The oldest dinosaur may have been shorter than former basketball star Wilt Chamberlain and lighter than football star William "Refrigerator" Perry.

It was puny for a dinosaur. It scampered along on the toes of its rear feet but had "large claws on its forelimbs, used to grasp prey," University of Chicago paleontologist Paul Sereno said Thursday.More importantly, Sereno and other scientists said they believe the first drawing of the ancient Herrerasaurus may reveal important clues into the evolution of dinosaurs.

"Before, only a few bones of Herrerasaurus were known," said Sereno. "Now, we have everything.

"Basically we have the first relatively complete idea of what the primitive form of the dinosaur looks like. This will help us in trying to figure out the pathways of evolution that proceeded over the course of many millions of years after that."

Scientists welcomed Sereno's work, presented Thursday in Austin, Texas, at meetings of the Society of Vertebrate Paleontologists.

"I think it's extremely important to know what the thing looks like in detail," said Nicholas Hotton, curator of fossils, amphibians and reptiles at the Smithsonian National Museum of Natural History. "If you've got that kind of information, you can tell which way evolution is going."

Sereno said the artist's reconstruction of the dinosaur - named after an Argentine goat herder - was based largely on the recent discovery of a skull and two nearly complete skeletons in South America.

Working with South American colleagues Alfredo Monetta and Jose Bonaparte, Sereno discovered the fossils in the Andes.

"There is definitely a certain amount of good fortune in these things," said Sereno, who last month won a $500,000 Packard Foundation Award that will allow him to continue work on the Herrerasaurus and other research projects, including a study of ancient birds.

The Herrerasaurus, which scampered the Earth some 230 million years ago, was Earth's first true dinosaur. "Basically, you go back further and you get dinosaur-type things but not a dinosaur," he said.

Herrerasaurus weighed a mere 300 pounds and stood between 6 feet and 8 feet tall, Sereno said. The Chicago Bears' Perry weighs in at 325 pounds, while Chamberlain stands 7 feet, 1 inch.