248 LAND MAMMALS IN THE WESTERN HEMISPHERE 



went back to the earliest South American Tertiary. In the 

 Miocene and PUocene the order was represented by two very 

 distinct families, the fMacrauchenidse and fProterotheriidae, 

 which were superficially very unUke. In the Santa Cruz beds 

 is found a genus {]Theosodon) which was apparently the di- 

 rect ancestor of the Pampean ^Macrauchenia. The Miocene 

 genus was a much smaller animal and had hardly more than 

 an incipient proboscis, but otherwise was very like its Pam- 

 pean successor; it was somewhat larger and heavier than a 

 Llama and probably bore some resemblance to that animal in 

 appearance. The long, narrow head, with its prehensile 

 upper lip, must have had an almost reptilian likeness from the 

 numerous uniform and sharp-pointed teeth with which the 

 front of the jaws was supplied ; the neck was elongate, the body 

 short and rather slender and the legs long, ending in three 

 nearly equal toes. 



The fproterotheres, on the other hand, were almost the 

 only Santa Cruz ungulates which had nothing outre or grotesque 

 about them to the eye of one habituated to the faunas of the 

 northern hemisphere. They were small, graceful animals, 

 very like the Miocene horses of the north in their proportions, 

 though having much shorter necks and shorter, heavier heads. 

 In some genera of this family {e.g. ]Diadiaphorus, ^Protero- 

 therium) the feet were three-toed and most surprisingly horse- 

 like in shape, but one genus {'\Thoatherium) was absolutely 

 single-toed, more completely monodactyl than any horse. 

 The horse-likenesses ran all through the skeleton and are so 

 numerous and so striking that several writers have not hesitated 

 to incorporate the fLitoptema with the Perissodactyla, but 

 this I believe to be an. error. If the fproterotheres were not 

 perissodactyls, as I am convinced they were not, they afford 

 one of the most remarkable examples of convergent evolution 

 among mammals yet made known. 



