TWENTY-FIFTH ANNUAL MEETING. 121 



AN INTERESTING FOOD HABIT OF THE PLESIOSAURS. 



BY S. W. WILLISTON, STATE UNIVEK8ITT, LAWBENOE. 



In the report on the geology of Kansas in the Frst Biennial Report of the State 

 Board of Agriculture, page 62, by Professor Mudge, occurs the following : "In the 

 Plesiosauri we found another interesting feature showing an aid to digestion, similar 

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

 bles, 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." As a mem- 

 ber of Professor Mudge's party, I have a very distinct recollection of the different 

 specimens which afforded these pebbles. The first, found by myself, had, scattered 

 among the ribs, a quart or more of the stones. The others gave a less number, but 

 they were found imbedded in the matrix surrounding the ribs. If my memory is 

 correct, all of the specimens belonged to the genus Polycot.yliis, and were of medium 

 size. The conclusion that the pebbles had been in the stomach of the reptiles was 

 irresistible, and was all the more interesting from the fact, as stated by Mudge, that 

 such stones were entirely foreign, otherwise, to the chalk. 



A little over a year ago, the University museum received from Mr. . of 



Ellsworth, Kas., a large plesiosaur vertebra and, with it, a rounded pebble, with the 

 request for information concerning both. At the first opportunity, I visited Ells- 

 worth, and, in company with Mr. , examined the locality whence they had 



been obtained, the bones were found in a poor state of preservation, from the 

 effects of frost, but, by carefully digging over the loosened shale and soil in which 

 they were contained, we succeeded in securing about 12.5 of the pebbles, together 

 with a number of characteristic bones. Some of the pebbles were attached by the 

 original soft limestone matrix to the ribs and thoracic vertebrae, so that that there 

 could not be a shadow of doubt of the contemporaneity of deposition. So remark- 

 able had these strange pebbles appeared to those persons who had visited the local- 

 ity, that many had been carried off as keepsakes, and were called "gizzard stones." 

 It was estimated that, first and last, but little less than a peck of them had been 

 found. 



The saurian is one of the largest of the order, measuring, when alive, probably 

 not less than 50 feet. Its specific, or even generic, determination is difficult at pres- 

 ent, owing to our lack of knowledge of the allied forms. I believe, however, that 

 it will prove to be a Trinacromerum. The pebbles are, all of them, extremely hard, 

 consisting almost wholly of silica. They vary in weight from less than 1 gram to 

 170 grams, and in their greatest diameters from about one-fourth of an inch to over 

 three inches. In color they are all conspicuous, either white, black, or pink, and all 

 show a great amount of abrasion. The smaller ones have been worn into more or 

 less perfect ellipsoids, and all are quite smooth. The larger ones have rounded 

 angles, indicating a less amount of abrasion. 



The pebbles undoubtedly formed a part of the contents of the stomach of the 

 saurian, and had as certainly been gathered up by the animal from the distant 

 beaches of the Benton sea. Professor Mudge states that many reptiles have this 

 habit of swallowing stones; but in this, I think, he was in error. Certainly no other 

 reptiles of the Kansas cretaceous have ever presented any evidence whatever of a 

 similar habit, and, I think, among living reptiles few, except the crocodiles, are 

 known to do so. The reptilian stomach never presents the strong, muscular struc- 

 ture of the gallinaceous birds, which thus use hard substances as an aid to digestion. 



At first sight, it will seem remarkable that so monstrous an animal could have 



