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 wdth 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. 259 — 262. 
\ Osborn, H. F., “ An Armadillo from the Eocene,” p. 163. 
