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Upright lizard leaves dinosaur standing

November 3, 2000
Web posted at: 6:27 AM EST (1127 GMT)

LONDON, England -- The first known creature to walk upright on two feet was not a dinosaur but a speedy, long-legged lizard, scientists have discovered.

The two-legged lizard scurried onto the scene some 80 million years before dinosaurs walked the earth, a fossil just discovered in a German quarry shows.

It took researchers more than two years to painstakingly remove the rock that encased the fragile, 25 cm (10 inch)-long fossil.

The lizard, about 30 centimetres long and weighing 0.45kg, was a plant-eating reptile.

Researchers believe the creature used his speed and unique way of running to avoid the hungry meat-eaters that roamed the world 290 million years ago.

Walking upright on two feet is an example of "repeated evolution," where a physical advantage evolves in different species at different times in history, Robert R. Reisz, a University of Toronto researcher, said.

Bipedalism passed on

Reisz, co-author of a study appearing on Friday in the journal Science, said bipedalism developed independently in dinosaurs, which passed it on to birds, and then later it developed in mammals.

"It was just such a good idea that it happened again and again," he said. "To find an example of an animal that did this before dinosaurs or mammals is particularly exciting."

When the remains were analysed, it was clear the lizard was a new species, now called Eudibamus cursoris, and that it was designed for swift, two-footed running, Reisz said.

"The most compelling evidence for bipedalism is the length of the hind limbs. They are much longer than the forelimbs and it would have been relatively awkward for this animal to move around on four legs."

The hind legs are actually longer than the body. Trailing behind is a tail that is about as long as the body. The forelegs are short, as would be expected from a bipedal lizard, the researcher said.

"If they (forelimbs) were longer, they would actually get in the way," Reisz said.

The formation where the fossils were found has been age-dated at about 290 million years. The first dinosaur is thought to have appeared about 210 million years ago.

"This little animal was built for speed," David S. Berman of the Carnegie Museum of Natural History and the first author of the study, said. "It was very, very fast."

Some modern lizards run on their hind feet, Berman said, including the fringe footed and collared lizard of the deserts in the U.S. Southwest.

There is also the Jesus Christ lizard, a Central American animal famed for being able to run across the surface of water.

"Modern lizards have been measured at about 20kph (12mph) in short bursts," said Berman. "I think this animal (Eudibamus) would be faster than any modern lizard, maybe about 24kph (15mph)."

That speed was essential to its survival, he said. The world 290 million years ago was populated with a variety of meat-eating reptiles, including the Dimetrodon, a fierce carnivore whose fossils were found in the same German quarry as the Eudibamus.

Even so, Berman said the Eudibamus and its close relatives made only a brief appearance in the fossil record and was gone by the time dinosaurs appeared.

But why they died off -- despite its speed advantage -- remains unknown, Reisz said.

Being able to walk upright on two feet gave Eudibamus a distinct advantage over most other reptiles that are destined to "sprawl and crawl" their way through life, he added.

Most modern lizards, such as Indonesia's Komodo dragon, move awkwardly, holding their entire weight off the ground by muscle power.

"These animals are actually doing continual push-ups to get their chest off the ground," said Reisz. "When you are upright, part of the weight is being borne by the skeleton itself, instead of the muscles. It is much more efficient."

The Eudibamus also had distinctive joints and feet, he said. The knee joint was like that of dinosaurs and humans, hinged so the lower leg swung forward freely.

The hip joint allowed the upper legs to extend directly under the upper body, unlike the joints of the sprawling reptiles. The legs could move forward from the hips while keeping the body upright and aligned with the forward motion. And the feet were oversized, with long middle toes.

"It ran on its toes, especially when it got going," said Berman. "That's what all fast animals do."

Reisz said the long tail helped the animal keep its balance as it raced. "The unusually long tail brings the centre of gravity close to the hips to help balance the front part of the animal."

Other paleontologists were excited by the new discovery. "When I first heart about this fossil, I was just amazed," Hans-Dieter Sues of the Royal Ontario Museum in Toronto said in Science. "I didn't expect a bipedal creature that far back in time."

The Associated Press contributed to this report.



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