TERTIARY. 419 



the present day. Among fishes, the Protospondylic family of 

 Pycnodontid.-r is the sole typically Mesozoic group still sur- 

 viving; and this is no longer met with after the Upper Eocene. 

 All the existing sub-orders, and many of the existing families 

 or even genera, seem to occur in the Eocene ; and the chief 

 interest of the Tertiary fish-fauna consists in its varying distri- 

 bution at different times both in the seas and freshwaters. 

 Except the ordinary turtles and a solitary rhynchocephalian 

 (Ckarnpsosaurus), no vertebrates higher than fishes have been 

 found in the marine deposits at the base of the Tertiary series ; 

 but both Cetacea and Sireriia begin to usurp the functions of 

 the marine Mesozoic reptiles before the close of the Eocene 

 period. 



The terrestrial vertebrata are of much more importance ; 

 for the Mammalia suddenly appear as the dominant type on 

 all the continents, and the evolution of many of their minor 

 groups can be traced through the Tertiary formations. During 

 the whole of this period, however, Australia and New Zealand 

 seem to have been separated by sea from the other existing 

 land-areas of the globe ; while South America must have been 

 quite an isolated region from the close of the Cretaceous to the 

 dawn of the Pliocene. 



Basal Eocene. 



The earliest known mammalian fauna of a typical Tertiary 

 type occurs in a deposit (Cernaysian Formation) quite at the 

 base of the Eocene near Rheims in France, and in a still more 

 extensive lake-deposit (Puerco Formation), doubtless of corre- 

 sponding geological age, in New Mexico and Colorado, U.S.A. 

 In this fauna there are still typical, though highly specialized 

 members of the Jurassic group of Multituberculata (Neoplagi- 

 aulax, Ptilodus, Polymastodon) ; but the large majority of the 

 genera belong to the Creodonta and Condylarthra, or ancestors 

 of the Carnivora, Insectivora, and Ungulata. In the Puerco 



there also seem to be traces of the ancestors of the New World 







Edentata (the so-called Ganodonta). 



272 



