SUCCESSIVE MAMMALIAN FAUNAS 261 



South America. — The older continental Tertiary forma- 

 tions of South America cannot be correlated with those of North 

 America or Europe, because they have nothing in common. 

 Difficult as it is to give a correct and adequate conception of 

 the Tertiary mammalian Ufe of the northern hemisphere to 

 one who has not made a study of it, it is far more difficult in 

 the case of South America. The stock of adjectives, such as 

 "peculiar," "bizarre," "grotesque" and the like, already 

 overworked in dealing with northern forms, is quite hopelessly 

 inadequate where everything is strange. In addition to this, 

 we are seriously handicapped in treating of the Oligocene and 

 Eocene of South America by very incomplete knowledge. 

 Many fossils have been collected and named, but the great 

 majority of these are known only from teeth; a few skulls 

 and limb-bones have been described, but no skeletons, and 

 therefore much is very uncertain regarding these faunas. 



The Deseado formation (Pyrotherium Beds) h^s been 

 variously referred by different writers from the upper Creta- 

 ceous to the lower Miocene, but its most probable correlation 

 is with the Oligocene. Though most of the mammahan groups 

 are the same as those of the Santa Cruz, the proportions of the 

 various orders in the two faunas are very different, but, to 

 some extent, the difference is probably illusory and due to the 

 conditions of fossilization, for, as a rule, the small mammals 

 are much less frequent and well preserved in the older beds. 

 As in the Santa Cruz, the marsupials were the only predaceous 

 mammals, and some of them attained gigantic size; but no 

 such variety of these beasts of prey has been found in these 

 beds as occurred in the middle Miocene. In addition, there 

 were numerous small herbivorous marsupials. One of the 

 most striking differences from the Santa Cruz fauna was in 

 the very much smaller number of Edentata, which, instead of 

 being extremely common, are quite rare among the fossils. 

 No doubt there was a real and substantial difference in this 

 respect, but it was probably not so great as it seems, and the 



