the Cretaceous-Tertiary Problem, 213 



are scarcely enough to affect materially the great f aunal 

 change that comes with the true Eocene, with its abundant 

 peris so dactyls, its artiodactyls, rodents, adapid primates, 

 progressive creodonts, and abundant Coryphodon}'^ 



The antique character of all these Paleocene faunae is 

 seen in their retention of primitive characters in teeth and 

 feet, as urged by Cope long ago, and abundantly confirmed 

 by our later studies. They stand in marked contrast with 

 the prevalent fauna of the Lower Eocene (Wasatch), 

 already much advanced in tooth and foot structure. 

 They can only be understood as representing a varied^ 

 often specialized, but unprogressive series of faunae, 

 which was largely displaced at the beginning of the 

 Eocene by a far more advanced one, the survivors linger- 

 ing along for a time but dropping out one by one in spite 

 of their continued specialization on their more archaic 

 lines. 



Characteristics of Early Tertiary Yertehrate Faunas. 



In the following tabulation of range I have starred 

 those families and orders which I regard as modernized 

 and essentially Tertiary^^ in type. It will be seen that 

 some of them appear somewhat before the Wasatch, but 

 the great majority make their first appearance at that 

 stage. 



The Tertiary land vertebrates consist principally of 

 placental mammals, the greater part of them of modern 

 orders (perissodactyls, artiodactyls, Carnivora, rodents. 

 Primates, etc.) and including the ancestral stock of the 

 modern quadrupeds; but in the Eocene there is also a 



"■ CorypJiodon has been recorded from the ' Montien ' upon the evidence of 

 a tibia which I had opportunity to examine last summer through Dr. DoUo ^s 

 courtesy. It may be a large taligrade, or of :some other group; it is not 

 characteristically amblypod, still less CorypJiodon. My doubt in 1914 ia 

 regard to the correlation value of this record was warranted by what I knew 

 at the time regarding the evidence, and is now fully confirmed. Dollo has 

 recently secured from the Orsmael locality many separate teeth of a tiny 

 mammal, which when studied and identified will be very interesting and 

 important. 



" The criteron used is not the geological range as per the known record, 

 but the fact that the principal evolution and specialization of the family, its 

 differentiation from the generalized ancestral stock, took place during the 

 Tertiary. Also, and supplementing this criterion when the data are insuf- 

 ficient for definite conclusions as to the derivation and evolutionary history 

 of the group, the evidence that it was most abimdant, varied and flourishing 

 during the Tertiary serves to indicate its essentially Tertiary character. 



