508 LAND MAMMALS IN THE WESTERN HEMISPHERE 



but little is known about them. The latest known member of 

 the family so far discovered is a genus {^Epitherium) from the 

 upper Pliocene of Monte Hermoso, a tridactyl form like ]Dia- 

 diaphorus. It is a noteworthy fact that the most advanced 

 and specialized genus of the entire family ended with the 

 Santa Cruz, while the less differentiated types survived till a 

 considerably later period. Possibly, it was the incoming of 

 the highly efficient Carnivora from North America that led 

 to the extermination of the last fproterotheres. 



Turning backward from the Santa Cruz, the family may be 

 traced without any question to the Deseado stage of the Oligo- 

 cene, though nothing but teeth has yet been obtained, while 

 in the Eocene it would appear to have become merged in the 

 same group of small, fCondylarthra-like animals with quad- 

 ritubercular molars, as those which are regarded as the probable 

 ancestors of the fmacrauchenids. However likely this con- 

 clusion may seem to be, its confirmation must await the dis- 

 covery of much more complete specimens than are now avail- 

 able. 



Order fAsTRAPOTHERiA. jAstrapotheres 



In the Santa Cruz another group of peculiar South American 

 ungulates, the fAstrapotheria, made its last recorded appear- 

 ance. Though not at all uncommon in that formation, no 

 complete or even partial skeleton has yet been found, but 

 merely the skull and a few bones of the limbs and feet. For 

 this reason there is much doubt as to the systematic position 

 and relationships of these animals, which were among the most 

 curious of the many strange mammals which made up the 

 Santa Cruz fauna. They were mentioned in connection with 

 the fAmblypoda (p. 456) as possible representatives of that 

 order in South America, but, as will be seen later, this is an 

 improbable conclusion, and the group appears to have been 

 indigenous in the southern continent, in which, at all events, 



