People, birds and even many dinosaurs — two-legged runners all — were late starters in the evolutionary footrace, it turns out.
The first known animal to walk or run upright, a newly unearthed fossil shows, was a 10-inch lizard that raced on its two hind legs and inhabited a vast, long-vanished supercontinent known as Laurasia about 290 million years ago.
The newly discovered species, called Eudibamus cursoris, apparently didn't survive very long — perhaps no more than 30 million years — but it preceded the earliest bipedal dinosaur by at least 60 million years, its discoverers say.
The diminutive plant-eating lizard developed its ability to run upright at startling speeds in order to evade much larger meat-eating reptiles, they say.
The team of fossil hunters, led by David S. Berman of the Carnegie Museum of Natural History in Pittsburgh, Pa., and Robert R. Reisz of Canada's University of Toronto, found the reptile remains, almost perfectly preserved, in a German rock quarry.
The team reported on the unique find today in the journal Science.
Berman said in an interview that, based on the shape and size of the ancient reptile's leg and foot bones, he estimates the tiny creature's long strides could carry it across dry ground in bursts of speed reaching 20 mph.
"Who'd have ever thought that you'd find such a sophisticated little animal so very long ago?" Berman said with delight. "Most of the reptiles I've seen from that time were all sprawlers, not runners; they couldn't even do it on four legs."
The reptile's tail helped balance it and served as a rudder as it ran, and its short forelegs could pump like arms as it strode along — very much the way humans run today, Berman said. The shape of its teeth shows conclusively that it was a plant-eater.
A few modern species of lizards can run on two legs, but they bear only the most distant relationship to the fossil Eudibamus species, Berman said.
One is the famed Jesus Christ basilisk lizard of South America, so named because it moves so swiftly it can run atop water. The other is the common collared lizard, which inhabits arid regions of the American West, ranging from California to southern Colorado.
It appears that the evolution of body structures to permit bipedal walking and running must have occurred independently several times during the evolution of reptiles, said Reisz.
"It happened in some dinosaurs and their bird descendants," he said, "and it happened in mammals, so it must have been a good idea in terms of evolution."