234 LAND MAMMALS IN THE WESTERN HEMISPHERE 



great variety of dogs, large and small, all belonging to extinct 

 genera, as indeed is true of the other carnivores also. True 

 felines have been found, but as yet, none of the jsabre-tooth 

 series ; the abundance of the latter, however, in both preceding 

 and succeeding formations, is sufficient proof that the discovery 

 of them in the middle Miocene is merely a question of time. 

 Mustelines were present, and especially noteworthy is the 

 appearance of the first American otters, immigrants from the 

 Old World. 



Of the hoofed animals, the most interesting are the Pro- 

 boscidea, the most ancient of which that are definitely deter- 

 minable in America occur in this horizon. The place of origin 

 and ancestry of these animals were long exasperating puzzles. 

 Appearing suddenly in the Miocene of Europe and North 

 America, in which regions nothing was known that could, 

 with any plausibility, be regarded as ancestral to them, they 

 might as well have dropped from the moon, for all that could 

 be told concerning their history. The exploration of the 

 Eocene and Oligocene beds of Egypt has dispelled the mystery 

 and shown that Africa was the original home of the group, 

 whence they gradually spread to every continent except 

 Australia. Little is known of these earliest American pro- 

 boscideans, but they were doubtless small fmastodons of the 

 four-tusked type. 



Among the Perissodactyla, the rhinoceroses were perhaps the 

 most conspicuous ; the native American stocks of this family 

 appear to have mostly died out and to have been replaced by 

 two or more phyla of immigrants from the Old World, some 

 of which were hornless, others had a small horn on the tip of 

 the nose and others again had a second and smaller horn on the 

 forehead. Tapirs, though unquestionably present, are rare as 

 fossils and not well known. Several distinct phyla of horses 

 may be distinguished, which were like small ponies in size, 

 but of more slender form ; they were all three-toed, but there 

 were marked differences among them with regard to the degree 



