HISTORY OF THE PERISSODACTYLA 349 



not SO heavy or so widely expanded as in the White River 

 genus, and the skeleton was less massive. 



The genus "fAmynodon is also represented in the upper 

 Bridger-beds, but by a species different from that of the Uinta 

 stage. This more ancient species was a smaller animal than 

 its upper Eocene successor and had less enlarged canine tusks, 

 but it already possessed the typical rhinoceros molar teeth, the 

 only Bridger mammal of which this is true. Beyond this 

 species the line, as at present understood, cannot be traced, 

 though probably some species of ^Hyrachyus, or an allied 

 genus, will prove to be the ancestor sought ; but the connecting 

 link has not yet been brought to light. 



The history of the rhinoceroses and rhinoceros-Uke animals, 

 of which a very much simpUfied sketch has just been given, 

 is a highly complex one, much more so than that of the horses, 

 ftitanotheres, or tapirs, and is less fully recorded, the earUer 

 chapters of the story being still missing. However, in the 

 progress of discovery these chapters will almost certainly 

 be recovered, and it is already possible to draw close inferences 

 as to what they will reveal. The complexity of the history 

 is chiefly due to the fact that, as compared with the other 

 perissodactyl groups, the rhinoceros stem ramified more widely 

 and gave rise to more divergent and diversified forms. At one 

 extreme, we find huge, massive, slow-moving types; and, at 

 the other, Ught, slender, cursorial creatures, almost horse-like 

 in appearance, with intermediate forms of moderate size. 

 Some were long and others short legged, mostly adapted to 

 terrestrial life, but some with aquatic habits. The three very 

 different sorts of modification which the anterior teeth (incisors 

 and canines) underwent in the three principal series may be 

 taken as an illustration of this divergent development, and 

 to these may be added a fourth, the complete suppression of 

 all the incisors and canines above and below, as is exemplified 

 by the modern African species. 



Of the three rhinoceros groups, whatever rank be assigned 



