Postosuchus was a basal archosaur which lived in what is now North America during the middle through to the late Triassic period (228-202 million years ago). It was a rauisuchian, a cousin of crocodiles and came from the same ancestry as dinosaurs. Its name means "crocodile from Post", named after the Post Quarry in Texas, where many fossils of the species were found. It was one of the top 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.

Postosuchus was a quadrupedal reptile with a wide skull and a long tail. This carnivore attacked with its large curved claws. It was about 4-5 meters long (12-15 feet), and was held up by columnar legs (a quite uncommon feature in reptiles). A crocodile-like snout, filled with many large-sized dagger-like teeth, was used to kill its prey. Rows of protective plates covering its back formed a defensive shield.

A partial skeleton of Postosuchus from Durham County, North Carolina was discovered in 1994 and named in 2008 as new species P. alisonae. The specific name is in reference to Alison L. Chambers, who worked to popularize paleontology in North Carolina. The skeleton of P. alisonae consists of a few cranial bones, seven neck, one back, and four tail vertebrae, ribs, gastralia ("belly ribs"), chevrons, bony scutes, much of the shoulder girdles, most of the forelimbs except the left wrist and hand, most of the hindlimbs except for the thigh bones, and pieces from the hip. This specimen is unusual in preserving gut contents: bones from at least four other animals, including a partial skeleton of an aetosaurid, a snout, coracoid, and humerus of the traversodontid cynodont Plinthogomophodon, two phalanges from a dicynodont, and a possible temnospondyl bone. Furthermore, the Postosuchus was positioned on top of a skeleton of the sphenosuchian Dromicosuchus, which included tooth marks on the skull and neck.

It was a comtemporary of Gojirasaurus and Placerias