Postosuchus, meaning “Crocodile from Post”, is a genus of rauisuchid reptiles comprising two species, P. kirkpatricki and P. alisonae, that lived in what is now North America during the Late Triassic. Postosuchus is a member of the clade Pseudosuchia, the lineage of archosaurs that includes modern crocodilians (the other main group of archosaurs is Avemetatarsalia, the lineage that includes non-avian dinosaurs and their descendants, birds). Its name refers to Post Quarry, a place in Texas where many fossils of the type species, P. kirkpatricki, were found. It was one of the apex predators of its area during the Triassic, larger than the small dinosaur predators of its time (such as Coelophysis). It was a hunter which probably preyed on dicynodonts and many other creatures smaller than itself.
The skeleton of Postosuchus is large and robust with a deep skull and a long tail. The total body length is about 4 to 5 metres (13 to 16 ft). The extreme shortness of the forelimbs relative to the hind limbs, the very small hands, and measurements of the vertebrae suggest that Postosuchus may have been committed to bipedal locomotion.
Postosuchus was one of the largest carnivorous reptiles during the late Triassic. Adults reached around 1.2 m (3.9 ft) in height, 4 m (13 ft) in length from snout to tail tip and their mass might have ranged from 250 to 300 kg (550 to 660 lb). It had a massively built skull bearing dagger-like teeth. The neck was elongated, expanding to a short torso and long tail. Along with remains of the skeleton, paleontologists also identify osteoderms, which were thick plates forming scales. These were on its back, neck, and possibly above or under the tail.
Postosuchus lived in a tropical environment. The moist and warm region consisted of ferns, such as Cynepteris, Phelopteris and Clathropteris, gymnosperms, represented by Pelourdea, Araucarioxylon, Woodworthia, Otozamites and Dinophyton, and cycads like Sanmiguelia. Plants of the Dockum Group are not well known since the oxidizing of the environment has destroyed most of the plant fossils. However, some of them may provide information about the climate in Dockum Group during the late Triassic period. For example, the discovery of large specimens belonging to Araucarioxylon determine that the region was well watered. The fauna found in Dockum Group confirm that there were lakes and/or rivers containing fish such as the cartilaginous Xenacanthus, the lobe-finned Chinlea and the dipnoan Ceratodus. On the shores of these rivers lived labyrinthodonts (Latiscopus) and reptiles such as Malerisaurus and Trilophosaurus. Also living on the margins of the lakes were the archosaurs Leptosuchus, Nicrosaurus and Rutiodon. Postosuchus lived in the uplands along with Coelophysis and other archosaurs such as Desmatosuchus and Typothorax. Postosuchus was one of the largest animals in that ecosystem and preyed on herbivores such as Trilophosaurus and Typothorax.