REPTILIA. 101 



REPTILIA. 



The Eocene period, was, of the divisions of the Tertiary, the most 

 prolific of reptilian life. It is true that the orders of reptiles which charac- 

 terized the Mesozoic periods no longer existed. The Dinosauria had perished 

 from the land; the Ichthyopterygia, Sauropterygia and Pythononiorpha no longer 

 inhabited the sea, and the Pterosauria had disappeared from the air. The 

 Eocene reptiles were not a new creation, nor a new evolution, but a remnant of 

 the types that had coexisted with those monarchs of life during previous ages. 

 We must except from this statement the serpents, which first appear at this 

 time.* The crocodiles, tortoises, and lacertilians represent orders already 

 abundant in the Mesozoic faunae. Their decadence in central North America 

 did not commence until the Miocene period, when the crocodiles and nearly 

 all the tortoises disappeared. From the Loup Fork or Upper Miocene, 

 only a few traces of lizards have been obtained, and snakes were apparently 

 not very numerous. On the eastern coast regions crocodiles existed, and 

 tortoises were more numerous during the Miocene period; but here also 

 they were less abundant and varied than during the Eocene. 



The Crocodilia did not differ in important respects from those now 

 existing. I have distinguished five species from the Wasatch beds, and six 

 different ones from the Bridger. 



The Tesiudinata include a great variety of forms. I have seen sixteen 

 species from the Wasatch formation, and thirty-two from the Bridger and 

 Washakie. Of these, six are common to the two formations, as indicated 

 by imperfect material, leaving a total of forty-two. Three genera, Emys, 

 Trionyx, and f Plastomenus hold over from the Cretaceous period, while six 

 appear for the first time. Of these, five genera are not known to continue 

 later than the Eocene period. 



Of lizards I have obtained the remains of a half dozen of species, but 

 none of them in a complete state of preservation. Professor Marsh has been 

 more fortunate, as he has described from his material from the Bridger beds, 

 twenty-one speciesf He arranges these under five generic heads, as fol- 



• Since the above was written, it is reported that Dr. Sauvage, of Paris, has discovered the remains 

 of a serpent in the cretaceous formation. 



i American Journal of Science and Arts, 1871, June, and October, 1872. 



