of one of its hindmost tail-vertebrae. A specimen of the closely related Styxosaurus contained fragmented fish bones and stones in the abdominal region behind the pectoral girdle. The fish remains were identified as Enchodus and other clupeomorph fish. The stones match rock from away from where the specimen was found. Several different functions have been proposed for gastroliths, including aiding in digestion, mixing food content, mineral supplementation, and storage and buoyancy control. Elasmosaurid remains provide some evidence they were preyed upon. A humerus of an unidentified subadult elasmosaurid was found with bite marks matching the teeth of the shark Cretoxyrhina, while a crushed Woolungasaurus skull has tooth-marks matched to the pliosaur Kronosaurus. Paleoecology Elasmosaurus is known from the Sharon Springs Member of the Campanian-age Upper Cretaceous Pierre Shale formation of western Kansas, which dates to about 80.5million years ago. The Pierre Shale represents a period of marine deposition from the Western Interior Seaway, a shallow continental sea that submerged much of central North America during the Cretaceous. At its largest, the Western Interior Seaway stretched from the Rockies east to the Appalachians, some wide. At its deepest, it may have been only deep. Two great continental watersheds drained into it from east and west, diluting its waters and bringing resources in eroded silt that formed shifting river delta systems along its low-lying coasts. There was little sedimentation on the eastern margin of the Seaway; the western margin accumulated a thick pile of sediments eroded from the western land mass. The western shore was thus highly variable, depending on variations in sea level and sediment supply. The soft, muddy sea floor probably received very little sunlight, but it teemed with life due to steady rains of organic debris from plankton and other organisms farther up the water column. The bottom was dominated by large Inoceramus clams, which were covered with oysters; there was little biodiversity. Clam shells would have accumulated over the centuries in layers under the sea floor's surface, and would have provided shelter for small fish. Other invertebrates known to have lived in this sea include various species of rudists, crinoids and cephalopods (including squids and ammonites). Large fish known to have inhabited the sea include the bony fishes Pachyrhizodus, Enchodus, Cimolichthys, Saurocephalus, Saurodon, Gillicus, Ichthyodectes, Xiphactinus, Protosphyraena and Martinichthys; and the sharks Cretoxyrhina, Cretolamna, Scapanorhynchus, Pseudocorax and Squalicorax. In addition to Elasmosaurus, other marine reptiles present include fellow