(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "A History of Land Mammals in the Western Hemisphere"

Google 



This is a digital copy of a book lhal w;ls preserved for general ions on library shelves before il was carefully scanned by Google as pari of a project 

to make the world's books discoverable online. 

Il has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one thai was never subject 

to copy right or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books 

are our gateways to the past, representing a wealth of history, culture and knowledge that's often dillicull lo discover. 

Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the 

publisher lo a library and linally lo you. 

Usage guidelines 

Google is proud lo partner with libraries lo digili/e public domain materials and make them widely accessible. Public domain books belong to the 
public and we are merely their custodians. Nevertheless, this work is expensive, so in order lo keep providing this resource, we have taken steps to 
prevent abuse by commercial panics, including placing Icchnical restrictions on automated querying. 
We also ask that you: 

+ Make n on -commercial use of the files We designed Google Book Search for use by individuals, and we request thai you use these files for 
personal, non -commercial purposes. 

+ Refrain from automated querying Do not send automated queries of any sort lo Google's system: If you are conducting research on machine 
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the 
use of public domain materials for these purposes and may be able to help. 

+ Maintain attribution The Google "watermark" you see on each lile is essential for informing people about this project and helping them find 
additional materials through Google Book Search. Please do not remove it. 

+ Keep it legal Whatever your use. remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just 
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other 

countries. Whether a book is slill in copyright varies from country lo country, and we can'l offer guidance on whether any specific use of 
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner 
anywhere in the world. Copyright infringement liability can be quite severe. 

About Google Book Search 

Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers 
discover the world's books while helping authors and publishers reach new audiences. You can search through I lie lull lexl of 1 1 us book on I lie web 
al |_-.:. :.-.-:: / / books . qooqle . com/| 



* -fl 



\ 



/^ 



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 

YEARS 7 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 sma 1? * 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 ; ,ihem y 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 

sense 7 ' (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 . 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 cr r r ty, cleaning out the stony matrix 
which fills it ami. Ling liquid gelatine or plaster of 
Paris into the cf r 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 in T 
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 species y 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- f iq 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 ne urai spine, pu., 

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

long-necked forms the peg is converted into a «*. tr ., transverse P ro- 
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, ?•""•• v ****™ 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 

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

verse process. f ew 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 anc j on ^ cen t ra 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. «., ma l 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, i ess f ree 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 anc j {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 oTwoif 1 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- p i ace by the internal and 

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

internal, middle and ex- the external malleolus. 

ternalruneiforms. Mil, ^[^ th(J pU U ey _Iike 

rudimentary first meta- 

tarsal, ml ii-v. nwond surface the astragalus 
'di ,* «™f ta k af i BB *' 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 digitigrade y that is 
to say, the feet in the stand- 
ro. «. -Left pes of Black Bear (Ursus ' m S 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, th e 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 ^j j§7*51 / ta S e °^ * 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 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, J the 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 (A r asua), 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 



% 1 ,' 


k ] '4 
IP 




&<~Z+fi> i 


4 

,•.,■ i 






1§P 


| 



I 



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[pacificus f 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 
{]Smilodon y 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. ohioensis f 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 f m &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 ]Hyperhippidium y 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 \Mylodon y 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 t m yl&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 t m yl a g&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 ( \Oxydactylus y 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 o f ^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' r s >f unmistakably Neotropical type have 
been found, but \\ ler arbo^ y f 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, fHycenodon y 
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 \Protoceras y 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 fLwmtiniicl 86 ! 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 (\Diplaeodon y 
\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 tg roun d-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 t 1 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 per 1 ""' ' 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, man y 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 ^ sub j oined tab l e 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. ]Teleoceras f mid. Mioc. to low. Plioc. 
VI. fHYRACODONTiDiB. fHyracodonts and fAmynodonts, cursorial and 
aquatic Rhinoceroses. 
]Hyrachyus y 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. ? ^Schizotherium t 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 \Eohippus y 
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 Dea9 ts, 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 species 1 (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 simus y 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 Riv r .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[Camopus 9 
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 small er 
»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 



__ - 




^SBf^!'' 


-: 


=t£r ""' v - 






■■ 1 




£ 


; 


It : 


t 

k 






r 

"V. S 

^1 



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. \Dinohyus t 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 , m i d !™ ,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 \Entelodon y 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[Merycochcerus 7 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 t or e°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 i 4 s 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 ]Protoreodon y 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& n thracotheres 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 " tgi ra ff e " came l s " (\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- 
pus 7 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 }Hypertragulus y 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 



W r W i £ 


ife • - 




#1f WJgHi 




, 




P**" l! -"If ^ 






/\\/^ 


l 


0fwdKPP^^*£. 






•'■" 3^^^^H 


^&- 




W'*-i*:.*r- 


^4^*^- "" » r= 


~ - 



la). Restored from a 



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- 



0p' 


,> 


H 










2te&$ ; wl 








•J*" '■' 



Fia. 222. — Miocene t deer-ante] opes OMerycodus otbor 
furcatus, upper Miocene). Restored frnm •nwimmi 



n Musci 



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 Antilocapra y 
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 t m &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 an J j„ jjjg pj ew -p n j s jg fa e S pe C i e9 f which 
the manus of the - , , , . 

iodian Eicphaot. complete carcasses with hide and hair have 
u lower end of been found m the f rozen gravels of northern 

ulna. L. lunar. 

m. magnum. Siberia, its structure and appearance being 
cf£ai third /TT ^ us a ^ mos t M we U 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 c h Vh m h 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(Britherium y 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 thef f •" *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 t TALIGRADA 

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. 

\Leontinia y 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 Pleurocododon y 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 \Toxodon y 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 f TOX D ONTIA 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 (\Notohippus y 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, \Typotherium y 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 t T O x O D ONTIA 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, \Hegetotherium f 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[Homalodontotherium 9 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 the t metacarpals 
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 t T OXODONTIA 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- 
brinitherium y 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 . A v x v 

m, magnum, u., un- but k ss 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 tP r °- 
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. Howe v > 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. 

Ursu8 t 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 />„., pyrBni i da i. />,.. 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 1fDaphcenu8 y leading through IfCynodesmus and \Tephro- 
cyon, of the Miocene, to the wolves. A short-lived series, 
apparently given off from 1[Tephrocyon y 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[Borophagus f 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 : 
l irht c i» Ps=Ti m i- 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 imperfectly ossified, and 
the perforations, or foramina, in the base of the skull, by 
which the nerves and blood-vessels communicated with the 
brain-chamber, were quite different and had more resemblance 
to those of the ancient dogs {e.g. fDaphcenus). In the classi- 
fication of the Fissipedia much stress is laid upon the number 
and arrangement of these cranial foramina, and it is very 
significant to find the primitive dogs and cats agreeing so 
much more closely than do the modern members of these 
families. The lower jaw was relatively much stouter than in 
^Smilodon and the anterior flanges much more prominent, 
projecting downward so far that, when the jaws were closed, 
the points of the tusks did not extend below the flanges. 
The animal could have made no use at all of the sabre-tusks 
unless the mouth could have been opened so widely as to clear 
their points. 

With close general resemblance, allowing for the very inferior 
size, the skeleton of fHoplophoneus had many significant differ- 
ences from that of fSmilodon. The neck was shorter and the 
body, especially the loins, longer, lighter and more slender and the 
tail very much longer, equalling that of the Leopard in relative 
length and surpassing it in thickness. The limbs were much 
less massive and somewhat differently proportioned, the upper 
arm being shorter and the fore-arm longer. The humerus, 
though far more slender than that of fSmilodon, was remarkable 
for the great development of the deltoid and supinator ridges, 
the latter, together with the shape of the radius, indicating 
very free rotation of the fore paw. The very prominent in- 
ternal epicondyle was pierced by a foramen, and the femur had 
a distinct remnant of the third trochanter. The five-toed 
feet were comparatively small, but the claws were as completely 



538 LAND MAMMALS IN THE WESTERN HEMISPHERE 

retractile and as fully hooded as in any of the subsequent 
genera. 

That fHoplophoneus was a fierce destroyer, is made evident 
by every part of its skeleton, and, like other cats, it no doubt 
subsisted upon warm-blooded animals, which it killed for itself, 
the size of the prey being determined by the size and power of 
the particular species of the fsabre-toothed genus. In view of 
the probable extent of the Oligocene forests, the restoration 
(Fig. 264) gives the animal a spotted coat and the general 
aspect is that of one of the modern spotted cats, but the pro- 
truding ends of the tusks and the relatively long head distin- 
guish it from any existing cat. "The presence of long, 
knife-like canines is correlated with powerful grasping feet 
possessing highly developed retractile claws. With its power- 
ful feet the animal clung to its prey, while it struck repeatedly 
with its thin, sharp sabres " (J. C. Merriam). 

In the latter part of the White River stage lived one of the 
most highly specialized of the fmachairodonts, so far, at least, 
as the dentition is concerned, for only the skull is known. 
This genus, ^Eusmilus, which also occurred in the Oligocene 
of Europe, was apparently an example of premature specializa- 
tion which led to nothing, for none of the subsequent genera 
could have been derived from it. The teeth were reduced to 
a minimum in number : i §, c \, p \ , m \, X 2 = 24, one lower 
incisor and at least one premolar less in each jaw than had 
]Hoplophoneus. The canine tusk was very large and the 
flange of the lower jaw for its protection correspondingly 
elongated, being more prominent than in any other fmachairo- 
dont. The American species, fE. dakotensis, was the largest 
carnivore of its time and not greatly inferior in size to the Lion. 

Still another White River f m &chairodont, }Dinictis> 
differed in many interesting ways from its contemporary 
^Hoplophoneus, being more primitive and departing less from 
the ordinary fissipede type of structure. This is shown by 
the greater number of teeth, which was normally, i J, c \, p J, 



HISTORY OF THE CARNIVORA 



539 



m \, x 2 ™ 34. The upper caraassial had a considerably larger 
internal cusp and the trenchant blade did not have the accessory 
anterior cusp, which is present in almost all other cats and was 
thus more dog-like than cat-like. The lower carnassial was more 
feline, but retained a remnant of the heel and of the inner cusp, 
but the latter was variable, being sometimes present in one 
side of the jaw and not in the other, a sign that it was on the 




point of disappearance. The upper molar was plainly a re- 
duced form of the tritubercular tooth, in plan like that of the 
dogs, while the second lower molar was a very small, single- 
rooted tooth. No other American cat has such a primitive 
dentition as this, and, aside from the sabre-tusk, which was not 
nearly so long as in ^Hoplopkoneua, and the lower carnassial. 
it might almost as well have belonged to a dog or musteline. 

The skull was very like that of ^Hoplapkoneus, but was still 
longer and somewhat different in shape, owing to the higher 
forehead and lower occiput. The primitive features of the 



U< LASl> MAMMALS IN THE WESTERN HEMISPHERE 

txi'iaI h**. such as the foramina, the imperfectly ossified 
tv—.vuuV bull*, etc., were repeated in flhnictis, but the lower 
•*w had much less prominent flanges for the protection of the 
t'vk*. The limbs differed considerably from those of fHop- 

■ ','(,"**"«;•• in being relatively longer and more slender and 
retaining more primitive features, such as the larger third 
irvvhsnttT of the femur. The five-toed feet were decidedly 
small and weak, and the claws, though retractile, were less 




so than in the other genus and were not hooded. The gait 
was probably plantigrade or semi-plantigrade, 

The relationships of ^Dinictis and fHoplophoneus are 
rather puzzling ; none of the known species of the former could 
have been ancestral to the latter, for the two genera were 
contemporaneous. ^Diniclis was apparently the somewhat 
modified survivor of the ancestral stage and represented very 
nearly the common starting pointof both the feline and tmachai- 
rodont subfamilies. Dr. Matthew has propounded the bold 



HISTORY OF THE CARNIVORA 



541 



theory that this genus was the actual ancestor of the felines, 
continuing the series through ^Archadurus and fNimravus 
of the John Day to the unmistakable felines of the middle 
Miocene. This view runs contrary to the supposed "law of 
the irreversibility of evolution," a rule which many authorities 
look upon as well established. The 
theory postulates a different mode 
of development from anything that 
we have so far encountered in the 
series previously described and sup- 
poses that the upper canine first lost 
its«original form, becoming a thin, 
elongate and scimitar-like tusk, while 
the lower canine was reduced almost 
to the proportions of an incisor and 
the lower jaw acquired a straight, 
flat chin and inferior flanges for the 
protection of the tusks. Then, after 
specialization had advanced so far, 
it was reversed and the original con- 
dition regained. This interesting 
hypothesis may possibly turn out 
to be true, though personally I can- 
not accept it, and, should it do so, 
it would necessitate a thoroughgoing 
revision of current opinions as to 
the processes of mammalian de- 
velopment. 

The only John Day cat which 
was assuredly derived from iDinictis was the large \Pogonodon, 
previously mentioned. 

Also in the John Day stage lived ^Archalurus and fJVim- 
ravus, which, as was noted above (p. 249), have been called the 
"false sabre-tooths," for in them the upper canine was not 
much larger than the lower and the latter, though smaller 




Fia. 267. — Left pes of iDinictie 
ftlina. Col., calcaneum. 
At., astragalus. Cb., cuboid. 

Princeton University Museum. 



542 LAND MAMMALS IN THE WESTERN HEMISPHERE 

than in the felines, was yet very much less reduced than in 
the true fmachairodonts. The skull closely resembled _ that 
of ^Dinidis, but the lower jaw was without flanges. The 
limbs were long and slender and the feet long and digit igrade. 
The pes had only four digits, of which the median pair was 




elongated and the lateral pair shortened, so as to produce 
considerable resemblance to the pes of the dogs, and the claws 
were partially retractile. The proportions of the body, limbs 
and feet were suggestively like those of the Cheeta, or Hunt- 
ing Leopard {Cynwlurus jubatus) of India, the generic name of 
which means "dog-cat," and it is quite possible that the 



HISTORY OF THE CARNIVORA 543 

Cheeta may have been derived from some member of this 
" false fsabre-tooth " series, though the connecting links are 
unknown. These cursorial cats quite displaced the leaping 
fmachairodonts of the \Hoplophoneus type, at least in the 
Oregon region at a time when, it will be remembered, that 
region had a remarkable variety of dogs. In other parts of 
the continent, of which we have no record, the true fmachairo- 
donts must have been thriving, as may be inferred from their 
comparative abundance in the later formations. 

Concerning the habits of these cursorial cats, Professor 
Merriam says: "When the canines are not developed to the 
dagger-like form for stabbing, the premolar teeth serve a more 
definite purpose in the destruction of prey and would be less 
subject to reduction. The view suggested above finds support 
in that such evidence as we have indicates that during the 
deposition of the Middle John Day beds this region was in the 
main a country of open plains, offering advantages to running 
types of carnivores, and that during this epoch the Archcelurus- 
Nimravus type of feline was by far the most common form 
[i.e. of cats]." The derivation of these cats is still obscure, 
but their likeness to certain forms of the European Oligocene 
suggests that they were immigrants. 

The true cats of the subfamily Felinae include the great 
variety of living forms, large and small, from the Lion and Tiger 
at one extreme to the Domestic Cat at the other. There is 
great difference among naturalists with regard to the nomen- 
clature of the Recent cats ; some make a considerable number 
of separate genera, while others include all the species, except 
the lynxes and the Cheeta, in the genus Felis. For the pur- 
poses of this book the latter practice is the more convenient 
and will be followed. In Felis the dental formula is : if, c{, 
p^, m{, X 2 = 28-30; the canines are large and strong, of 
oval section, and the upper one is but little larger than the 
lower; there are two large and functional premolars in each 
jaw, and an additional very small one may or may not be present 



544 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



in the upper jaw. The upper sectorial has a large shearing 
blade, with well-developed anterior accessory cusp, and the 
inner cusp, which in ^Smilodon had almost disappeared, is 
quite large and carried on a separate root. The lower sectorial 

is composed of two cusps only, all traces 
of the heel and of the inner cusp having 
disappeared. The single upper molar 
is very small and usually concealed 
by the sectorial. The skull is very 
short and broad, and the shortening of 
the jaws gives great power to the biting 
muscles, because of the more favourable 
leverage. The zygomatic arches are 
very stout and curve out boldly, con- 
tributing much to the rounded shape 
of the head; the orbits are almost encircled in bone. The 
large tympanic bullae are two-chambered and there is no ali- 
sphenoid canal, but in several other respects the base of the 
cranium differs markedly from that of ^Smilodon. The lower 




Fig. 269. — Dentition of Lynx 
(L. rufux), left side. i. 8, 
external upper incisor, i. 1, 
first lower incisor, c. - canine. 
p. 3, p. 4, third and fourth 
premolars, m. /, first molar. 




0— to.I 



Fig. 270. — Upper teeth of Puma (Felis concolor), left side. p. 4* fourth 

premolar, m. /, first molar. 



jaw is without flanges and there is no angle between front 
and sides. 

The neck is short, the body long and the tail is long in most 
of the species, but short in the lynxes. The limbs are relatively 
longer and less massive than in fSmilodon, and there are five 
toes in the manus, four in the pes ; the claws are hooded and 
retractile. 



HISTORY OF THE CARNTVOBA 



545 



The western hemisphere at the present day contains none 
of the very large species, the Puma and Jaguar being the largest ; 
but this was not true of the Pleistocene, where a huge eat 
(Felts \alrox), surpassing the Lion in size, ranged over the 
southern half of North America. Enormous cats also lived 
in the lower Pliocene and upper Miocene of the Great Plains 




region, but are not sufficiently well known for reference to 
either subfamily. 

The history of the true felines has been but partially 
deciphered, and can, as yet, be traced back only to the middle 
Miocene, the genus fPteudcdunu representing the series both 
in Europe and North America. In this genus the dental 
formula was nearly the same as in Felis, but there was fre- 
quently an additional small premolar in the lower jaw and the 
sectorials were more primitive, the upper one having the acces- 
sory anterior cusp in a merely incipient stage and in the lower 



540 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



one there was a vestige of the heel. The upper canine was 
considerably longer than the lower, thinner and more blade- 
like than in Felis, which, so far as it goes, is in favour of Dr. 
Matthew's theory (p. 541). What little 
is known of the skull and skeleton of 
^PseucUelums agrees with the modern cats. 
While it is not feasible to trace the 
series of true felines to an earlier stage 
than the middle Miocene, there can be no 
doubt that the subfamily was derived 
from the same stock as the tmachairo- 
donts and it is probable that the White 
River \Dinictis nearly represents the com- 
mon starting point for both series ; the 
resemblances between ^Dinictia and such 
primitive dogs as ]Daph<entts are sugges- 
tive of a common origin. 

3. Procyonidte. Raccoons, etc. 
An almost exclusively American family 
Fig. 272.— Left m&nusof of Fissipedia is that of the raccoons, which 
%£?!£,"££. i " cludes ■">' °"'y the Istter (Procyon), but 
The homy claws are left also the coatis (Nasua), curious animals, 
un^lh^n^ 8 tbB with lon 8> flexible, pig-like snouts, the 
cacomistles (Bassaiiscus) and kinkajous 
(Potos). In addition to these American forms, there is an out- 
lying Asiatic genus, the Panda (JUlurua) of the southeastern 
Himalayas, the last of a series which goes back to the Euro- 
pean Pliocene. 

The Procyonidffi are animals of small and moderate size, 
largely arboreal in habits and subsisting upon a mixed diet 
of fruit, eggs, insects and the like; the teeth are adapted to 
this diet and the sectorials have mostly lost their shearing 
form and the molars are tuberculated for crushing and grind- 
ing. The species generally have long tails, except in the rac- 





HISTORY OF THE CARNIVORA 547 

coons proper, in which the tail is of medium length, and five- 
toed, plantigrade feet, with naked soles. Fossil members of 
this family are very rare in Tertiary formations and its history 
is therefore but scantily known; in the lower Pliocene have 
been found fragmentary remains with less 
specialized teeth, which appear to belong 
to the direct ancestor of Bassariacus. The 
upper Miocene genus ]Lej>tarctus was an 
undoubted member of the family, and, 

f . Fia. 273. — Dentition of 

while it would seem not to have been in Raccoon (Procyon 
the direct line of any of the modern forms, U)tor)t { f\ * de ' ** 3t 

external incisor. c, 

it was near to the common ancestry of the canine, p. 4, fourth 
American genera, so far as the imperfect ^X^' **' '' *"* 
specimens enable us to judge. 

By far the most primitive representative of the family 
yet discovered is the lower Miocene genus ^Phlaocyon, which 
connected the Procyonidae with the Oligocene genus of dogs, 
^Cynodictis (p. 529). The dentition resembled that of the 
latter, with several differences, which were all changes toward 
the Procyonidae. All the cusps were lower and blunter than 
in ^Cynodictis ; the premolars were small, thick and closely 
crowded together and the upper sectorial, while still trenchant, 
had a postero-internal cusp, which is found in none of the 
Canidae and was a first step toward the tuberculated pattern 
of the raccoons, and the lower sectorial had a very low cutting 
blade and large heel ; the other molars of both jaws were low, 
wide and of subquadrate shape. The skull was short and broad, 
with the face as much shortened and the orbits as far forward 
as in Procyon, but the brain-case was narrower, less capacious, 
and the lower jaw had the curved form and much the same 
character as in the modern genus. The limbs were relatively 
more slender than in the latter and the five-toed feet were 
more canine than procyonine in the proportions of the 
digits. 

The discovery of ^Phlaocyon by Dr. Matthew was an 



548 LAND MAMMALS IN THE WESTERN HEMISPHERE 

event of capital importance, as showing the highly probable 
derivation of the raccoons from ]Cynodictis and thus bringing 
another fissipede family into relationship with the dogs. 

4. Ursidce. Bears 

The present distribution of the bear family is all but ex- 
clusively northern, as there is but one African species, confined 
to the northwestern corner of that continent, and one in the 
Andes of Peru and Ecuador, all the others belonging to Eurasia 
and North America. 

Structurally, the family is very distinct and the dentition 
is quite peculiar. The incisors and canines resemble those of 

other Fissipedia; the three anterior 
premolars are very small, single- 
rooted and often shed early; the 
carnassials have lost their trenchant 
character ; and the molars, which are 
usually longer than wide, are tubercu- 
lated, somewhat resembling those of 




*•• 



pigs. Almost all the bears live prin- 

Fio. 274. — Dentition of Black ^ & ^ 

Bear (Ursu* americanus). cipally upon vegetable food, and even 

i. 3, external incisor, c ca- the p j ar g wh j ch feedg n figh 

nine. p. 1, first premolar. 7 * 

p. 4, fourth premolar, and seals, will eat grass and berries in 

a m iw fir fn rL^tt; of ^e brief Arctic summer; thus, the 
the grinding surface of the shearing teeth of the strictly carnivor- 

fourth premolar and first . , .-, 

molar, upper jaw. ous types are unnecessary to these 

animals. The skull is not unlike that 
of the dogs in shape, but the tympanic bullae are much flattened 
and the entrances to them are long, bony tubes, while the cranial 
foramina are nearly as in the dogs. The body is very heavy 
and the tail always short. The limbs are short and thick; 
the humerus has lost the epicondylar foramen in all existing 
species except the South American Spectacled Bear (Tre- 
marctos ornatw). The plantigrade feet have naked soles 
(except in the Polar Bear) and each foot has five well-developed 



HISTORY OF THE CARNIVORA 



549 



and functional digits, armed with very long, sharp and non- 
retractile claws. 

The Pleistocene representatives of the family in America 
included species of the true bears (Ursus) and of the very large 
fshort-faced bears tfArctotherium) which ranged over both 
North and South America. In ^Arctotherium the dentition 







|L . M 




,' J- 










£ 






■ 




Wm 



was less modified ; the larger premolars were very closely 
crowded together and the molars were nearly square ; the lower 
jaw was almost as much curved as in the raccoons. The 
humerus retained the epicondylar foramen. The family, 
which was of Old World origin, may have reached America 
in the lower Pliocene, but was rare until the late Pleistocene. 
fArctotherium has not been found in the eastern hemisphere, 
but that, of course, is no proof that the genus was not an im- 



650 LAND MAMMALS IN THE WESTERN HEMISPHERE 

migrant from Asia. On the other hand, it may have been 
a peculiar American development from Pliocene immigrants. 
In the Old World, bears were first distinguishable in the upper 
Miocene, and may be there traced back to forms which were 
unmistakably derivatives of the early dogs. 

5. Mustelidce. Mustelines 

The last fissipede family, which has, or has had, representa- 
tives in the western hemisphere is that which includes a great 
variety of small carnivores, such as minks, martens, skunks, 
badgers, otters, etc., and was likewise of Old World origin, 
though now of universal distribution, except in Australia and 
Madagascar. These are fierce and bloodthirsty beasts of 
prey, most of them strictly carnivorous and often killing in 
mere wantonness more than they can devour. Though now 
quite numerous and varied in North and South America, they 
are decidedly less so than in the eastern hemisphere and com- 
paratively few peculiar types have originated here. Owing 
to the small size and fragility of the skeletons, they have not 
been well preserved as fossils, and little can be done as yet in 
tracing out the genealogy of the various phyla. 

The mustelines have shortened jaws and a reduced number 
of teeth, the molars being \ or even \ and the premolars vary- 
ing from four to two, though three in each jaw is the usual 
number. The cranium is generally very long and the facial 
part of the skull short, but the soft snout may add considerably 
to the length of the face. The tympanic bullae are single- 
chambered and little inflated, and the lower Up of the entrance 
is extended; the hard palate is usually continued well back 
of the teeth. The body is very long and the tail variable and, 
in most of the genera, is short rather than long. The limbs are 
short, the feet, except in one genus, five-toed and plantigrade or 
semi-plantigrade, and the claws are non-retractile. Terrestrial, 
arboreal, burrowing, aquatic and marine forms are all repre- 
sented in the family. 



HISTORY OF THE CARNIVORA 551 

So far as North America is concerned, it is scarcely practi- 
cable to do more than catalogue the genera of the successive 
geological epochs. Pleistocene mustelines were very modern 
in character, differing little from those now inhabiting the con- 
tinent, though in some cases with different ranges, according 
to climatic fluctuations. Badgers, martens, skunks and others 
occurred then very much as they do now and the Boreal Wol- 
verene extended down to Pennsylvania. Little is known of 
Pliocene mustelines, the Blanco having yielded fragments 
of only one genus of uncertain affinities and though several 
genera occurred in the lower Pliocene, but one, a marten 
{Maries) , can be identified. Unquestionably, North America 
had many more Pliocene members of the family, but the con- 
ditions 9f preservation were unfavourable. 

Much the same is true of the Miocene stages. In the upper 
Miocene there were a marten {Maries), a weasel {Mustela) 
and two otters {^Potamotherium and the modern Lutra), of 
which the marten and the more primitive otter went back to 
the middle Miocene. In the lower Miocene were several 
mustelines quite different from any now existing. One of 
those, ^Megalictis, was truly gigantic, with a skull nearly as 
large as that of a Black Bear and having heavy, pointed claws. 
This and a similar genus, \M\urocyon, were related to the Ratel 
{Mellivora) of India and Africa and, more closely, to the 
Wolverene. ^Oligobunis, a much smaller animal, was ap- 
parently of the same group. This genus was also in the upper 
Oligocene, but there represented by a larger species, which 
was as large as a badger. 

The White River beds have yielded but a single genus, 
^Buncelurus, which was the most primitive of American 
mustelines and had four premolars and two molars in each 
jaw, though the second upper molar was extremely small. 
The face was much less shortened than in the modern weasels 
and the tympanic bullae were short and strongly inflated and 
had no tubular entrance, and were thus canine rather than 



552 LAND MAMMALS IN THE WESTERN HEMISPHERE 

musteline in form. The bony palate was not extended back 
of the teeth as it is in the modern genera. The same primitive 
group was much more abundant in the European Oligocene, 
migrating probably from Asia into Europe as well as into 
North America. 

SOUTH AMERICAN FISSIPEDIA 

The history of the South American carnivores is a com- 
paratively brief one ; the southern continent has representatives 
of the same five families as the northern, but most of the genera 
are different, the time since the great southward migration 
having been sufficient for the development of peculiar forms 
in the new environment. Among the dogs, there are to be 
noted the curious, close-haired, long-bodied and short-legged 
Bush-Dog (Icticyon) and the fox-like wolves {Cerdocyon) , but 
there are no true foxes. Of the cats, the Puma differs little 
from that of North America, and the Jaguar (Felis onca) and 
Ocelot (F. pardalis) also range into the northern continent, 
but several small cats are confined to South America, which 
has no lynxes. There is but one bear (Tremarctos ornatus) of 
Andean range. Of the Procyonidae, the northern Procyon 
lotor is replaced by the Crab-eating Raccoon, P. cancrivorus, 
while the coatis {Noma) and kinkajou (Potos) are chiefly 
Neotropical. Except for the otters, the genera of Mustelidae 
are nearly all different ; there are no badgers and a different 
genus of skunks {Conepatus) replaces the northern Mephitis; 
the Grison (Grison) y Tayra (Tayra) and the Patagonian Lyn- 
codon are peculiar. 

Even less can be done to trace the evolution of the South 
American genera than for the forms of the northern continent, 
whence migrated the more or less different ancestors of the 
former. The Pleistocene has yielded most of the modern 
genera, both existing and extinct species. An example of 
the latter was Procyon ^ursinus from the Brazilian caverns, 
a truly gigantic Raccoon, as large as a bear. The fsabre-tooth 



HISTORY OF THE CARNIVORA 553 

tigers (^Smilodori) and short-faced bears {^Arctotherium) were 
shared with North America. In the Pliocene a bear, a raccoon 
and a dog were the only known fissipedes, and in the 
Miocene none have been found, their place being taken by 
flesh-eating marsupials. 

While the history of the Fissipedia, as outlined in the pre- 
ceding pages, is sadly incomplete as compared with that of 
many ungulates, it is nevertheless highly suggestive. In each 
family the advance of specialization and adaptation to a 
narrow range of habits may be followed ; generally speaking, 
the teeth were diminished in number and increased in size and 
were either simplified by the loss of parts, as in the cats, or 
complicated by the addition of new elements, as in the bears 
and raccoons. The brain grew larger and more convoluted 
and the cranium more capacious; in most of the families, 
the face was shortened, notably in the cats and mustelines, 
while in others, especially the dogs, it was elongated. In all 
of the early types there was a long and heavy tail, but in most 
series it underwent more or less reduction. There was little 
reduction of digits, and no fissipede has less than four. In 
modern dogs and cats there are five digits in the manus and 
four in the pes and the hyenas have four in each, as has one 
genus of mustelines ; other modern genera throughout the sub- 
order are pentadactyl. 

It is significant that the more ancient members of the various 
families differed less than do the modern ones ; the various 
groups, as they are traced back in time, would seem to be 
converging to a common ancestry, of which the lower Oligocene 
dogs were the least changed representatives, and it is probable 
that all the families of the Fissipedia were derived, directly 
or indirectly, from a single Eocene group of primitive flesh- 
eaters. The families, none of which is extinct, are not all of 
equal antiquity. So far as now appears, the dogs and viverrines 
are the most ancient, having become distinct in the upper 



554 LAND MAMMALS IN THE WESTERN HEMISPHERE 

Eocene ; in the Oligocene were added the mustelines and cats ; 
the raccoons branched off from the dogs in the lower Miocene, 
as did the bears in the upper Miocene. Finally, the hyenas 
appeared in the lower Pliocene, seemingly derived from the 
viverrines. The dogs passed through the greater part of 
their development in North America, where, during the Oli- 
gocene and Miocene, they were very abundant and varied, 
while at the same time they were comparatively rare in Europe 
and belonged chiefly to the phylum of the fbear-dogs. On the 
other hand, the remaining four families are of Old World 
origin, the bears and mustelines migrating to America, while 
the viverrines and hyenas did not. 

Suborder fCREODONTA. fPitiMrnvE Flesh-eaters 

This group long preceded the Fissipedia in time, for they 
began their recorded history in the Paleocene and became 
extinct in the Oligocene. Through one family, the fMiacidae, 
the fcreodonts were broadly connected with the fissipedes, 
and it seems probable that that family was the ancestral 
stock from which all the fissipede families were derived. The 
other fcreodont families died out without leaving descendants. 

There is some difference of practice as to the number of 
families to be admitted; the table contains those listed in 
Professor Osborn's book and also adopted by Dr. Schlosser. 
I should prefer a somewhat larger number of family groups, 
but the matter is one of secondary importance. Many genera 
are omitted. 

I. fOXYCLiENID^S. 

]0xyckenu8, Paleoc. ^Deltatherium, do. 

II. fARCTOCYONIMS. 

^Clcenodon, Paleoc. ^Anacodon, low. Eoc. 

III. fMESONYCHID^S. 

tTVitsodon, Paleoc. ^LHssacuSy do. ^Pachycena, low. Eoc. ^Mes- 
onyx, mid. Eoc. ^Dromocyon, do. t Harpagolestes, mid. and up. 
Eoc. 



HISTORY OF THE CARNIVORA 555 

IV. fOXYjENUXB. 

t Palaonictis, low. Eoc. \Oxyaena, do. t Patriofelis, mid. Eoc. 
\Limnocyon, do. ^Machairoides, do. ^Ozy&nodon, up. Eoc. 

V. tHYjENODONTIOfi. 

^Sinopa, mid. Eoc. \Stypolophu8y low. and mid. Eoc. iTritemnodon, 
mid. Eoc. ^Pterodon, low. Oligo. ^Hycenodon, do. 

VI. fMlACID.fi. 

\Didymictis, Paleoc. and low. Eoc. ]Viverr<wu8, mid. Eoc. \Mia- 
cw, low. Eoc. \Uintacyon, low. to up. Eoc. ^Oodedes, mid. Eoc. 
]Vulpavu8, do. f PaUeardonyz, do. 

The fCreodonta were an extremely varied assemblage, of 
carnivorous, omnivorous and presumably insectivorous habits, 
so that few statements, not subject to exceptions, can be made 
of them all. Only seven genera are known from skeletons, and 
several more from skulls, but most are represented only by jaws 
and teeth ; limb- and foot-bones, however, give us a conception 
of the general structure of a considerable number. As a 
rule, the dentition was complete, according to the formula, 
* i> c i> V if m h X 2 = 44, but the first premolar or the last 
molar may be lost. The canines were always large, as was be- 
fitting for beasts of prey. In only one family, the Miacidae, 
were the carnassial teeth confined to a single pair and those 
the same as in the Fissipedia, the fourth upper premolar and first 
lower molar; in all the other families there were either no 
sectorial teeth, or else there was more than one pair. In the 
Fissipedia the first is the largest of the lower molars, while in the 
fCreodonta (except the f Miacidae) it was usually the smallest. 
The premolars were generally simple, compressed-conical teeth 
and the molars, with all their great variety, may be reduced to 
a common plan ; those of the upper jaw were primitively tri- 
tubercular, with a triangle of two external and one internal 
cusps, and those of the lower jaw were in two distinct parts, 
an anterior, elevated triangle of three cusps and a low heel 
of two. 

The skull was almost always very large in proportion to the 
size of the animal; the cranium, though long, was of small 



556 LAND MAMMALS IN THE WESTERN HEMISPHERE 

capacity and the face varied much in length in the different 
families. Primitively, the face and jaws were short in correla- 
tion with the small size of the teeth, and this primitive con- 
dition was modified in two opposite directions; in one the 
face and jaws were elongated, as the teeth enlarged, and in the 
other they were shortened stiU further. The zygomatic arches 
were stout and curved out strongly from the sides of the skull, 
making very wide openings, and, in almost all cases, the sagittal 
and occipital crests were very high, as would be necessary from 
the combination of powerful jaws and small brain-case (see 
p. 63). The tympanic bullae were not ossified. The brain 
was extremely small, especially in the more ancient genera, and 
the convolutions were almost always few and simple, which in- 
dicates a low grade of intelligence and very marked inferiority 
to the Fissipedia. 

In all the genera of which sufficient material has been ob- 
tained the body was long and had 19 or 20 trunk-vertebrae : 
in the lumbar and posterior part of the dorsal regions the pro- 
cesses by which the successive vertebrae were articulated to- 
gether (zygapophyses) were cylindrical and interlocking, as 
in the artiodactyl ungulates (p. 360). To this general state- 
ment, the fMiacidae formed a partial exception. The tail 
was very long and heavy in all the forms of which the caudal 
vertebrae are known, and this was probably true of all. The 
limbs were short and generally heavy; the femur had the 
third trochanter and the humerus, save in a few of the later 
genera, the epicondylar foramen, and the manus could, in 
nearly all, be freely rotated. Except in the most advanced 
forms of one family, the fMesonychidae, the feet were five- 
toed and plantigrade, or semi-plantigrade, and of decidedly 
primitive structure. The scapholunar bone of the Fissipedia 
(see p. 519) was not formed, its three elements, with very few 
exceptions, remaining separate. The astragalus nearly always 
had a shallow groove, or none at all. The claws were thick and 
blunt and the ungual phalanges cleft at the end, except in the 



HISTORY OF THE CARNIVORA 557 

f Arctocyonidae and fMiacidae, which had sharp claws and 
uncleft phalanges. 

From this brief description, it is obvious that the fMiacidae 
occupied a very isolated position among the fcreodonts and, in 
my judgment, it would be better to transfer that family to the 
Fissipedia and include the others in a separate order. 

Throughout the Paleocene and Eocene epochs the f Creo- 
donta were numerous and varied, the first of the Fissipedia 
appearing in the upper Eocene. Till then the fcreodonts 
were the only predaceous mammals in North America and 
Europe, and they were especially abundant in the former. 
Most members of the suborder and all the Paleocene forms were 
of small or moderate size, but some of the Eocene species were 
very large. In the Uinta the fcreodonts were greatly de- 
creased in numbers and in the White River there were only 
two genera of one family, the f Hyaenodontidae, and since the 
Oligocene the suborder has been extinct. 

1. fMiacidae. Fissipede-like \Creodonts 

It is unfortunate that no member of this family is known 
from a complete skeleton, but the material collected is suffi- 
cient to give a fairly adequate conception of these most in- 
teresting animals. These were the only fcreodonts with a 
single pair of carnassials, the fourth upper premolar and first 
lower molar, but in some of the genera the carnassials did not 
differ greatly from the other teeth. In the various genera the 
skull differed considerably in length and in the proportions of 
cranium and face ; the brain-case was larger than in most 
other fcreodonts and the brain more advanced, though smaller 
than in the fissipedes, and the sagittal and occipital crests were 
very prominent ; the tympanic bullae were not ossified. The 
humerus had the epicondylar foramen and the femur the third 
trochanter ; in the wrist the scaphoid, lunar and central were 
separate, almost the only important difference from the Fissi- 
pedia and merely the primitive stage of the latter. The feet 



558 LAND MAMMALS IN THE WESTERN HEMISPHERE 

were pentadactyl and the digits were arranged in spreading 
fashion ; the claws were small, sharp and partially retractile 
and the ungual phalanges not cleft at the tip. 

Within the family several different phyla may be distin- 
guished, one of which (]Miacis — ^Uintaqjori) led to the dogs, 
another to the fbear-dogs, or famphicyons. A third phylum 
( ^Didymictis — t Viverravus) is by several authorities regarded 
as ancestral to the civet family, or viverrines, of the Old World, 
and a fourth tfOodectes, ^Vulparrus) as the forerunner of the 
kinkajous (Potos). Except for the connection with * the dogs, 
the hiatus in time between the supposed ancestors and descend- 
ants is too great to permit any confident statements. It 
seems very probable, however, that the fMiacidse represented 
the common stock, from which the fissipede families were all 
derived, directly or indirectly, though for most of them the 
details of the connection remain to be learned. 

We find thus a group separating itself from the other fcreo- 
donts in the older Paleocene and gradually assuming fissipede 
characteristics, at the same time dividing into several phyla. 
In the upper Eocene this group passed almost imperceptibly 
into the Fissipedia, more obviously into the dog family, which, 
as we have seen, represents the central line of fissipede develop- 
ment. 

2. ^Mesonychidce 

This family displayed, in certain respects, the highest 
degree of specialization attained by any fcreodonts, for they 
were the only ones which acquired cursorial limbs and feet. 
The fniesonychids were prevailingly, but not exclusively, a 
North American family and their range in time was through 
the Paleocene and Eocene. 

The teeth, in the more advanced genera, had a curious 
mingling of primitive and specialized characters and none were 
sectorial in the proper sense of the word. The incisors were 
small, the canines large and bear-like and the premolars simple. 
The upper molars were very primitive, retaining the original 



HISTORY OF THE CARNIVORA 559 

tritubercular pattern, except that the two outer cusps were 
joined together, but the lower molars had lost all the internal 
cusps, which gave them a carnassial appearance; they were 
not sectorial, however, for their cusps wore directly against the 
upper teeth, not shearing past them, and were greatly blunted 
and worn down by use. 

The last of the family was ^Harpagolestes, of the Uinta 
and Bridger, one of the largest of the fcreodonts. The skull, 
which was of disproportionate size, exceeded that of the Grizzly 
Bear ; the upper profile of the skull had considerable resem- 
blance to that of a bear in the steep forward descent at the fore 
head. The teeth were more reduced than in the other mem- 
bers of the family through the loss of the second premolar and 
third molar of the upper jaw. The skeleton is little known, but 
the humerus had a long and prominent deltoid crest and an 
epicondylar foramen. 

In the middle Bridger stage were closely allied and very simi- 
lar genera, ^Mesonyx and fDromocyon (Fig. 139, p. 269), which 

ml. 




Fig. 276. — Upper teeth, right side, of fMesonyx obtusidens, showing the 

grinding surface. 

were like small, big-headed wolves, for the skull was as long as 
that of a Black Bear. Though the cranium was very long, the 
brain-chamber was very small and the sagittal crest enormously 
high, to afford surface for the attachment of the powerful jaw- 
muscles. The tympanic bullae were ossified and had quite 
long, tubular entrances, a feature which has been found in no 
other fcreodont skull. The face and jaws were also elongate, 
giving the head quite a wolf-like appearance. The neck and 
body were of moderate length, but the tail was extremely 
long, slender and whip-like. 



560 LAND MAMMALS IN THE WESTERN HEMISPHERE 

The limbs and feet were more specialized than in any other 
fcreodont and the changes were all in the direction of adapta- 
tion to swift running. The humerus was very smooth, with 
low ridges, and, alone among fcreodonts, had in these genera 
no epicondylar foramen, though the femur retained the third 
trochanter. The radius was broad and so interlocked with the 
humerus as to prevent any rotation of the manus. The feet 
were four-toed and much resembled those of the modern dogs 
and hyenas. In each foot the metapodials were closely ap- 
pressed and parallel, not spreading, but arranged in two sym- 
metrical pairs, a longer median and shorter lateral pair, much 
on the artiodactyl plan ; the ankle-bone (astragalus) also had 
an artiodactyl look, with its deeply grooved surface for the tibia 
and pulley-like lower end. The ungual phalanges were so short 
and broad as almost to suggest hoofs rather than claws. It is 
clear that the gait was as fully digitigrade as in a modern wolf 
and these were the only fcreodonts of which this is known to be 
true. These were somewhat puzzling animals; the whole 
structure of the limbs and feet was that of cursorial types, but 
the broad, blunt claws do not suggest the running down and 
capture of prey, nor were the teeth those of savage killers. 
The speed may have been defensive, to escape from enemies, and 
the food may have been largely vegetable. 

Ancestors of these Bridger genera have not been found yet 
in the Wasatch, a time when the family was represented by 
\Pachycena, some of the species of which were very large, rival- 
ling 1(Harpagolestes, which was descended from one or more of 
them. ^Pachycena had extremely massive teeth and was not 
improbably a carrion-feeder of hyena-like habits, and it re- 
tained the epicondylar foramen of the humerus and pentadactyl 
feet. 

Much more primitive was ^Dissacus, of the upper Paleo- 
cene, which was very probably the direct ancestor of both the 
Wasatch and the Bridger genera. The upper molars were 
substantially as in the latter, but the lower molars had the in- 



HISTORY OF THE CARNIVORA 561 

ternal cusp of the primitive triangle, though the heel was trench- 
ant, and had lost its inner cusps. The feet had five well- 
developed digits, which were arranged in spreading fashion, 
and the gait was plantigrade. The claws were longer, more 
pointed and much less hoof-like than in the Bridger genera. 
The Puerco genus \Triisodon mayor may not have been directly 
ancestral to ^Dissacus ; at all events, it was very nearly what 
the desired ancestor must have been. The teeth were much 
less specialized than in ^Dissacus; the tritubercular upper 
molars were broader and their external cusps were more sepa- 
rated, while in the lower molars the anterior triangle was made 
up of three nearly equal cusps and the heel was low and basin- 
shaped. The skull had an extremely narrow brain-case and a 
long, heavy sagittal crest. 

The most interesting feature in the history of the fMeso- 
nychidae is the demonstrable derivation of the cursorial, digiti- 
grade, four-toed and almost hoofed Bridger genera from the 
plantigrade, five-toed Torrejon genus, which had sharp claws. 
To all appearances, this family was the fcreodont analogue 
of the hyenas. 

3, 4. ^Arctocyonidoe and IfOxyclcenidce 

This second fcreodont family which had no carnassial teeth 
has received the not very happily chosen name of fArctocy- 
onidae, or " bear-dogs/ ' though they were not related to either 
bears or dogs. The family was a very ancient one and has 
been found only in the Paleocene and lower Eocene (Torrejon 
and Wasatch) of North America and Europe. The molar 
teeth were very low-crowned and quadritubercular, with 
numerous small tubercles in addition to the four principal 
cusps, a pattern which was rather pig-like than bear-like. The 
Wasatch genus \Anacodon, known only from jaws and teeth, had 
reduced premolars, both in size and number, while in the Torre- 
jon genus, ^Ckenodon, the premolars, though small, were present 
in full number. The skull was like that of \Mesonyx in the 

2o 



562 LAND MAMMALS IN THE WESTERN HEMISPHERE 

relative lengths of cranium and face, the very small size of the 
brain-case and the great prominence of the occipital and sagittal 
crests. The feet were pentadactyl and plantigrade and the 
claws were long, thin and pointed, and the ungual phalanges 
were not cleft at the tip, the only fcreodont family, except the 
fMiacidae, of which this was true. 

Of the f Oxyclaenidae, very little is known and they may not 
have been f creodonts at all. They were quite small animals, 
with sharp-cusped tritubercular upper molars and lower molars 
with high anterior triangle and low heel. This is the type of 
dentition from which all the divergent fcreodont types were 
doubtless derived. The family was Paleocene. 

5. ^Hycenodontidce 

This was the last of the fcreodont families to survive, being 
quite common in the lower Oligocene of North America and 
Europe and in the upper Eocene of the latter also. The family 
became extinct in the upper Eocene of North America and the 
White River genera were not of native origin, but migrants 
from the Old World. One of the more abundant predaceous 
genera of White River times was the European fHycenodon ; 
it was represented by several species which ranged in size from 
a fox to a Black Bear. In this genus the dentition was some- 
what reduced, the incisors often numbering f and the molars 
constantly f ; there were three pairs of carnassial teeth on 
each side, of which the pair formed by the second upper and 
third lower molar was the largest and most efficient, the other 
pairs being the first upper and second lower molar, the fourth 
upper premolar and first lower molar, the latter the smallest 
of the three. The upper molars had lost the internal cusp and 
the remaining, external portion consisted of a flattened-conical 
anterior cusp and a posterior trenchant ridge ; the milk-teeth 
of \Hyamodon, as well as the permanent dentition of the an- 
cestral genera, show that the anterior cusp was composed of 
the two external cusps of the primitive tritubercular tooth fused 



HISTORY OF THE CARNIVORA 563 

into one and that the trenchant ridge was a superadded ele- 
ment. The fourth upper premolar was a sectorial like that of 
the Fissipedia, but of an unfinished, ineffective sort. The third 
lower molar was very similar in shape to the caraassial of the 
cats and was composed of only two large, thin and trenchant 
cusps, which made a shearing blade, having lost the inner cusp 



IlF^fr^;-*-— 


* 'W-r »* MflBI 

flK: ■ !*', •■•si, 7\J 


n»*v 


It fc. _' 


■ 




jjtt 


• 





Fig. 277. — \Hyanodon horridut, a While Rive 
mtryx evansi. Restored from skeletons i: 

of the primitive triangle and the heel. The first and second 
molars were like the third except in size and in retaining a 
vestige of the heel. The premolars were large and massive, 
almost hyena-like, which suggested the generic name. The 
canines were prominent and strong. 

The skull, as in almost all fcreodonts, was relatively very 
large, but in the various species there was considerable differ- 
ence of shape; more commonly it was long and narrow, with 
elongate jaws, and was quite wolf-like in appearance, but in 



564 LAND MAMMALS IN THE WESTERN HEMISPHERE 

some of the species it was shorter and wider. The brain-case 
was more capacious and the brain more richly convoluted 
than in any other known fcreodont, but the sagittal and oc- 
cipital crests were very prominent. The neck was rather short, 
not equalling the head in length, the body elongate and the 
loins very muscular; the tail was fairly long and thick, but 
much less so than in most fcreodonts. The limbs were short 
and, in most of the species, quite slender, though in some they 
were much stouter ; the primitive features, such as the third 




Fig. 278. — Skeleton of \Hytenodon. American Museum. 



trochanter of the femur, the epicondylar foramen of the hu- 
merus, the separate scaphoid, lunar and central in the carpus, 
were retained. The feet had five digits arranged in spreading 
fashion and were probably semi-digitigrade ; the claws were so 
thick and blunt that they could hardly have served in seizing 
prey. 

The restoration gives the animal quite a near resemblance 
to the modern hyenas and perhaps errs in making the likeness 
so close. From the whole structure of the skeleton and the 
form of the claws, it may be inferred that ^Hycenodon was not 
a swift runner or very efficient in the capture of prey. While 
probably savage fighters, they doubtless subsisted chiefly as 
carrion-feeders and scavengers. 



HISTORY OF THE CARNIVORA 



565 





Another doubtfully distinct genus, ^Hemipsalodon, was 
so closely like, 
if not identical 
with, the much 
better known 
European fPter- 
odon, that the 
latter may be 
taken in place 
of it. ^Pterodon 
was similar in 
most respects to 
^Hyamodon, but 
distinctly less 
advanced, and 
though not the 
ancestor of the 
latter, serves to 
connect it with 
the older mem- 
bers of the 
series. fPfero- 
don did not, so 
far as we know, 
penetrate North 
America south 
of the Canadian 
border, occur- 
ring in the lower 
White River of 
Alberta. In 
this genus the 

Upper molars re- Fig. 279. — Lower teeth, right side, of fhyamodontids. A , tSt- 

tainpd a larffP nopa. B, ^Tritemnodon. C, IPterodon. D, ^Hycenodon. X, Ox- 

fe yctna. The dotted line connects the first molar of each, lost 

internal CUSp, in \Pterodon. See explanation of Fig. 280. (After Matthew.) 






S,*S tVM> MAMMALS IN THE WESTERN HEMISPHERE 




W./. 





<*&■ 




a 




Fia. 280. —Upper teeth of thyaenodontids, right side, showing 
the grinding surface. A, \Sinopa, Wasatch and Bridger. 
B, \Tritemnodon, Bridger. C, iPterodon, upper Eocene and 
lower Oligocene of Europe. D, IHycenodon, White River. 
The dotted line connects the first 'molar of each. For 
comparison is added X, lOxycena, one of the tOxyaenidse. 
C and D are much larger than the others, but all, except 
X, are reduced to the same length. (After Matthew.) 



and the third 
molar, though 
small and not sec- 
torial, had not 
been lost ; the 
two external cusps 
were connate, but 
not completely 
fused together and 
the posterior ridge 
was not so well 
developed as in 
^Hycenodon, nor 
was the fourth 
upper premolar so 
nearly a carnas- 
sial. The lower 
molars were shear- 
ing blades, but 
distinct vestiges 
of the heel re- 
mained. So far 
as they are known, 
the skull and 
skeleton resem- 
bled those of 
\Hyoenodon. 

\Hycenodon and 
\Pterodon were 
evidently derived 
from a group of 
small fcreodonts 
which, in the lower 
and middle Eo- 
cene, were spread 



HISTORY OF THE CARNIVORA 567 

all over the northern hemisphere, but it is not yet possible 
to select from the crowd of allied genera those which formed 
the actual steps of descent. These small animals were numer- 
ous and varied and are far better known in North America 
than in Europe and it is not at ail improbable that some of 
the lower Eocene genera migrated to the Old World and 
there gave rise, among other forms, to ^Hycenodon and 




\Pterodon, which eventually returned to the land of their 
earlier ancestry. If confirmed, this will be an exceptionally 
interesting case of back and forth migration. However that 
may be, the American Eocene genera, \Sinoipa and \Tritem- 
nodon, illustrate very well the ancestry of the Oligocene genera, 
as they must have been similar to the actual progenitors. 

The first and most obvious difference from the Oligocene 
genera was the very much smaller size of the animals, few of 
the Eocene forms equalling a fox in height. The teeth were 



568 LAND MAMMALS IN THE WESTERN HEMISPHERE 

unreduced in number, and there were three pairs of carnassials. 
The first and second upper molars were not far removed from 
the primitive tritubercular form, but the two external cusps 
were close together and a small posterior cutting ridge was 
present; the third molar was progressively reduced in size. 
The three lower molars were carnassials of a rather imperfect 
kind and the first was the smallest of the series ; the two outer 
cusps of the anterior primitive triangle formed the shearing 
blade and there was a basin-shaped heel. The skull was long, 
narrow and low and the cranial portion, despite the very small 
brain-case, was especially elongate, though face and jaws were 
also long; the sagittal crest was very prominent. The neck 
was of moderate length, the body long and slender and the 
tail extremely long. The short and delicate limbs were of 
very primitive character, but the radius had already lost the 
power of rotation ; the feet had five spreading digits, armed 
with sharp claws. The fhyaenodont relationships of these 
small animals are obvious in every part of their structure and 
yet, as would be expected, they were far less specialized. 
Probably, too, they were more active and successful punters 
of prey, the smaller mammals and birds, less given to carrion- 
feeding. The line probably originated in the fOxyclaenidae of 

the Paleocene. 

6. ^Oxycenidce 

The genera of this family had such feline characters that 
more than one writer has been misled into the belief that they 
were the ancestors of the cats. In this family there were two 
pairs of sectorial teeth, of which the larger pair was composed 
of the first upper and second lower molar, the smaller pair of 
the fourth upper premolar and first lower molar, as in the fissi- 
pedes. Of the three phyla within the family, the most special- 
ized one ran a brief career, through the Wasatch, Wind River 
and Bridger, and then died out. The terminal member of 
this series, the Bridger genus }Patriofelis y had a skull as large 
as that of a lion, but the rest of the skeleton was not so large 



HISTORY OF THE CARNIVORA 5b9 

in proportion. The teeth were considerably reduced in num- 
ber, the formula being: i$,c{, p\,m\, a loss of at least twelve 
from the primitive total of 44. The single upper molar was a 
large sectorial, which was formed much as in the fhyanodonts, 
the two external cusps connate, but not indistinguishably 
fused together, and a long, trenchant ridge behind, while the 
inner cusp had almost vanished. The second lower molar 




was very cat-like ; its cutting blade was formed of two shearing 
cusps ; of the inner cusp no trace was left, and of the heel merely 
a vestige. The first lower molar was smaller and less specialized, 
since it retained a small internal cusp and quite a large heel. 

The skull was very large and massive, with elongate cra- 
nium and shortened face, the muzzle broad and abruptly trun- 
cate, not tapering; the brain-case was exceedingly small, 
with very long and prominent sagittal crest ; the zygomatic 
arches were extremely heavy and curved outward boldly, so 



570 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



that the head was very wide, notwithstanding the absurdly 
small brain-case. The lower jaw was very deep and heavy and 
the chin abruptly rounded, with almost vertical front. The 
very unusual massiveness of the zygomatic arches and the great 
development of the crests and ridges for the attachment of the 
jaw-muscles, and the short, 
heavy lower jaw, all indicate a 
degree of power in the biting 
and shearing apparatus such as 
occurred in no other known 
fcreodont. 

The neck was of medium 

length, while the body, though 

actually elongate, was rather 

short as compared with most 

other fc re °donts ; the loins 

were very heavy and must have 

been extremely powerful in the 

living animal ; in this region 

the articulations between the 

successive vertebrae were more 

V complex than in any other 

^f^S-I^^S ™«*er of the suborder; re- 

(dim. cb., cuboid. JV., navicular, sembling the structure found in 

Cn. 1,2, 3, internal, middle and e»- . . , , _, ., 

temai cuneiform*. (After Wortman.) certain artiodactyls. The ribs 
were long and thick, the chest 
deep and capacious. Even for a fcreodont, the tail was long 
and uncommonly thick. 

The limbs, especially the anterior pair, were short and very 
stout ; the humerus had an immensely developed deltoid ridge, 
which extended down for two-thirds the length of theshaft, and a 
very prominent supinator ridge ; the fore-arm bones, particularly 
the ulna, were heavy and the radius had but a limited power of 
rotation. The feet were short and broad, with five complete, 
spreading toes, ending in thick and blunt-pointed claws. 




HISTORY OF THE CARNIVORA 571 

^Patriofelis was by far the most formidable of the Bridger 
Carnivora and, with the exception of ]Harpagolestes } the larg- 
est. Its appearance must have been very curious, judged from 
the modern standpoint, with its disproportionately large, 
broad and roundec^ leonine head, thick body and long, ex- 
tremely heavy tail. The short, powerful limbs and broad feet 
must have given it something of the appearance of an otter. 
As in the case of so many other fcreodonts, the combination 
of characters in the skeleton makes the question of habits a 
very puzzling one. The teeth had a form suited only to 
seizing and devouring prey, but the short legs and feet were not 
at all adapted to the swift movements, whether by long-con- 
tinued running, or by stealthy approach and sudden leap, 
which are required in capturing agile prey, while the blunt 
claws could have rendered no service in holding a struggling 
creature. The form of the humerus and fore foot suggests 
burrowing habits, but it seems most unlikely that so large an 
animal could have lived in any such fashion. Terrestrial, ar- 
boreal and aquatic modes of life have all been suggested, and, all 
things considered, perhaps the least improbable conclusion is 
that \Patriofelis was more or less aquatic and preyed chiefly 
upon the fishes and turtles with which the Bridger waters 
abounded. This hypothesis of Dr. Wortman's is supported 
by the otter-like form of the animal. Whatever the principal 
kind of food was, it must have been something that greatly 
abraded the teeth, which in old animals were mere stumps. 

The Wind River representatives of the series are known 
only from fragments, which, so far as they go, are not separable 
from \Patriofelis. On the other hand, the Wasatch genus, 
1[0xyama, is fairly well understood. This genus was very like 
its Bridger successor, but differed from it in just such ways as 
would be expected in an immediately ancestral form, that is to 
say, in smaller size and less advanced specialization. The 
number of teeth was not so far diminished : i |, c \, p |, m § , X 2 
= 40 ; the carnassial teeth were the same, but they were less 



572 



LAND MAMMALS IN THE WESTEHN HEMISPHERE 



effective ; the fourth upper premolar and first upper molar 
had large inner cusps, and in the latter the postero-external 
trenchant ridge was shorter. The second upper molar, lacking 
in iPatriofelis, was a transversely placed ridge, which engaged 
the heel of the second lower molar. The latter tooth, though 
larger than the first molar, was much less completely trenchant 
than in iPatriofelis and retained a small internal cusp and quite 




large heel. The skull resembled that of the Bridger genus, 
but the face was not so much shortened, the zygomatic arches 
were not so widely expanded or so massive, the lower jaw was 
not so heavy, nor the chin so steep. The body was relatively 
longer and more slender, the ribs being thinner and the chest 
shallower ; the tail was even longer, but not nearly so thick. 
The articulations of the lumbar vertebra were less complex. 
Except for their greater length and slenderness the limbs and 
feet were nearly identical with those of \Patriofelis. 



HISTORY OF THE CARNIVORA 573 

In appearance, \Oxyaena must have been merely a smaller, 
lighter and less powerful variant of the Bridger genus, and, no 
doubt, its habits of life were substantially the same ; but in the 
details of structure were many minor differences, all of them in 
the direction of greater primitiveness in the more ancient 
animal. 

The second phylum of the family was represented in the 
Uinta and Bridger stages by a group of small species, which 
were survivors of still more ancient and primitive progenitors 
of the family. In the typical genus, ^Limnocyon y the dental 
formula was the same as in ^Oxycena : i f , c \, p £ , m \ , but the 
first upper molar had its two external cusps well separated and 
a much lower posterior cutting ridge, while the inner cusp was 
much larger. The second upper molar, though transversely 
placed, had all the elements of the primitive tritubercular tooth, 
the pattern from which all the varied types of fcreodont upper 
molars were derived by the addition or suppression of parts. 
The two lower molars were very primitive, having a high an- 
terior triangle of three cusps, forming an imperfect shearing 
blade, and a low heel. This dentition was on nearly the same 
plan as that of the small, contemporary fhyaenodonts, but the 
emphasis of development, so to speak, was differently placed. 
In the fhyaenodonts there were three pairs of sectorials and the 
best-developed pair was made up of the second upper and third 
lower molar ; while in \Limnocyon the third molar was lost, and 
there were but two pairs of sectorials, of which the largest pair 
was the first upper and second lower molar, as was also true of 
\Oxycma and jPatriofelis. 

The skull of \Limnocyon had a much longer facial region, and 
more elongate and slender jaws than in the last-named genera, 
and the feet must have been quite different, with less spreading 
digits. \Limnocyon thus tends to indicate a common origin 
for the foxyaenids and fhyaenodonts, though these common 
ancestors are still unknown. 

A very interesting genus of this series, ^[Machairoides, of 



574 LAND MAMMALS IN THE WESTERN HEMISPHERE 

the Bridger, shows another imitation of the cats, the flanges of 
the lower jaw indicating sabre-like upper canines. 

Another genus, ]Palceonictis y of the Wasatch, found also 
in France, is sometimes referred to the fOxyaenidae and some- 
times made the type of a distinct family, but is too incom- 
pletely known for final reference. It had the same number of 
teeth as \Oxyama y but the principal pair of carnassials was the 
fourth upper premolar and first lower molar, as in the Fissi- 
pedia, the first upper and second lower molar forming the sub- 
sidiary pair. The first upper molar was hardly sectorial at 
all ; its two outer cusps were long, sharp-pointed cones, and the 
posterior cutting ridge was a mere tubercle. The skull had a 
short, cat-like face. The genus left no successors. 

This concludes the long story of the Carnivora, so far as it 
has been recovered from the rocks. Incomplete as it is, and 
full of unsolved problems, it yet enables us to follow, some- 
what vaguely, but with a general kind of accuracy, the develop- 
ment of the various modifications which characterized the 
different families and genera of the group. 

The more ancient and primitive suborder, the fCreodonta, 
made its first recorded appearance in the lower Paleocene and 
was, no doubt, derived from Mesozoic ancestors, which cannot 
yet be distinguished among the very imperfectly understood 
mammals of that era. In the upper Paleocene, if not before, 
the fcreodonts had spread over the northern hemisphere and 
had begun to diverge into a number of families, which con- 
tinued to diverge more and more widely throughout the Eocene 
epoch, as they became more specialized and adapted to differ- 
ent habits of life. From the most primitive group, represented 
more or less accurately by the fOxyclaenidae, may be traced 
the several lines of diverging adaptations incorporated in the 
various families, some of which had become distinctly recogniz- 
able in the lower Paleocene, others in the upper, while all were 
in existence in the lower Eocene. In one series, the fMeso- 



HISTORY OF THE CARNIVORA 575 

nychidae, the upper teeth underwent comparatively little change, 
while the lower ones lost the inner cusps, but no carnassials 
were formed. The face and jaws were elongated and the limbs 
and feet became adapted to cursorial habits, and the more ad- 
vanced genera had four-toed, completely digitigrade feet, with 
blunt, almost hoof-like claws. A second series, the fArctocy- 
onidae, likewise failed to develop sectorial teeth, the molars 
becoming quadritubercular, with many accessory tubercles, 
and assuming a bear-like or pig-like pattern, while the premolars 
were reduced in size. The pentadactyl feet had sharp claws. 

In the fOxyaenidae two pairs of carnassial teeth were 
formed, of which the larger and more effective pair were the 
first upper and second lower molar, the smaller pair the fourth 
upper premolar and first lower molar. The teeth were dimin- 
ished in number, first by the loss of the last molar, then the 
suppression of the first premolar and finally by that of the third 
incisor and second upper molar ; the remaining teeth were en- 
larged. The upper carnassial molar (the first) was formed by 
the approximation and partial fusion of the two external cusps 
and the addition of a trenchant ridge behind these, and by the 
reduction and eventual loss of the internal cusp, thus becoming 
more exclusively shearing in function. The second lower 
molar also lost the inner cusp and the heel, becoming remark- 
ably cat-like in form ; the first was similar, but less simplified. 
The face and jaws were greatly shortened, which, with the 
widely expanded zygomatic arches, gave the head a very cat- 
like appearance. The body and tail were long, the limbs short 
and thick, and the feet had spreading toes and blunt claws. 
Save for a notable increase in size and muscular power, the 
foxyaenids showed but little change within the family. 

The fHyaenodontidae differed from the foxyaenids in the 
retention of all or nearly all the teeth and in having three pairs 
of sectorials, of which the largest pair was the second upper and 
third lower molar, but resembled them in the mode of forming 
these sectorials and in the cat-like form of the inferior ones. 



576 LAND MAMMALS IN THE WESTERN HEMISPHERE 

Although the actual line of descent was not through these 
genera, the series, 1[Sinopa — ^Tritemnodon — ]Pterodon — 
1[Hyamodon t extending from the lower Eocene into the Oligo- 
cene, displays perfectly the successive steps in the transforma- 
tion of the teeth. The skull underwent a corresponding series 
of changes, ending in long-faced, long-jawed, wolf-like forms, 
with larger brain-case than in any other fcreodonts. The 
elongated form of body was retained, but the tail was reduced 
to moderate proportions. The limbs and feet did not change 
greatly, except in size and in the greater bluntness of the claws. 
The fMiacidfie, if not actually referable to the Fissipedia, 
at least anticipated them in the mode of carnassial develop- 
ment. The upper molars changed very little from the primi- 
tive tritubercular plan, but the fourth upper premolar was en- 
larged and acquired a trenchant ridge behind the original single 
outer cusp. The lower molars were at first all alike, except in 
size, the first being the largest ; they had the primitive pattern 
common to the earlier members of nearly all the fcreodont 
families, of an elevated anterior triangle of three subequal 
cusps and low, basin-like heel. The first molar grew larger 
in the successive genera and, by the enlargement of the two 
external cusps of the primitive triangle and reduction of the 
inner one, gradually became an efficient sectorial, the fourth 
upper premolar keeping pace with it. In proportion as the 
first lower molar was elaborated, the second and third were 
reduced in size and the anterior triangle was lowered to the 
level of the heel, these teeth thus becoming tubercular. All 
the fMiacidae were small animals, none attaining the stature 
of a fox, though some had heads as large. From this family, 
as was pointed out above, probably arose all of the Fissipedia, 
the history of which it is needless to repeat. 



CHAPTER XV 

HISTORY OP THE PRIMATES 

This order embraces the lemurs, monkeys, man-like apes 
and Man, though in the general account Man will be omitted 
from consideration. The Primates are clothed in dense fur 
or shaggy hair. The teeth are always low-crowned and rooted 
and reduced in number, the incisors generally to f and the 
premolars to f-f; the molars are trituberculate or quadri- 
tuberculate. The cranium is unusually capacious and the 
orbit is entirely encircled in bone. The tail varies much in 
length and may be entirely wanting. The bones of the fore- 
arm and lower leg are separate and the radius has much freedom 
of rotation, in correspondence with the grasping power of 
the hand. The pes is also a grasping organ and, with few 
exceptions, the thumb and great toe are opposable to the other 
digits ; the bones of the wrist do not coossify and frequently 
the central is present. The feet are plantigrade and almost 
always pentadactyl and, with a few exceptions, have neither 
claws nor hoofs, but flat nails; the ungual phalanges are 
correspondingly modified and do not taper toward the free 
end, but expand at the tip. The Primates are characteristically 
arboreal in habit, but a few, such as the baboons, have become 
secondarily adapted to a terrestrial mode of life. They inhabit 
at present all the tropical regions of both hemispheres, Aus- 
tralia excepted. Extratropical North America has no existing 
member of the order and, so far as we know, has had none since 
the Eocene epoch. The most important of the genera of the 
western hemisphere are listed below. 

2p 577 



578 LAND MAMMALS IN THE WESTERN HEMISPHERE 

Suborder LEMUROIDEA. Lemurs 

I. fNoTHARCTIDiE. 

^Pelycodus, low. and mid. Eoc. ^ Nothardus, Eoc. 

II. fANAPTOMORPHIDiE. 

t Anaptomorphus, low. and mid. Eoc. ^Omomys, mid. Eoc. 
t Hemiacodon, do. 

Suborder ANTHROPOIDEA. Monkeys, Apes, Man 

Section Platyrrhina 

III. Hapalioe. Marmosets. 

Hapale. Pleist. and Rec. Midas, Rec. 

IV. CebidjE. South American Monkeys. 

Cebus, Pleist. and Rec. Alouatta, Howling Monkeys, Pleist. and 
Rec. Ateles, Spider Monkeys. Pithecia, Sakis. Cacajao, 
Uakaris. Nyctipithecus, Douroucoulis. ^Eriodes, Pleist. ]Ho- 
munculus, Santa Cruz. ^Pitheculus, do. 

The existing Primates are divided into two suborders, 
Lemuroidea and Anthropoidea, which are quite clearly distin- 
guished from each other, but the fossil forms largely efface the 
distinction. 

Suborder Lemuroidea. Lemurs 

The name Lemur, which Linnaeus gave to a genus of this 
suborder, signifies in Latin a spectre or ghost and was prob- 
ably suggested by the very strange appearance and nocturnal 
habits of these curious creatures. The term has been adopted 
as the English name for the group, as there was no vernacular 
word for it. The lemurs are very obviously the more primitive 
division of the Primates. Omitting for the present the extinct 
forms, the dental formula is usually : i f , c \, p f, m §, X 2 =36 ; 
the upper canine is a long, sharp, dagger-like tooth, but the lower 
one, in nearly all of the genera, is like an incisor and its place is 
taken by the anterior premolar; the premolars are simple, 
compressed and trenchant and the upper molars tritubercular. 
The skull usually has a long and tapering facial portion, so 
that the living head has some resemblance to that of a raccoon. 
The orbits almost always have a more or less lateral presenta- 



HISTORY OF THE PRIMATES 579 

tion, instead of being directed forward, as they are in the An- 
thropoidea ; they are encircled in bone, but are not walled in 
by a bony funnel ; the lachrymal bone is extended on the face 
and the foramen is outside of the orbit. The hind legs are 
longer than the fore; the humerus retains the epicondylar 
foramen and the femur has a third trochanter ; the feet are 
plantigrade, almost always five-toed, with opposable thumb 
and great toe, and having a varying proportion of flat nails 
and sharp claws. The brain is of a primitive type and not 
much convoluted. 

All the existing and most of the fossil lemurs are small 
animals, some quite minute, and only in the Pleistocene of 
Madagascar have large ones been found. They are chiefly 
nocturnal and arboreal in habits, and feed upon fruit and leaves, 
but vary their diet with insects, small reptiles, birds and eggs. 
Their present geographical distribution is very remarkable; 
more than two-thirds of the existing species are confined to 
Madagascar ; the others are in tropical Africa, southern Asia 
and the Asiatic islands, as far east as Celebes and the Philippines. 
In the Eocene epoch they extended all over the northern hemi- 
sphere, but have not been found in any subsequent formation 
outside of their present range. 

Lemurs occurred in the Uinta stage, but were much more 
abundant in the Bridger, of which the best-known genus is 
^{Notharctus. These Eocene forms did not have the aberrant 
peculiarities of the modern lemurs, but departed less from the 
primitive stock common to both of the suborders. In f Noth- 
arctus the dental formula was : i §, c \, p |, m § , X 2 =40, the den- 
tition being reduced only to the extent of losing one incisor on 
each side above and below ; the lower canine was not incisiform 
nor had the anterior premolar taken its place ; the upper molars 
were quadritubercular, and in the lower ones the anterior 
triangle was hardly higher than the heel. The two halves of 
the lower jaw were coossified at the symphysis, and the femur 
had lost the third trochanter. It is not likely that ^Notharctus 



580 LAND MAMMALS IN THE WESTERN HEMISPHERE 

was ancestral to any of the existing lemurs, but may have 
been to the numerous forms of the European upper Eocene. 

The Wasatch genera are known from very fragmentary 
material, but it suffices to show that some of the genera, 
at least (e.g. ]Pelycodus) } were decidedly more primitive than 
those of the Bridger. The incisors had already been reduced 
to |, the well-nigh universal formula among the Primates; 
the upper molars were tritubercular, but with a minute fourth 
cusp beginning to appear, and in the lower molars the anterior 
triangle was elevated above the heel. The two halves of the 
lower jaw were separate. 

The Paleocene has yielded nothing that can be positively 
referred to the Primates, but there was a group of genera (e.g. 
1[Indrodori), known only from jaws and teeth, which have been 
variously assigned to the lemurs and the Insectivora and may 
have belonged to either order, or have represented the transi- 
tion between them. This very uncertainty is in itself a signifi- 
cant fact, for it is another of the many examples of the way 
in which, at that early period, the mammalian orders were so 
approximated that it is often very difficult to distinguish 
them. 

It was stated above that the distinction between existing 
lemurs and anthropoids was a very clear one, but to this 
statement there is one partial exception. The curious little 
Tarsier (Tar sins spectrum), an animal about the size of the 
Grey Squirrel, an inhabitant of the Malay Archipelago, is 
thus described by Mr. Beddard : "The ears are large and the 
eyes are extraordinarily developed. The fingers and toes 
terminate in large, expanded disks and are furnished with 
flattened nails, except on the second and third toes, which 
have claws. The tail is longer than the body and tufted at 
the end. . . . The Tarsiers are nocturnal and particularly 
arboreal; they live in pairs, in holes in tree stems and are 
mainly insectivorous in their food. . . . Like so many 
Lemurs, this animal is held in superstitious dread, which is 



HISTORY OF THE PRIMATES 



581 



the result of its most weird appearance." ' The skull is 
more anthropoid in character than is that of any other 
lemur, the face being greatly shortened, the cranium en- 
larged and the orbit not merely encircled in a bony rim, 
but with a thin posterior wall of bone. There are also struc- 
tural features in the soft parts, which are more anthropoid 
than lemuroid. 

The particular interest which Tarsiua possesses for the stu- 
dent of American mammals is its resemblance to the Wasatch 
genus iAnaptomorphus, the type of a family which was abun- 
dant and varied in the lower 
and middle Eocene. This 
genus was remarkably ad- 
vanced in view of its great 
antiquity. The dental for- 
mula was : if, c \ , p j! 5 , 
mf, x 2 = 34-36 ; in the 
upper jaw the premolars 
were bicuspid and the 
molars tritubercular, while 
the lower premolars were 
simple. The face was very 
much shortened ; the orbits 
were very large and encircled in bone, but without the pos- 
terior wall. This produces a decided likeness to the Tarsier 
and is no doubt indicative of nocturnal habits. The cranium 
was remarkably large, and no other Wasatch animal had a 
brain-case so capacious in proportion to its size. A lemurine 
character was the position of the lachrymal foramen outside 
of the orbit. The two halves of the lower jaw were separate. 
It is hardly likely that these American lemurs were the actual 
ancestors of the anthropoids, but they closely represent what 
those ancestors must have been. 

1 F. E. Beddard, Mammals, London, 1902, pp. 550, 551. 




Fio. 285.— Head of monkey-like lemur (Mn- 
aptomorphut Aomunculm) from the Wasatch. 
Restored from a skull la the American 



582 land mammals in the western hemisphere 

Suborder Anthropoidea. Monkeys, Apes, Man 

The specifically human characters will be omitted in defin- 
ing the suborder. The Anthropoidea are plantigrade, usually 
arboreal and pentadactyl, with opposable thumb and great toe 
and thus the pes is like a hand, hence the term " Quadrumana " 
formerly given to the apes and monkeys. Except in the South 
American marmosets (Hapalidse) all of the digits have nails. 
The canines are generally more or less tusk-like, projecting 
above (or below) the level of the other teeth ; the premolars 
mostly have two tubercles, like the human bicuspids, the upper 
molars have three, or more commonly four, cusps and the lower, 
four or five. Save in the baboons, the skull has a very short 
muzzle and a very large cranium, the capacity of which is 
relatively greatest in the large apes ; the brain is large and com- 
plexly convoluted. The orbits present directly forward and 
are deep, funnel-shaped cavities for the lodgment of the eye- 
balls, a thin bony wall completely enclosing them externally 
and posteriorly. The lachrymal bone and its foramen are 
within the edge of the orbit ; the nasal bones are short and 
have a nearly vertical position. The two frontal bones are 
early fused into one and usually there is no sagittal crest; 
the two halves of the lower jaw are coossified at the symphysis. 
The tail is extremely variable in length and may be three 
times as long as the body, or entirely absent. The fore and 
hind legs are sometimes of nearly equal length, but far more 
frequently the anterior pair are much the longer. The length 
of the legs in proportion to that of the body is very different 
in the different families. The humerus is much like that of 
Man and has no epicondylar foramen ; the radius has a very 
complete movement of rotation ; the femur never has the third 
trochanter and the lower leg bones are always separate. The 
thumb is more or less opposable to the other digits, except in 
the marmosets, but never so perfectly as in Man ; the great 
toe is also opposable, but shorter than the other digits. 



HISTORY OF THE PRIMATES 583 

The Anthropoidea are divisible into two sections, the 
Catarrhina, characteristic of the Old World, and the Platyr- 
rhina, confined to the New. In the Catarrhina, or Old World 
apes and monkeys, the dental formula is the same as in Man : 
i h c h V h m $ > X 2 = 32 ; the nostrils are close together and the 
tympanic bullae have tubular entrances. Many, but not all, 
have cheek-pouches opening into the mouth. The tail is never 
prehensile and, except in most of the large, man-like apes 
(Simiidse), there are naked callosities on the buttocks. With 
these Old World forms we have no further concern, though 
it may be noted in passing that Dr. Schlosser has discovered 
in the Oligocene of Egypt certain monkeys {\Parapithecus) 
which he thus describes: "The number and structure of the 
teeth, character of the jaws and bodily size make complete 
the transition from the Anaptomorphids and Tarsiids to the 
Simiids." 

Section Platyrrhina. South American Monkeys 

In these animals the nostrils are separated by a broad 
septum, and there are always three premolars above and below 
(pf). The tail is frequently prehensile and serves as a fifth 
limb, being capable of supporting the whole weight of the body. 
There are no cheek-pouches and no callosities, and the tympanic 
bullae have no bony tubes leading into them. The thumb is 
but partially, or not at all, opposable and in some genera is absent. 

The New World monkeys are, in general, smaller and lighter 
than those of the eastern hemisphere ; there are no very large 
ones and they are all arboreal and are confined to the forested 
parts of the Neotropical region, except the West Indies, 
which have none. The marmosets (Hapalidse), the first of the 
two families into which the Platyrrhina are divided, are little 
creatures, no longer than squirrels, with long, non-prehensile 
tails. They are characterized by the dental formula : i § , c \, 
p § , m |,X2 =32, and are the only Primates which have no third 
molar above or below. The thumb is not opposable, though 



584 



LAND MANUALS IN THE WESTERN HEMISPHERE 



quite long, and the hallux, or 
great toe, is very small ; they 
are thus deficient in grasping 
power. Instead of the flat 
nails common to all the other 
Anthropoidea, they have long, 
sharp claws. All other South 
American monkeys are in- 
cluded in the family Cebidai 
which, in turn, is divided into 
four subfamilies. It is not 
necessary to consider these 
or do more than cite a few 
illustrative examples. 

Some twenty species ef 
the genus Cebua are distrib- 
uted from Central America 
to Paraguay ; they have long, prehensile tails completely 




Fid. 288. — Common Marmoset (Hap- 
alt). — By permission of W. L. Berridge. 
London. 




HISTORY OF THE PRIMATES 585 

their limbs; the tail is very long and perfectly prehensile, 
naked on the lower side near the end, which improves its grasp- 
ing power. The hand has lost the thumb, but is used very 
effectively as a hook. The species, ten or more in number, have 
a wider range than those of Cebus and extend from Uruguay 
to Mexico. 

The howling monkeys (Ahuatta, more commonly, but im- 
properly, called Mycetes) are gifted with most unusual vocal 
powers. Mr. Bates says of them : "Morning and evening the 
howling monkeys make a most fearful and harrowing roar." 
"The brief evening chorus of animals then began, the chief 
performers being the howling monkeys, whose frightful un- 
earthly roar deepened the feeling of solitude which crept on 
as darkness closed around us." l The tremendous volume of 
sound which these small creatures are able to produce is due 
to a resonating apparatus, formed by the great inflation of one 
of the hyoid bones (see p. 67), normally the bony support of the 
tongue. The tail is long and prehensile, with the end naked 
beneath ; the thumb is well developed. 

The sakis (Pithecia) have long and non-prehensile tail 
and complete thumb. The species of this genus have a re- 
markable kind of distribution, which is rare among mammals, 
though not infrequent for insects and birds. Each species 
is limited to a definite area of forest along the Amazon and 
its tributaries, which it occupies to the exclusion of the others. 
The uakaris (Cacajao) are distinguished by the tail, which is 
much shorter than in any other of the Cebidae. 

Finally, may be mentioned the nocturnal douroucoulis 
(Nyctipithecus), which have long, non-prehensile tail and well- 
developed thumb. Mr. Bates describes them thus: "A third 
interesting genus of monkeys, found near Ega, are the Nycti- 
pitheci, or night apes, called Ei-d by the Indians. . . . They 
sleep all day long in hollow trees and come forth to prey on 
insects and eat fruits only at night. They are of small size, 

1 Bates, Naturalist on the Amazons, London, 1875, pp. 32, 140. 



586 LAND MAMMALS IN THE WESTERN HEMISPHERE 

the body being about a foot long and the tail fourteen inches, 
and are thickly clothed with soft gray and brown fur, . ; . and 
the eyes are large and yellowish in colour, imparting the staring 
expression of nocturnal animals of prey." * 

The Brazilian caverns have preserved the remains of many 
Pleistocene monkeys belonging to existing South American 
genera, and even several modern species are represented, while 
others are extinct. There is also one extinct genus (1[Eriodes), 
a larger animal than any of the existing Neotropical monkeys. 
The Pampean deposits of Argentina, on the other hand, have 
yielded no remains of Primates, nor is this surprising, for the 
Pampas would seem to have been open plains in the Pleistocene, 
as they are to-day. Between the Pleistocene and the Santa 
Cruz Miocene there is a long gap in the history. It is true 
that some bones have been found in the Pliocene of Monte 
Hermoso which have been referred to the Primates, but they 
are too few and imperfect to be of any real assistance in the 
inquiry. 

In the Santa Cruz beds fossil monkeys are very rare, but 
that they were present in Patagonia at all, is strong evidence 
that the climate was then far milder than it is at present. 
These were essentially members of the modern family Cebidae. 
The best-known genus, ^Homunculus, retained a few primitive 
characters, which the existing genera have lost. For example, 
the premolars were relatively smaller and of simpler form and 
the humerus had the epicondylar foramen, though the femur 
no longer had the third trochanter. The radius was very 
modern in form and evidently could rotate freely upon the 
humerus. 

No monkeys have been found in the Deseado formation, 
though too much stress should not be laid upon this fact, 
because of the general scarcity of small animals in those beds. 
But the same is true of the still more ancient stages ; . despite an 
abundant and varied fauna of small mammals, they have 

1 Bates, Naturalist on the Amazons, London, 1875, pp. 332, 333. 



HISTORY OF THE PRIMATES 587 

yielded no Primates, nor anything which could be seriously 
regarded as ancestral to them. The facts are essentially the 
same as we have found them to be with reference to the South 
American rodents and insectivores. All three of these orders 
appeared suddenly and unheralded in the Deseado (Rodentia) 
or Santa Cruz (Insectivora, Primates), and all of them were 
allied to African or European rather than to North American 
types. If we may assume the existence of a land-connection 
with Africa to account for the remarkable distribution of the 
hystricomorph rodents, the same connection will equally well 
explain the introduction of the Primates into South America. 

Concerning the relations of the Old and New World mon- 
keys, Mr. Beddard remarks : "Not only are these two groups 
of the Primates absolutely distinct at the present day, but they 
have been, so far as we know, for a very long time, since no 
fossil remains of Monkeys at all intermediate have been so 
far discovered. This has led to the suggestion that the Mon- 
keys are what is termed diphyletic, i.e., that they have origi- 
nated from two different stocks of ancestors. It is hard, 
however, to understand on this view the very great similarities 
which underlie the divergences that have just been mentioned. 
But, on the other hand, it is equally hard to understand how it is 
that, having been separated from each other for so longaperiod, 
they have not diverged further in structure than they have." * 

The fossil monkeys of the Santa Cruz beds show that, as 
a matter of fact, the South American Primates have undergone 
little change in the essentials of structure since that remote 
period, and thus is removed this objection to the conclusion 
that the Platyrrhina and Catarrhina were derived from a 
common ancestry. In a certain sense also, the discovery of 
^Parapithecus in Egypt has diminished the gap between these 
two sections of the Anthropoidea. The evidence, though by 
no means conclusive, is distinctly in favour of the derivation 
of the South American monkeys from Old World ancestors. 

1 Beddard, op. cit. t pp. 555, 556. 



588 LAND MAMMALS IN THE WESTERN HEMISPHERE 

The Catarrhina have developed and advanced from the point 
of divergence far more than have the South American forms, 
which have changed relatively little since their invasion of the 
Neotropical region. So far as has been ascertained, South 
America never had any of the lemurs. 

MAN IN THE WESTERN HEMISPHERE 

Though to most people this is undoubtedly the most inter- 
esting chapter of all the mammalian history, little space can 
be given to it here, for the reason that the subject belongs rather 
in the domain of Anthropology and Ethnology than in that of 
Palaeontology. There can be no question that Man originated 
in the eastern hemisphere and at a very remote period; 
abundant remains of his handiwork and of himself have been 
found in Europe as far back as the early Pleistocene, and recent 
discoveries in England have increased the already known 
length of the human habitation of Europe. So primitive and 
ape-like were some of these ancient men that they have been 
named as species (Homo ]neanderthalensis and H. \heidel- 
bergensis) distinct from the existing H. sapiens. Recently 
discovered and very ancient remains in England have even 
been referred to a separate genus, ^Eoanthropus. 

As has been repeatedly pointed out in the preceding 
chapters, America received numerous successive waves of mam- 
malian immigrants during the Pleistocene epoch, at a time 
when there was a broad land-connection between North 
America and Asia, where now is Bering Strait ; and to this late 
connection is due the fact that the Boreal zone of North 
America (seep. 150) is zoologically a part of the Old World and 
forms a division of the Holarctic region. Now, there is no 
known reason why Man, whose powers of dispersal are so 
superior to those of any other mammal, should not have 
accompanied these migrations, and it is entirely possible that 
he actually did so, but the fact has not been demonstrated. 
It is true that discoveries of Pleistocene Man have been fre- 



HISTORY OP THE PRIMATES 589 

quently reported from both North and South America, but 
these have not stood the test of critical examination, though 
such examination has by no means disproved the presence of 
Pleistocene Man in America. 

Dr. A. Hrdlicka has recently concluded a series of exhaust- 
ive studies of the bones of early Man in both North and 
South America and of the localities where these bones were 
found. For both continents he has reached a negative result. 
As to North America he says : "Thus far on this continent no 
human bones of undisputed geologic antiquity are known." 1 
For South America the result is the same. "A conscientious, 
unbiased study of all the available facts has shown that the 
whole structure erected in support of the theory of geologically 
ancient man on that continent rests on very imperfect and in- 
correctly interpreted data and in many instances on false 
premises, and as a consequence of these weaknesses must com- 
pletely collapse when subjected to searching criticism." "The 
conclusions of the writers with regard to the evidence thus far 
furnished are that it fails to establish the claim that in South 
America there have been brought forth thus far tangible traces 
of either geologically ancient man himself or any precursor 
of the human race. 

"This should not be taken as a categorical denial of the 
existence of early man in South America, however improbable 
such a presence may now appear." 2 

On the other hand, the coexistence in North America of 
Man with several extinct species of mammals has been made 
extremely probable, if not certain. One of the most striking 
and best authenticated cases of this was the discovery by 
Professor Williston in western Kansas of a flint arrowhead be- 
neath and in contact with the skeleton of the extinct Bison 
1[occidentalis. Professor Russell found in lake deposits of 

1 A. Hrdlicka, Smithsonian Institution, Bureau of Ethnology, Bulletin 
33, 1907, p. 98. 

1 Ibid., Bulletin 52, 1912, pp. 385, 386. 



590 LAND MAMMALS IN THE WESTERN HEMISPHERE 

Nevada an obsidian spearhead in association with the bones 
of an elephant or fmastodon, and other such instances have 
been reported. In these cases the doubt is as to the geological 
antiquity of the "finds," for the implements are of the type 
made by the pre-Columbian Indians. 

In brief, there is no convincing evidence that either North 
or South America was ever inhabited in prehistoric times by 
races of men different from those first encountered by the 
European discoverers. 



CHAPTER XVI 

HISTORY OF THE EDENTATA 

As here employed, excluding the so-called edentates of the 
Old World, the Edentata form a highly variegated, but natural, 
assemblage of related forms. The order is at present exclu- 
sively American and almost confined to the Neotropical region, 
an armadillo which extends into Texas being the sole exception. 
These animals are so peculiar and so isolated from other mam- 
mals, that it has been proposed to treat them as a separate 
subclass ; and there is much to be said in favour of this pro- 
cedure, though it would perhaps be premature, until more is 
learned concerning these most curious and exceptional ani- 
mals. In the subjoined table only the more important and 
better known genera are included. 

Series PILOSA. Hairy Edentates 

Suborder TARDIGRADA. Tree-Sloths 

I. Bradypodimj. 

Bradypus, Three-toed Sloth, Rec. Cholcepus, Two-toed Sloth, Rec. 

Suborder VERMILINGUA. Anteaters 

II. MyRMECOPHAGIDjE. 

Myrmecophaga, Ant-Bear, Rec. Tamandua, Lesser Anteater, do. 
Cyclopes, Tree Anteater, do. 

Suborder fGRAVIGRADA. fGround-Sloths 

III. fMEGATHERIIDiE. 

^Megatherium, Plio. and Pleist., S. A.; Pleist., N. A. ? \Prepothe- 
rium, Santa Cruz. ? ^Planops, do. 

591 



592 LAND MAMMALS IN THE WESTERN HEMISPHERE 

IV. fMYLODONTIDiE. 

^Mylodon, Plio. and Pleist., S. A.; Pleist., N. A. \Paramylodon, 

Pleist., N. A. IGrypotherium, Pleist., S. A. iPsetidole&todon, 

Plio. and Pleist., S. A. IScelidotherium, do. \Nematherium, 
Santa Cruz. ^Analcitherium, do. 

V. fMEGALONYCHIOB. 

^Megcdonyx, Pleist., N.A. t Nothrotherium, Pleist., S. A. ^Mega- 
locnus, Pleist., Cuba. ^Hapalops, Santa Cruz. ^Schismotherium, 
do. \Pdecyodon^ do. iMegalonychotherium, do. ^Protobradys, 
Casa Mayor. 

Series LORICATA. Armoured Edentates 

Suborder DASYPODA. Armadillos 

VI. Dasypodioe. 

Dasypus, 6-, 7- and 8-Banded Armadillos, Pleist. and Rec, S. A. 
Cabassons, 11-Banded Armadillo, do. Priodontes, Giant Arma- 
dillo, do. Tolypeutes, Apar, Rec., S. A. Zaedyus, Pygmy 
Armadillo, do. Scleropleura, do. Chlamydophorus, Pichiciago, 
do. Tatu, 9-Banded Armadillo, Pleist. and Rec., S. A. ; Rec., 
Texas. ^Eutatus, Plio. and Pleist., S. A. iChlamydotherium, 
do. t Proeutatus, Santa Cruz, f Prozaedins, Deseado and Santa 
Cruz. ^Prodasypu8 y do. ]Stegotherium y Santa Cruz. ^Meteu- 
tatus, Deseado. ^Sadypus, do. }Amblytatus, do. iPrceuphrac- 
tus, do. 

VII. PeLTEPHILIDjE. 

t Peltephilns, Deseado and Santa Cruz. 
VIII. IncertjE Sedis. 

iMetacheiromys, mid. Eoc, N. A. 

Suborder fGLYPTODONTIA. fGlyptodonts 

IX. tGLYPTODONTID.B. 

^Glyptodon, Plio. and Pleist., N. and S. A. ^Dcedicurus, Pleist., 
S. A. ^Panochthus, do. ^Sclerocalyptus, Plio. and Pleist., 
S. A. ^Glyptotherium, mid. Plio., N. A. f PropcUeeohoplo- 
phorns, Deseado and Santa Cruz. ^Cochtops, Santa Cruz. 
1 Eucinepeltus, do. ] Asterostemma y do. 

In the section Pilosa, which includes the sloths (Tardigrada) , 
anteaters (Vermilingua) and the extinct tground-sloths (fGra- 
vigrada) , the skin is thickly clothed with long hair, and in the 
Loricata, armadillos and tglyptodonts, the head, body, tail and 
legs are more or less completely encased in an armour of bony 
scutes covered with plates of horn, but with some hairs also. 



HISTORY OF THE EDENTATA 593 

The name Edentata (toothless) is not very happily chosen, 
for only the anteaters are quite toothless. Almost all the 
genera have no teeth in the front of the mouth and the teeth are 
nearly always alike, so that the distinction of regions among 
them is entirely a matter of position in the jaws. In the tree- 
sloths and many fground-sloths the foremost tooth in each 
jaw is a more or less enlarged, canine-like tusk. The teeth are 
always rootless, growing from permanent pulps, and are without 
enamel, made up of dentine, which is sometimes homoge- 
neous and sometimes in layers of different hardness, and with 
a covering of cement, usually thin and film-like. The number 
of teeth varies from £ to \% or more, and their form usually 
approximates a simple cylinder, worn off flat at the end, 
though the ends may be bevelled or grooved, differences which 
are in no way due to pattern but simply to the mode of wear. 
In the fglyptodonts the teeth were divided by deep vertical 
grooves into two or three pillars, connected by narrow necks. 
In most of the edentates there is no change of teeth, the 
milk-dentition having been completely suppressed, but in the 
9-Banded Armadillo (Tatu) each of the permanent teeth is pre- 
ceded by a two-rooted milk-tooth, and some other armadillos 
have milk-teeth. 

The skull varies much in form and proportions, according 
to the character of the food and method of feeding. The tree- 
sloths and tground-sloths have short, rounded heads ; in the 
tglyptodonts, the skull was short and remarkably deep verti- 
cally ; while the armadillos have long, shallow heads, with 
tapering muzzle, the length and slenderness of which differ in 
the various genera. In the anteaters the skull is extraordinarily 
elongate and slender. The sagittal crest is seldom present at 
all and never prominent. The zygomatic arch may be com- 
plete or interrupted ; in the tree-sloths, fground-sloths, tglypto- 
donts and some extinct armadillos, there is a descending, plate- 
like process given off beneath the eye. 

The backbone displays some of the most remarkable 

2q 



594 LAND MAMMALS IN THE WESTERN HEMISPHERE 

peculiarities of the order. The neck* in the tree-sloths has 
eight or nine vertebrae, the only instances known among mam- 
mals in which the normal number of seven is departed from. 
In the armadillos and fglyptodonts several of the neck- vertebrae 
are coossified into a single piece, but the atlas is always free, 
so as to permit the movements of the head. In the posterior 
part of the dorsal and in the lumbar region the articulations 
between the successive vertebrae are by far the most complex 
and intricate known among mammals; in the tree-sloths 
these have degenerated, though still plainly indicated. In the 
fglyptodonts, which were covered with a huge, tortoise-like 
carapace, mobility of the backbone was needless, and so all of 
the dorsal vertebrae were united into one long piece and the 
lumbars were coossified with one another and with the sacrum. 
The sacrum consists, throughout the order, of a very large 
number of vertebrae and is attached to the hip-bones at two 
different points, instead of only one, as in other mammals. 
The tail varies much in length and thickness; in the tree- 
sloths it is extremely short and in the anteaters very long and 
bushy, prehensile in the arboreal members of the group ; in 
the fground-sloths, especially the gigantic forms, it was of 
immense thickness ; while in most of the fglyptodonts a vary- 
ing number of the terminal vertebrae were fused together. The 
sternal ribs are better developed than in any other mammals, 
and in the anteaters and f ground-sloths they articulate with 
the breast-bone by regular synovial joints, and each rib has 
head and tubercle like a vertebral rib. 

In the limbs and feet there is great variety, according to the 
manner of their employment. The shoulder-blade has a very 
long acromion and very large coracoid, which long remains 
separate from the scapula; collar-bones are very generally 
present, though often in much reduced condition. The hip- 
bones have in the tree-sloths, fground-sloths and fglypto- 
donts a much expanded anterior element, which in the other 
groups is narrow. The humerus usually has very prominent 



HISTORY OF THE EDENTATA 595 

deltoid and supinator ridges and epicondylar foramen; the 
fore-arm bones are always separate, and there is generally much 
freedom of rotation of the manus. In the wrist there is no 
distinct central and usually there are the ordinary eight sepa- 
rate bones. The tibia and fibula are frequently coossified. 
The tree-sloths, which lead most strictly arboreal lives and are 
almost helpless on the ground, are unique among mammals in 
that the body is habitually suspended from the limbs, not carried 
upon them ; the feet are curved hooks, which fit over the tree- 
branches and support the weight without muscular exertion. 
The limb-bones are very long and slender, the claws long, 
curved and sharp, and the metapodials of each foot, two or three 
in number, are fused into a single mass. In the tground-sloths 
there was much change in foot-structure during the course of 
their recorded development ; they were usually five-toed and 
the feet were armed with one or more great claws ; the later 
and larger representatives of the suborder walked upon the 
outer edge of the feet. 

The . armadillos, which are largely burrowers, have five- 
toed feet and long, heavy, pointed claws, but in some of them 
the pes has a varying number of flat, hoof-like nails. The 
immense fglyptodonts had very short, broad feet, shod with 
hoofs, which, in some of the genera, were longer and more 
claw-like in the manus. 

The recorded history of the edentates was developed almost 
entirely in South America. In the Casa Mayor formation there 
were numerous armadillos, but as only scutes of the carapace 
have been found, little is known of them. The tground-sloths 
(fProtobradys) have been reported, but from such imperfect 
material that the reference is uncertain. The first assuredly 
determinable members of this suborder were in the Astra- 
ponotus beds and, associated with them, the most ancient 
known tglyptodonts. In the Deseado stage were many 
armadillos, some of them extremely peculiar, several tglypto- 
donts and tground-sloths, some species of the latter very 



596 LAND MAMMALS IN THE WESTERN HEMISPHERE 

large. Edentates were far more numerous and varied in the 
Santa Cruz than in any of the preceding stages. Tree-sloths 
and anteaters have both been reported, but the evidence is 
insufficient, though there can be little doubt that these sub- 
orders had begun their separate existence in some part of 
South America other than Patagonia. The three families of 
fground-sloths were already distinguishable, though much less 
clearly separated than they afterwards became ; none of them 
were large animals, smaller even than some of the Deseado 
species and veritable pygmies in comparison with the giants 
of the Pliocene and Pleistocene. The fglyptodonts were 
likewise far smaller than their Pliocene and Pleistocene suc- 
cessors and in several respects more primitive, approximating 
the armadillos more closely; nor was there any such variety 
of forms as in the later stages. The armadillos were extremely 
numerous and varied; they all belonged to extinct genera 
and most of them apparently have no descendants at the 
present day. The tropical forests of Brazil and the Guianas 
must then, as now, have swarmed with mammals which did 
not extend their range to Patagonia and of which we conse- 
quently have no record. No doubt, it was in these forests 
that the ancestors of most modern armadillos, as well as of the 
tree-sloths and anteaters, lived in Miocene times. 

Pliocene edentates were of the same suborders as those of 
the Santa Cruz, but far larger in size. Most of them are known 
only from very incomplete specimens, but the Pleistocene has 
yielded an enormous mass of beautifully preserved material. 
Of the tree-sloths and anteaters, only questionable remains 
have been found. That these tropical and forest-loving ani- 
mals should not have occurred in the open Pampas of Argen- 
tina is not surprising, but it is difficult to account for their 
absence from the extremely rich cave-faunas of Brazil. Nearly 
all the existing genera of armadillos have been obtained, and 
with these were associated several extinct genera, some of 
them (\Chlamydotherium, \Eutatus) relatively huge, as large 



HISTORY OF THE EDENTATA 597 

as tapirs. There was a wonderful variety of fglyptodonts, 
most of them enormous creatures, of which no less than five 
genera have been collected in Argentina and Brazil, and the 
tground-sloths were even more numerous and varied. Nine 
genera, with many species, of these great beasts, which ranged 
in size from an elephant to a tapir, are already known and no 
doubt the list is still incomplete. These tgtyptodonts and 
tground-sloths must have been among the most conspicuous 
elements of the Pleistocene fauna. 

Aside from certain problematical Eocene forms, the first 
North American edentates, which were immigrants from the 
southern continent, appeared probably in the middle Miocene 
of Oregon in the form of tground-sloths, but the specimen, 
as well as a similar one from the lower Pliocene of Nebraska, 
is not sufficiently complete for positive reference. In the 
middle Pliocene the tground-sloths and tglyptodonts were 
unquestionably present, and in the Pleistocene these two sub- 
orders were numerously and conspicuously represented. Three 
or four genera of the huge, elephantine tground-sloths co- 
existed in Pleistocene North America. \Megalonyx was 
abundant in the forested regions east of the Mississippi, from 
Pennsylvania southward, and on the Pacific coast ; \Mylodon 
was transcontinental in distribution ; while ^Megatherium was 
apparently confined to the southern states. While all three 
genera undoubtedly originated in South America, \Megalonyx 
has not yet been found in that continent. 

This genus was originally named by President Jefferson in 
1805 from an ungual phalanx found in a cave in Virginia, and he 
imagined that it belonged to a colossal lion which must still 
be living iii the mountains of western Virginia. This was 
deduced from the assumption that no species could become 
extinct, and the passage is of interest as showing the prevalent 
belief of the time, although Cuvier had already demonstrated 
that many species had actually been extinguished. The pas- 
sage is as follows : ' * The movements of nature are in a never 



598 LAND MAMMALS IN THE WESTERN HEMISPHERE 

ending circle. The animal species which has once been put 
into a train of motion is still probably moving in that train. 
For, if one link in nature's chain might be lost, another and 
another might be lost, till this whole system of things should 
evanish by piece-meal." 

The fglyptodonts were also southern in distribution, and only 
very imperfect remains of them have yet been recovered from 
the North American Pleistocene, quite sufficient, however, to 
make the identification certain. 

There were several genera of rather small fground-sloths in 
the Pleistocene of Cuba. The best known of these, \Megalocnus y 
had several peculiarities of structure, but was plainly a member 
of the fMegalonychidse. The ancestors of this genus probably 
invaded Cuba in the Pliocene, when the island was joined to 
Central America. 

Suborder fGRAViGRADA. IGround-Sloths 

As the fground-sloths would appear to have had a more 
central position within the order than any of the other groups, 
our study of development may well begin with them. In the 
Pleistocene there were three families of these gigantic brutes, 
which ranged through the western hemisphere from Pennsyl- 
vania and California to Patagonia. Unfortunately our know- 
ledge of the developmental stages within the different families 
is very unequal, and it is therefore impracticable to do more 
than sketch the changes of the suborder as a whole and in a 
general way. In the successive geological stages the pro- 
portionate representation of the different phyla varied greatly ; 
in the South American Pliocene and Pleistocene the fMylo- 
dontidse and f Megatheriidse were the abundant forms, while 
the fMegalonychidse were but scantily represented. In the 
Santa Cruz Miocene, on the other hand, the overwhelming 
preponderance was with the fMegalonychidse, the other two 
families being comparatively rare and incompletely known. 
From the still more ancient formations, the material so far 



HIBTORT OF THE EDENTATA 599 

collected is so fragmentary that family distinctions have little 
meaning. After all, there was no very wide range of variation 
among the contemporary members of the three families, and 
the differences were principally in size, in the form and number 
of the teeth, the shape of the skull and the number of digits ; 
in essentials they were all much alike. 

The genus ^Megatherium (Fig. 122, p. 220) included the 
largest and most massive members of the suborder, jM . america- 
num being as large as an elephant, but very differently propor- 
tioned, as it was much longer and lower in stature, owing to the 
shortness of the extraordinarily heavy limbs ; some of the 
skeletons measure 20 feet or more in length. The teeth, which 
were £ in number, formed an uninterrupted series on each side ; 
all had the same quadrate form and by abrasion were worn 
into two transverse ridges, formed by the meeting of the harder 
dentine with the thick coating of cement. The result was a 
form of tooth which much resembled the lower molars of a 
tapir, but it was not a tooth-pattern in any proper sense of 
the word, being due entirely to the mode of wear. 

The skull was very small in proportion to the huge body 
and was low and narrow in shape ; the cranium had a broad, 
flat roof, without sagittal crest; the orbit was completely 
encircled in bone, and the descending process of the zygomatic 
arch beneath the eye was very long and conspicuous. The 
nasals were short, and the slender, toothless premaxillaries 
projected far in front of them, which makes the presence of 
some sort of a proboscis likely. The lower jaw had a long, nar- 
row, spout-like symphysis, which was abruptly rounded at the 
free end, not pointed ; below the teeth, the lower margin of 
the jaw was very strongly convex, descending in a great flange. 
The neck was short, the body very long and enormously heavy, 
as was also the tail. The immense shoulder-blade had a very 
long acromion, which curved forward and inward, fusing with 
the coracoid and forming a bony loop or bridge. The hip- 
bones had the anterior element (ilium) enormously expanded 



600 LAND MAMMALS IN THE WESTERN HEMISPHERE 

transversely, so as to support the huge mass of viscera in the 
semi-erect position which the animal, it is believed, frequently 
assumed in feeding. Collar-bones were present. 

The fore limb was very much more slender than the hind, 
but of nearly the same length. The humerus had a com- 
paratively slender upper portion and extremely broad lower 
end, due to the great development of the internal epicondyle 
and supinator ridge ; there was no epicondylar foramen. The 
radius evidently had the power of very free rotation upon the 
humerus. The femur was short, flattened antero-posteriorly, 
but excessively broad and heavy, and had no third trochanter. 
The tibia and fibula were likewise short and very massive and 
were extensively coossified at each end, leaving but a short 
interspace open between the bones. The very peculiar feet 
were so connected with the limb-bones, that the animal must 
have walked upon the outer edge of the foot, somewhat as the 
existing Ant-Bear (Myrmecophaga jvbaia) uses the fore foot. 
The manus had four functional digits, the first being a mere 
vestige; the fifth, upon which the weight rested in walking, 
had two very small phalanges and no claw, while the second, 
third and fourth had long, sharp claws. The pes had but 
three functional digits, for the first and second were reduced 
to rudiments ; digit III had an enormous claw and of this digit 
the metatarsal was short and very heavy and the first two 
phalanges were fused together; the two external digits, Nos. 
IV and V, had no claws. The astragalus had a very peculiar 
shape, made necessary by the application of the external border 
of the foot to the ground and thus in both fore and hind feet 
the great claws were turned inward and, in the case of the pes, 
it must have been impossible to rest the sole upon the ground. 
The heel-bone was enormous and club-shaped and formed the 
hinder portion of the weight-carrying outer edge of the foot. 

Almost all who have studied the structure of this extraor- 
dinary beast are agreed as to its habits. That it fed prin- 
cipally, if not exclusively, upon leaves, is indicated by the 



HISTORY OF THE EDENTATA 601 

teeth. The general opinion as to its manner of life is well 
summed up by von Zittel : "The hip-bones, hind legs and tail 
are characterized by enormous strength. The entire structure 
of the extremities proves that the gigantic sloth could move 
over the ground but slowly and clumsily ; on the other hand, 
the fore limbs served as grasping organs and were presumably 
employed to bend down and break off twigs and branches and 
even to uproot whole trees, while the weight of the body was 
supported upon the hind legs and tail." 1 It would be quite 
absurd to suppose that such ponderous animals could have 
been climbers or burrowers, hence the function of the enormous 
claws, especially the single one of the pes, is not obvious, though 
they may have been merely the weapons of the otherwise 
defenceless monsters. The great claw in the fore foot of the 
Ant-Bear is a terrible weapon, with which the creature vigor- 
ously and successfully defends itself against dogs, and it may 
even be dangerous to men, if incautiously molested. 

^Megatherium had no bony scutes, or other ossifications in 
the skin, so far as is known, and was probably covered with 
long and coarse hair, as is known to have been the case in 
another fground-sloth. 

Less specialized in many respects than the t m ©gatheres 
was \Mylodon, type of a family which was numerously and 
variously represented in the Pleistocene of South America, 
much less so in that of North America \Mylodon was smaller 
and lighter, being from \ to \ smaller in linear dimensions 
than | Megatherium, and the contemporary \Scelidotherium 
was no bigger than a tapir. The teeth numbered £ and the 
anterior one above and below had a somewhat tusk-like form ; 
the others were worn off evenly, with nearly horizontal grind- 
ing surface, but a vertical groove on the inner side gave them 
a subtriangular, lobate form. The skull was short and broad, 
with flat top, and orbit only partially enclosed behind; the 
premaxillaries were very short and the muzzle very broad and 

1 K. von Zittel, Handbuch der Palaeontologie, Bd. IV, p. 132. 



602 LAND MAMMALS IN THE WESTERN HEMISPHERE 

abruptly truncated, the nasal opening very large. The lower 
jaw had a straight inferior border, a short, very wide and shovel- 
shaped symphysis and square chin. Nothing indicates a pro- 
boscis, and the head must have been very different from that 
of ^Megatherium. 

Within the family of the fmylodonts there was some variety 
in the dentition and more in the shape of the skull. In fLes- 
todon, for example, the first tooth in each jaw was a large, 
sharp-pointed tusk, the muzzle was greatly broadened, and the 
whole animal was larger. \Scelidotherium, the smallest 
Pleistocene member of the family, had a much narrower and 
more elongate skull than the others. In \Glos8otherium, 
which also had an elongate skull, there was an arched bony 
bridge connecting the anterior end of the nasal bones with the 
premaxillaries and dividing the nasal opening into two parts. 

The neck, body and tail of \Mylodon did not differ mate- 
rially from those of \Megatherium, except in being smaller and 
less massive. The fore limb was relatively somewhat shorter 
and much stouter, but otherwise similar ; the humerus had no 
epicondylar foramen and the femur no third trochanter; the 
tibia and fibula were separate. The manus had five digits, 
Nos. I, II and III carrying claws, that of III being especially 
large ; IV and V had no claws and the outer edge of the manus 
rested on the ground in walking, the sole turned inward. The 
pes had lost the first digit, the second and third had claws, but 
not the fourth and fifth ; the weight rested on the outer edge. 

The skin is definitely known from large pieces belonging 
to the allied genus ^Grypotherium, found in a cavern near 
Last Hope Inlet, Patagonia, where it had been preserved by 
burial in dry dust. Externally, the skin was thickly covered 
with coarse hair and in the deeper layers was a continuous 
armour of small ossicles, which were close set and in the Last 
Hope specimens show like a cobble-stone pavement on the 
inner side of the skin, the innermost layers of which have been 
destroyed; in life, these small bones were not visible. Simi- 



HISTORY OF THE EDENTATA 





^-^jd 




E^K _-A 


f: 




*°]ffl 






■ 




**£■ *£ V 




k.-. ^mm 


L -L» 


'k 






^F 


1 , AT ,. 




Cil 


L/ 


Ja 


•", 












/\ 


HB 1 










■•^tf^ 




i f ' - 










S ^ ! 


3f 



604 LAND MAMMALS IN THE WESTERN HEMISPHERE 

lar ossicles have been found in association with several skele- 
tons of \Mylodon. The habits, diet and mode of feeding of 
the latter were no doubt essentially similar to those of \Mega- 
therium, but ^Scelidotherium, which had a much shorter and 
lighter tail, was probably more quadrupedal and browsed 
upon low shrubbery. 

The third family, the fMegalonychidae, was scantily 
represented in the Pleistocene of South America, but relatively 
common in North America. \Megalonyx was, on the whole, 
less specialized than \Mylodon or j Megatherium, but had a 
strong resemblance to both of them. The teeth, £ in number, 
had the foremost one in each jaw separated by a considerable 
space from the others and more or less tusk-like in form; 
the grinding teeth were worn smooth, without ridges, and of 
somewhat trihedral shape. The skull was short, broad and 
deep, resembling in shape that of the tree-sloths ; there was a 
long, but feebly developed sagittal crest, and the orbits were 
widely open behind, with hardly a trace of any posterior boun- 
dary. The muzzle was very short and broad and abruptly 
truncated and the premaxillary bones were extremely small. 
The lower jaw was short, thick and massive, with very broad 
symphysis and almost vertical chin. Neck, body, tail, shoulder 
and hip-bones did not differ sufficiently from those of ^Mega- 
therium to require particular notice. 

The fore limb was shorter and more slender than the hind ; 
the humerus had the epicondylar foramen and the very massive 
femur retained the third trochanter; the tibia and fibula 
were separate. The feet had five digits, three of which carried 
claws; the calcaneum was very peculiar, not at all like the 
massive, club-shaped bone of ^Megatherium and \Mytodon, but 
long, comparatively thin and sickle-shaped. Nothing in the 
skeleton suggests that the creature's habits differed in any im- 
portant way from those of the genera last named. 

\Megalocnus, of the Cuban Pleistocene, a member of this 
family, was apparently peculiar to the island and was prob- 



HISTORY OF THE EDENTATA 605 

ably derived from ancestors which in the Pliocene migrated 
from Central America. Aside from certain remarkable pecu- 
liarities of the teeth, this animal was more primitive, as well as 
smaller, than any other of the Pleistocene genera. 

Although remains of f Gravigrada are comparatively com- 
mon in all of the f ossilif erous formations between the Pampean 
and the Santa Cruz, the material is too imperfect to throw 
any useful light upon the development of the various families. 
From the Santa Cruz beds, on the other hand, a great wealth of 
specimens has been obtained, and it is possible to give some 
fairly adequate account of the fground-sloths of that time. 
These animals were then extremely abundant individually and 
of extraordinary variety; evidently, they were in a state of 
rapid expansion and divergent evolution along many lines, for 
hardly any two specimens are alike and therefore the satis- 
factory discrimination of species is well-nigh impossible. Yet, 
with all this remarkable variability, the range of structural 
differences was not great ; the group was a very homogeneous 
and natural one, and separation into families was not obvious. 
Two of the three families were, however, une