Apr. 1903. North American Plesiosaurs — Williston. 75 



A PECULIAR FOOD HABIT OF. THE PLESIOSAURS. 



More than twenty years ago, Professor B. F. Mudge published, 

 in the First Biennial Report of the Kansas State Board of Agricul- 

 ture (p. 62), the following: "In the Plesiosaurs we found another 

 interesting feature showing an aid to digestion, similar to that of many 

 living reptiles and some birds. This consisted of well-worn siliceous 

 pebbles, from one-fourth to one-half an inch in diameter. They were 

 the more curious, as we never found such pebbles in the chalk or 

 shales of the Niobrara." The specimens which led to this conclusion 

 were collected while I was a member of Professor Mudge's party, and 

 are now preserved in the Yale collection. Nearly ten years ago some 

 plesiosaur bones collected near Ellsworth, Kansas, from the Benton 

 limestone, were sent to the Kansas University museum, together with 

 a lot of siliceous stones, with a request for information concerning 

 both. At the first opportunity 1 visited the locality whence they had 

 been discovered and collected what had been left of the specimen. 

 The bones were in a poor state of preservation, due to the effects of 

 frost, but by carefully digging over the shale in which they occurred 

 we obtained about one hundred and twenty-five of the pebbles, 

 together with several dorsal vertebra.' and ribs. Some of the pebbles 

 were still attached to the ribs by the original matrix, making it cer- 

 tain that their deposition was contemporaneous with that of the skel- 

 eton. The plesiosaur is one of the largest of the order, the dorsal 

 centra measuring five or more inches in diameter. In all probability 

 the species is identical with that mentioned in the preceding pages 

 as coming from the vicinity of Beloit. It is impossible to 

 determine the genus, and the species is yet undescribed. The 

 pebbles vary in weight from less than one gramme to more 

 than one hundred and seventy grammes. The smaller ones were 

 worn into more or less perfect ellipsoids, but the larger ones are 

 more irregular in shape, having suffered less abrasion. It seems 

 probable that the most of the pebbles had been obtained by the 

 animal from the sea beaches bordering the Black Hills, but not a 

 Jew of them, consisting of red quartzite, are quite identical with the 

 quartzite boulders so often found in the drift of eastern Kansas, 

 which have come from the vicinity of Sioux City, Iowa. 



The specimens show conclusively that the pyloric orifice of the 

 plesiosaurs must have been well provided with a sphincter, and that 

 no solid substances passed into the intestinal canal. One need 



