Postosuchus had rather short legs, a large head, and a long tail. It's skull was narrow and full of teeth. It was built for crushing prey, not slicing it. Small plates covered it's long back and formed armor. Postosuchus was acually distantly related to crocodiles. Although it's legs were short, they were underneath it's body, pointing out it was probobly a fairly fast runner, reaching speeds of perhaps 15 miles an hour.