Fuly 21, 1870] 
~ 
‘ 
NATURE oA3 
to the coarse-plaited varicty Z. colusibé of Dr. Falconer. 
There were also at least three species of Hipparion, and 
two ancient forms of horse (Merychippus and Protohippus), 
which recall to mind the simplicity of pattern represented 
by equine milk molars. The true horse was represented 
by £guus excelsus; the beaver by the Castor tortus, which 
was half its size. There was also a porcupine (H/ystrix 
venustus) which, strange to say, is more closely allied to the 
crested European than to the living American species. The 
wolves and foxes of the American Pliocenes are scarcely 
to be distinguished from those still living in the United 
o2 
1 
a ee ee eee ee ee 
PRE 
> . . 
same direction. 
States. One (Cands sevus Leidy) “isa near relative, if not 
progenitor, of the existing American wolf (C. occédentalis).” 
C. temerarius is intermediate between the prairie wolf 
and the red fox, while Dr. Leidy admits that the third (C. 
vafer) “may reasonably be supposed to belong to the 
existing swift fox.” The fourth (C. Hayden) probably 
belenged to a large variety of the western wolf. The 
larger felines are represented by the Pseudeelurus (/e/¢s 
quadridentatus), which was intermediate in size between 
the panther and the American lynx; and the bear- 
tribe by the Leftarctus primus, a creature allied to the 
coati. 
The evidence afforded by this group of animals, of the 
physical geography of North America during Pliocene 
times, is extremely valuable. The absence of the Edentata 
and of the Rodents of South American type implies that 
North America at the time was insulated from the south 
by a barrier which could not be overcome by those ani- 
mals, The absence of the opossums also points in the 
The Isthmus of Panama had not yet 
risen above the waves to sever the Atlantic from the 
Pacific Ocean, and to be a bridge for animals migrating 
from the one continent to the other. On the other hand, 
the Pliocene genera which dwelt in the basin of the 
Mississippi point indisputably to an influx of animal life 
from some other area. The deer, the mastodon, and the 
elephant, the hipparion, and the true horse, and among the 
’ carnivores the genus Cazzs and the Pseudzlurus, are per- 
haps the most significant of the new forms which charac- 
terise the American Pliocene. From what region did they 
come? A glance at the Miocene and Pliocene Mammals 
of Europe affords a satisfactory answer to this question. 
All these genera sprang into being during the European 
Miocene, and with the exception of the last lived also in 
the succeeding period. It is therefore only reasonable to 
infer that they found their way into North America from 
the Euro-Asiatic area, and the fact that they are Miocene 
genera in Europe renders it possible that their migration 
began at that time. Whether this reasoning be accepted 
or not, the lapse. of time required, not merely by one 
or by two genera, but by a group of herbivores with 
their accompanying carnivores, to fight their way from 
Europe or Asia into the Southern States—a region which 
was already occupied by the Oreodonts and other forms— 
must have been enormous, and probably sufficient to 
account for the difference between the American and 
European Pliocenes. If the migration be not admitted, 
then we must fall back on the now exploded hypothesis 
of different centres of creation, for there is no other mode 
of accounting for the presence of the same genera or 
Species in now widely separated regions. It may there- 
fore be inferred from the study of American Mammals, 
that North America was isolated from the great southern 
mainland, and that it was connected with Euro-Asia 
during the Pliocene, as well as during the preceding Mio- 
cene epoch, 
The Quaternary group of Mammals, in Dr. Leidy’s 
synopsis, points to a considerable geographical change 
having taken place in the interval that separates the epoch 
of their existence from the Pliocene. The strange extinct 
South America Edentates, the Megatherium, Megalonyx, 
and Mylodon spread over the Southern States, and testify 
that the barrier, which had confined them to their ancient 
home in South America, had been removed. In other 
words they poured northwards over the bridge offered by 
the Isthmus of Panama, and occupied the valley of the 
lower Mississippi. They were accompanied also by ex- 
tinct forms of the Chinchilla and Cavy. In this way the 
date of the elevation of Panama above the waves may be 
satisfactorily ascertained. The Northern extension, there- 
fore, of the South American genera, which at the present 
time range as far as Mexico and occupy the province of 
“ Austro-Columbia,” dates from the Quaternary or Post- 
Pliocene epoch. 
There was, however, no similar geographical change in 
the relation of North America to the old world. The 
bisons, horses, and elks, if not identical specifically, are 
merely varieties or representative species. The Mammoth 
is common to the whole of North America, and to the vast 
area in the old world north of a line drawn through the 
Altai mountains, the Caspian, and the Mediterranean 
Seas. The musk sheep, so widely spread through Europe 
in the Quaternary, ranged through Asia along with 
the Mammoth to the Arctic Ocean, and was found by Cap- 
tain Beechy in the frozen loam on the American side of 
Bheerings Straits. In the basin of the Mississippi it 
is represented by a cognate species, Ovibos bombifrons 
(female), and O. cavifrons (male). That these remains 
really belong to one species of Ovibos, is rendered almost 
certain by the concurrent and independent testimony of 
Dr. Riitimeyer and myself. The Cave-lion of Europe was 
also represented by the F. atrox of Natchez. Many 
other cases might be quoted to show that in those days 
the connection by land between North America and Asia , 
must have been maintained. It therefore follows, as one 
might have expected from the soundings in Bheerings 
Straits, that Northern Asia has been separated from 
North America in comparatively recent times. 
There is one striking fact to be noted in the Post- Pliocene 
America fauna, Just as certain European Miocene genera 
appear in the American Pliocene, so two forms which in 
Europe died out in the Pliocene, the Mastodon and Hip- 
parion, lived on in America into the Post-Pliocene age. It 
would almost seem as if America was the refuge of 
forms which had been driven from the old world. That 
the musk sheep of the Post-Pliocenes of Europe and Asia 
still lingers only in the high northern latitudes of North 
America, isa parallel case. These inferences are based on 
facts accumulated with very great care by Dr. Leidy. 
His work is an admirable attempt to grapple with most 
difficult problems ; it would have been of far greater value 
had its author abstained from founding species and genera 
in some cases from very scanty materials, and in others 
on the slightest variations from the ideal type. 
W. BoyD DAWKINS 
