The history and composition of the Carnegie Diplodocus

Diplodocus is a sauropod dinosaur from the Upper Jurassic Morrison Formation of North America. It is known around the world primarily because of a single skeleton, that of the Carnegie Diplodocus, because the millionaire industrialist Andrew Carnegie had casts of this specimen mounted in nine prominent cities around the world between 1905 and 1930. As well as these iconic casts, the original fossil material was mounted at the Carnegie Museum (now Carnegie Museum of Natural History) in 1907, and underwent a series of minor changes through the years before a major remount as part of the Carnegie's Dinosaur Hall renovation in 2005–2007. The composition of the original mount was never fully described, and the changes made since the initial mount have not been extensively documented. The bulk of the skeleton consists of bones from the Diplodocus carnegii holotype CM 84. The paratype CM 94, a referred specimen CM 33985, and a specimen of a related species CM 307 all provide additional fossil material. However, significant parts of this mount are casts or sculptures, including the skull, atlas, numerous caudal vertebrae, forelimbs (including forefeet), and most of the left hindlimb. The left forelimb and both forefeet used in the original mount were cast from a camarasaurid, and the right forelimb from that of the diplodocine Galeamopus (= “Diplodocus”) hayi. The humeri, radii, and ulnae were replaced in the 2007 remount by scaled-up sculptures based on probable diplodocid elements; and the forefeet by scaled- up sculptures of another diplodocine specimen. Numerous divergent length measurements exist for this specimen, but the current mount is about 26.1 m long based on photogrammetric and LIDAR models