Apatosaurus of gigantic sauropod dinosaurs. The family includes some of the longest creatures ever to walk the earth, including "Diplodocus", "Supersaurus", and "Barosaurus". "Apatosaurus" is sometimes classified in the subfamily Apatosaurinae, which may also include "Suuwassea", "Supersaurus", and "Brontosaurus". Othniel Charles Marsh described "Apatosaurus" as allied to "Atlantosaurus" within the now-defunct group Atlantosauridae. In 1878 Marsh raised his family to the rank of suborder, including "Apatosaurus", "Atlantosaurus", "Morosaurus" (="Camarasaurus") and "Diplodocus". He classified this group within Sauropoda, a group he erected in the same study. In 1903 Elmer S. Riggs said the name Sauropoda would be a junior synonym of earlier
Apatosaurus of another "Apatosaurus" individual originally described as "Atlantosaurus immanis"; as a consequence, some elements cannot be ascribed to either specimen with confidence. Marsh distinguished the new genus "Apatosaurus" from "Atlantosaurus" on the basis of the number of sacral vertebrae, with "Apatosaurus" possessing three and "Atlantosaurus" four. Two years later, Marsh announced the discovery of a larger and more complete specimen at Como Bluff, Wyoming. He gave this specimen a new name based on the conventions of his age and the relatively sparse fossil record available at that time. It was later recognised that the features he had used to distinguish