The discovery of a remarkably preserved, 130-million-year-old fossil dinosaur covered with feathers is providing researchers with the most conclusive evidence yet of an evolutionary link between birds and dinosaurs.
The find was announced today in the science journal Nature by a team of Chinese and U.S. scientists. It's the first time a dinosaur has been discovered covered from head to tail with downy fluff and primitive feathers.
Farmers dug up the specimen last spring in the fossil beds of Liaoning, China, an area noted for the number and quality of its dinosaur finds, including the first discovery of a dinosaur with a few primitive feathers in 1995.
The new discovery will likely change the way people picture dinosaurs. The fossil has been identified as a dromaeosaur, a group of dinosaurs known as advanced theropods -- two legged predators that include Tyrannosaurus rex -- whose bones are strikingly similar to those of modern-day birds.
"This fossil radically modifies our vision of these extinct animals," said Mark Norell, head of the paleontology division at the American Museum of Natural History in New York and one of the research-team leaders who describes the find in Nature. "It shows use that advanced theropod dinosaurs may have looked more like weird birds than giant lizards."
The fossil is on display at the American Museum of Natural History in New York, on loan from the National Geological Museum of China.
Since the 1995 discovery of a dinosaur with feathers, several new species with feather-like structures have been found. But the fossil specimens were so incomplete or mixed up it was difficult to interpret the remains.
Although most researchers accept the theory that modern birds evolved from dinosaurs, some critics have questioned the idea, arguing that the feather-like structures could be explained as the mixed up fossils of early birds and dinosaurs.
But the detail on the new discovery is so fine that scientists are able to see how the feathers were attached to the dinosaur's body. "This is the specimen we've been waiting for," says Ji Qiang of the Chinese Academy of Geological Sciences. "It makes it indisputable that a body covering similar to feathers was present in non-avian dinosaurs."
The region of China where the fossil was discovered has been a major source of fish, birds, insects and mammals from the period between 145 and 120 million years ago. It is thought that when volcanic explosions rained fine ash on the surrounding countryside, animals that were killed were quickly buried under the sediment. Because of the quick burial and little oxygen available to promote decay, many of the fossils found in this area are extremely well preserved.
Researchers speculate that animals developed feathers to keep warm, before evolution had shown that they were essential for flight. Because dromaeosaurs are more primitive than birds, researchers believe the fossil supports the contention that feathers developed before the ability to fly.
Writing in the same issue of Nature, Hans-Dieter Sues, vice-president of research and collections at the Royal Ontario Museum in Toronto, said there is now overwhelming anatomical evidence that birds evolved from theropods.
"Feathers predate the origin of birds and avian flight. They clearly evolved for some purpose other than flight, perhaps thermal insulation or behavioral display or both, functions they retain in present day birds," he said. Staff
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