The Tyrannosaurus rex (T. rex) was one of the most ferocious dinosaurs that roamed Earth in the very late Cretaceous period — about 66 million years ago. Over the years, scientists have collected substantial information on the tiny-armed reptile itself. However, very little is known about how the vicious predator evolved. Now paleontologists at the Badlands Dinosaur Museum in North Dakota believe they may have found an essential missing link to the T. rex's lineage.