TERTIARY. 429 



Of the Primates, the primitive lemuroids appeared in the 

 Eocene similarly on both continents; but in North America 

 they soon became extinct, while in the Old World they were 

 followed by the true apes and still have some specialized 

 survivors. 



South American Tertiary Faunas. 



As already mentioned, South America seems to have been 

 completely separated from North America from the dawn of 

 the Eocene to the close of the Miocene period. Its character- 

 istic mammalian fauna thus appears to have been developed 

 quite independently of that of the northern hemisphere. It 

 may well have received its mammals originally from the same 

 unknown region which furnished the Puerco and Lower Eocene 

 faunas of North America. Here there are undoubted lemuroids 

 and probably ancestral edentates, which soon become extinct, 

 but may well have flourished vigorously on the southern 

 continent, eventually furnishing it with monkeys, sloths, and 

 armadillos. There are also traces of generalized animals, which 

 might have evolved into the characteristic carnivores, rodents, 

 and ungulates which appeared in the later Tertiaries of South 

 America. No equally remote fauna, however, has hitherto 

 been found on the South American continent itself; and the 

 earliest known deposits containing mammalian remains in that 

 area (the Pyrotherium Formation and the Santa Cruz For- 

 mation of Patagonia) are intimately associated with a marine 

 deposit (the Patagonian Formation), which would be termed 

 Miocene or even Lower Pliocene if it occurred in Europe. The 

 Pyrotherium and Santa Cruz mammalia, indeed, have an 

 essentially South American aspect. They include monkeys 

 and hystricomorphous rodents much like those now living in 

 the same region, and several strange sub-orders of Ungulata 

 which flourished there in the later Tertiaries and only became 

 extinct after the dawn of the Pleistocene. They also comprise 

 innumerable well-marked armadillos and sloths, few of them 

 exhibiting more primitive characters than those presented by 

 the same animals of later date. Finally, there is an abundance 

 of small marsupials closely related to the South American 



