Crocodile Morphing 2

The fossilized skeleton of a small crocodile relative excavated last year at Petrified Forest National Park in Arizona throws a wrench into theories of how and where the dinosaurs arose more than 210 million years ago at the end of the Triassic Period.

The animal, one of many creatures from the Late Triassic known only from their teeth, was thought to be an ancestor of the plant-eating ornithischian dinosaurs like Stegosaurus and Triceratops, which roamed the world millions of years later in the Jurassic and Cretaceous periods.

The fact that this presumed dinosaur, Revueltosaurus callenderi, is instead a crocodile ancestor does not merely disappoint rockhounds, who sell the abundant teeth as "dinosaur teeth," but it also throws into question the identity of other presumed dinosaur ancestors known only from teeth, which includes all Late Triassic ornithischians outside South America.

"Because the teeth look like those we know from herbivorous ornithischians, people assigned them to the dinosaurs," said Randall Irmis, a graduate student in the Department of Integrative Biology and the Museum of Paleontology at UC Berkeley. "We think we've shown that you can't rely on the dentition to determine what is an early dinosaur, which casts doubt on all the ornithischians from the Triassic of North America."

This suggests, he said, that the herbivorous ornithischians and the meat-eating theropods, like Tyrannosaurus rex, did not evolve together in the Late Triassic as many paleontologists thought. Rather, the theropods were well established worldwide before the ornithischians spread out into North America, Europe and Africa at the very end of the Triassic, perhaps from possible origins in South America.

"We have pretty much erased the record of Triassic ornithischian dinosaurs from North America, Europe and worldwide, except for South America," said the fossil's discoverer, park paleontologist William Parker. "Even the fossils in South Am
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Source:University of California - Berkeley