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New Dinosaur Species Discovered in Argentina

John Roach
for National Geographic News
February 23, 2005
 
A newfound dinosaur species from Argentina suggests that fleet-footed, meat-eating dinosaurs with sickle-like claws on their hind feet roamed both the Southern and Northern Hemispheres through the end of the dinosaur age.

The new species, named Neuquenraptor argentinus, was about seven feet (two meters) long and similar in shape and size to Velociraptor mongoliensis, the smart, speedy, sickle-clawed dinosaurs immortalized in the movie Jurassic Park.

Both species were of the deinonychosaur group. Deinonychosaurs were in turn part of the theropod group—small, ferocious, bipedal, short-armed carnivores that were closely related to birds.

They were widely distributed throughout the Northern Hemisphere. But prior to the discovery of Neuquenraptor in northwestern Patagonia, fossil fragments only hinted that deinonychosaurs inhabited Gondwana, the supercontinent that about 160 million years ago began its split into the current southern continents.

"This is the first time in which we have firm and unquestionable evidence—an almost complete hind foot," said Fernando Novas, a paleontologist with the Argentine Museum of Natural Sciences in Buenos Aires.

Novas and his colleagues describe Neuquenraptor in tomorrow's issue of the science journal Nature. The paleontologists say their discovery advances understanding of dinosaur evolution and diversification.

Neuquenraptor lived during the late Cretaceous, the geologic period from 89 to 65 million years ago. At the time, the southern continents were approaching their present-day positions, suggesting that the deinonychosaurs must have inhabited both hemispheres for millions of years, Novas said.

Thomas Holtz, a paleontologist at the University of Maryland in College Park who specializes in theropod dinosaurs, agreed with the researchers' conclusions. He said their discovery confirms that deinonychosaurs were present in the Southern Hemisphere during the Cretaceous period.

"This helps us better understand the South American Cretaceous faunas, and the diversity within Deinonychosauria," Holtz said.

Dinosaur Diversification

Novas, the Argentine paleontologist, said evidence that deinonychosaurs and related theropods were present in the Southern Hemisphere during Cretaceous period is allowing paleontologists to "reinterpret the evolutionary history of predatory dinosaurs."

According to Novas, for several years the available fossil evidence suggested that Gondwana was populated almost exclusively by dinosaurs found nowhere else. Examples include the abelisauroids, a group of bizarre theropods represented by the horned, bull-like Carnotaurus and the claw-wielding Noasaurus, among other species.

"I was lucky to discover in Patagonia the remains of several theropod dinosaurs—the advanced deinonychosaurians and kin, which are different from the abelisauroid range," Novas said.

This newer evidence suggests that deinonychosaurs were widely dispersed throughout the world before the northern and southern continents broke up and drifted apart, Novas said.

As the landmasses separated, populations of deinonychosaurs that descended from early ancestors in the Northern and Southern Hemispheres were similar, but not identical. As time passed, the differences between these populations grew more distinct.

"Patagonian deinonychosaurs represent branches that emerged early from the [family tree] of deinonychosaurs and do not belong to the specialized deinonychosaurs from Asia and North America," Novas said.

Holtz, the University of Maryland paleontologist, said he is not at all surprised at the worldwide distribution of the sickle-clawed dinosaurs.

He said fossil evidence shows that birds were present at least as early as the late Jurassic, a geologic period from 154 to 144 million years ago. If birds were present, then so, too, were deinonychosaurs, a sister group of birds, Holtz noted.

"And during the late Jurassic there was greater connection between the various landmasses, allowing for the spread of various land-dwelling groups," he said.

The paleontologist added that the discovery of Neuquenraptor shows that deinonychosaurs existed in Gondwana into the late Cretaceous.

Tiny Bones

It was in 1996, during an excavation of a giant plant-eating dinosaur known as a titanosaur, that Novas and his colleagues discovered the tiny foot bones of Neuquenraptor.

Originally, the paleontologists thought the theropod died while scavenging the carcass of the titanosaur. But further analysis of the surrounding sediments, together with the well-preserved state of the fossils, suggested their association was accidental.

"We interpret that Neuquenraptor was not scavenging the [titanosaur] carcass but [that] both were transported by a river until their respective burial in sandstone," said Novas, whose research was supported in part by a grant from the National Geographic Society's Committee for Research and Exploration.

In addition to Neuquenraptor, the Patagonia fossil site has yielded several other meat-eating dinosaur species new to science over the years. These include the ostrichlike Patagonykus puertai, the large and big-handed Megaraptor namunhuaiquii, and the birdlike Unenlagia comahuensis.

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