Paleontologists working in China have unearthed the first fossil of a dinosaur that appears to have had full-fledged feathers a finding they say settles once and for all the debate over whether dinosaurs and birds are related.

Researchers said the 3-foot fossil also reinforces the idea that at least some dinosaurs were warm-blooded creatures that needed feathers for insulation, not flight.

In the top image, a complete dromaeosaur fossil, dated about 128 million years old, is shown in a rock slab discovered in Liaoning Province in northeast China. Scientists say it is the first fossil of a nonflying dinosaur that had feathers with the same features as modern birds, demonstrating the evolutionary link between dinosaurs and birds. The fossil is about 3 feet long. The bottom image magnifies a single feather. A trained eye can see the feather's central shaft, or rachis, and the branching barbs that hook together feathery filaments.

The specimen is believed to be about 128 million years old. It is a small, fleet-footed theropod, a two-legged carnivore that could not fly and belongs to the same family as the larger and more fearsome Tyrannosaurus rex.

The researchers said the dinosaur that appears to have had mature feathers identical to those of modern birds, including long, showy plumage on its tail and hind legs. Some of the feathers are more than 5 inches long.

They said the evidence consists of impressions of feathers in the rock and, under magnification, “feather residue” and tiny recognizable features, including the hollow shafts and barbs that hold the feathers and their filaments.

The findings were published in today’s issue of the journal Nature. The fossil is housed at the Beipiao Paleontological Museum in China.

“We have unequivocal feathers on an unequivocal non-avian dinosaur,” said the study’s lead author Mark A. Norell, paleontology chairman at the American Museum of Natural History in New York City.

Some not convinced

The dinosaur-bird connection is one of the more hotly debated aspects of evolution.

In recent years, northeastern China has yielded a succession of fossils of dinosaurs that appeared to have had feathery and downy coverings, at least during their juvenile years. But some scientists have disputed whether the fossils really do show feathers.

This latest discovery is no more convincing, they argue.

Storrs Olson, senior zoologist at the National Museum of Natural History at the Smithsonian Institution, said he was unable to discern from photographs any modern feathers or feathery structures.

If there are feathers, they could have come from actual birds of a later period that were mixed into the rock formation, he said. Or, the specimen could be a composite from several sources, he said.

“I am not impressed,” said Olson, an ardent critic of the dinosaur-bird theory. “I would want to be very certain that the fossil has not been deliberately salted with feathers from some other source.”

Birdlike behavior

Last year, Norell’s group unearthed a dromaeosaur dated to 130 million years old. It appeared to have been insulated by a coat of fuzzy down.

The latest specimen also is a dromaeosaur, but more recent by 2 million years. Its hollow bones were strikingly birdlike, and it was armed with a killing talon on each foot.

It was unearthed from what was once a pond that became filled with volcanic ash. The dense layer contained little trapped oxygen, preserving rare details.

Norell said the specimen has a much more extensive tail plume than previous specimens. Feathers also fringe the back of the forelimbs and hindlimbs, as well as the front and back of the hand.

Dromaeosaur could not fly. But the details suggest it would run toward its prey, then would silently glide in for the kill.

Because theropods date back at least 235 million years, Norell believes they probably developed the first primitive feathers. Studies suggest theropods and birds share some 100 anatomical similarities.

The first bird, Archaeopteryx, appeared about 150 million years old. It blended dinosaur and avian traits, though critics say it was an evolutionary dead-end.