[The following is an exact transcript of this podcast.]

Ask any young dinosaur fanatic about the mighty Tyrannosaurus rex and you’ll probably get a fairly accurate description: huge reptile, big head, powerful jaws, tiny little arms. Scientists had thought that the animal evolved its bizarre proportions as it grew to its gargantuan stature. But in this week’s issue of the journal Science, paleontologist Paul Sereno describes a newly discovered miniature tyrannosaurid that evolved millions of years earlier—and has all the attributes of the larger one.

The tiny dino had been excavated in Mongolia illegally and sold to a private collector. He contacted Sereno to evaluate the preserved tyrannosaurid. Sereno agreed to do so if the dinosaur was donated to science, and eventually returned to China.

The dinosaur is about nine feet long and had an estimated weight of only 150 pounds. But it’s all there—the tiny arms, the huge head, the large teeth and muscular jaw. A hundred-twenty-five million years later, that animal’s descendants had ballooned into an almost exact replica more than 90 times larger. Sereno and his colleagues say the body plan must have been a successful structure for hunting prey—and ultimately thrilling dinosaur lovers everywhere.

—Cynthia Graber

See a side-by-side comparison of the skulls of T. rex and the new dino.