Scientists Find Oldest Ancestor Of T. Rex

By Guy Gugliotta
Washington Post Staff Writer
Thursday, February 9, 2006

Paleontologists working in the desert wilderness of northwestern China have unearthed the oldest ancestor yet of Tyrannosaurus rex , a mid-size, long-armed predator with razor-sharp teeth and a spectacular inflatable crest atop its snout.

Unlike T. rex , however, Guanlong wucaii -- "crown dragon from the land of five colors" -- was not the top-of-the-line predator of its time, but scientists suggested yesterday that it could probably outrun anything it could not outfight.

"When you become a giant animal, the entire [body] has to be modified," said Mark A. Norell, a paleontologist at the American Museum of Natural History. "This is a very gracile animal; T. rex is elephantine."

Guanlong , which lived 160 million years ago, predated T. rex by 90 million years and is the oldest tyrannosaur ever found by at least 30 million years. Norell was part of an eight-member discovery team led by Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.

They describe their find in today's issue of the journal Nature.

Team co-leader James M. Clark of George Washington University said he and Xu decided to investigate the badlands of the Junggar Basin west of the Gobi desert after Chinese geologists prospecting for oil in the 1970s mentioned finding fossils there.

"You depend on previous discoveries," Clark said at a news conference. "You get as many people as you can and start looking at outcrops." The team has been working in the basin since 2000 and has dug up several dozen fossils.

Clark said the team found Guanlong in 2002. At first, excavators thought they had only one specimen, but after chipping away the "mud rock" encasing the fossil, they found a second skeleton below the first.

Analysis showed the lower fossil was that of a "juvenile," about seven years old, while the top skeleton was that of a 12-year-old adult. Clark said the mature Guanlong was about 10 feet long, "a not particularly small, not particularly large dinosaur." T. rex averaged 40 feet long and weighed 6 tons.

The most distinctive feature of Guanlong was a long, bony crest on top of the snout, unusual for meat-eating dinosaurs. Clark said the crest was a thin membrane over an air-filled sac. Such features, he added, could have evolved to attract mates or as distinctive markers for species identification.

Clark said Guanlong had many tyrannosaur-like attributes, including sharp, cutting teeth, a flared tailbone and the configuration of its snout. But the fossil was older by at least 30 million years than the oldest-known tyrannosaur, and that animal, reported by Xu and Norell in 2004, was smaller than Guanlong . Nevertheless, a detailed numerical analysis of the data showed with 90 percent certainty that Guanlong was a tyrannosaur.

"The features they discuss are pretty convincing," said paleontologist Matthew Lamanna of the Carnegie Museum of Natural History. "It's three-clawed, while T. rex is two-clawed, but that's to be expected, since tyrannosaurs evolved from three fingers to two."

Team member David A. Eberth of Canada's Royal Tyrell Museum said the Junggar Basin during Guanlong's time was a marshy, subtropical wetland, rife with rivers and lakes, far different from today's austere wilderness.

Clark said that the team has found larger predators in the area, but that Guanlong was probably a fleet hunter well able to take care of itself in a hostile environment.

"Bigger is not always better," said Jack Horner, a paleontologist at the Museum of the Rockies at the University of Montana and a leading advocate of the theory that T. rex was an outsize scavenger too slow to run down its own game. "This one has good size and grasping arms. You start getting them too big, and they get pretty clunky."

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