It's not so much the dinosaur's towering size that makes Tyrannosaurus rex seem so scary. It's that massive head — huge, even relative to its big body — packed with long, razor-sharp teeth. Says University of Chicago paleontologist Paul Sereno: T. rex's body plan is simply "jaws on fast-running legs." Until this year, dinosaur experts thought the dinosaur's big head and mostly irrelevant little forearms evolved along with the animal's overall size. Not anymore: in September, Sereno and his colleagues announced in the journal Science the discovery of a miniature version of T. rex, dating to about 125 million years ago. The big-headed, puny-armed body plan, in other words, was in place about 60 million years before Tyrannosaurus came along. The scientists named the new find Raptorex kriegsteini, after Henry Kriegstein, a fossil collector who bought the ancient bones without realizing they were probably smuggled out of China. When he found out, he agreed to donate the bones for scientific study and eventual repatriation.