New Early Dinosaur Fossils Shift Family Tree

Scientists have discovered a four-foot-long, meat-eating dinosaur, with serrated teeth and long finger bones, that roamed the earth some 230 million years ago. The fossils are among the earliest dinosaur bones ever found, and the finding, which was published Thursday in the journal Science, has shaken up the creature's family tree.

The bones of the tiny dinosaur, which scientists have named Dawn Runner, or Eodromaeus murphi , were found encased in rock chunks in an arid Argentinian valley, known as "Valley of the Moon."

"It's significant for dinosaur origins because it's a relatively complete skeleton, and there's more than one of them," said Sterling Nesbitt, a paleontologist from the University of Washington, who specializes in early dinosaurs. "There are many questions, and the only way they can be answered is through new material."

Dawn Runner roamed the earth during the late Triassic era, before dinosaurs rose to dominance, when continents with vast desert belts were shoved together and primitive mammals and early crocodiles were abundant. It had grasping hands, walked on two feet and had air sacks in its neck vertebrae like a bird. It was svelte and scrappy, "not a big chunky bruiser animal by any means," said Mark Norell, chairman of paleontology at the American Museum of Natural History in New York City. "It was sort of the Kate Moss of the dinosaur world."

Paul Sereno from the University of Chicago was one of the two lead authors, along with Ricardo Martinez of the National University of San Juan in Argentina.

"It was a scrappy meat-eater that would come at you, and you'd be twisted around before you knew which way it went," Sereno said. "A 10 to 15-pound ball of energy. And it's got canines that are definitely for slicing and dicing meat."

Using bones from different dinosaurs, the paleontologists were able to piece together almost an entire skeleton and with it, more evidence of the beginnings of the dinosaur lineage. Scientists have identified the animal as a theropod, which means it may be a distant ancestor to both Tyrannosaurus Rex and modern birds.

The discovery has also led to the reclassification of the dinosaur, Eoraptor, which was discovered in the early 1990s by the same team. Eoraptor was originally thought to be a theropod, but this study redefines it as sauropod, an herbivore.

The finding may be controversial, Nesbitt, says, "because everyone has previously found Eoraptor to be a carnivorous dinosaur. It solves a couple questions, but creates a lot more to be answered." But, he adds, the paper puts forward convincing evidence.

"For me, the take home message is to realize that this is a good approximation of a primitive dinosaur," Sereno says. "Great things come from small beginnings like this. And...if you went back 230 million years ago, you'd likely be eaten by a crocodile. Dinosaurs would come and pick your bones."