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 the time of the creature's maturity. This was first noted in 1903 and again in 1936. Long-bone histology enables researchers to estimate the age that a specific individual reached. A study by Eva Griebeler etal. (2013) examined long-bone histological data and concluded the "Apatosaurus" sp.SMA0014 weighed , reached sexual maturity at 21years, and died aged 28. The same growth model indicated "Apatosaurus" sp.BYU 601–17328 weighed , reached sexual maturity at 19years, and died aged 31. Compared with most sauropods, a relatively large amount of juvenile material is known from "Apatosaurus". Multiple specimens in the OMNH are from juveniles of an