Chinese researchers announced Wednesday the discovery of a feathered dinosaur that glided on four wings -- a diminutive plumed dragon that could be a long-sought evolutionary link between dinosaurs and the first true birds.
As the remnants of nature's earliest experiments with avian flight, they rank among the most important fossil finds of the last century, several experts on avian evolution said. They reveal the distant past as a foreign country in which creatures soared on four wings, not two, and predators prowled in suits of down.
The curled and crushed skeletons of Microraptor gui, as the new creature is named, preserve clear impressions of long, aerodynamic feathers. The feathers form airfoils along spindly arms and legs in what appear to be both forewings and hind-wings. The dinosaur, measuring about 30 inches in length, also has a long, feather-fringed tail.
The discovery lends weight to the idea that feathered flight began with creatures like these flapping between the treetops of ancient forests, not with small downy dinosaurs skittering along the ground, as many other experts have theorized.
"It's an incredible discovery, the kind of thing that we've wished for, well, for centuries now," said Kevin Padian, a paleobiologist at UC Berkeley who studies the origins of flight.
Luis Chiappe, an expert on avian evolution at the Los Angeles County Museum of Natural History who has examined the fossils, pronounced the creature "the winged Mercury of the dinosaur world," referring to the divine messenger of mythology who had wings on his feet.
So far the researchers, whose findings were published today in the journal Nature, have found six relatively complete fossilized skeletons of the creatures, all unearthed from deposits of volcanic and sedimentary rock in northeastern China's Liaoning province.
All six specimens indicate that the body of the dinosaur was covered with inch-long feathers. The wing feathers were almost 5 inches long, with vanes that resembled modern flight feathers. Such long feathers around the feet would make it hard for the animal to run on the ground, the researchers said, lending credence to the idea that it was a tree dweller.
The four-winged Microraptor lived in China about 128 million years ago, some 20 million years after the appearance of Archaeopteryx, a two-winged flier widely considered to be the first bird. It in turn gave rise to an estimated 9,000 species worldwide today.
The Microraptor may have lived after the first bird evolved, but it belongs to a much older family of small feathered predatory dinosaurs that predate the origin of birds, said ornithologist Richard Prum at the University of Kansas in Lawrence. Its distinctive wings, like its feathers, are holdovers from an earlier day.
The newly discovered dinosaur "takes a critical position in the evolution of flight," said paleontologist Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, who led the team that analyzed the finds.
"We now know the closest relatives of birds have four wings and live in trees," Xu said.
The fossils were discovered at two sites about 20 miles apart near the town of Chaoyang.
Xu and his colleagues excavated one fossilized skeleton in 2001 and purchased four others from local farmers who regularly comb the bone deposits for new specimens. The sixth specimen was purchased by the Tianjin Museum of Natural History last year.
In the last five years, these deposits have yielded a steady stream of unusually well-preserved fossils of unique dinosaurs and at least one embarrassing forgery of a purported missing link between dinosaurs and birds.
The researchers took care to test the authenticity of the Microraptor fossils. Xu and his colleagues subjected them to computerized X-ray analysis and assured themselves the specimens were genuine.
Many earlier finds forced scientists around the world to rewrite the book of life. In the same way, the newest fossils to emerge from Liaoning will require scientists to reconsider much of what they had taken for granted about how birds first took wing.
"These are weird animals," said paleontologist Mark Norell at the American Museum of Natural History in New York. "We can create lots of scenarios about what was going on with them, but they require tests -- computer simulations, models, aerodynamic studies -- to pin it down."
The kinship of birds and dinosaurs was a radical notion not so many years ago, but today it is conventional wisdom. Even so, no one is sure just how the animals first took to the air.
Just as feathers came before birds, so perhaps did true wings and some form of primitive flight. The Microraptor discovery "suggests the dinosaurian ancestor of birds first learned to glide by taking advantage of gravity before flapping flight was acquired in birds," Xu said. "Four wings might make gliding easier."
While enthusiastic about the discovery, several experts questioned the biomechanics of the creature's shoulder sockets, hip joints and limbs. Do they fit together in a way that could have allowed the animal to move its feathered limbs as wings?
Even if the animal could glide effectively, there is no reason to assume that ability led directly to the evolution of flight in birds, the experts said.
It is too soon to know whether these creatures truly flapped their wings, soared, glided, parachuted or flew in some other as yet undetermined mode. Multiple sets of wings could have been fairly common -- or, just as easily, an evolutionary dead end.
"Was this one really on the direct line of bird evolution, or was it a side branch, something that evolved those peculiar feathers?" Chiappe asked. "Evolution was experimenting with many designs."