The Astrapotheria, gigantic Santa Cruzian (Lower Miocene) forms with long downwardly growing tusks, may be highly spe cialized derivatives of some early member of the Entelonychia.
Toxodontia (q.v.).—These were perhaps the most numerous in species of all the notoungulate series. The Santa Cruzian (Lower Miocene) Nesodon was about the size of a rhinoceros but with the back curved and the limbs shorter. The front teeth were enlarged and flattened for cropping vegetation, the upper molar teeth had extremely long oblique outer walls and folded wearing surfaces. The three-toed feet, although rhinoceros-like in appearance, agreed with those of the litopterns in their fundamental characters. The Pampaean (Pleistocene) Toxodon was still larger, with a gigantic head and a huge curved back. This was one of the famous fossil South American mammals studied by C. Darwin (see Voyage of the Beagle).
Typotheria.—The smaller genera of this group, named proty potheres, included some that broadly resembled Hyrax and others that were rabbit-like. They were very abundant in the Lower Miocene of Patagonia. The extremely high-crowned molar teeth were much curved transversely, as in some rodents, and were adapted for grinding tough vegetation. The later form, Typothe rium, from the Pampaean or Pleistocene of Argentina, had rodent like incisors. It was about as large as a brown bear. This group is rather closely related to the toxodonts.
Pyrotheria.—In these curious animals the molars were bilopho dont, that is they bore two cross-crests like those of tapirs and dinotheres. The skull in some ways resembled those of the Pro boscidea (q.v.) and the same is true of the tusks, but on the whole it seems more likely that the pyrotheres are simply the South American analogues of the Proboscidea.
Hyracoidea (q.v.).—This characteristically African group is represented to-day by the "coneys" or dassies of southern and west Africa, Abyssinia, Arabia and Syria. These furry little ani mals have but slight external resemblance to ungulates but their jaws and teeth abound in resemblances to ungulates of many groups. The internal anatomy shows a curious mixture of resem blances to elephants and perissodactyls. There is no satisfactory evidence, however, of the relationship of Hyrax to any of the groups so far named. The hyracoids as a group must have been
in Africa for many millions of years, since various forms of fossil hyracoids have been found in the Lower Oligocene of the Fayarn district in Egypt. In some of these very ancient hyracoids (Megalohyrax) the molar teeth recall those of Eocene titanotheres or of Meniscotherium among the condylarths. In its skull Megalo hyrax was more or less swine-like.
Embrithopoda.—While the hyracoids played the part of the small ruminants in the ancient fauna of the Fayfim, the economic roles of the rhinoceroses and elephants were assumed by gigantic beasts named Arsinoitherium (q.v.) in honour of an Egyptian queen. In these very strange animals the whole fore-part of the skull was surmounted by an enormous pair of bony horns, which in the front view rose to a great height. The folded surfaces of the molar teeth remotely recall those of the American Eocene amblypods, but the premolars rather suggest relationships with the hyracoids. The body was very massive and the skeleton shows a curious mingling of resemblances to elephants and amblypods, doubtless the results of similar adaptations to slow browsing movements and the support of the immense body weight. The existence of these highly specialized animals in Africa at such an early date as the Lower Oligocene and their apparent isolation, in spite of their adaptive resemblances to elephants and ambly pods, all indicate a very long line of less and less specialized ancestors, traces of which may some day be discovered when still older fossil-bearing horizons are discovered elsewhere in Africa.