A (relatively) miniature Tyrannosaurus rex skeleton—with the classic outsize jaws, long legs, and teensy arms—has been discovered in China, and is providing scientists insight into the evolutionary line that produced the beast that would someday inspire a million Halloween costumes. This scaled-down Tyrannosaurus ancestor, called Raptorex kriegsteini, was nine feet long and weighed only about as much as a human: 150 lbs. (A whippet compared to its descendant, which was nearly 100 times heavier and five times longer.) The discovery disproves a long-held belief among paleontologists that T. rex's distinctive features developed as a consequence of its enormous size. Scientists now think of Raptorex’s traits as “a body blueprint for a predator—jaws on legs, as it were—that is one of the most successful of the Mesozoic…" And they were scalable as Tyrannosaurus grew: “When they did there was no turning back until the asteroid hit."