A University of Chicago paleontologist discovered recently the dino ancestor of the Tyrannosaurs rex -- and the little guy's tiny.
"It really is the blueprint for the later (T. rex) dinosaurs," Sereno said. "It was a blueprint that was scalable."
Or, as he told the Chicago Sun-Times, "it was "a blueprint for a fast-running set of jaws."
The 150 pound "punk size" predator -- 100 times smaller than T. rex, but just as fierce -- evolved millions of years earlier.
The giant T. rex dominated much of the planet from about 90 million years ago until the great extinction 65 million years ago. Raptorex was around earlier, about 125 million years ago, Serano said.
Kriegstein, for whom the animal is now named, donated the materials to science and they will be returned to China.
The fossil was encased in a single block of stone, Sereno said. That stone allowed the researchers to trace the find to its original location.
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, calling the report interesting but adding that the drawing in the paper shows some differences from a T. rex in addition to being smaller.
However, he added, he didn't see anything that would disprove their theory that Raptorex was an ancestor of T. rex.