| Named By: | M. G. Mehl in 1915 |
| Time Period: | Late Triassic, 216 Ma |
| Location: | USA, including Arizona - Chinle Formation (Blue Mesa Member, Mesa Redondo Member, Owl Rock Member, Petrified Forest Member, Sonsela Member), Texas - Colorado City Formation, Cooper Canyon Formation, Tecovas Formation, Utah - Chinle Formation (Monitor Butte Member) and Wyoming - Popo Agie Formation |
| Size: | Up to 4 meters long |
| Diet: | Herbivore |
| Fossil(s): | Fossils of various individuals revealing almost all of the post cranial skeleton. Partial skull remains are also known |
| Classification: | | Chordata | Reptilia | Rauisuchia | Paracrocodylomorpha | Poposauroidea | Poposauridae | |
| Also known as: | | Lythrosuchus | |
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.