264 LAND MAMMALS IN THE WESTERN HEMISPHERE 



were on the verge of extinction, and included both very small 

 and very large species. The fPyrotheria, a suborder which 

 is not met with in the Santa Cruz or later formations, likewise 

 included some very large forms. The typical genus, ^Pyro- 

 therium, included large, relatively short-legged and very mas- 

 sive animals; the upper incisors formed two pairs of short, 

 downwardly directed tusks, and in the lower jaw was a single 

 pair of horizontally directed tusks; the grinding teeth were 

 low-crowned and had each two simple, transverse crests. 

 These grinding teeth and the lower tusks so resemble those of 

 the ancestral Proboscidea in the Oligocene of Egypt, that 

 the fpyrotheres have actually been regarded as the beginnings 

 of the fnaastodons and elephants, but this is undoubtedly an 

 error. The fAstrapotheria, another group which became ex- 

 tinct at or soon after the end of the Santa Cruz, were rel- 

 atively abundant in the Deseado and counted some very large 

 species. Finally, the fLitopterna were represented by the 

 same two families as continued through the PUocene and one of 

 them far into the Pleistocene. The horse-Uke fproterotheres 

 were present, but not enough of them has been obtained to 

 show whether or not they were in a notably less advanced 

 stage of development than those of the Santa Cruz. The 

 fmacrauchenids were quite similar to those of the latter for- 

 mation, though considerably smaller. In addition, there 

 were a few genera, survivals from earlier times, which were not 

 referable to either of these famiUes. 



The large number of genera, especially among the ftoxo- 

 donts and ftypotheres, which had high-crowned, cement- 

 covered teeth, may be taken as an indication that grazing 

 habits had already begun to be prevalent. 



Of this wonderful assemblage of hoofed animals, divisible 

 into six separate groups, whether of ordinal or subordinal 

 rank, not a trace remains to-day. Not only are all the species, 

 genera and families extinct, but the suborders and orders also. 

 Further, this was a very strictly autochthonous fauna, so far 



