206 Wortman — Studies of Eocene Mammalia in the 



met with in its incipient stages in the typical North American 

 Eocene group Omomyinae. As we have just seen, this char- 

 acter is found in the upper molars of all the species, and may 

 be said to be especially characteristic of them. We know, 

 moreover, that they are Primates ; that the dental formula for 

 the lower jaw and presumably for the upper is the same 

 as in the Cebidse ; that the number, structure, and relations of 

 all the teeth of certain species, at least, so completely fulfil the 

 requirements and conditions which one would naturally seek in 

 an ancestor of these living Cebidse, as to make it scarcely possible 

 to believe that such striking resemblances can be altogether 

 accidental. In fact, this is the only group of Primates that 

 has ever been found, among either living or extinct forms 

 outside of South America, which exhibits any approximation 

 to any of the Cebidse, and until some tangible evidence to the 



141 



Figure 141. — Lower jaw of Chrysothrix sciurea ; side view ; twice natural 

 size. 



contrary is forthcoming we are compelled to regard these 

 extinct North American types as the source from which the 

 ape fauna of the Neotropical realm had its origin. 



It has been assumed by some who have sought to solve the 

 problem of the origin of the Cebidse, that they were derived 

 from Africa, and making their way thence across an Antarctic 

 land connection, thus reached South America. This view is 

 based upon the presence in the Patagonian Miocene of the 

 remains of numerous Marsupials closely allied to those now 

 living in Australia, which argues strongly for a land connection 

 with that continent during the Tertiary. From resemblances 

 among certain living species from South America to those of 

 Africa, as well as among some of the extinct forms, it is fur- 

 ther assumed that this land bridge extended to Africa, and that 

 there was an interchange of species between the two Hemi- 

 spheres. While this may perhaps satisfactorily account for the 

 presence of those African types in South America, it does not 



