An exceptionally preserved skeleton of a petite dinosaur clad in a jacket of downy feathers is more evidence that feathers arose for warmth, not for flight, scientists announced today.

The fossil is the first feathered dinosaur discovered with its fluffy body covering fully preserved and scientists claim the find provides further evidence for the theory that modern birds evolved from meat-eating dinosaurs.

Over the last two decades, most paleontologists have accepted the theory that present-day birds evolved from a group of meat-eating dinosaurs known as theropods. A minority remain skeptical, claiming that the evolutionary timing can't make sense. This specimen bolsters arguments that our fine feathered friends did evolve from dinosaurs.

The unique fossil also offers clues about why feathers arose in the first place.

Oversized Duck

The creature is a dromaeosaur — a group of small predators related to the Velociraptor — which traveled on two legs. Since the creature walked and most certainly didn't fly, Mark Norell, chairman of paleontology at the Museum of Natural History in New York and an author of the report published this week in Nature, says the 2-foot-long fossil proves that feathers first developed for warmth rather than flight.

"This specimen really nails it," says Norell. Warmth, he says, "is what the origin of feathers was really all about." To the naked eye, downy impressions can be seen sprouting from all over the animal's body.

The fossil was found flattened in light gray, fine-grained shale that has been split into two mirroring pieces. Resembling an oversized duck with teeth, its large head indicates it died as a juvenile, researchers say. It is dated between 126 million and 147 million years old.

Farmers carved the fossil from the famous Liaoning fossil beds in northeastern China last spring, where many other soft-bodied animals were preserved in ancient freshwater lakes. The beds have yielded a huge variety of fossil fish, birds, insects, reptiles, dinosaurs and even flowers.

Since 1995, when the first feathered dinosaur, Sinosauropteryx, was discovered in China, several specimens have promised to shed light on the bird-dinosaur debate, but they have usually been fragments of fossils and revealed only the very debatable presence of feathers.

"People in paleontology are used to showing pieces of rubble, "says Norell. "This fossil is fantastic." Under a microscope, the herringbone pattern of feathers can clearly be seen sprouting from the creature's arms, he says. Scientists say the dinosaur didn't fly because the forearms aren't long enough in relation to the rest of the body.

Still Skeptical

Despite the new find, a small group of paleontologists remain skeptical that birds evolved from dinosaurs because the feathered dinosaur fossils don't predate the time when birds are said to have evolved, which most scientists say is about 150 to 180 million years ago.

Alan Feduccia, a paleontologist at the University of North Carolina, is one a few paleontologists who reject the bird-from-dino theory.

"A lot of things look like feathers," he says. "Where ever birds came from, it's much earlier [than the new fossil]. There's this timing problem."

Norell counters it isn't useful to think of evolution as a linear process.

"When you're looking at these animals, you're really looking at a family tree," he says. Because dromaeosaurs are more primitive than birds, Norell believes the new fossil shows that feathers developed before flight, perhaps along with warm-bloodedness.

Scientists says they won't know if the fossilized creature represents a new species until they see three-dimensional CAT scans of its bones. It will be on display through the summer at the Museum of Natural History in New York.

纽约自然历史博物馆的古生物学家马克·诺莱尔本周在《自然》杂志上发表了他的研究报告，声称两脚恐龙化石证明了最早的羽毛的生长不是因为要飞翔，而是为了取暖。