340 LAND MAMMALS IN THE WESTEKN HEMISPHERE 



6. \Hyracodontid(e. ^Cursorial and ^Aquatic Rhinoceroses 



The luxuriant diversification of the rhinoceros-stem was 

 not exhausted by the many phyla of what we have called the 

 true rhinoceroses. Two other series, very distinctly marked 

 and rather distantly connected with the first, are yet to be 

 considered. These two series, the thjo^acodonts (in the narrow 

 sense) and the famynodonts, ran courses which, in certain 

 respects, were singularly alike ; both were of North American 

 origin and one, the fhyracodonts, was entirely confined to 

 that continent, while the other sent out late migrants, which 

 entered Europe, no doubt through Asia, and both ended their 

 careers before the close of the White River time. Their history 

 was thus a brief one when compared with that of the true 

 rhinoceroses, three phyla of which persist to the present day, 

 though their geographical range is greatly restricted in com- 

 parison with what it was in the Miocene and PHocene, when 

 they ranged over every continent except AustraUa and South 

 America. 



Just how to classify these three series of rhinoceroses and 

 rhinoceros-like animals, so as most accurately to express their 

 mutual relationships, is a question that has received several 

 answers. One method suggested is to include them all in a 

 single family and to make a subfamily for each of the three 

 well-distinguished series; this is the arrangement which 

 personally I should prefer. A second plan is to accord family 

 rank to each of the three groups; while the most elaborate 

 scheme, that of Professor Osborn, is as follows : for the rhi- 

 noceroses, in the broader sense, he makes two famiUes, the 

 Rhinocerotidse and the tHyracodontidse, and divides the former 

 into four subfamilies, which include all of the true rhinoceroses, 

 living and extinct, of the Old and New Worlds, and the latter 

 into two subfamilies, the fHyracodontinse and fAmynodontinse. 

 It is not a matter of very great moment as to which of these 

 three schemes is followed, and I shall therefore adopt the one 



