Chinese scientists have unearthed the fossils of a small, four-winged, feathered dinosaur that they say may have flown by gliding from trees. The novel anatomy may help explain the origins of flight.
Few scientists doubt that birds are close relatives of dinosaurs because the two species share a similar body design. Now, researchers led by Xing Xu of the Chinese Academy of Sciences say the nearly 130 million-year-old fossils they dug up in Liaoning Province provide new information important for understanding how birds evolved from dinosaurs.
As they report in the journal Nature, the six one meter-long dinosaur specimens have feathered wings on both their hindlimbs and their forelimbs, an anatomy never before seen in dinosaur remains.
The animal is a small member of the branch of meat-eating, two-legged dinosaurs that are anatomically closest to birds and gave rise to the giant Tyrannosaurus rex.
The Chinese scientists suggest that, with four wings and a long feathered tail, these animals probably could glide from tree to tree, like flying squirrels.
At the American Museum of Natural History in New York, dinosaur hunter Mark Norell agrees. "If I were placing bets on it, I would say the odds are that it was a glider," he said.
Mr. Norell has also dug up feathered dinosaurs in Liaoning Province. Last March, he reported a discovery similar to the latest one. It was a larger specimen with modern veined feathers on its hindlimbs. But his fossils were not detailed enough to describe their entire structure, as the Chinese researchers have done.
"At the time, everybody thought that I was nuts, but this really vindicates that there actually are animals that have seemingly airfoils [wings] on their hind limbs," he said.
The Chinese scientists say their discovery shows that some dinosaurs moved into trees close to the transition to birds. As for the fate of the hind wings, the researchers believe they were lost as flight evolved.
The discovery is certain to revive the century-old debate on the origin of flight. Some scientists argue that flight began in ground animals through a powered running stage. But others say flight arose in tree-dwelling creatures through an intermediate gliding stage, and University of Kansas bird expert Richard Prum says the latest discovery supports this notion.
"What this new fossil points out quite strongly is that there was a new anatomy that we didn't know that indicates that there was a gliding stage early in avian flight," he said. "This is pretty critical evidence against the hypothesis that birds started flapping directly from the ground."
But Mark Norell of the American Museum of Natural History says that, before he is fully convinced, he must see more evidence such a dinosaur actually could glide and where it belongs in the dinosaur lineage.
"It's going to take a lot more work to really figure out exactly what the role of this animal is in the whole story of the origin of flight," he said.