Poposaurus, Postosuchus, and the Dinosaur Mimic Croc Walk
by Brian Switek
Poposaurus walked like a dinosaur. That’s weird, because the Triassic critter wasn’t a dinosaur at all, but a peculiar archosaur more closely related to crocodiles. Even though paleontologists traditionally thought that dinosaurs had an immediate edge over all over forms of Triassic life thanks to muscular legs held close together right beneath their bodies, rather than sprawled out to the sides, there were also croc copycats that cramped dinosaurian style.
Two years ago, I wrote a short ScienceNOW piece aboutPoposaurus and a monograph describing the creature’s postcranial skeleton. Even though the 225 million year old archosaur was named almost a century ago, it has only been recently that more complete individuals have shown how strange Poposaurus truly was.
In the big picture of archosaur evolution, Poposaurus was a pseudosuchian – a group solely represented by alligators, crocodiles, and gharials today, but encompassed a surprising and frightening array of related lineages in the deep past. Roughly, the pseudosuchians are “croc-line archosaurs.” The group not only includes scattered modern species, but totally extinct groups such as the “armadillodile” aetosaurs, terrifying rauisuchians, and the strange lineage of animals that Poposaurus belonged to, called poposauroids, which included bipedal herbivores and sail-backed carnivores such as Arizonasaurus in their ranks…