Because birds and some dinosaurs, particularly theropods, have so many anatomical features in common, most paleontologists and dinosaur enthusiasts have come to believe that birds evolved from dinosaurs.
The presence of feathers does not necessarily mean that a dinosaur could fly. Some non-avian dinosaursespecially smaller speciesmay have acquired a downy coat to help maintain their body temperature, the scientists speculate.
"Modern birds are warm-blooded and their feathers play an integral role in keeping them warm, so a reasonable idea is that non-avian dinosaurs developed primitive feathers at the same time they developed warm-bloodedness," said Norell.
Whether dinosaurs were warm- or cold-blooded is still open to debate. The widely assumed connection between birds and dinosaurs is also the subject of contention among a small but influential group of scientists.
The bird-dinosaur link was first proposed more than a century ago by Thomas Henry Huxley, a contemporary of Charles Darwin. The idea got a considerable boost in the 1970s when a Yale University scientist named John Ostrom documented close similarities between dinosaurs and the skeleton of a well-defined early birdlike creature.
Storrs Olson, curator of birds at the Smithsonian Institution's Natural History Museum, is one of the most highly vocal critics of the theory that modern birds evolved from dinosaurs. He and others of a like mind say the theropod origin of birds has been oversold on the basis of "wishful thinking," and that fossil evidence suggesting that some dinosaurs had feathers is too sketchy to bear out the claims. Any true feathers that have been documented could have come from birds that nested amid theropods, some suggest.
In an open letter he sent in 1999 to National Geographic's Committee for Research and Exploration, which has funded some of the recent dinosaur fossil discoveries, Olson called the theory of feathered dinosaurs the "paleontological equivalent of cold fusion."
He issued the highly critical letter after National Geographic magazine published a story in November 1999 reporting on several feathered dinosaur specimens that scientists claimed were "a missing link" between terrestrial dinosaurs and birds that could fly. One of the specimens from China was later found to be a composite, which prompted an internal investigation of the incident.
Among his comments, Olson said that "none of the structures illustrated in [the] article that are claimed to be feathers have actually been proven to be feathers."
Whether the fossilized dinosaur now on display in New York represents a new species is not yet clear. Clark speculates that it may belong to one of several theropod species that have emerged in recent years.
The paper in Nature describes the embedded creature as having matted tufts of feather-like filaments on nearly every part of its body. Downy fibers sprout from its head and tail; its arms bear branched structures that resemble the barbed feathers of modern birds.
While the new dinosaur specimen is clearly exciting for the level of detail it provides, Clark said the discovery should be viewed in the context of a steadily growing body of evidence that is rapidly advancing scientific knowledge about dinosaur "integuments," or bodily coverings. "We already knew that some dinosaurs had this kind of feathered integument," Clark said, "but this [latest fossil] is giving us a much better picture of what it was like."
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