38 FOSSIL TURTLES OF NORTH AMERICA. 



In North America no turtles are known to have existed in deposits below the 

 Morrison beds of the Upper Jurassic. Dr. Edward Hitchcock has indeed assigned 

 to the tortoises certain tracks observed by him in the Triassic sandstones of Massa- 

 chusetts and Connecticut; but, while there is no improbability that turtles occurred 

 there and then, there is no certainty of it. As is seen from table i, 2 species of 

 turtles, both belonging to the Amphichelydia, have been found in the Morrison beds 

 of the Rocky Mountain region. These beds are sometimes regarded as belonging to 

 the Lower Cretaceous, equivalent to the Wealden of Europe, but it is more probable 

 that they correspond to the Kimeridge Clay or the Purbeck (Fraas, Zeitschr. deutch. 

 geol. Gesellsch., LIII, 1902, briefl. Mitth., p. 59) or even a little lower. So far as now 

 known, no other group than the Amphichelydia are represented until we reach the 

 Benton, of the Upper Cretaceous, in the lowest division of this there occurs an 

 undoubted marine turtle belonging to the Cryptodira. A species of Glyptops is 

 found in the Potomac beds near Washington, District of Columbia, and another 

 species of probably the same genus in the Washita beds of Kansas. 



Turtle remains are not uncommon in the Niobrara beds of Kansas, but when we 

 come to examine the list, we find the species not numerous, and they belong to only 

 four genera. The species of Toxochelys and of Porthochelys appear to have lived in 

 the Niobrara ocean near the coasts. The species of Protostega, on the other hand, 

 evidently ventured far out on the high seas. Toxochelys and Porthochelys appear to 

 have continued on into the Pierre; Protostega was there replaced by, or transformed 

 into, the huge Archelon. 



About the middle of the Upper Cretaceous, conditions were favorable for the 

 existence and the inhumation of many species of turtles. These are found now in 

 two widely removed regions and in deposits made under widely different conditions. 

 On the Atlantic border, especially in New Jersey, occurs a series of marine deposits 

 from which have been derived about 40 species of turtles, including 9 species 

 of Pleurodira and 2 species of Trionychidae. The remainder are Cryptodira, among 

 them many coast-inhabiting Thalassemydidse, all of which were probably furnisht 

 with jaws fitted for crushing hard mollusks and crustaceans. The family of Dermate- 

 mydidae, represented now by only 3 genera and 4 species, appear in great numbers 

 and variety, especially in the New Jersey Cretaceous greensand. Whence this 

 assemblage of turtles came we have no clue. Scant remains indicate the existence 

 of two species of large marine turtles, Atlantochelysznd Neptunochelys. 



In the heart of the continent at nearly the same time, possibly a little earlier, 

 there were being laid down fresh and brackish water deposits, now known as the 

 Judith River beds. They are found in Montana and British America, and have 

 furnisht about 15 species of turtles; but these are quite different from those of the 

 Atlantic coast deposits just mentioned. There are, indeed, 4 or 5 species of triony- 

 chids of the genus Aspideretes, a genus living now in Asia, a species of Plastomenus, 

 and 3 or 4 species of Dermatemydidae; but the latter belong to genera distinct from 

 those found in the New Jersey deposits. In these Judith River beds reappear rep- 

 resentatives of the Amphichelydia, turtles which we have found to characterize the 

 Upper Jurassic and the Lower Cretaceous. In America the turtles of this group 

 appear generally to have avoided true marine conditions. 



Succeeding the Pierre and the Fox Hills epochs came that of the Laramie. In 

 the fresh and brackish water deposits laid down during this time there were buried 

 remains of a great variety of turtles, but unfortunately these remains are usually 

 very fragmentary; 16 species are recognized as belonging here. Their relationships 

 are close to the turtles of the Judith River beds, some species being as yet undis- 

 tinguishable. The conditions under which the two deposits were laid down were so 



