802 GEOLOGY 



Mammals continued their rapid evolution without interruption, 

 and perhaps even with some acceleration. The Carnivora came 

 into clear definition, and were represented in the White River 

 beds by ancestral dogs, cats, coons, and weasels, while some creo- 

 donts remained. Rodents were represented by squirrels, bea\> 

 pocket-gophers, rabbits, and mice. Among perissodactyls, the 



Fig. 539. Titanotherium validum Marsh, photograph of a mounted speci- 

 men in the Carnegie Museum. (Holland.) 



rapidly developing horse family was represented by MeW/// 

 and Anchippus. The rhinoceros tribe had deployed int. 

 branches, one a lowland form, ancestral to the existing family, 

 another aquatic, and a third an upland, horse-like. running form. 

 The tribe had a cosmopolitan range. 



The titanotheres, an erratic branch of the odd-toed 

 which arose late in the Eocene, reached their climax in the 

 cene (White River), and then disappeared. They were interme- 

 diate in proportions between the rhinoceros and the elephant, and 

 were distinguished by a long, depressed skull armed with a pair of 



