aleontologists have discovered in China a fossil dinosaur with clear traces of feathers from head to tail, the most persuasive evidence so far, scientists said, that feathers predated the origin of birds and that modern birds are descendants of dinosaurs.
Entombed in fine-grained rock, the dinosaur's unusually well-preserved skeleton resembles that of a duck with a reptilian tail, altogether about three feet in length. Its head and tail are edged with the imprint of downy fibers. The rest of the body, except for bare lower legs, shows distinct traces of tufts and filaments that appear to have been primitive feathers. On the backs of its short forelimbs are patterns of what look like modern bird feathers.
Other dinosaur remains with apparent featherlike traces have been unearthed in recent years, but nothing as complete as this specimen, paleontologists said. Etched in the rock like a filigree decoration surrounding the skeleton are imprints of where the down and feathers appear to have been.
The 130-million-year-old fossils were found a year ago by farmers in the Liaoning Province of northeastern China. After a careful analysis by Chinese and American researchers, the fossil animal was identified as a dromaeosaur, a small, fast-running dinosaur related to Velociraptor. These dinosaurs belong to a group of two-legged predators known as advanced theropods.
The findings are described today in the journal Nature by the discovery team led by Dr. Ji Qiang, director of the Chinese Academy of Geological Sciences in Beijing, and Dr. Mark A. Norell, chairman of paleontology at the American Museum of Natural History in Manhattan. The specimen, on loan from China, went on public display at the museum today.
"This is the specimen we've been waiting for," Dr. Norell said in a museum statement. "It makes it indisputable that a body covering similar to feathers was present in non-avian dinosaurs."
This dinosaur's forelimbs were too short to have supported wings, Dr. Norell said in an interview, and so it was flightless. But some of its bone structure, notably the furcula, or wishbone, and the three forward-pointing toes, bears similarities to those of birds. Other recent discoveries of birdlike dinosaurs and dinosaurlike birds have encouraged support of the theory of a dinosaur-bird ancestral link.
A few dissenters, however, particularly among ornithologists, continue to dispute the theory. They argue that birds evolved from some earlier, yet undiscovered, reptile. They said that previously found fossils associating featherlike traces with dinosaur skeletons were too mixed-up to determine if the feathers belonged to the dinosaur and not to a primitive bird buried at about the same time.
But the Chinese and American researchers said the new discovery enabled them to see with microscopes how the feathers and downy fluff were attached to the dinosaur's body. A similar, though not as complete, fossil find reported last month by another Chinese-American team, including Dr. Richard Owen Prum of the University of Kansas, appeared to reinforce the conclusion that some theropod dinosaurs indeed had feathers.
Accordingly, most paleontologists consider the case for such a dinosaur-bird link now virtually airtight. Dr. Hans-Dieter Sues, a dinosaur paleontologist at the Royal Ontario Museum in Toronto, said the two discoveries from Liaoning Province "further strengthen the case for the theropod-bird connection, but also establish that feathers originated and eventually diversified in nonflying, nonavian theropod dinosaurs."
Not that these particular dinosaurs were ancestors of birds; but they may be descendants of the ancestors. Some dromaeosaurs evolved earlier than birds. Feathered, flightless birds are known to have existed as early as the 145-million-year-old Archaeopteryx, found in Germany in the 19th century. Dr. Norell said the feathered fossil showed that there was "a more general distribution of feathers than in birds alone." Studying theropods that lived later than the first birds, he explained, should provide insights into bird evolution just as related "chimps and gorillas and lemurs help us understand human evolution."
In a commentary that accompanied the journal report, Dr. Sues wrote that, because feathers must have been present before the origin of birds and flight, they "clearly evolved for some purpose other than flight, perhaps thermal insulation or behavioral display (or both)."
The Chinese and American researchers favored the idea that the feathers served to keep the dinosaurs warm. In that case, the discovery seemed to support the theory that some predatory dinosaurs were warm-blooded like modern birds rather than cold-blooded like other reptiles. They would thus have required something like feather covering to maintain their body temperature. "Insulation implies higher metabolic rates than for the average reptile," explained Peter Makovicky, a paleontologist at the American Museum who is completing Ph.D. studies at Columbia and has made a detailed study of the specimen.
The region of northeastern China where the skeleton was uncovered has some of the world's richest fossil beds, which have been actively explored over the last decade. Between 145 million and 120 million years ago, the land was covered by many lakes and erupting volcanoes rained down fine ash. This probably buried animals as soon as they died, increasing the chance of their remains fossilizing and surviving the ages. Two other dromaeosaurs have been recovered from these fossil beds: Sinornithosaurus, a small dinosaur first described in 1999, and Microraptor, the smallest known theropod, found last years. But one specimen, reported in the early 1990's, turned out to be a hoax, a clever composite of bones and some featherlike imprints.
Researchers said they were sure the latest find is genuine. The skeleton was embedded in two slabs sliced from the mudstone. Close examination, the scientists said, show that both sides "match up perfectly," which would be extremely difficult to fake. The latest find, Mr. Makovicky noted, appears to have been a juvenile. Its oversized head, relative to its body, suggests that the animal was not fully grown. Although most of the skeleton's covering appears to be down or filaments suggesting primitive feathers, the forelimbs had traces of feathers with a herringbone pattern, which is found in bird feathers.
If nothing else, Dr. Norell said, the discovery "shows us that advanced theropod dinosaurs may have looked more like weird birds than giant lizards."