THE EVOLUTION OF THE MAMMALIA. 227 
and Indian species may be identified, though time would fail us 
to trace out all the steps of their descent. In the Pleistocene 
occurred some exceedingly large species with enormous horns. 
One species was very common in Siberia, which it shared with 
the mammoth, and was especially adapted to a cold climate, being 
provided with a dense covering of hair and wool. Another huge 
rhinoceros {Ela smother iurri) had a single immense horn on the 
forehead, which was raised into a great dome to support it, and 
ranged over Pleistocene Siberia and Russia. This wonderful 
animal had greatly elongate and very complex grinding teeth, 
covered with cement and with " elaborately crimped " enamel 
ridges. At first sight, these teeth bear a remarkable resemblance 
to those of a gigantic horse. Here again, one is much puzzled 
to account for the sudden disappearance of so many large ani- 
mals, which were seemingly so well adapted to their surround- 
ings. 
Besides this main line of rhinoceros descent, there are two 
other series which are worthy of mention and which had separa- 
ted from each other and from the main stem at a very early 
date, for they are quite distinct in the middle Eocene. Both of 
these series have completely vanished from the earth since White 
River times, and nothing in the existing fauna corresponds to 
them. Of one of these lines, the oldest representatives yet dis- 
covered occur in the Bridger beds in certain animals of moderate 
size, having molar teeth of an unmistakably rhinoceros-like 
pattern, but with canines which are erect and pointed. The toes 
number four in the front foot and three in the hind, and this num- 
ber persists throughout the series. In the succeeding Uinta beds 
are found larger species of the same genus, whose canine teeth 
have grown to formidable lacerating tusks. The series culmi- 
nates in the genus Metamynodon of the White River, which would 
seem to have been a rhinoceros of aquatic habits, and was not un- 
like a hippopotamus in appearance. This likeness is increased by 
the great, curved tusks, but the head is much shorter and wider, 
and it is entirely exceptional among all rhinoceroses for the short- 
ening of the face and for the great width and massiveness of the 
