WASHINGTON -- A fleet, long-legged lizard that darted onto the scene some 80 million years before the dinosaur is the first known creature to walk upright on two feet, according to an analysis of a new fossil.
In a study Friday in the journal Science, researchers say the lizard was a plant-eating reptile that probably used his speedy way of running to avoid meat-eaters that roamed Earth 290 million years ago.
Walking upright on two feet is an example of "repeated evolution," where a physical advantage evolved in different species at different times, said Robert Reisz, a University of Toronto researcher and co-author of the study.
Bipedalism developed independently in dinosaurs, which passed it on to birds, and it developed later in mammals, said Reisz.
"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."
Remains of the lizard were found in a German quarry. It took researchers more than two years to painstakingly remove the rock that encased the fragile, 10-inch-long fossil.
When the remains were analyzed, said Reisz, it was clear the lizard was a new species, now called Eudibamus cursoris, and that it was designed for swift, two-footed running.
"The most compelling evidence for bipedalism is the length of the hind limbs," said Reisz. "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 longer than the body. Trailing behind is a tail about as long as the body. The forelegs are short, as would be expected in a bipedal lizard, said the researcher.
"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," said David Berman of the Carnegie Museum of Natural History, first author of the study. "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 southwestern United States. There also is the Jesus Christ lizard, a remarkable Central American animal famed for being able to run across the surface of water.
"Modern lizards have been measured at about 12 to 13 miles an hour in short bursts," said Berman. "I think this animal (Eudibamus) would be faster than any modern lizard, maybe about 15 miles an hour."
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 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 were gone by the time dinosaurs appeared.
Just why it died off despite its speed, Reisz said, "we really don't know. It is one of those continuing mysteries."
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.
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