4 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



In the Santa Cruz fauna the edentates form one of the most conspicuous 

 elements, both in the abundance of individuals and in the number and 

 variety of the genera and species. As a whole, they are strikingly dif- 

 ferent from those of recent times, for of the three orders which are repre- 

 sented among the fossils, armadillos, glyptodonts and ground-sloths, only 

 the first-named persists to the present day, the other two being extinct- 

 On the other hand, no trace has yet been found in the Santa Cruz beds 

 of the true sloths or of the anteaters. It can hardly be doubted that both 

 of these orders had already become differentiated and were in existence 

 as such. If so, however, they must have originated in some other part of 

 the South American continent and were prevented by climatic, or other 

 barriers from extending their range into Patagonia. One fact which 

 clearly justifies this assumption is the relatively small degree of structural 

 change that took place between the edentates of the Santa Cruz and those 

 of later periods, such as the Pampean. There are many differences of 

 detail between the earlier and the later forms, but nothing comparable to 

 what would be implied in the derivation of the sloths or anteaters from 

 any known Santa Cruz fossils. 



As will be shown more at length in a later section, much the same 

 statement applies to the armadillos of the Santa Cruz beds, with reference 

 to their connection with those of modern times. Speaking broadly, the 

 latter would appear not to have been derived from the former, which sug- 

 gests that Miocene Patagonia was rather an outpost of the South Ameri- 

 can fauna than the main area of its development. 



The Santa Cruz glyptodonts are, on the whole, markedly more primi- 

 tive than those of the Pampean and in many structural details show a 

 closer connection with the armadillos than do the latter, but, for the most 

 part, the Santa Cruz genera do not appear to be directly ancestral to those 

 of the Pampean. Like the armadillos, they seem to be aside from the 

 main lines of descent which terminated in the giant types of the Pleisto- 

 cene. 



On the other hand, the Gravigrada appear to be more directly ancestral 

 to the great Pampean forms, and representatives, if not the actual ances- 

 tors, of almost all the later genera may be observed in this fauna. How- 

 ever, no entirely convincing solution of these problems can be obtained 

 until the fossils intermediate in time between the Santa Cruz and the 

 Pampean are more fully known. 



