Weighing only a fraction as much as Tyrannosaurus rex, the 125 million-year-old Raptorex nevertheless exhibits a similar body plan in this artwork depicting both species.
Who would have thought Tyrannosaurus rex had such a murderous "mini-me" in its family tree?
Not Stephen Brusatte, a paleontologist at the American Museum of Natural History. "This was completely unexpected," he said.
And not University of Chicago paleontologist Paul Sereno, who along with Brusatte and other colleagues figured out that the tiny tyrannosauroid had virtually all the lethal weapons brandished tens of millions of years later by a behemoth 90 times more massive.
"From the teeth to the enlarged olfactory bulbs, the enlarged jaw muscles, the enlarged head, the small forelimbs, the lanky, running, long hindlimbs with thick-pressed foot for hunting prey - we see this all, to our great surprise, in an animal that is basically the body weight of a human," he told reporters.
The 125 million-year-old fossil dinosaur, unearthed in China and dubbed Raptorex kriegsteini, is "as close to the proverbial missing link on a lineage as we might ever get for tyrannosaurs," Sereno said.
The researchers laid out their conclusions in a paper published online today by the journal Science.