SAUROPTERYGIA 93 



pebbles. He believed that their occurrence with the skeleton was 

 not accidental, but that they had been intentionally swallowed 

 by the animal when alive, and formed at its death a part of its 

 stomach contents. Even earlier than this the same habit had been 

 noticed. Nearly at the same time that Seeley mentioned the 

 peculiar discovery he had made the present writer found several 

 specimens of plesiosaurs in the chalk of western Kansas with which 

 similar pebbles were associated, an account of which was given 

 soon afterward by the late Professor Mudge. Since then numerous 

 like discoveries have made it certain that the plesiosaurs usually, if 

 not always, swallowed such pebbles in considerable quantities, for 

 what purpose we do not yet feel sure; one can only hazard a guess. 

 The small size of the pebbles, or gastroliths, as they have been 

 called, a half-inch or less in diameter, found with skeletons of large 

 size, indicate much more complete digestion of the hard parts of 

 their food than is the case with many other reptiles; no solid sub- 

 stance of size could have passed out of the plesiosaur stomach, and 

 such is the case with the modern crocodiles, which have a like habit 

 of swallowing pebbles. That the plesiosaurs picked up these sili- 

 ceous pebbles, sometimes weighing a half-pound, accidentally with 

 their food is highly improbable; they surely had something to do 

 with their food habits. It is not at all unreasonable to suppose 

 that the plesiosaurs, because of their comparative sluggishness, fed 

 upon anything of an animal nature, whether living or dead, which 

 came in their way; that carrion, squids, crustaceans, and fishes 

 were all equally acceptable; they were probably largely scavengers 

 of the old oceans. Barnum Brown found among the stomach 

 contents of a plesiosaur fragments of fish and pterodactyl bones, 

 and.cephalopod shells. Gallinaceous birds, most of which have the 

 same pebble-swallowing habit, have a thick-walled muscular stomach 

 or gizzard, in which the pebbles serve as an aid in the trituration 

 of food. Modern crocodiles, with the same pebble-swallowing 

 habit, have a thick-walled muscular stomach, gizzard-like, though 

 of course not as large as in birds; and the same habit has been 

 noted by Des Longchamps in the ancient teleosaur crocodiles. 

 It is hardly possible yet to decide whether or not the plesiosaurs 

 were denizens of the open oceans for the most part, far from land. 



