Sept. 18 (Bloomberg) -- A dinosaur 1 percent the size of Tyrannosaurus rex and with most of the predator’s distinctive features was found to have lived 60 million years earlier, scientists said, throwing a wrench into an evolutionary theory.

Raptorex kriegsteini, as the newly found 125 million-year- old species is called, shares traits including enlarged jaw muscles and head, short arms and lanky legs with the much larger T-rex, said Paul Sereno, a University of Chicago paleontologist and lead author of a study appearing in Science Express.

The discovery in China turns on its head a theory that T- rex’s small arms and outsized head were necessary evolutionary steps to develop into the 6-ton predator that dominated the food chain in Asia and North America 65 million years ago.

“We really thought that many of these features evolved in the course of gaining large body size,” Sereno told reporters in a conference call. “What we can now say is that this is a body blueprint for a predator: Jaws on legs, as it were.”

Aside from its scientific importance, the raptorex specimen has a shadowy past, according to Sereno. The fossil was likely smuggled out of China before being sold to Henry Kriegstein, an eye surgeon and private collector after whom the species was named, Sereno said. Kriegstein then contacted the paleontologist and asked him to describe the fossil for science.

“The specimen was found perhaps in the dark of night, spirited out of China and ultimately sold,” Sereno said. “I said after verifying the quality and uniqueness and importance of the specimen that I would (describe it) if it could be returned 100 percent lock, stock and barrel back to science, and ultimately to China, from where it came.” Kriegstein agreed.

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Sereno said the new species probably would have had no predators itself and would have hunted smaller plant-eating dinosaurs, birds, turtles and carnivores.

The near-complete specimen of raptorex came from northern China and was a young adult aged 5 or 6, which Sereno described as a ‘punk-size’ version of T-rex. The level of fusion of the animal’s bones indicated it wasn’t a juvenile, he said. Raptorex would have measured about 3 meters (10 feet) in length at most, weighing some 65 kilograms (143 pounds), according to the paper.

Previous fossil finds of tyrannosaurus ancestors dating as far back as 165 million years had shown that the lineage of dinosaurs culminating in T-rex included smaller, more slender and longer-armed species, said Stephen Brusatte, a co-author and paleontologist at New York’s American Museum of Natural History.

“Much of what we knew about tyrannosaur evolution turns out to be simplistic or out-and-out wrong,” Brusatte said on the conference call.

Advanced Sense of Smell

Similarities with the larger dinosaur include the same 29- percent size ratio for the humerus, or upper arm bone, versus the femur, or thigh bone, and enlarged olfactory bulbs within the skull indicating an advanced sense of smell, the paper said.

“The thinking has been that as tyrannosaurs developed truly giant size over time, they needed to modify their entire skeleton so that they could function as a predator at such a colossal size,” Brusatte said. “Raptorex really throws a wrench into this observed pattern.”

Sereno said it now seems that the tyrannosaurus “body plan” emerged with raptorex 125 million years ago, and 90 million years ago the creatures began to increase in size first by a scale of 50 and then eventually to 100 times the size.

“This is an animal that really ran down its prey and it used its enlarged large skull, nipping incisors and powerful jaw muscles to dispatch the prey,” he said.

This increase in size was possibly as a consequence of other large predators dying out, allowing T-rex to become the apex predator, the paleontologist said. “When they did, there was no turning back until the asteroid hit,” he said.

Tyrannosaurus rex featured prominently in the 1993 movie “Jurassic Park,” based on the novel by Michael Crichton. On release, the film was the highest-grossing of all time and has taken in $914 million at the box office, according to the Web site www.boxofficemojo.com.

Defying the film’s title, T-rex actually lived after the Jurassic period, in the Cretaceous time that stretched from 145 million to 65 million years ago.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.

Last Updated: September 17, 2009 18:02 EDT