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Tyrannosaurus is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex is commonly abbreviated to T. rex. It lived throughout what is now western North America. Fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous Period, 67 to 66 million years ago. It was among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.

Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hindlimbs, Tyrannosaurus forelimbs were short and bore two clawed digits. Although other theropods rivaled or exceeded Tyrannosaurus rex in size it is one of the largest known land predators in history. The most complete specimen measures up to 12.3 m in length, up to 4 m tall at the hips, and up to 6.8 MT in weight. Tyrannosaurus rex would have been an apex predator, preying upon hadrosaurs, ceratopsians, and possibly sauropods.

More than 50 specimens of Tyrannosaurus rex have been identified, some of which are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology. Its taxonomy is also controversial: some scientists consider Tarbosaurus bataar from Asia to be a second species of Tyrannosaurus and others maintaining Tarbosaurus as a separate genus. (see more...)