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 names; he grouped "Apatosaurus" within Opisthocoelia. Sauropoda is still used as the group name. In 2011, John Whitlock published a study that placed "Apatosaurus" a more basal diplodocid, sometimes less basal than "Supersaurus". Cladogram of the Diplodocidae after Tschopp, Mateus, and Benson (2015). It was believed throughout the 19th and early 20th centuries that sauropods like "Apatosaurus" were too massive to support their own weight on dry land. It was theorized that they lived partly submerged in water, perhaps in swamps. More recent findings do not support this; sauropods are now thought to have been fully terrestrial animals. A study