WASHINGTON — About 125 million years ago, a tiny version of Tyrannosaurus rex roamed what is now northeastern China. Tiny, that is, by T. rex standards -- you still wouldn't want to meet it face to face.
Described by paleontologist Paul Sereno as "punk size," this early predator would have weighed about 150 pounds.
It just seems small compared with the giant T. rex that evolved millions of years later and was as much as 100 times more massive.
"It really is the blueprint for the later [T. rex] dinosaurs," Sereno said. "It was a blueprint that was scalable."
Described for the first time in Thursday's Science Express, the online edition of the journal Science, the new dinosaur has been named Raptorex kriegsteini.
Sereno reports that Raptorex has all the hallmarks of T. rex, including a large head, tiny arms and lanky feet -- just in a smaller size.
"What we're looking at is a blueprint for a fast-running set of jaws," Sereno said at a briefing arranged by the American Assn. for the Advancement of Science.
The giant T. rex dominated much of the planet from about 90 million years ago until the great extinction 65 million years ago.
Raptorex would have stood 9 feet tall, said Sereno, of the University of Chicago and also a National Geographic explorer in residence.
The remains were found by fossil hunters in northern China, smuggled out of that country and offered for sale to collector Henry Kriegstein of Hingham, Mass., Sereno said. Kriegstein donated the fossil to science on the condition that the creature be named for his parents, Polish Jews who survived the Nazi death camps.
When Sereno is finished, the fossil will be returned to China.
The way the bones were fused indicates the animal died at the age of 5 or 6, which is nearly adult. It would have matured at 8 or 10 and been old by 20, added co-author Stephen Brusatte of the American Museum of Natural History.
The find also shows that features such as the animal's tiny arms did not evolve as T. rex evolved but were present in the much earlier forms, Brusatte said.
"Much of what we thought we knew about T. rex turns out to be simplistic or out-and-out wrong," Brusatte said.
Sereno said Raptorex was a predator. Some scientists debate whether T. rex was a predator or scavenger.
Dinosaur expert John R. Horner of the Museum of the Rockies at Montana State University was cautious about the find.
"It's hard to evaluate their conclusions," he said, adding that he didn't see anything to disprove their theory that Raptorex was an ancestor of T. rex.
The research was funded by the Whitten-Newman Foundation and the National Geographic Society.
Kriegstein, 60, said he's thrilled the creature's scientific name honors his 86-year-old father and 82-year-old mother, who live in New York.
"I wanted to find a way to let their name live on in immortality," he told the Chicago Tribune. "The fossil of this dinosaur has survived for 125 million years. My parents came close to not surviving. This name symbolically represents that they have survived despite great odds."