Raptorex--T. Rex precursor and how science works

This is a fine example how some areas of science are subject to change. Science is an evolving disciple of knowledge.

"Fossil Find Challenges Theories on T. Rex"

by

Henry Fountain

September 18th, 2009

New York Times

Paleontologists said Thursday that they had discovered what amounted to a miniature prototype of Tyrannosaurus rex, complete with the oversize head, powerful jaws, long legs — and, as every schoolchild knows, puny arms — that were hallmarks of the king of the dinosaurs.

But this scaled-down version, which was about nine feet long and weighed only 150 pounds, lived 125 million years ago, about 35 million years before giant Tyrannosaurs roamed the earth. So the discovery calls into question theories about the evolution of T. rex, which was about five times longer and almost 100 times heavier.

“The thought was these signature Tyrannosaur features evolved as a consequence of large body size,” Stephen L. Brusatte of the American Museum of National History, an author of a paper describing the dinosaur published online by the journal Science, said at a news conference. “They needed to modify their entire skeleton so they could function as a predator at such colossal size.”

The new dinosaur, named Raptorex kriegsteini, “really throws a wrench into this observed pattern,” Mr. Brusatte said.

The nearly complete fossil was found in northeastern China and bought by a collector, Henry J. Kriegstein, who alerted Paul C. Sereno, a paleontologist at the University of Chicago and lead author of the paper. The fossil, which was illicitly excavated, will be returned to a museum in China.

Dr. Sereno said the fossil was that of a young adult, about 5 or 6 years old and near the end of its growth period. Besides the oversized head, jaws and legs, it had long shinbones and long, compressed feet that helped it run fast after smaller dinosaurs and other prey. “We see this all, to our great surprise, in an animal that is basically the body weight of a human,” Dr. Sereno said.

Raptorex, like T. rex, would have killed animals with its teeth and jaws. The forelimbs would not have been the primary means for attacking prey. In fact, Dr. Sereno said, the forelimbs would have gotten smaller as the head got larger. “This is an agile, fast-running animal,” he said. “By adding a lot of weight at the top, something has to give way. What gave way was the forelimb.”

Thomas R. Holtz Jr., a paleontologist at the University of Maryland who was not involved in the work, said the discovery helped “clear up the origin of the characteristic features of the Tyrannosaurs.”

Dr. Holtz, who cautioned that the findings needed to be independently confirmed, noted that there had been a gap in the family tree between earlier, more primitive Tyrannosaurs that had relatively short legs and long arms and the later giants with opposite features. “This clarifies the sequence,” he said.