Postosuchus was lightly built for its large size and was originally reconstructed as a mostly bipedal animal. It was thought that it walked on two legs like a theropod dinosaur; but rested, fed, and drank on all fours. However, the posture of Postosuchus has been a topic of much debate. Later paleontologists regarded it as a quadruped that spent most of its time on four legs. Eventually, a new analysis of its skeleton in 2013 concluded that Postosuchus usually walked on two legs, after all.
Postosuchus was a meat-eating rauisuchid reptile with a deep snout and serrated dagger-like teeth. Unusually for a reptile it had straight legs and an upright stance. It could walk on its longer back legs, or sometimes on all fours. It had five-toed hands, four-toed feet, and a long tail. It had bony scutes distributed in rows along the top if its back and tail. Large adults reached up to 13 feet long.
Postosuchus hunted other large reptiles that lived alongside it. Its jaws had a particularly wide gape and some of the bones in its skull were flexible. These adaptations allowed it to bite and manipulate large chunks of flesh.
An expedition from Texas Tech University in 1980 discovered the remains of a new reptile in the Triassic mudstone of Garza County, West Texas. The animal was represented by three skeletons of young individuals and a skeleton of an adult. In the following three years, eight more skeletons were discovered in the same area. This wealth of material allowed paleontologists to conduct a detailed study of its anatomy, and in 1985 of a full description of this new carnivore was published.
It was named Postosuchus, meaning ‘Post crocodile’, in reference to the town of Post, near to where the remains were discovered. Some of the original skeletons described in 1985 actually belonged to different types of animals, but additional skeletons of Postosuchus have since been discovered in North Carolina and New Mexico. These provided even more accurate information on its anatomy, including bony armor that ran along the top of its spine.
Postosuchus belonged to a group of reptiles called rauisuchids, and it is one of the best known examples of this family. It is also one of the largest, and was the top carnivore during the late Triassic, about 210 million years ago.