Before we discuss Postosuchus, a short primer in evolution is in order. Starting in the middle Triassic period—about 230 million years ago—the prehistoric reptiles known as the archosaurs (“ruling lizards”) began to evolve in three separate directions: pterosaurs, prehistoric crocodiles and the first dinosaurs. In fact, for tens of millions of years, large, dinosaur-like archosaurs coexisted with two-legged crocodiles, which themselves bore an uncanny resemblance to the first true theropod dinosaurs—and if you think this sounds confusing, just place yourself in the shoes of a paleontologist trying to sort out the mess.
A true archosaur—despite its marked resemblance to the large theropod dinosaurs of the Jurassic period, and also despite the fact that the last part of its name is Greek for “crocodile”—Postosuchus was the apex predator of middle to late Triassic North America. In fact, when its fossils were first discovered, Postosuchus was assumed to be a theropod dinosaur, but closer analysis of its ankle bones (not to mention the very un-dinosaur-like plates along its back) revealed its true place on the reptile family tree. This large “rauisuchian,” as it’s known, preyed on the prehistoric crocodiles and small dinosaurs it so much resembled, and was doubtless preyed on by them in return (assuming they were smart enough to team up for the kill!)