240 WATER REPTILES OF THE PAST AND PRESENT 



seas, it is not likely that it fed on other than relatively slow-moving 

 prey. Lydekker looked upon the broad mandibles and broad 

 palate of Lytoloma as specializations for a mussel diet; and very 

 similarly in Archelon, while the decurved beak would easily trans- 

 form him into a most formidable enemy, the heavy premaxillaries 

 and vomer, and the flat but deep lower jaw, suggest an adept 

 crusher of crustaceans. The presence of vast quantities of Nautilus 

 dekayi, which I found accompanying one of the specimens, was 

 doubtless accidental, but it plainly suggests that this cephalopod 

 was one of the teeming sources of food in the Archelon environ- 

 ment. 



"The huge bulk of the mature Archelon might account for the 

 shearing off and loss of the flippers of younger forms caught between 

 the shells of the 'elder boatmen of the Cretaceous seas/ as Cope 

 has called them, during any sudden rush while herding on the shores. 

 But probably the young turtles did not much frequent the shores 

 at either egg-laying or other times. Whence it is much more likely 

 that it was a mosasaur or some of the gigantic fishes like Portheus 

 which bit off the right hind flipper in the type specimen of Archelon 

 ischyros, well above the heel, as I have described it. That this 

 happened rather early in life is shown by the arrested growth of 

 the right femur and remaining portions of the tibia and fibula, 

 which are all uniformly 10 per cent smaller than the corresponding 

 bones of the left flipper." 



While there were many small fishes in the Niobrara seas which 

 the Protostegas inhabited, the most striking thing in the fauna is 

 the great abundance of molluscal shells, especially Ostrea congesta. 

 And with them were great hordes of larger pelycypod mollusks, 

 some of them of enormous size. Some of the largest reach a 

 diameter of nearly four feet, with shells so thin that one can hardly 

 understand how they could have supported such large, oyster-like 

 creatures. One can imagine that such shell-fish might have afforded 

 an almost inexhaustible source of food for the large turtles; and 

 several times the writer has found remains of Protostega associated 

 with such shells. From all of which evidence it seems very prob- 

 able indeed that Dr. Wieland is right in imputing to these gigantic 

 turtles a shell-feeding habit, a habit which required neither speed 



