344 



LAND MAMMALS IN THE WESTERN HEMISPHERE 



the fore foot had already been reduced to three, the only known 

 Bridger perissodactyl of which this is true, all the others having 

 four digits in the manus and three in the pes. 



In the middle and lower Bridger, and even in the Wind River, 

 occurs a genus {\Hyrachyus) which contained a large number 

 of species, ranging in size from a full-grown modem tapir to 

 creatures no larger than foxes. It is among these smaller 

 species that the most ancient member of the fhyracodont 

 line is to be sought, though it is not yet practicable to select 

 any particular one. \Hyrachyus, indeed, may very possibly 

 have contained among its many species the ancestors of all 

 three lines of the rhinoceroses and rhinoceros-Uke animals, 

 and thus formed the starting point from which they developed 







Fig. 182. — Primitive tcursorial rhinoceros (,1: Hyrachyus eaamitis), lower Bridger. Re- 

 stored from a skeleton in the American Museum of Natural History. 



in diverging series. It is always a very significant fact when 

 two or more groups approach one another the more closely, 

 the farther back in time they are traced, because that can only 

 be interpreted to mean that ultimately they converged into 



