 (2015) showing "A. altus" as the basalmost diplodocid.In his 2006 re-evaluation, Carpenter examined the paleobiology of giant sauropods, including "Amphicoelias", and addressed the question of why this group attained such a huge size.He pointed out that gigantic sizes were reached early in sauropod evolution, with very large sized species present as early as the late Triassic Period, and concluded that whatever evolutionary pressure caused large size was present from the early origins of the group.