An Elasmosaur with Stomach Contents and Gastroliths from the Pierre Shale (Late Cretaceous) of Kansas

Abstract

A nearly complete skeleton of an elasmosaurid plesiosaur (NJSM 15435) from the Sharon Springs Member (Middle Campanian) of the Pierre Shale, Logan County, Kansas, is associated intimately with fragmentary fish remains and numerous gastroliths. The fish bones and gastroliths were located just behind the pectoral girdle in the abdominal region. Identifiable prey includes Enchodus and other small clupeomorph fishes. An isolated tooth of the anacoracid shark Squalicorax cf. S. pristodontus also was recovered in this area. Ninety-five gastroliths (6.8 kg) were present, with the largest stone measuring 15.1 × 8.5 × 5.7 cm (5.0 × 3.3 × 2.2 in.) and weighing 1.06 kg (2.3 lb.). Many of the gastroliths are composed of pink or gray Sioux Quartzite, which suggests that the source of these stones was about 600 km (475 mi) to the northeast of where the elasmosaur remains were discovered. The association of fragmentary fish remains and gastroliths within the abdomen of NJSM 15435 supports the contention that the stones aided in the breakdown of food in plesiosaurs.