Ancient Crocodile Fossil Defies Dinosaur Label

July 6, 2005 — -- 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.

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.