At 12 meters long and weighing 7,250 kilograms, the T. rex was the largest meat-eating animal that ever lived. One look at this tooth indicates how fierce this predator must have been. They had approximately 60 teeth for grasping and tearing food, and to use as weapons during fights. The T. rex reigned during the late Cretaceous period some 65-70 million years ago. Size: 12cm.