Dystrophaeus

Discovery and naming Few dinosaur fossils had been collected in the American West until the 1850s, with expeditions by naturalists like Joseph Leidy and Ferdinand Vandeveer Hayden in South Dakota and Montana finding fragmentary fossils, mostly teeth, from dinosaurs in 1855 and 1856. which launched another expedition to the site the same year to recover additional material left behind by the Macomb Expedition. Another expedition was launched in 2017, the two recent expeditions recovering various elements including teeth, vertebrae, and additional limb bones, though many remain unprepared. == Description ==

Not much can be surmised due to the fragmentary nature and uncertain phylogenetic position of Dystrophaeus. As a sauropod, Dystrophaeus would have been a large, long-necked herbivore. It would have been of moderate size for a sauropod; it may have been approximately long, with a mass of roughly . The ulna of the only known specimen is long; for comparison, the ulna of the holotype of Camarasaurus lewisi is . The scapula bears a subtriangular projection on the base of the scapular blade, which Tschopp et al.'s analysis found to be an autapomorphy of the taxon, though this trait also occurs in various other sauropods. The ulna is very slender, and the metacarpals are relatively short. == Classification ==

The classification of Dystrophaeus has been rather confusing. Cope in 1877 merely concluded it was some Triassic dinosaur. Tschopp and colleagues included D. viaemalae in a phylogenetic analysis in 2015, and found its phylogenetic position to be highly unstable. They concluded that positions in Dicraeosauridae or Camarasauridae were equally well-supported, but that it was probably not a diplodocid, and concluded that further study was required to determine its affinities. However, many researchers consider the taxon to be a nomen dubium. Newer finds of Dystrophaeus have led paleontologist John Foster and colleagues to suggest it was most closely related to Macronarian or Eusauropod dinosaurs, although much material has yet to be prepared. According to Foster, the newly found teeth and caudal vertebrae suggest diplodocid affinities are unlikely. ==Notes==