Poposaurus is a genus of reptile from the Late Triassic. It was a crurotarsan archosaur which lived in what is now Wyoming, Utah, Arizona, New Mexico and Texas. The type species, Poposaurus gracilis, was described by M. G. Mehl in 1915. The second species, P. langstoni was originally the type species of the genus Lythrosuchus, however discovery of new specimens has led to it being reclassified within Poposaurus. Poposaurus gives its name to Poposauridae, a family of Late Triassic crurotarsans. Other members of the clade include Shuvosaurus, Sillosuchus and Effigia.