100 ANNALS NEW YORll ACADEMY OF SCIENCES 



a separation ensued until the Miocene, after which there has been a per- 

 manent connection. It is exactly from the Eocene till the Miocene that 

 South America evolved its typical mammalian fauna, whose last remains 

 are the anteaters, armadillos, csenolests, sloths and a few tropical mar- 

 supials. This indicates that the primitive ancestors of these animals 

 along with others entered South America during the Cretaceous to the 

 early Eocene. It was during late Miocene time that the second important 

 change in South American mammalian life took place. This invasion 

 was without doubt from the north. The third wave was also from the 

 north. It was composed of man and his domesticated animals. The 

 replacement of the older fauna by the later invasions is still seen on all 

 hands in different tropical animals, which still retain the old paleotelic 

 northern characters which are, however, more or less masked by the 

 specialized cenotelic characters. 45 



In view of all the preceding, the writer, while still in the field, changed 

 his previous views concerning all of the hypothetical connections between 

 South America and the eastern hemisphere, and he now believes that all 

 of the South American animals originally came from North American 

 stock. 



I am also inclined to believe that the evolution of paleotelic characters, 

 especially of families and orders, has taken place faster in the northern 

 than in the southern hemisphere. This is indicated by the fact that 

 many tropical animals are often a few geological ages behind their north- 

 ern living or extinct relatives. The edentates, monotremes, ratite birds, 

 many South American birds (screamers, seriamos, sun bittern, etc.), the 

 characins, dipnoi, crossopterygians and osteoglossids (fishes), South Afri- 

 can secretary bird, note Aardvark (Orycteropus) , scaly anteaters (Manis), 

 tapirs, camels and many marsupials are examples of tropical animals 

 which are a few geological ages behind time. This retarded evolution of 

 paleotelic characters in the southern hemisphere may be due to a greater 

 stability of the vast Piano Alto of South America. 



It is not, in my opinion, the stable portions of the earth which have 

 produced the bulk of evolution, but it is the ever-changing regions either 

 by elevation and submergence or tremendous changes produced by ero- 

 sion, like the recent formation of the Amazon Valley. These violent 

 changes produced in the environmental complexes appear to pull the 

 trigger of evolution. Inasmuch as geology shows that more radical 



45 In taking this view, I have assumed that Matthew and Gaudry are correct in con- 

 sidering the Patagonian heds to be later than the upper Cretaceous. Roth, however, 

 considers the Notostylops heds to be upper Cretaceous, and Ameginho considers them to 

 be still earlier. 



