When Xu studied the fossil over the next few weeks, though, it dawned on him what an odd creature he had discovered. It had four slender limbs and was covered in feathers from head to foot. It appears to have been adapted for gliding through the air from tree to tree, much like a present-day flying squirrel. He found to his surprise that several farmers had discovered similar fossils. He tested them with X-rays and found them to be authentic. “I thought, ‘Maybe this is the greatest discovery I’ve ever made’,” he told NEWSWEEK.

Xu’s dinos would make a valuable addition to any rogues’ gallery of terrifying creatures. Among the remains he and his team have studied is a new species of microraptor, a 120-million-year-old cousin of the velociraptors of “Jurassic Park.” Named Microraptor gui after a Chinese paleontologist, it measured just under a meter in length–about the size of a large eagle–but boasted sharp teeth and claws and an appetite for fresh meat. And it could swoop down from the treetops on unsuspecting ground-dwellers.

Xu’s findings, published last week in the journal Nature, have paleontologists buzzing with excitement. “This is clearly a really amazing specimen,” said Kevin Padian, a professor at the University of California, Berkeley. Scientists now generally agree that birds most likely descended from dinosaurs, and Xu’s find adds to the already solid body of evidence. But in other respects, his creature throws the field in disarray. Almost all feathered dinosaurs had feathers on their winglike arms but none on their hind legs, which tend to be big and powerful–suited to running fast. For this reason, scientists have favored the “ground up” hypothesis–that dinosaurs first sprouted feathers on their arms to help them run faster up hills, like partridges, and only later evolved the ability to fly. Xu’s creatures have skinny hind legs, and all four limbs are winglike. They suggest that some dinosaurs first took to the trees and evolved the ability to glide and later to fly. “The new fossil has provided very strong evidence that some dinosaurs were living in trees,” says Xu.

The idea that birds might have evolved from dinosaurs is about as old as Darwin’s theory of evolution. The first fossil evidence of a link was Archaeopteryx, a 150-million-year-old birdlike reptile found in 1860 in southern Germany. Although commonly considered to be the first bird, scientists have been trying to connect the dots ever since. In 1915, zoologist William Beebe ventured that birds evolved from four-winged dinosaurs, but he had no evidence. Scientists wrote off his idea as speculation, but he now seems prescient.

The new four-winged dinosaurs are still giving scientists plenty to argue about. Padian, for one, is cautious about Xu’s claim that Microraptor gui lived in trees and glided like a squirrel. “That’s a big thing to say,” he says, “so you have to test it.” Mark Norell, chairman of the department of paleontology at the American Museum of Natural History in New York, has examined the specimens himself. “It looks unlike anything we ever knew existed,” he says. But he doesn’t think the find is the last word on birds and dinos. Most likely, scientists will find places in the evolutionary tree for both dinosaurs who learned to fly on the ground and in trees.

For the time being, the 34-year-old Xu, who led the team from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, is enjoying all the fuss. Growing up in a remote village in China’s western Xinjiang province, Xu wanted to go into computer technology or business, but didn’t have guanxi–the right connections. So he wound up in paleontology instead. Now he’s glad of it. “I feel like I’m the most lucky paleontologist in the world,” he says. And his career is just starting to take wing.