OLIGOCENE 



509 



abundant; the Horses are represented by the little three-toed 

 Mesohippus (Fig. 166), the Tapirs by Protapirus, and the Rhinoce- 

 roses by many types, all of them hornless ; thus Metamynodon 

 was a heavy, aquatic animal, somewhat like a hippopotamus in 

 appearance ; Ccenopus was a stout terrestrial form, and Hyraco- 

 don (Fig. 167) a long-legged, slender, running animal. The 

 Titanotheres culminate in the huge Titanotherium, which had a 

 pair of long horns on the nose. Artiodactyls are now much more 

 numerous than the Perissodactyls, but are quite different in the 



FIG. 166. — Skeleton of Mesohippus Bairdi. (Farr.) 



two continents. Besides a number of curious extinct types com- 

 mon to the two regions, such as Ancodus, Anthracotherium, 

 Elotherium, America has Oreodonts, Camels (Poebrotheriuni) , 

 Peccaries (Perch cents), and the extraordinary little Protoceras, 

 while Europe had a remarkable variety of Xiphodonts, Anoplo- 

 theres, true Swine, and true Ruminants. The Rodents of the 

 White River stage are m'uch more numerous and varied than 

 before. Marmots, Squirrels, Beavers, Mice, Pocket-gophers, and 

 Rabbits are already well established. 



From the change in the character of the vegetation and of the 

 reptiles we may infer that a slight change had taken place in the 

 climate, which was not quite so warm as before, at least in the in- 

 terior of the continent. A similar change occurred in northern 

 Europe in the later Oligocene. 



