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Massive Birdlike Dinosaur Unearthed in China

James Owen
for National Geographic News
June 13, 2007
 
The remains of a huge beaked dinosaur with the looks of an ostrich but the weight of a rhino have been discovered in China's Gobi desert, fossil hunters have announced.

The previously unknown dinosaur weighed in around 1.5 tons (1.4 metric tons) and stood more than 16 feet (5 meters) tall—an extraordinary size given its birdlike appearance, say the Chinese researchers who found it. (See a photo gallery of the giant dinosaur.)

Gigantoraptor erlianensis, which lived some 70 million years ago, is the largest toothless dinosaur known to date and possibly the biggest feathered animal ever to have lived, according to a team led by Xu Xing from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China.

The research study also suggests the fossil specimen was still relatively young when it died and that a fully-grown Gigantoraptor would have been considerably heavier.

"The size is just amazing," Xu said.

Describing Gigantoraptor in this week's issue of the scientific journal Nature, the researchers say the creature also challenges thinking about the way birds might have evolved.

Most theories suggest two-legged dinosaurs known as theropods gave rise to birds after certain groups became progressively smaller, but Gigantoraptor appears to contradict this evolutionary trend, the paleontologists report.

"We thought previously that we had a relatively simple pattern—as dinosaurs became smaller in size they became more birdlike," Xu said. "Now, after the discovery of Gigantoraptor, things get more complicated.

"That doesn't mean birds aren't descended from dinosaurs, but the transition is very complicated," Xu added. (Related: "'Feathered' Dinosaur Was Bald, Not Bird Ancestor, Controversial Study Says" [June 1, 2007].)

Inherited Feathers

The team says the newly discovered species belonged to a group of theropod dinosaurs called oviraptorosaurs, yet it was about 300 times heavier than earlier fossil relatives found with arm and tail feathers (a picture of one such dinosaur).

While the dinosaur's remains didn't include any feathers, which rarely fossilize, its close link to more primitive feathered oviraptorosaurs suggest it very likely did have a feathered tail and arms, the team said.

"We believe Gigantoraptor kept those feathers from its ancestors," said Xu, who likened the dinosaur's appearance to that of a mammoth-size ostrich.

Previously the biggest known feathered animal was an 1,100-pound (500-kilogram) prehistoric flightless bird that lived in Australia six to eight million years ago, he added.

The researchers theorize that Gigantoraptor may have used its feathers for display or for incubating its eggs. Past studies suggest oviraptorosaurs may have had long feathers on their arms and bodies for covering their eggs.

"This is one of the hypotheses to explain how long feathers evolved on arms," Xu said.

Gigantoraptor may also account for huge clutches of fossilized theropod eggs measuring ten feet (three meters) in diameter previously found in China, said Luis M. Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County.

"It is perfectly possible that animals like Gigantoraptor were responsible for laying these gigantic nests," Chiappe said.

The species shows "gigantism needs not to be correlated with loss of birdness" in theropod dinosaurs, he added.

Birdlike Bones

The fossil also revealed various unexpected features, the team said, including more birdlike arms and legs than those seen in related dinosaurs.

"It looks like it has a number of features which are present in birds which it didn't inherit from its own relatives," said dinosaur researcher Paul Barrett of the Natural History Museum in London, England.

"Those birdlike features may have appeared once in this animal and once in birds," he added.

The massive oviraptorosaur also "throws up all sorts of questions regarding the biology of these animals," Barrett said. "It makes it even more difficult to work out whether these things would have been herbivores or carnivores."

The study team notes that the toothless dinosaur shares other physical traits with herbivores such as a small head and a long neck. (Related: "'Bizarre' New Dinosaur Shows Evolution to Plant Eating, Study Says" [May 4, 2005].)

But it was also armed with fearsome claws almost 20 centimeters (8 inches) long. "The claws are so long they are more like those of a meat-eating dinosaur," Xu, the lead researcher, said.

"Maybe it ate small animals, or clams, or plant seeds, or even eggs," he added.

His team says the dinosaur seems to have had an accelerated growth rate, faster than that of other large theropods.

"That would probably be the mechanism by which it got to its large body size," Barrett, of the Natural History Museum, said. "Instead of growing for longer to get larger, it probably grew faster."

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