244 ORIGIN OF LIFE IN AMERICA 



peared. In the Oligocene deposits of the northern continent, 

 as above mentioned, there are no distinctly South American 

 species. Yet, curiously enough, when we come to still earlier 

 strata, we again meet with remains of animals that exhibit 

 characteristically South American features. In the Puerco 

 formation, in north-western New Mexico, a number of 

 peculiar mammalian bones have been discovered, which were 

 referred by Professor Cope to the extinct order Tillodontia, 

 whereas Dr. Wortman endeavoured to show that Cope's 

 genera Psittacotherium, Onychodectes and Conoryctes were 

 ancestral to the Gravigrada or ground sloths of South America. 

 Dr. Wortman * proposed that they be placed in a new sub- 

 order of the edentates, which he named Ganodonta. But he 

 did not look upon these animals as immigrants from South 

 America. He thought this order of primitive mammals must 

 have actually arisen in North America, and have thence emi- 

 grated to South America before the close of the Eocene 

 Period. Although these Ganodonta are no longer considered 

 as ancestral to the ground sloths, the same Puerco formation 

 has yielded other mammals which show distinctly South 

 American or rather Patagonian affinities. Dr. Wortman's 

 theory as to the North American origin of the Ganodonta 

 has not found favour. Dr. Osborn, in fact, urges that a 

 direct land connection with South America is indicated at 

 this stage of geological history in order to account for the 

 South American features in the North American fauna. This 

 view has been amply confirmed by the remarkable discovery in 

 Wyoming, in a deposit of Middle Eocene age (Bridger), of 

 the remains of a true armadillo closely related to the modern 

 armadillos, but exhibiting a few more primitive characters. f 



Since Dr. Ameghino's researches in Patagonia have brought 

 to light such a wealth of edentates from the earliest 

 Tertiary, and probably even from Mesozoic deposits, scarcely 

 anyone can doubt that South America is the original home 

 of that group of mammals, and that they have passed from 

 there during the Eocene Period and earlier into North 

 America, and not vice versa, as Dr. Wortman suggested. 

 But very few would assert that the physical geography of the 



* Wortman, J. L., " Psittacotherium," pp. 259262. 



i Osborn, H. F., " An Armadillo from the Eocene," p. 163. 



