The Post-Pliocene deposits of Europe have further yielded the remains of numerous Rodents—­such as the Beaver, the Northern Lemming, Marmots, Mice, Voles, Rabbits, &c.—­together with the gigantic extinct Beaver known as the Trogontherium Cuvieri (fig. 270).  The great Castoroides Ohioensis of the Post-Pliocene of North America is also a great extinct Beaver, which reached a length of about five feet.  Lastly, the Brazilian bone-caves have yielded the remains of numerous Rodents of types now characteristic of South America, such as Guinea-pigs, Capybaras, tree-inhabiting Porcupines, and Coypus.

[Illustration:  Fig. 270.—­Lower jaw of Trogontherium Cuvieri, one-fourth of the natural size.  Post-Pliocene, Britain.]

The deposits just alluded to have further yielded the remains of various Monkeys, such as Howling Monkeys, Squirrel Monkeys, and Marmosets, all of which belong to the group of Quadrumana which is now exclusively confined to the South American continent—­namely, the “Platyrhine” Monkeys.

We still have very briefly to consider the occurrence of Man in Post-Pliocene deposits; but before doing so, it will be well to draw attention to the evidence afforded by the Post-Pliocene Mammals as to the climate of Western Europe at this period.  The chief point which we have to notice is, that a considerable revolution of opinion has taken place on this point.  It was originally believed that the presence of such animals as Elephants, Lions, the Rhinoceros, and the Hippopotamus afforded an irrefragable proof that the climate of Europe must have been a warm one, at any rate during Post-Glacial times.  The existence, also, of numbers of Mammoths in Siberia, was further supposed to indicate that this high temperature extended itself very far north.  Upon the whole, however, the evidence is against this view.  Not only is there great difficulty in supposing that the Arctic conditions of the Glacial period were immediately followed by anything warmer than a cold-temperate climate; but there is nothing in the nature of the Mammals themselves which would absolutely forbid their living in a temperate climate.  The Hippopotamus major, though probably clad in hair, offers some difficulty—­since, as pointed out by Professor Busk, it must have required a climate sufficiently warm to insure that the rivers were not frozen over in the winter; but it was probably a migratory animal, and its occurrence may be accounted for by this.  The Woolly Rhinoceros and the Mammoth are known with certainty to have been protected with a thick covering of wool and hair; and their extension northwards need not necessarily have been limited by anything except the absence of a sufficiently luxuriant vegetation to afford them food.  The great American Mastodon, though not certainly known to have possessed a hairy covering, has been shown to have lived upon the shoots of Spruce and Firs, trees characteristic