266 LAND MAMMALS IN THE WESTERN HEMISPHERE 



presence in the succeeding White River was probably due to 

 immigration. 



The Perissodactyla were the preponderant type of hoofed 

 animals, and ancestral forms of most of the White River genera 

 have already been identified. The ftitanotheres {\Diplacodon, 

 '\Protitanotherium) were much smaller and lighter than those 

 of the lower White River and had much shorter horns. The 

 fhyracodonts, the Ughtly built, cursorial rhinoceroses, were 

 represented by a genus {'\Triplopus) which was smaller and 

 more slender than the White River form {\Hyracodon) and 

 its teeth were of distinctly more primitive character. The 

 heavy, massive and presumably aquatic famynodonts {^Amyn- 

 odon) were likewise smaller and less speciahzed than their 

 descendants of the Ohgocene. No member of the true rhinoc- 

 eros series has yet been identified in the Uinta, but there is 

 some reason to think that they were nevertheless present. 

 Tapirs are distinctly indicated by certain fossils, but they are 

 still too incompletely known to make possible any statement 

 as to their degree of development. The horses ('\Epihippus), 

 like the other famihes mentioned, were much smaller and dis- 

 tinctly more primitive than their successors in the Ohgocene. 



The Artiodactyla were, for the first time in the history of 

 North America, as numerous and as varied as the perisso- 

 dactyls and, with the exception of the peccaries and fanthra- 

 cotheres, representatives of all the White River famihes are 

 known. The finding of the peccaries is merely a question of 

 further exploration, but the fanthracotheres were migrants 

 from the Old World, and there is no likehhood that they will 

 be discovered in the Uinta at any future time. Fairly large, 

 pig-like animals, probably referable to the fgiant-pigs or fen- 

 telodonts, occurred, but nothing has yet been found which can 

 be considered as the direct ancestor of the White River genus. 

 As was true of the perissodactyls, the Uinta artiodactyls were 

 nearly all much smaller and more primitive than their Ohgocene 

 descendants and the differences are most interesting from the 



