As originally described by Cope (1868), the type specimen of Elasmosaurus platyurus from western Kansas included more than 100 vertebrae, portions of the skull, and the reasonably complete pectoral and pelvic girdles of what was then the largest known plesiosaur. Within four years of its discovery, however, both of the limb girdles had disappeared with no official explanation. Here we document the events leading up to the loss of important portions of this unique specimen.