Fossil of early, 3-foot dinosaur found 'Eoraptor' offers important clues

January 06, 1993|By Douglas Birch | Douglas Birch,Staff Writer

WASHINGTON -- A team of scientists working in Argentin has found the closest thing yet to the granddaddy of all dinosaurs, an artful dodger that was about the size of a small dog and sprinted after prey on its hind legs.

The creature, named Eoraptor by its discoverers, appeared only 1 or 2 million years after the first dinosaur evolved from a line of ancient reptiles.

"We're just a few steps away from the common ancestor" of all dinosaurs, Paul Sereno, a University of Chicago paleontologist, said at a news conference yesterday. "Eoraptor may be the closest we ever come."

The 35-year-old scientist, who led the U.S.-Argentine expedition that discovered the creature, said the finding supports theories that the earliest dinosaurs were small, carnivorous animals that walked on two legs. Geological evidence suggests that the fossil is 225 million to 230 million years old.

It is one of the two earliest dinosaurs found. The other, which lived about the same time, was the meat-eating, 15-foot long herrerasaur, also found in Argentina. But Dr. Sereno said Eoraptor was clearly a more primitive kind of animal.

Eoraptor had the teeth and claws of a carnivore, he said, making it an ancestor to a group of meat-eating dinosaurs called theropods, which included the towering tyrannosaur. But the ancient creature lacked the flexible jaws and broad pelvic bones of its descendants, he said.

David Weishampel, a paleontologist who teaches at the Johns Hopkins School of Medicine, said the fossil will help scientists understand the rapid increase in the number of dinosaur species after their first appearance.

"We know very little about the first ones, the most primitive forms," he said. "It's always a good idea to have a good idea about who's there at the very beginning, because they'll tell us a lot about the historical pathways followed by the descendants."

After they appeared, the dinosaurs quickly won out over mammals and other land animals for dominance of the earth. They ruled for 165 million years -- far longer than the 4 million years mankind has existed -- until some catastrophe, possibly the impact of a giant asteroid, wiped them out.

But when Eoraptor was scrambling around, there were relatively few dinosaurs. Asked to rate the importance of the discovery, Dr. Weishampel said, "On a scale of one to 10? A hair less than 10."

The first formal reports of the discovery appear in this month's National Geographic magazine and in this week's Nature, a British journal.

Scientists found Eoraptor Oct. 3, 1991, in a vast, dusty badlands called the Ischigualasto Valley, at the foot of the Andes in northwestern Argentina.

After five weeks of scouring the barren hills for fossils, "we were starting to wonder whether we were going to find what we were looking for," recalled Catherine Forster, Dr. Sereno's graduate student assistant.

But Argentine student Ricardo Martinez stumbled on an odd-shaped rock with a single, blackened tooth exposed.

The rock turned out to be Eoraptor's skull. Mr. Martinez had lifted it off what turned out to be an almost intact skeleton, making the find the paleontologist's equivalent of a grand-slam home run.

The fossil was sent to Chicago, where a specialist at the Field Museum of Natural History separated it from the surrounding rock. After studying the specimen, Dr. Sereno and his team decided to call it Eoraptor, which means "dawn stealer."

That's because the creature emerged near the dawn of the dinosaur era, Dr. Sereno said. And, based on its small size and light bones, the animal probably depended more on stealth than size to catch its prey.

The fossil eventually will be returned to a museum in Argentina.

Judging from tooth marks on some of the bones, he said, another animal came along to nibble on the carcass. But not for long. Soon it was buried in about a foot of sediment, probably from seasonal flooding.

Dr. Sereno compared the discovery to finding the earliest bones of human ancestors in Africa. He would have been delighted if his team had found the original dinosaur, he said, but "to come this close is pretty exciting."

Baltimore Sun Articles
|
|
|
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.