Tyrannosaurus rex teeth mandible fossil. Tyrannosaurus rex was a carnivorous dinosaur that lived during the Upper Cretaceous period, 68 to 66 million years ago. Complete skulls and skeletal remains from around 20 individuals have been discovered, allowing for detailed scientific reconstructions. Research has revealed that the Tyrannosaurus rex possessed a powerful bone-crushing bite, which was made possible by a stiff lower jaw. This stiffness was facilitated by a specialized, boomerang-shaped bone that crossed the joint, reinforcing the lower jaw. Found in North Dakota, USA.