Ancient Crocodile Fossil Defies Dinosaur Label

In the world of dinosaurs, the species known as Revueltosaurus callenderi was the Rodney Dangerfield of dinosaurs. It was only about three or four feet long, an ugly critter that is little more than a footnote in the dinosaur record.

But these days it's getting a lot more respect. Until last year, paleontologists had no more than teeth and a few scattered bones, which may or may not have come from the same animal, but they were pretty sure that Revueltosaurus was a member of one of two lines of dinosaurs that emerged at about the same time, during the late Triassic Period more than 210 million years ago.

Since teeth are usually the only thing that survives in the fossil record for that many years, numerous other animals with teeth similar to Revueltosaurus's were classified as dinosaurs also.

And that's the way it stayed until Bill Parker, a paleontologist at the Petrified Forest National Park in Arizona, dug down in the dry soil there last year and found a complete skull -- and later an entire skeleton -- of Revueltosaurus, teeth and all.

That little find has sent the world of paleontology into a tailspin. Revueltosaurus, it turns out, wasn't a dinosaur at all. It was an early ancestor of a modern crocodile.

The Triassic's Two Classes of Dinos

It's a stunning development because Revueltosaurus is only one of many late Triassic animals known only by their teeth that were thought to be the ancestors of plant-eating dinosaurs. But the fact that the teeth came from an early crocodile, and not from a dinosaur, suggests that many of the animals that roamed North America more than 200 million years ago have been erroneously classified as dinosaurs.

"Because the teeth look like those we know from herbivorous ornithischians (one line of dinosaurs) people assigned them to the dinosaurs," says Randall Irmis, a graduate student at the University of California, Berkeley, who has been working with Parker. But the latest discovery shows that the dental record is not a reliable factor, and that "casts doubt on all the ornithischians from the Triassic of North America," Irmis says.

"There's two main groups of dinosaurs, ornithischian dinosaurs like Stegosaurus and Triceratops, and then there's the saurischian dinosaurs which are your big dinosaurs like Brontosaurus and later, large meat-eating forms," Parker says.

"The Triassic is supposedly the period when both of these branches formed, and we have lots of saurischian dinosaurs, but the ornithischian record is really, really spotty. All we have are teeth which are supposed to be ornithischian. So by finding a crocodilian with these teeth suddenly you can't say that all these teeth belonged to dinosaurs. We've wiped away the entire ornithischian dinosaur record for the late Triassic," Parker says.

Parker and his colleagues reported their findings in the journal of the Proceedings of the Royal Society, Biological Sciences.

The Old Stomping Grounds

The animal they exhumed once roamed an area that looked far different than it does today. The Petrified Forest National Park, known primarily for the fossilized remains of what was once a great forest, is also one of the richest repositories of ancient fossils in North America, if not the world.

Today it is an arid desert, but in the late Triassic it was more like an oasis with rivers that harbored all sorts of life.

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