"Feathered" Fossil Bolsters Changing Image of Dinosaurs
National Geographic News
|April 25, 2001|
From a series of fossil discoveries in recent years, scientists have
been expanding the picture of dinosaurs to include creatures that
apparently sported tufts of primitive feathers. On Wednesday, the
American Museum of Natural History in New York City unveiled what
observers say is a "remarkable" specimen showing a small dinosaur that
had a feathered covering from head to foot.
The fossilized skeleton, which is on loan from the National Geological Museum of China, is embedded in two mirror slabs of rocks estimated to be 130 million years old. It was unearthed last spring by farmers digging in Liaoning Province in northeastern China.
Covered by lakes and active volcanoes millions of years ago, the region has yielded a treasure trove of fossils over the past decade that are unusually well preserved because the animal remains were buried in the lake bottom's fine sediment of volanic ash and muck. The anatomical details in the new specimen are so well etched that the scientists who analyzed it could discern a herringbone pattern in some of the creature's primitive feathers and even observe how they were attached.
"I've seen the specimen and other feathered dinosaur fossils, and this one is a visually spectacular specimen with a halo of feathers," said James Clark, an associate professor of biology at George Washington University. "It's well preserved and amazinga small dinosaur surrounded by fur."
Clark said the new fossil is important because it offers far more complete and compelling evidence of "feathered dinosaurs" than most of the other similar specimens that have turned up in recent years, which have shown only patches of feathery fibers.
The team of U.S. and Chinese scientists who describe the find in this week's issue of the journal Nature say the fossilized creature belonged to a group of small, fleet-footed dinosaurs known as dromaeosaurs, which are the most closely related dinosaurs to modern-day birds.
"We're pretty confident it's a dromaeosaurus," said Mark Norell, chairman of the division of paleontology at the American Museum of Natural History. The discovery is part of a long-time research collaboration by Norell and Ji Qiang of the Chinese Academy of Geological Sciences.
Norell said the scientists based their conclusion on the presence of several anatomical features that are unique to dromaeosaurs, including a hyper-extendable curved claw on the middle toe and stiffening rods in the tail.
Dromaeosaurs are a subgroup of a dinosaur class known as advanced theropods, whose members included the well-known predator Tyrannosaurus rex.
Norell said the new fossil and similar evidence of feathered dinosaurs acquired in the past decade is "radically" altering common ideas about the nature of dinosaurs such as theropods. "We've experienced dramatic changes in the way we view dinosaurs, going from scaly Godzilla lizards to weird birds," he said.
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."
|© 1996-2008 National Geographic Society. All rights reserved.|