Perhaps no restoration of the great carnivore has been as influential or celebrated as the genetically engineered tyrant that terrorizes Jurassic Park, which is being re-released in 3D today. Revived through computerized special effects and puppetry, the film's T. rex is a muscular, agile predator far more imposing than the tottering, tail-dragging representations that had appeared on film before. And in the 20 years since Jurassic Park debuted, as knowledge about T. rex has increased, the dinosaur has become even scarier still.

"It's hard to pick a single coolest discovery about Tyrannosaurus rex itself over the last 20 years," says University of Maryland tyrannosaur expert Thomas R. Holtz, Jr. Paleontologists have started to understand how drastically T. rex