HISTORY OF THE PERISSODACTYLA 353 



increasing body-weight being the determining factor in both 

 cases. When this increase began to be decided, the reduction 

 of digits ceased at the point which had already been reached 

 in any particular series, three in both manus and pes in the 

 true rhinoceroses, four in the manus and three in the pes 

 in the f^niynodonts. Very heavy animals require broad, 

 columnar feet to support them, and hence the similarity of 

 appearance in such widely separated groups as elephants, 

 rhinoceroses and hippopotamuses, not to mention several 

 extinct orders and families. Among the larger and heavier 

 rhinoceroses, as in those of the present time, there was great 

 variety in the proportionate lengths of the limbs, body and 

 feet. 



In brief, the great complexity of the history of the rhinoc- 

 eroses is due to the many divergent and parallel phyla into 

 which these animals may be grouped. Broadly speaking, 

 they may be subdivided into the slender, cursorial types and 

 the heavy, slow-moving types, the former developing in a man- 

 ner similar to that shown by the horses, while the latter were 

 modified after the fashion of the jtitanotheres. Obviously 

 the load to be supported by the legs and feet was a very impor- 

 tant factor in determining the character of evolutionary 

 change. 



II. tANCYLOPODA. fCLAWED PeRISSODACTYLS 



The very extraordinary and aberrant animals which are 

 referable to this suborder have been understood only since 

 the year 1888, for, as was shown in an earlier chapter (p. 41) 

 their scattered parts had been assigned to two different mam- 

 maUan orders, the skull to the perissodactyls and the feet to 

 the pangolins, or scaly anteaters (PhoUdota) of the Old World, 

 since it occurred to no one that the same animal could have 

 such a skull and teeth in combination with such feet. 



The history of the Ancylopoda is still very incomplete, 

 only four genera, of the lower Pliocene, middle and lower 



