'Missing Link' Connects Dinosaurs, Birds


Scientists have unearthed two feathered creatures they are calling "unambiguous evidence" that birds are the direct descendants of dinosaurs, and that many meat-eating dinosaurs--perhaps even Tyrannosaurus rex--may have sported tufts of feathers or coats of down.

Preserved in volcanic ash on an ancient lake bed in northeastern China, these 120-million-year-old fossils of two small carnivorous dinosaurs had beaks lined with teeth serrated like tiny steak knives and tails tipped with plumes. The remains clearly show that feathers were common long before birds appeared on Earth or the beginning of bird-like flight.

"These are animals with true feathers, and they are not birds, and they did not fly," said Kevin Padian, a professor of integrative biology and curator of the Museum of Paleontology at UC Berkeley. "This tells us that feathers did not evolve [first] for flight."

The new specimens, excavated by the National Geologic Museum of China over the past year, were unveiled Tuesday at the National Geographic Society in Washington and are documented in detail for the first time in research published this week in the journal Nature.

The two creatures--named Protoarchaeopteryx robusta and Caudipteryx zoui--belong to a branch of the dinosaur clan called theropods that includes a number of fearsome predators like the agile Velociraptors of "Jurassic Park" fame.

Feathered Ferocity

Based on their close kinship and the likelihood of shared family traits among theropods, the fossils raise the possibility that many carnivorous dinosaurs--once depicted as drab, leathery creatures--may have had feathers.

Indeed, as more well-preserved specimens are unearthed, researchers may discover that feathers, so long considered the distinguishing hallmark of birds, may simply be a legacy of their dinosaur heritage--a surviving trace of what was a relatively common characteristic of the denizens that dominated Earth for so many millions of years.

"We would predict on the basis of this evidence that many meat-eating theropods had proto-feathers, which is pretty dramatically different from our traditional view of dinosaurs," said Mark Norell, chairman of the department of vertebrate paleontology at the American Museum of Natural History in New York.

Even the fearsome Tyrannosaurus rex--one of the largest carnivores to stalk the planet and, the growing evidence suggests, a close relative of modern birds--may have had its own garish, downy plumes, several experts speculated.

For modern birds, feathers are crucial to flight, but no one is sure what purpose the dinosaur feathers may have served.

They may have been insulation or part of a mating display, not unlike the more spectacular plumage of modern peacocks and birds of paradise.

Philip Currie, curator of dinosaurs at the Royal Tyrrell Museum of Palaeontology in Drumheller, Canada, who analyzed the Chinese fossils, said that feathers may have been as common among theropods as spikes, horns, elaborate frills and bony crests were among other types of dinosaurs.

"What it suggests to me is that it is a general characteristic of at least the small meat-eating dinosaurs," Currie said. But "I would also include Tyrannosaurus rex."

The idea of a six-ton feathered Tyrannosaur may be farfetched because such a large creature may have overheated if it had an insulating coat of feathers, said Norell, who also studied the finds and their relationship to modern birds.

But the new fossils do suggest at least that feathers may have been ubiquitous among smaller predators, Norell said.

"Here we have two animals that document the transition from dinosaurs to birds. The truly remarkable thing about them is that they were flightless, but they have feathers," he said. "It goes a long way to proving beyond a shred of doubt that birds are the descendants of dinosaurs."

Indeed, for many experts, the Chinese fossils may be the last word in an argument over the origin of birds that is as old as the study of evolution itself.

Decades of Debate

Ever since quarrymen in 1861 discovered what is still considered the oldest known bird--a 150-million-year-old species called Archaeopteryx--avian experts and paleontologists have feuded bitterly over the ancestry of birds, arguably the most successful of all terrestrial life forms.

But the fossil remains of ancient birds are so rare that until recently, there was little more than passionate guesswork to fuel the scholarly debate.

The Chinese fossils, however, are the newest in a cascade of finds that have scientists sharply revising their ideas of how all dinosaurs looked and behaved. Recent studies reveal a lost world of raptors that brooded protectively over their eggs like mother hens, of duckbill dinosaurs that honked like big band trombones, and apatosaurs that cracked their two-ton tails like bullwhips.

At the same time, new fossil finds from around the world have strengthened the evidence of family ties between birds and dinosaurs:

* In Madagascar, researchers from the State University of New York recently discovered a 70-million-year-old bird, about the size of a small hawk, that featured a single large, sickle-like claw resembling the deadly talon of the theropod predator Velociraptor. Although the creature lived 80 million years after the first known bird, scientists nonetheless said it was strong support for the theropod origin of birds.

* In the Gobi Desert, Norell at the American Museum and his colleagues at George Washington University recently found a Velociraptor fossil revealing that the dinosaur had a wishbone, an anatomical characteristic that, like feathers, was long considered a key characteristic of birds. The dinosaur's wishbone was thinner and more angled than that found in modern birds, the researchers said. Even so, they argued that it reinforced the close evolutionary ties between birds and dinosaurs.

* In Argentina, researchers discovered the 90-million-year-old fossil of a flightless, 8-foot-long dinosaur that had shoulder bones oriented in the same way as modern birds, so that it could move its arms up and down in a primitive flapping motion. Again, the fossil dated from a period later than the earliest known birds, but researchers suggested its anatomy demonstrated a kinship and might have been a surviving intermediate species.

* In China, researchers earlier this year announced the discovery of a small, ground-dwelling predator, called Sinosauropteryx, that appeared to be covered with primitive down-like filaments, as well as hundreds of skeletons of one of the most primitive birds known--Confuciuornis--all dating from between 120 million years ago and 140 million years ago.

The same site yielded the specimens of Protoarchaeopteryx and Caudipteryx, preserved in such unusual detail that the fossils show clear evidence of body feathers and tail feathers, experts said.

"The [new fossils] represent a missing link between dinosaurs and birds, which we had expected to find," said Ji Qiang, director of the National Geological Museum in Beijing, at a news conference Tuesday in Washington.

Based on the geologic evidence, the scientists believe that some sudden catastrophe, like a lethal volcanic eruption, may have killed all the life forms around the lake site more than 120 million years ago. Gentle blankets of ash preserved an instant in the life of the period in almost unprecedented detail.

For Padian at Berkeley and other experts, the new fossils are persuasive evidence that modern birds--encompassing roughly 9,000 species and more than 300 billion creatures--are the living descendants of dinosaurs.

"All the things we used to associate with birds--feathers, a wishbone, a breastbone, a three-toed foot, hollow bones, long arms and hands--all these things turn out, one by one, to be found in small carnivorous dinosaurs that did not fly and were not themselves birds," Padian said.

"Birds branched off from these small, carnivorous dinosaurs in the Jurassic period, just as humans later branched off from other apes," Padian said. "We are still apes and birds are still dinosaurs."


Feathered Dinosaurs

New fossils suggest that feathers may have been as common as horns among many dinosaurs. A specimen of Protoarchaeopteryx robusta, left, discovered in China, shows distinct tail feathers. Tail featers





All in the Family

Fossils of two feathered meat-eaters buttress the kinship between modern birds and the dinosaur family known as theropods, experts said. A model of one 120-million-year-old specimen, Caudipteryx zoui, looks more like a bird than the conventional image of a dinosaur. The fossils were discovered recently in northeastern China and detailed this week in the journal Nature.

Source: National Geographic Society

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