One reason why certain authors, such as Boule and Depéret, have placed this stage in the Upper Pliocene is that the mammals include so many surviving Pliocene forms, such as the sabre-tooth tigers (_Machærodus_), the 'polycladine' deer with the elaborate antlers (_C. sedgwicki_), the Etruscan rhinoceros, and the primitive Steno's horse. But we have recently discovered that, with the exception of the 'polycladine' deer, these mammals certainly survived in Europe as late as the _Second_ Interglacial Stage, and there is said to be evidence that some even persisted into the _Third_ Interglacial Stage. It is, therefore, the extinction or disappearance from Europe of many of the animals very abundant even in late Pliocene times which marks this fauna as early Pleistocene. Anthropoid apes are no longer found; indeed, there is no evidence of the survival of any of the primates, except macaques, which survive in the Pyrenees to late Pleistocene times; the tapir has entirely disappeared from the forests of Europe; but the most significant departure is that of the mastodon, which is believed to have lingered in north Africa and which certainly survived in America into very late Pleistocene times. The animal life of western Europe, like the plant life, has lost one part of its Pliocene aspect while retaining another part, both in its mammalian fauna and in its forest flora. [Illustration: FIG. 28. The sabre-tooth tiger (_Machærodus_), which survives from the Upper Pliocene and is widely distributed over western Europe until the Middle Pleistocene. After a painting by Charles R. Knight, in the American Museum of Natural History.] The living environment as a whole, moreover, takes on a novel aspect through the arrival, chiefly from the north, of the more hardy animals and plants which had been evolving for a very long period of time in the temperate forests and meadows of Eurasia to the northeast and northwest. From this Eurasiatic region came the stag, or red deer (_Cervus elaphus_), also the giant deer (_Megaceros_), and from the northerly swamps the broad-headed moose (_Alces latifrons_). The presence of members of the deer family (_Cervidæ_) in great numbers and representing many different lines of descent is one of the most distinctive features of First Interglacial times. Beside the new northerly forms mentioned above, there was the roe-deer (_Capreolus_), which still survives in Europe, but there is no longer any record of the beautiful axis deer (_Axis_), which has now retreated to southern Asia. The 'polycladine' deer, first observed in the valley of the Arno, is represented in First Interglacial times by Sedgwick's deer (_C. sedgwicki_), in Norfolk, and by the species _C. dicranius_ of northern Italy, where there also occurs the 'deer of the Carnutes' (_C. carnutorum_).