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"Bizarre" New Dinosaur: Giant Raptor Found in Argentina

José Orozco
for National Geographic News
December 17, 2008
 
Scientists have discovered what they say is a completely unexpected new giant dinosaur that lived 70 million years ago in Argentina.

At 16.5 to 21 feet long (5 to 6.5 meters) long, depending on its tail size, Austroraptor cabazai is among the largest of the slender, carnivorous, two-legged dinosaurs called raptors, said Fernando Novas, the lead researcher behind the discovery.

The dinosaur's incomplete skeleton—including head, neck, back, and foot bones—was extracted from rocks in the far-southern Patagonia region.

Novas and colleagues were able to virtually reconstruct Austroraptor's complete skeleton, by using the dinosaur's closest relatives as references, said Novas, who received funding for his work from the National Geographic Society's Committee for Research and Exploration. (The National Geographic Society owns National Geographic News.)

The new raptor, or dromaeosaur, belongs to a South American dromaeosaur group known as the unenlagiines, Novas said.

In contrast to their relatives in the Northern Hemisphere, including the Velociraptors from Jurassic Park, unenlagiines had long, low heads and small conical teeth.

Northern dromaeosaurs had taller, shorter heads with fewer, but stronger, blade-like teeth.

The new raptor represents the "the largest dromaesaurid discovered in the Southern Hemisphere," according to a paper by Novas and colleagues published today in the journal Proceedings of the Royal Society of London.

Seventy million years ago Patagonia was a series of plains crossed by rivers filled with fish and turtles, whose fossils were found alongside Austroraptor, Novas said.

Living in this fertile land alongside duck-billed herbivores such as titanosaurs and hadrosaurs, Austroraptor preyed on larger animals than its smaller relatives, thanks to its increased heft and girth, he said.

Turns History Upside-Down

Because paleontologists have found mostly smaller crow- and turkey-size raptors in South America, the new find turns the evolutionary history of raptors—northern and southern—upside-down, said Novas, who is based out of Museo Argentino de Ciencias Naturales in Buenos Aires.

"It's the first documentation of giant raptors in Patagonia measuring 5 meters [16.5 feet] or more," Novas said. "No one expected this, it's a new lineage."

The researchers call Austroraptor "bizarre" because of its short arms, which, along with its large size, distinguishes the new raptor from its unenlagiine relatives.

Novas says the new raptor is the first ever found with short arms.

Its shorter arms and more robust thigh bones, which supported the heavy animal, rule out any possibility of flying, Novas said. Smaller, longer-armed crow- and turkey-size relatives in Patagoni probably did fly, he added.

The size of the Austroraptor probably made it a vicious predator, said Paul Sereno, a paleontologist at the University of Chicago. The new find places raptors in the "big league" of dinosaurs, he said.

"This was a monster raptor that makes the Velociraptor look like kid's play," said Sereno, also a National Geographic Explorer-in-Residence. "At five meters long with a sickle-shaped claw, it was an amazing predator."

"Normally you'd hold an ostrich-size raptor's skull in your hand. This one's skull is almost a meter long."

The new fossils, combined with new finds from China, show that dromaeosaurs "weren't trying to become birds—they were, like all animals, diversifying over time," said Thomas Holtz, a vertebrate paleontologist from the University of Maryland.

(Related: "New Birdlike Dino Adds to Debate on Origins of Flight" [October 18, 2005].)

The new dinosaur also has a "weird" long skull, Holtz said.

"On first glance it looks like a pterodactyl," he said. "In fact, there has been a small and closely related dinosaur found in South America which has a similar skull. This suggests the whole radiation of southern dromaeosaurs have these long tapering skulls.

"What it does show is that we think we know a lot about the raptors, but even a relatively familiar group of dinosaurs continues to surprise us with their diversity," Holtz added.

Suddenly, the world of southern raptors looks a lot bigger and more complex.

Not only was the Southern Hemisphere home to giant raptors as well as smaller, birdlike specimens, but those large southern raptors were still living at a time when their northern counterparts had died off, Novas said.

"It means that raptors here had very different evolutionary paths from those up north," he said.

"This Austroraptor shows us that here in South America giant raptors evolved and survived until the end of the dinosaur age.

"This new evidence clearly indicates that South America was the site of a very prolific lineage of carnivorous dromaeosaurs, whose evolutionary history now begins to reveal itself," Novas added.
 

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