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Poposaurus
''Poposaurus'' is an extinct genus of pseudosuchian archosaur from the Late Triassic of the southwestern United States. It belongs to the clade Poposauroidea, an unusual group of Triassic pseudosuchians that includes sail-backed, beaked, and aquatic forms. Fossils have been found in Wyoming, Utah, Arizona, and Texas. Except for the skull, most parts of the skeleton are known. The type species, ''P. gracilis'', was described by M. G. Mehl in 1915. A second species, ''P. langstoni'', was originally the type species of the genus ''Lythrosuchus''. Since it was first described, ''Poposaurus'' has been variously classified as a dinosaur, a phytosaur, and a "rauisuchian".
Like theropod dinosaurs, ''Poposaurus'' was an obligate biped, meaning that it walked on two legs rather than four. However, as a pseudosuchian, it is more closely related to living crocodilians than to dinosaurs. ''Poposaurus'' is thought to have evolved this form of locomotion independently, possibly from early archosaurs' ability to high walk.
==Description==
''Poposaurus'' was about long, with the tail comprising about half the body length. It is estimated to have weighed around , with the largest individuals reaching .〔 The body of ''Poposaurus'' is laterally compressed, with a long and narrow hip structure. The pubis and ischium are elongated. The end of the pubis forms a distinct hook that is unique to ''Poposaurus'' and a few other early pseudosuchians. ''Poposaurus'' has five sacral vertebrae connecting the spine to the hip, three more than most early archosaurs. The hind legs are about twice as long as the arms and placed close together. Five digits are present on the foot, but the fifth is reduced to a small splint of bone next to the metatarsals. The middle three toes are well-developed, giving the foot a tridactyl appearance. The calcaneum bone extends far from the ankle to form a distinct heel.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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