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Elasmosaurid plesiosaur remains containing gastroliths have been recently recovered from the Late Cretaceous Cape Lamb Member of the Snow Hill Island Formation, Antarctic Peninsula, as well as from the Sharon Springs Formation of the Pierre Shale Group, South Dakota. The significance of the Antarctic specimens lies in the large number and relatively small size of the stones, whereas those from South Dakota and elsewhere have larger stones but relatively small numbers. All specimens compared are of relatively large elasmosaurids, and rib diameters indicate similar overall size. One testable hypothesis was whether or not the weight of the gastroliths might be similar among similarly sized individuals. However, comparisons between the gastroliths recovered from an Antarctic specimen and those recovered from the Pierre Shale show great differences in both the size and number of gastroliths. The total mass of the stones collected in the specimen from Antarctica was 3.0 kg, whereas those recovered from the South Dakota specimens totaled 2.2 kg and 8.3 kg, respectively. Perhaps not all stones originally within each plesiosaur were found, but efforts were designed to recover every stone. The number of stones recovered from the Antarctic plesiosaur was exceptionally large (2626) and appears to represent the most gastroliths recovered from a single plesiosaur. Those recovered from South Dakota elasmosaurids totaled only 124 and 253, respectively. Therefore, neither weight nor number of stones corresponds among these large individuals, perhaps mirroring the temporal or behavioral differences. Lack of correspondence among individuals furthers questions concerning the utilization of gastroliths for neutral buoyancy, ballast, or as an aid in digestion. Many parameters remain unexplored, and questions arise not only as to the utilization of the gastroliths but also as to whether physiology of the Antarctic plesiosaurs differs from those at lower latitudes.

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