Abstract When E.D. Cope described the type specimen of Elasmosaurus platyurus 1868 more completely in 1869, he noted that a number of dorsal vertebrae were missing, along with the gastralia, the limbs, and most of the skull. Although the military surgeon who discovered the remains, Dr. Theophilus H. Turner, made additional searches the missing material was never located. Interest in the specimen eventually faded as dinosaurs were discovered further west, and portions of the specimen, including the pectoral and pelvic girdles, were mysteriously lost. More recently, three collections of associated plesiosaur material, including dorsal vertebrae, ribs, gastralia, and large gastroliths were made from a second site near the type locality of E. platyurus. The additional material is curated in the Sternberg Museum of Natural History, Hays, KS, the University of Kansas Museum of Natural History, Lawrence, KS, and the Cincinnati Museum Center, Cincinnati, OH. Examination the more recently discovered remains in these three repositories, and comparisons with the those of the type specimen at the Academy of Natural Sciences of Philadelphia, a review of the letters and other historical documents related to the discovery of E. platyurus, and on–site evaluation of the stratigraphy of the both localities suggest that the more recently collected remains were originally part of the type specimen and were separated prior to burial when the floating carcass began to fall apart.

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