repeated
migrations from continent to continent comes in to obscure
the evidence. Had each of the great land areas received its
original stock of early mammals and then been shut off from
communication with any other, many of the difficulties would
be removed, but the story would lose half its interest.

Within the limits of the family, giving to that group the
broad and elastic definition which has hitherto been employed,
we have repeatedly found it feasible to construct a phylogenetic
series which very nearly represents the steps of structural
modification as they occurred in time. Much less frequently
is it possible to trace allied families to their common starting
point, and, so far as the hoofed animals are concerned, in no
case have we yet succeeded in doing this for the separate orders.
The obstacle lies in the fact that the ordinal groups were al-
ready distinct, when they made their first appearance in the
known and accessible records, and the hypothetical ancestors
common to them all, or to any two of them, are to be sought
in regions of which we know little or nothing. Nevertheless,
certain legitimate inferences may be drawn from the available

2l

514 LAND MAMMALS IN THE WESTERN HEMISPHERE

evidence. It remains to be proved whether the assemblage
of hoofed mammals, as a whole, was of single or multiple origin.
Have all ungulates been derived from a common stock, or did
they arise independently from several groups of clawed mam-
mals ? While the records cannot be followed back to the point,
or points, of origin of the various orders, yet it is a noteworthy
fact that, between several of them, the differences grow less
marked as the more ancient members are reached, as though
they were converging to a common term ; others again show
little such approximation, and the most probable conclusion
from the evidence now at hand is that the ungulate assemblage
is composed of several independent series.

One such series is that of the Hyracoidea and Proboscidea,
to which Dr. Schlosser has given the name "Subungulata,"
and has pointed out its relationship to the fCondylarthra,
which, however, is not a close one and may be illusory.
Another apparently natural group is that of the peculiarly
South American forms, the fToxodontia, with its four sub-
orders, the flitopterna and the fAstrapotheria, which all
appear to be traceable to closely allied families in the Eocene,
whose teeth strongly suggest derivation from the fCondy-
larthra ; but the material does not permit any positive state-
ments. The Artiodactyla and Perissodactyla have so many
similarities that they have always been regarded as closely
related groups, but the distinction between them was almost as
sharply drawn in their most ancient known members as it is
to-day, and there was no distinct tendency to converge back
into a common stem. Their mutual relationships are thus ob-
scure, but the Perissodactyla, at least, seem to be derivable from
a f condylarthrous ancestry.

The fCondylarthra, as a whole, were by far the most
primitive of the ungulates, which they connected with the
clawed mammals. None of the genera yet discovered can be
regarded as ancestral to any of the higher orders, but it is en-
tirely possible that in the upper Cretaceous period the fCon-

HISTORY OF THE fASTRAPOTHERIA 515

dylarthra were spread over all the continents, except Australia,
and that from them the other ungulate orders arose in dif-
ferent regions. At all events, the fCondylarthra show how
the transition from clawed to hoofed types may have occurred
and perhaps actually did so, but it would be premature to
affirm this.

CHAPTER XIV

HISTORY OP THE CARNIVORA

The story of the hoofed mammals, as sketched in brief
outline in the preceding chapters (VIII-XIII), is a curious
mixture of relatively full and satisfactory paragraphs, with
scanty, broken and unintelligible ones, not to mention those
which have not yet been brought to light at all. With all its
gaps and defects, which inhere in the nature of things, the
history of the various ungulate series is the best that the
palaeontology of mammals has to offer and constitutes a very
strong and solid argument for the theory of evolution. For
the Carnivora the story is less complete and for obvious reasons.
Individual abundance was a very large factor in determining
the chances of preservation in the fossil state for any given
species, and, as a rule, whole skeletons are found only when the
species was fossilized in large numbers. In any region the
Carnivora are less numerous than the herbivora upon which
they prey, and while most ungulates live in larger or smaller
herds, the carnivores are mostly solitary.

The Carnivora are divisible into three well-marked sub-
orders, called respectively the Pinnipedia, Fissipedia and
fCreodonta. The Pinnipedia, seals, walruses, etc., which
are almost purely marine in habitat, are not dealt with in
this book, since so little can be learned of them from the
fossils, and the fCreodonta, an extremely ancient and primi-
tive group, will be treated separately. The Fissipedia are
chiefly terrestrial, though they include the otters, and their
subdivisions, so far as the American forms are concerned, are

516

HISTORY OP THE CARNIVORA 517

shown in the following table, which, it should be observed,
omits several genera. Unless otherwise noted, the genera are
North American.

Suborder FISSIPEDIA. Land Carnivora

I. CanidjB, Dogs, Wolves, Foxes, etc.

Cants, Wolves, Pleist. and Rec. Vulpes, Red Fox, do. Urocyon,
Grey Fox, do. Cerdocyon, fox-like wolves, S. A., do. Idicyon,
Bush-Dog, S. A., do. ICyon, Dhole, mid. and up. Mioc. ]Dino-
cynops, S. A., Pleist. \Mhurodtm, up. Mioc. and low. Plioc.
^Tephrocyon, mid. Mioc. to low. Plioc. ^Borophagus, up.
Mioc. to mid. Plioc. ^Ischyrocyon, up. Mioc. ^Amphicyon,
mid. Mioc. to low. Plioc. ^Daphcenodon, low. Mioc. ]Enhy-
drocyon, up. Oligo. ^Temnocyon, up. Oligo. ^Mesocyon, up.
Oligo. ^Cynodesmus, low. Mioc. ^Daphwnus, Oligo. ]Cyno~
dictis, Oligo. ^Procynodidis, up. Eoc.
II. ProcyonidjE, Raccoons, etc.

Proqjon, Raccoons, N. and S. A., Pleist. and Rec. Na&ua, Coatis,
S. A., Pleist. and Rec, now extending to Calif. ^Cyonasua,
S. A., up. Plioc. Bassariscus, Cacomistle, low. Plioc. to Rec.
\Phlaocyon, low. Mioc. ^Leptardus, up. Mioc. Polos , Kinkajou,
Neotropical, Recent.

III. URSiDiE, Bears.

Ursu8t true Bears, Pleist. and Rec. Tremardos, Spectacled Bear,
S. A. \Ardotherium, fShort-faced Bears, N. and S. A., Pleist.

IV. MustelidjE, Martens, Weasels, etc.

Mustela, Weasels, mid. Mioc. to Rec. Grison, Grison, S. A., Pleist.
to Rec. Tayra, Tayra, do. Mattes, Martens, up. Mioc. to
Rec. Gvlo, Wolverene, Pleist. and Rec. \Canimartes, mid.
Plioc. t Brachypsalis, up. Mioc. ^Megalidis, low. Mioc.
\Mlurocyon, do. ^Oligobunis, up. Oligo. and low. Mioc.
^Buncelurus, low. Oligo. Mephitis , Skunk, Pleist. and Rec.
Spilogale, Spotted Skunk, do. Conepatus, S. A. Skunk, Pleist.
and Rec, N. A., Rec. Taxidea, Badger, Pleist. and Rec
Ladra, Otters, up. Mioc. to Rec, S. A., Pleist. and Rec. Lalax,
Sea-Otter.

V. FELiDiB. Cats.

Felts, true Cats, N. A., low. Plioc to Rec, S. A., Pleist. and Rec.
Lynx, Lynx, Pleist. and Rec ^Pseudodurus, mid. and up. Mioc
^Smilodon, Sabre-tooth Tiger, N. and S. A., Pleist. I^Machai-
rodus, mid. Mioc to Plioc ^Nimravus, up. Oligo. ^Archcelu-
rus, do. t Hoplophoneus, Oligo. ^Dinidis, do. ^Eusmilus,
low. Oligo.

518 LAND MAMMALS IN THE WESTERN HEMISPHERE

Two families, the hyenas (Hysenidae) and civet-cats (Viver-
ridae), are omitted from the table because they apparently
never reached the western hemisphere. The bears, of Old
World origin, invaded America at a very late period and are
not certainly known here before the Pleistocene. The other
four families were well represented in North American history,
though the great weasel tribe (Mustelidse) went through the
greater part of its history in the Old World. None of the
families is indigenous in South America, and all of the five
families which it now shares with North America came in in
the series of immigrations, of which the first recorded effects
are found in the Pliocene and continued into the Pleistocene.

The Fissipedia are adapted to a great variety of habits and
modes of life and consequently there is considerable diversity
of structure among them, though they all form a homogeneous,
natural group. The dogs (Canidae) are terrestrial, neither
swimmers nor climbers; some, like the foxes, are solitary,
others, like the wolves, hunt in packs and nearly all are strong,
swift runners. The cats (Felidae) which have a remarkable
range of size, are terrestrial or arboreal ; they take their prey
by stalking and leaping upon it, not by running it down. The
bears (Ursidae) are mostly omnivorous, not very often killing
prey, and largely vegetarian in diet. The raccoons (Pro-
cyonidae) are chiefly arboreal and omnivorous. The very
large and varied weasel family (Mustelidae) have different
habits, though nearly all are fierce and bloodthirsty.
Otters and sea-otters are aquatic and prey chiefly on fish ;
minks and fishers are semi-aquatic; martens are arboreal,
skunks terrestrial and badgers fossorial.

While there is thus much diversity of habit with corre-
sponding differences of structure among the Fissipedia, there is
a certain unity of plan recognizable among them all. With
but few exceptions, the incisors are present in full number and
the canines are formidable lacerating weapons. Especially
characteristic of the dentition are the " sectorial' ' or "car-

HISTORY OF THE CARNIVORA 519

nassial" teeth, always the fourth upper premolar and first
lower molar, which form a pair of shearing blades, the pre-
molar biting outside. In the bears and most of the raccoons
the teeth are tuberculated, in adaptation to the omnivorous
habit, and the carnassials have lost the shearing form, though
clearly derived from that type. The skull has powerful jaws,
and the crests and ridges for the attachment of the jaw muscles
are prominent except in very small animals, and the stout,
boldly outcurving zygomatic arches are very characteristic.
The face may be elongate, as in the dogs, or extremely short,
as in the cats, or of intermediate length; the brain-case is
relatively capacious, and the orbits, except in the cats, are
widely open behind. The neck is never very long, but the
body often is, and the tail varies greatly in length, as do also
the limbs. There is great difference, too, between the va-
rious families in the prominence of the processes on the limb-
bones for the attachment of muscles, as expressive of the mus-
cular development of the limbs, and also in the extent to which
the fore foot can be rotated and used for grasping. In all exist-
ing Fissipedia the femur has no third trochanter, but many
extinct genera possessed it. The bones of the fore-arm and
lower leg are always separate and uninterrupted.

In the wrist (carpus) there is always a large bone, the scapho-
lunar, which is made up by the coalescence of three elements,
the scaphoid, lunar and central, a feature which, though recur-
ring in a few other mammals, is essentially characteristic of
the modern Carnivora. The feet are armed with claws more
or less sharp, which in some families, notably the cats, are
retractile and may be folded back into the foot. The gait
may be plantigrade, as in the raccoons and bears, or digiti-
grade, as in the dogs and cats, or intermediate in character.

Throughout the Paleocene and most of the Eocene, there
were no Fissipedia, the flesh-eaters all belonging to the extinct
fCreodonta, and the first clearly recognizable fissipedes occurred
in the upper Eocene or Uinta.

520 LAND MAMMALS IN THE WESTERN HEMISPHERE

1. Canidce. Dogs, Wolves, Foxes, etc.

This family, which may with convenience be called simply
dogs, is at present the most widely distributed of the families of
Fissipedia, occurring in every continent, even Australia,
and ranging through all climates almost from pole to pole.
They are a singularly homogeneous family and show few
differences of structure; such differences as there are affect
chiefly the number and size of the teeth and external char-
acters, such as the size of the ears, length and colouring of the
hair, etc. The many domestic breeds are not here considered.
Almost alone among the Fissipedia the dogs capture their
prey by running it down, and they are endowed with remark-
able speed -and endurance. The entire organism, especially
the limbs and feet, are adapted to cursorial habits.

For the purpose of comparison with the extinct genera of
the family, some account of a wolf will suffice. The wolves,
like most other members of the family, have a larger number
of teeth than is usual in the suborder, as appears from the
formula : if, c\, p J, mf,x2=42, that is to say, only the third
upper molar has been lost from the typical number, though the
third lower is very small and seemingly on the point of dis-
appearance (Fig. 44, p. 93). The upper sectorial tooth,
the fourth premolar, has its shearing blade made up of two
sharp-edged cusps, one behind the other, and there is a small
internal cusp carried on a separate root ; the upper molars
are triangular and tritubercular and are used for crushing.
The lower sectorial, the first molar, has an anterior blade of
two shearing cusps, with the remnant of a third, and a low,
basin-like posterior "heel."

The skull is characterized by the long face and jaws and
by the structure of the auditory region ; the tympanic bones
are inflated into large oval bullae, which are hollow and un-
divided, and the external opening of each is an irregular hole,
without tubular prolongation. There is an alisphenoid canal

HISTORY OF THE CARNIVORA 521

for the passage of the internal carotid artery. The neck, body
and tail are of moderate length and the vertebrae of the loins
are not conspicuously large and heavy. There is no collar-
bone. The limb-bones have a distinct, though superficial,
resemblance to those of hoofed animals ; the humerus has no
very prominent ridges for the attachment of muscles and no
epicondylar foramen, and the femur no third trochanter. The
fore-arm bones are separate, but are so articulated together
and with the humerus as to give the fore foot no power of
rotation. The manus in all existing wild species has five digits,
though the pollex or first digit is very small, a mere dew-claw ;
the four functional digits are arranged in two symmetrical
pairs, very much as in the artiodactyls, a longer median pair,
of which the metacarpals have a nearly square cross-section,
and a shorter lateral pair (2d and 5th) of more trihedral
form. All the metacarpals are closely appressed and almost
parallel. The pes has four digits arranged in similar fashion.
The claws are blunt and non-retractile, and are of little use in
seizing or lacerating prey, but are useful in digging. The
ungual phalanges have no bony hoods reflected over the base
of the claw. All modern forms are digitigrade.

Materials are lacking for the construction of any such
detailed phylogeny of the dogs as has been accomplished for
many ungulates. Many of the extinct genera are known
only from skulls, or even jaws, and the well-preserved skulls
are too few to form distinctly defined and continuous series.
On the other hand, there is every reason to believe that the
canine genera of the successive geological stages did approx-
imately represent the successive steps of development within
the family, though it is difficult to distinguish between the
phyla.

The Pleistocene dogs, for the most part, differed little from
the Recent ones ; there were some very large species like the
Canis ]dirus (Frontispiece) of the Mississippi Valley and the
Pacific Coast. Two very peculiar genera have been reported.

522 LAND MAMMALS IN THE WESTERN HEMISPHERE

One (IfPachycyon), from a cave in Virginia, had remarkably
short, stout and strongly curved limb-bones, which suggest otter-
like habits; the other (^Hycenognathus) , from California, had
a very short face and extremely massive lower jaw and very
heavy teeth ; it was probably like a hyena in appearance.

As far back as the Blanco stage of the middle Pliocene,
remains occur which are assigned to the modern genus Cants,
though better preserved specimens would probably require their
removal from that genus. In the lower Pliocene the phylum
of the true wolves was represented by 1[Tephrocyon, which, so
far as it is known, differed only in minor details from Canis,

Fig. 255. — Skull of tCynodesmus thooides, a lower Miocene wolf. Princeton University

Museum. Compare with Fig. 7, p. 62.

and \Tephrocyon went back to the middle Miocene. What
would appear to be its direct ancestor is ^Cynodesmus, of the
lower Miocene, which, in view of the long lapse of time involved,
differed less from the modern wolves than one would have
supposed, but the differences are significant, as pointing back
to a far more primitive type of structure. ^Cynodesmus was
a small animal, intermediate in size between a Red Fox and
a Coyote. The dental formula was the same as in Canis,
but the teeth were relatively smaller and more closely crowded,
as the face and jaws were shorter and the cranium, though
longer, had a less capacious brain-chamber. The cast of
this chamber, which very perfectly reproduces the form of
the brain, shows that the latter was not only smaller but less

HISTORY OF THE CARNIVORA 523

convoluted than in the modern animals, and this, in turn,
denotes a lower grade of intelligence. The limb-bones were
like those of wolves, but the feet were quite different. In the
manus the first digit, or pollex, was much less reduced, though
considerably shorter than the other digits, which were not
in two symmetrical pairs, but were all of different lengths,
not closely appressed, but arranged in radiating fashion; the
metacarpals had not yet acquired the quadrate or trihedral
form, but were more oval in cross-section. The pes was more

Fig. 256. — Skull of primitive " bear-dog " {\Daphecnu8 fdinus). White River stage.

(After Hatcher.)

modernized, but had five digits, which is not true of any exist-
ing member of the family. The claws were thin and sharp
and were slightly retractile, a power which has been completely
lost in all the modern canids. Such an animal could hardly
have been preeminently cursorial.

Out of the crowd of dog-like creatures in the John Day
Oligocene, it is not yet practicable to select one which is to
be taken as the ancestor of the Recent wolves through
^Cynodesmus, nor can this be done with better assurance of
success in the White River, though the beginning ('fDaphoenus)
of the fbear-dogs in that formation probably closely represents
the ancestral stage sought for. It is likely that several of

524

LAND MAMMALS IN THE WESTERN HEMISPHERE

the phyla into which the family was divided became blended

in a common stock at that stage.

A second phylum, now entirely extinct, is that of the fbear-

dogs, which is not certainly recorded later than the middle
^j^fS^v Pliocene, though

s£K~f/^*?/to&) some have been
€£> jj ^/^q doubtfully reported

from the older Pleis-
tocene of the Great
Plains and the re-
markable Californian genus, \Hycenognaihus, may have been

an offshoot of the same stock. The phylum was characterized

by the unusually large size of the molars and by certain other

features, which, however, are not

known to have persisted through

the entire series from first to last.

In the middle Pliocene lived some

very large bear-dogs, of the genus

jBoropkagus, the teeth of which had

a strong likeness to those of the

hyenas and probably the animals

had hyena-like habits, feeding largely

upon carrion and crushing the stout-
est bones with their massive teeth.

The same, or a very similar, genus

lived in the lower Pliocene, but none

of the species of that date is at all J*

well known. In the upper Miocene Fja- 258. — Right manue of tDa-

occurred several species which have />„., pyrBniidai. />,.. piriform.

been referred to the European u- uniform. (After Hatcher.)

, , _. . Compare with Fig. 32. p. 82.

genera, jAmphiqjon and jDmocyon.

The latter was an enormous canid, equalling in size the largest
of living bears, the great Kadiak Bear of Alaska, and, though
probably having a long and heavy tail, was much like a bear
in appearance. The teeth indicate a more exclusively car-

HISTORY OF THE CARNIVORA

525

nivorous habit than that of the bears and these may well
have been savage and terrible beasts of prey.

\Amphicyon, which had three upper molars, continued
down through the middle Miocene, but was replaced in the
lower by ^Dapkcenodon, which may or may not have been its
direct ancestor. The uncertainty as to the exact relationship
between the two genera will remain until more complete
material shall have been obtained from the middle Miocene.

jDaphoenodon was the largest dog of its time, the contemporary
wolves (^Cynodesmus) having been hardly half so large, but
was much inferior in size to the huge fbear-dogs of the middle
and upper Miocene. The skull resembled that of a large
wolf, but the tympanic bullae were smaller and more loosely
attached and the molar teeth were relatively much larger,
a persistent characteristic of this phylum. The very long and
heavy tail was a cat-like feature. The limbs were compara-
tively short and stout; the humerus had the epicondylar

526 LAND MAMMALS IN THE WESTERN HEMISPHERE

foramen and the femur retained a trace of the third trochanter,
both of which are lost in the modern members of the family.
The feet were not at all canine in type, but rather resembled
those of the ancient and unspecialized flesh-eaters. There
were five digits in manus and pes and were not arranged in
parallel pairs, but diverging; the metapodials were of oval
cross-section, not squared, and their lower ends, which articu-
lated with the first row of phalanges, had hemispherical sur-
faces, not semicylindrical. The claws were sharp and a remnant
of former retractility was to be observed. Such an animal
could hardly have been a strong and enduring runner and its
structure suggests that it captured its prey by stalking and
leaping upon it. The wolf-like head, with cat-like body, tail
and limbs, made a strange combination, not closely paralleled
by any existing carnivore.

Through the Oligocene the phylum was carried back by
the several species of fDaphcenus, assuredly the ancestor of
]Daphcenodon and decidedly more primitive in many respects.
The Oligocene genus was a much smaller animal than its lower
Miocene successor, the larger species hardly equalling a Coyote ;
the teeth were smaller and more closely set, but the molars
were proportionately large, while the carnassials were less
finished and effective shearing blades. The skull was less
distinctively dog-like and had a smaller brain-case, with very
prominent sagittal and occipital crests, a longer cranium and
shorter face; the tympanic bones were very small and so
loosely attached to the skull that they are rarely found, a very
striking difference from all existing dogs. The backbone was
remarkable for the unusually large size of the lumbar vertebrae,
a point of resemblance to the cats and suggesting that fZ)a-
phcenus had great powers of leaping ; there was a long, heavy,
leopard-like tail, and the caudal vertebrae were very like those
of the long-tailed cats. The limbs and feet were similar in
character and proportions to those of ^Daphcenodon, but the
astragalus was less grooved for the tibia, the claws were rather

HISTORY OF THE CARNIVORA 527

more retractile and the gait was probably more plantigrade.
There were so many cat-like features in the skeleton of fDa-
phwnusy that the observer cannot but suspect that these resem-
blances indicate a community of origin, but, until the Eocene
ancestors of the cats are found, the question of relationship
must remain an open one.

The most ancient member of the bear-dog phylum yet
discovered appears to be one of the fcreodont family of the
fMiacidae, found in the Uinta Eocene.

A short-lived branch of the canine stock was that of the
so-called "fhyena-dogs," a peculiar American type, which
abounded in the upper Miocene and lower Pliocene and then
became extinct. Traced backward, this brief series of species
would appear to have sprung from the true wolves tfTephro-
cyon) of the middle Miocene. The upper Miocene and lower
Pliocene genus \Mlurodon had several species, which differed
considerably in size ; the commoner of these were large wolves
with very modern type of body, tail, limbs and feet, but having
short and massive heads. The premolars were extremely
thick and heavy, with such a resemblance to those of the hyenas,
that these animals have sometimes been mistakenly regarded
as ancestral to that family. The especial characteristic, how-
ever, of the series was in the form of the upper sectorial tooth,
which was much more feline than canine in construction and has
given occasion for the generic name which means " cat-tooth.' '

A fourth phylum of the Canidae, which would seem to be
represented in the modern world by the Indian Dhole, or Wild
Dog (Cyon)y and perhaps by the Brazilian Bush-Dog (Icticyori),
was characterized by the lower sectorial molar, the heel of which
was not basin-like, as in the typical dogs, but trenchant and
consisted of a single sharp-edged cusp, the external one of the
primitive basin. Although there is no inherent improbability
in the view that the Dhole and the Bush-Dog are derivatives
of this phylum, no positive statement can yet be made, for
the gap in the history is too great to be bridged with any assur-

528 LAND MAMMALS IN THE WESTERN HEMISPHERE

ance. The fossil members of the series did not come down
later than the middle or upper Miocene and it is quite possible
that the trenchant heel of the carnassial was developed more
than once. The middle and lower Miocene members of the
series are still very imperfectly known and it is only from the
upper Oligocene (John Day) that well-preserved skeletons
have been obtained. These pertain to an aberrant member
of the phylum, the genus ]Temnocyon> in which not only does
the sectorial have a trenchant heel, but the second lower
molar also was trenchant, having lost the two inner cusps,
while the upper molars were as large as in the fbear-dogs.

\Temnocyon was a comparatively large animal and its
skeleton had a mixture of primitive and advanced characters,
the latter predominating, so that this genus was not only
the largest but also the most specialized canid of its time.
There was the long, heavy tail, which all of the known Oligocene
carnivores possessed, but the limbs were long and the gait
was, it would seem, thoroughly digitigrade. While the epi-
condylar foramen was retained by the humerus and the third
trochanter by the femur, those bones were otherwise very
modern in form. The feet were five-toed, but the functional
metapodials were parallel, appressed and with something
of the quadrate shape. In very notable degree, therefore, the
feet of \Temnocyon anticipated the characters which the true
wolves acquired considerably later. The less specialized
^Mesocyon, which was smaller, was the ancestor of the Miocene
forms and was, in turn, very probably derived from the White
River ^Daphoenus.

Still a fifth phylum, that of the fshort-faced dogs (]Enhy-
drocyon), is very imperfectly known and has, so far, been found
only in the lower Miocene and upper Oligocene. These also
may have been descended from 1[Daphcenus, but the connection
is not clear, nor has the relationship of the American genus
to the extremely fshort-faced dogs of the European Pliocene
been determined.

HISTORY OF THE CARNIVORA

529

Finally, so far as North America is concerned, there was
a phylum of very small fox-like canids, which ranged from the
lower Miocene to the upper Eocene and were very abundant,
relatively speaking, in the White River and John Day. The
dental formula was the same as in Canis and the skull was
narrow and slender, though the brain-chamber was propor-
tionately capacious, and the face was quite short. The tym-
panic bulls were large and inflated. The body and tail were

long and the limbs quite short and weak. The humerus had
no epicondylar foramen and the femur no third trochanter.
The five-toed feet had the spreading arrangement of the meta-
podials seen in the more primitive fissipedes generally and the
claws were sharp. In proportions and appearance these
animals must have been more like civets or weasels than like
dogs and it is evident that they were not swift runners. The
series had its earliest representatives {\Procynodictis) in the
Uinta and was doubtless derived from the fcreodont family

530 LAND MAMMALS IN THE WESTERN HEMISPHERE

fMiacidse. The White River species are referred to the Euro-
pean genus ^Cynodictis, those of the John Day and lower
Miocene to 1[Nothocyon, and it has been suggested that this
series gave rise to the foxes, a suggestion which may prove to be
true, but the very long gap in time between these animals and
the most ancient known foxes prevents any conclusion.

To determine the mutual relationships of the six phyla of
Canidae which, from the Eocene onward, inhabited North
America in such numbers, is a task of great difficulty and only
a tentative solution of the problem can be offered. The central
stock would seem to be nearly represented by the White
River 1fDaphcenu8y leading through IfCynodesmus and \Tephro-
cyon, of the Miocene, to the wolves. A short-lived series,
apparently given off from 1[Tephrocyony was that of the fhyena-
dogs, which flourished greatly in the upper Miocene and lower
Pliocene and then became extinct. Another branch, that of
the fbear-dogs, was derived from ^Daphomus, through fDa-
phcenodon to 1[Amphicyon, \Dinocyon and 1[Borophagusf the
gigantic Miocene and Pliocene forms, ending perhaps in fHyce-
nognathus of the California Pleistocene. A third branch,
represented by ]Mesocyon and fTemnocyon, is believed to be
continued to-day by the Asiatic Dhole and the Brazilian Bush-
Dog. The fshort-faced dogs (\Enhydrocyori) are still very
obscure. The last phylum, that of ^Nothocyon, 1[Cynodicti$,
1[Procynodictis, had become distinct in the upper Eocene and
possibly gave rise to the foxes, but this is highly conjectural.

2. Felidce. Cats

The only other fissipede group whose development in North
America may be followed for a long period is that of the
^Sabre-Tooth Tigers, the subfamily ^Machairodontince, which
have been extinct since the Pleistocene ; the history of the True
Cats (Felinae) is much more obscure. In most respects the
two subfamilies agreed closely and, as they became separate
at least in the early Oligocene, they furnish instructive parallel

HISTORY OF THE CARNIVORA

531

series. The fsabre-tooth eats were terrible beasts of prey, which
in most of the Tertiary period ranged over the whole northern
hemisphere and in the Pleistocene or late Pliocene extended
throughout South America.

The Pleistocene genus iSmilodon (Frontispiece) belonged
to nearly the whole western hemisphere and its various species

were distributed from California and Pennsylvania on the
north, to the Argentine Pampas on the south. The most
obvious and striking peculiarities of ^Smilodon were in the
teeth, which were much reduced in number, the formula being :
lirht ci» Ps=Ti mi- The upper canine was a great, curved,
scimitar-like blade, eight inches or more in length, with broad

532 LAND MAMMALS IN THE WESTERN HEMISPHERE

inner and outer faces, but quite thin transversely, and with
finely serrate posterior edge. It is difficult to understand
how these great tusks, which would seem to have blocked
the entrance to the mouth, could have been effectively used,
unless the creature could open its mouth much more
widely than any existing mammal, so as to clear the points of
the tusks, and would then strike with them as a snake does
with its fangs. There are great anatomical difficulties in
the way of accepting this explanation and the problem,
which is the same as that presented by the fuintatheres
(p. 446), is still unsolved. It is, however, quite certain that
no arrangement which was disadvantageous, or even in-
efficient, could have
persisted for such vast
periods of time. The
lower canine was
much diminished and
Fig. 262. — Upper teeth of iSmiiodon, left side. p. 4, hardly larger than an

fourth premolar. m. i, first molar. (After incisor. The two
Ms,tthft^v ^

upper premolars were
the third and fourth of the original series ; the third was small,
but the fourth, the sectorial, was a very large and efficient
shearing blade. In addition to the two external trenchant
cusps of the blade, which are present in the Carnivora gener-
ally, the cats have a third small, anterior cusp which in ^Smilo-
don was large ; the internal cusp had almost disappeared. The
single upper molar was very small and so overlapped by the
great carnassial as to be invisible from the side. The third
lower premolar was small and unimportant and most speci-
mens had lost it, leaving only the fourth, which was larger
and evidently of functional value. The single molar was the
sectorial, a large, thin, flattened blade, consisting of only two
cusps, one behind the other, the trenchant edges of which met
at nearly a right angle, and there was no trace of a heel.

The skull was in appearance closely similar to that of

HISTORY OF THE CARNIVORA 533

one of the great modern cats, such as the Lion or Tiger;
with extremely shortened face, heavy and widely expanded
zygomatic arches and very prominent sagittal crest. The
tympanic bullae were large and inflated, each divided by a
septum into two chambers, but were not visible from the side,
being covered externally by very large processes, which served
for the attachment of some of the great muscles of the neck.
The short, rounded, bullet-head of the true cats was thus
repeated, but there were in the skull several interesting dif-
ferences of detail, which it is not worth while to enumerate
here. Suffice it to say, that some of these differences were due
to the retention of primitive characters in the skull of fSmilo-
don, which have been lost in the modern felines, and others to
special developments, in which the true cats did not share.
The lower jaw had on each side a small, descending flange for
the protection of the tusks, which, however, projected well
below these flanges when the jaws were shut. The neck
was heavy and the structure of its vertebrae was such as to
suggest the presence of unusually powerful muscles ; the back
and loins were also uncommonly stout, in the larger species
heavier than in the Lion or Tiger, but, in marked distinction
from those modern forms, the tail was short. The limbs were
shorter and much heavier in relation to the size of the body
than in the great existing cats and must have been extremely
powerful. The humerus usually had no epicondylar foramen,
which all the true felines possess, though it was sometimes pres-
ent. The feet also were very stout and armed with large retrac-
tile claws ; the base of each claw was covered by a thin bony
hood, an outgrowth of the ungual phalanx, which is very char-
acteristic of the entire family. The hind foot had five digits,
whereas no existing cat has more or less than four. The ap-
pearance of these animals must have been very much like that
of the Lion or Tiger, aside from the unknown factors of mane
and colour-markings, but differed in the great tusks, the short
tail and the shorter and more massive legs and feet.

534

LAND MAMMALS IN THE WESTERN HEMISPHERE

On account of the very incomplete preservation of the
material so far collected, little is known of the fsabre-tooth
series in North America during the Pliocene and Miocene
epochs. Remains of very large cats have been found in the
lower Pliocene and upper Miocene, but it is uncertain whether
they belong to the feline or the fmachairodont subfamily. Some

Fio. 263. — Skull of a t sabre-tooth tiger (IMachairodus palmidens) from the Miocene
of France. (After Filhol.) P. 4* fourth upper premolar, sectorial tooth.

of the species have been referred to the genus }Machairodus,
which ranged from the lower Pleistocene to the middle Miocene
of Europe, and the reference may be correct, but is uncertain.
However, the European representatives of that genus, which
are much better known, will serve to show the developmental
stage from which \Smilodon was undoubtedly derived. The
dental formula was the same as in the American genus, though
there were generally two premolars in the lower jaw and in fSmi-
lodon generally but one ; the individual teeth were formed on
the same plan as in the latter, but were relatively smaller, and
the very small, rudimentary upper molar was visible externally

HISTORY OF THE CARNIVORA 535

and was not overlapped and concealed by the great carnassial ;
the sabre-like tusk had not attained such great proportions.
The skull of ^MachairoduSj the only part of the skeleton which
is definitely known, was like that of \Smilodon on a much
smaller scale, but more primitive in several respects. It was
longer and had a less capacious brain-case and less prominent
sagittal and occipital crests. The large tympanic bullae were
conspicuous in the side-view of the skull, as the processes for
the attachment of the neck-muscles had no such development
as in \Smilodon. The descending flanges of the lower jaw
were larger than in the latter.

The upper Oligocene (John Day) contained a large variety
of cat-like forms, of which no less than five genera have been
described ; one of them (fPogonodon), nearly as large as a Lion,
would seem to have died out here without descendants, and
two others, to which we shall return later, so combined the
characters of true felines and fmachairodonts as to be of un-
certain reference. Two other genera, which are much com-
moner and better known, from the White River, will be described
from specimens of that stage.

The White River, or lower Oligocene, had three highly
interesting genera of fmachairodonts, two of them known from
nearly or quite complete skeletons. One of these tfHoplo-
phoneus) , which was, it can hardly be doubted, the direct an-
cestor of the later typical fmachairodonts, had several species,
which are found in the various levels of the White River beds.
The largest of these species was considerably smaller than
^Machairodus, and the smallest and most ancient was inferior
to the modern Wild Cat. The number of teeth was variable,
but normally greater than in the genera above described, being
if, c|, pf^f, m},x2 = 28-32. The foremost premolar in each
jaw was very small and often absent. The upper canine was
a long and curved, but very thin, scimitar, finely serrate on
both edges, while the lower canine was but little larger than
the incisors. The carnassial teeth had a significant likeness

536

LAND MAMMALS IN THE WESTERN HEMISPHERE

to those of other fissipede families ; the upper one, the fourth
premolar, was relatively smaller than in ^Machairodus and
its blade less effectively trenchant ; the accessory antero-
external cusp was present, though extremely small, and the
internal cusp, which in ^Smilodon had almost disappeared, was
quite large. The lower sectorial, the first molar, though already
cat like and consisting of two thin, broad and trenchant

Fig. 2»4. — -White River fsabre-tooth tiger (tWojifoM uncus primarui). Restored from
a skeleton in the American Museum. tOreodonta (I Meri/coidodon) in the back-
ground.

cusps in line, yet had vestiges of the heel and sometimes of the
inner cusp. These vestiges were a connecting link between
the highly specialized sectorial of the cats and the type usual
among the Fissipedia, which is exemplified by the dogs. The
small upper molar was less reduced than in the Miocene and
Pliocene genera and plainly consisted of a larger external and
smaller internal cusp.

Compared with that of other Fissipedia, the skull was short
and broad, but in comparison with that of the modern cats
and of ^Smilodon, it was decidedly longer and narrower and

HISTORY OF THE CARNIVORA 537

the face was less abbreviated ; the resemblance to ^[Smilodon
was very marked in the form of the cranium, but, of course,
the skull of ^Hoplophoneus was distinctly more primitive in
many respects. Thus, the orbit was much more widely open
behind, the tympanic bullae were but imperf