326 LAND MAMMALS IN THE WESTERN HEMISPHERE 



The White River genus {^Colodon), which is fairly well 

 known, might almost be described as combining the characters 

 of horses and tapirs ; but such an expression is not to be inter- 

 preted as meaning that this genus is in any sense a connecting 

 link or transition between the two families, but merely that 

 in certain important respects its course of development ran 

 parallel with that followed by the horses. The teeth were 

 very tapir-like, especially those of the lower jaw, which, 

 indeed, are hardly distinguishable from those of a tapir, and 

 the premolars had the molar-pattern. The limbs were very 

 light and slender and the feet long and narrow ; the fore foot 

 retained a small fifth digit ; the feet, especially the hinder one, 

 had a resemblance to those of the contemporary horses ( \Meso- 

 Mppws) , though the median digit was not so much enlarged, 

 nor the lateral ones so far reduced. It is highly probable that, 

 had this family persisted till the Pleistocene, instead of dying 

 out in the lower Oligocene, it would have eventually terminated 

 in monodactyl forms. 



The flophiodonts of the Eocene are represented by very 

 fragmentary material ; so far as that material goes, it does 

 not show much change from the White River genus, except 

 that the premolar teeth were smaller and simpler, the limbs and 

 feet retaining the same characteristics of length and slender- 

 ness. The Wasatch genus {'\Heptodon) had a similar light- 

 ness of limb and narrowness of feet, these characters thus ap- 

 pearing at the very beginning of the family history, so far 

 as their North American career is concerned. 



5. Rhinocerotidce. True Rhinoceroses 



The history of the great group of rhinoceroses and rhinoc- 

 eros-like animals is a very long and complicated one, inferior 

 in its completeness only to that of the horses. The com- 

 plexity of the story arises from the large number of phyla 

 into which the families are divisible, and, despite the great 



