A 9-foot dinosaur excavated illegally from northeastern China and purchased by a private collector who brought it to the attention of paleontologists (hey, they'll return it after they're done)  is about the same weight as a grown human yet had still evolved all the hallmark anatomical features of Tyrannosaurus rex - except 30 million years earlier, according to a study in Science.

Raptorex displays the hallmarks of its famous descendant, Tyrannosaurus rex, like an oversized head, tiny arms and feet well-suited for running. The Raptorex brain cast also shows enlarged olfactory bulbs, like T. rex, indicating a highly developed sense of smell.

Raptorex , said Sereno, a National Geographic Explorer-in-Residence, was "basically our bodyweight. And that's pretty staggering, because there's no other example that I can think of where an animal has been so finely designed at about 100th the size that it would eventually become.   It's really stolen from tyrannosaurids all the fire of the group."
Weighing 1/100th that of its descendant, T. rex, 125-million year old Raptorex shows off the distinctive body plan of this most dominant line of predatory dinosaurs. Drawing based on a fossil skeleton discovered in Inner Mongolia, China.  Drawing by Todd Marshall

Raptorex simply left for its descendants features related to getting bigger.  The scalability of the tyrannosaur body type, which dominated the predatory eco-niche in both Asia and North America  from 90 million years ago (by then it was full-sized) until the great extinction 65 million years ago at the end of the Cretaceous Period. 

"On other continents like Africa, you have as many as three large predators living in the same areas that split among them the job of eating meat," Sereno said. But in Africa, the allosaurs never went extinct, as they did in North America, possibly presenting an evolutionary opportunity for Raptorex. "We have no evidence that it was a competitive takeover," said Sereno, "because we have never found large tyrannosaurs and allosaurs together." 

Only 9 feet long but Raptorex already had the powerful jaws, puny arms, and quick legs of its much larger and more famous Tyrannosaurus Rex descendants.  Drawing by Todd Marshall

Henry Kriegstein, a private fossil collector, brought the nearly complete Raptorex skeleton to Sereno's attention after buying it from a vendor. After Sereno and colleagues finish a more detailed study of Raptorex, it will be returned to a museum in Inner Mongolia, the place where the Raptorex fossil was illicitly excavated.