Tyrannosaurus rex was one of the largest land carnivores of all time, measuring up to 43.3 feet long, and 16.6 ft tall, with an estimated mass that goes up to 7 tons. Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to the large and powerful hindlimbs, Tyrannosaurus forelimbs were small and they retained only two digits.


Fossils of T. rex have been found in North American rock formations dating to the last three million years of the Cretaceous Period at the end of the Maastrichtian stage, approximately 68.5 to 65.5 million years ago; it was among the last dinosaurs to exist prior to the Cretaceous-Tertiary extinction event. More than 30 specimens of T. rex have been identified, some of which are nearly complete skeletons. Some researchers have discovered soft tissue as well. The abundance of fossil material has allowed significant research into many aspects of its biology, including life history and biomechanics.