Ancient Arctogaea

The true elephants arose from the mastodons, and their earliest representatives are found in the Pliocene of India. Thence they migrated outwards, reaching Europe in the Pliocene and North America in Pleistocene times, but they never reached South America.

All the Holarctic members of the order died out at the end of Pleistocene times, one of them, the mammoth, which became adapted to Arctic conditions, living along the front of the great ice-cap which covered northern Europe and North America, until the ice finally disappeared, perhaps about 8000 B.C.

Hyracoidea.

The Lower Oligocene rocks of Egypt which contain the remains of Palaeomastodon yield also several genera of large hyracoids. The next representatives of this order are very small animals found in Middle Miocene rocks near Victoria. Nyanza, and in South West Africa. In the Lower Pliocene Pon tian fauna of Samos and Pikermi near Athens, they are rarely represented by a very large form. The existing animals are Ethiopian, except for a few individuals found in Syria and Arabia. The order thus appears to have arisen and carried out its evolution in Africa. The Lower Oligocene of Egypt also contains the remains of two orders, the Barytheria and Em brithopoda, no representatives of which are found elsewhere. Its fauna is therefore very isolated and contains only certain creo donts and anthracotheres of northern origin.

Notoungulata.

This extinct order of herbivorous mammals was until recently known only from South America, where it exhibits a number of evolutionary series. Most of these series can be traced upwards from the Eocene (Notostylops beds) of Patagonia into the Miocene or Pleistocene, although it has to be recognised that most of such series are only approximate. A single lower jaw of a member of this order has been found in the Lower Eocene of North America, and more abundant remains of a different genus occur in rocks (the Gashato beds in Mongolia) whose age is not certainly known but is probably Basal Eocene. This animal appears to be the most ancient member of the family yet discovered, and suggests that the group was of northern origin, although its later evolution took place entirely in Neogaea.

Condylarthra.

The Basal Eocene of North America con tains numerous remains of small animals which appear to repre sent a primitive group from which other ungulates have arisen.

The descendants of some of these forms lived on into the Lower Eocene and in a modified form, as the Amblypoda, even to the Upper Eocene. These latter forms had their headquarters in North America, but a single representative of them, of Upper Eocene age, has been found in Mongolia. The Basal and Lower Eocene of Europe contain a few animals which are probably condylarthrans, and the earliest Eocene members of the Litop terna (a group restricted to South America) are essentially identical in structure. Thus this group gives a further indication of the uniformity of the Basal Eocene fauna throughout the Palaearctic region, and of the probable derivation of the South American fauna from members of this widespread group of animals, which, becoming isolated about the beginning of Ter tiary time, and not being exposed to the competition of the northern groups, carried on an adaptive radiation, leading to the evolution of many very peculiar groups.

Perissodactyla.

Perissodactyls first appear at the bottom of the Lower Eocene in Europe and North America as small ani mals, presenting a very uniform structure and including the ancestors of the half-dozen families into which the group becomes divided.

The first of these, the Equidae (horses), is represented in North America at every stage of the Tertiary from the Lower Eocene to the Pleistocene. The remains of these animals provide the longest and most complete evolutionary series known; certain peculiarities, however, show that it is not entirely genuine but is built up from a series of forms constantly migrating into the area from northern Asia. It is therefore very remarkable that no remains of horses have been found below the Lower Pliocene in Mongolia and China. Horses extremely similar to those of North America, but forming a less complete evolutionary series. are found in Lower, Middle and Upper Eocene rocks in western Europe, and this region possesses the only representatives of a small group, the palaeotheres, which, derived from a horse stock, reached a large size and very peculiar structure as early as the Upper Eocene, becoming extinct in Lower Oligocene times.