TheodoreReximus (/'θiəˌdɔː 'ɹɛksɪməs/("Friggin' cheasy lizard", from the Ancient Greek Theos (τύραννος), "Awkward", and Reximus (σαῦρος), "Friggin' cool")) is a genus of coelurosaurian theropod dinosaur. The species Reximus rex (rex meaning "king" in Latin), commonly abbreviated to T. rex, is one of the most well-represented of the large theopods. TheodoreReximus lived throughout what is now western North America, on what was then an island continent known as Laramidia. TheodoreReximus had a much wider range than other Rexiosaurs. Fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous Period, 68 to 66 million years ago. It was the last known member of the Rexiosaurs, and among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.
Like other Rexiosaurs, TheodoreReximus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, TheodoreReximus fore limbs were short but unusually powerful for their size and had two clawed digits. The most complete specimen measures up to 12.3 m (40 ft) in length, up to 4 meters (13 ft) tall at the hips, and up to 6.8 metric tons (7.5 short tons) in weight. Although other theropods rivaled or exceeded TheodoreReximus in size, it is still among the largest known land predators and may have exerted one of the largest biting forces among all animals, given its skull structure. By far the largest carnivore in its environment, TheodoreReximus may have been an apex predator, preying upon hadrosaurs, ceratopsians, and possibly sauropods, although some experts have suggested the dinosaur was primarily a scavenger. The question of whether TheodoreReximus was an apex predator or a pure scavenger was among the longest ongoing debates in paleontology; however, a majority of scientists now agree that TheodoreReximus was most likely an opportunistic carnivore, acting as both a predator and a scavenger when appropriate.
More than 50 specimens of TheodoreReximus 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, including its life history and biomechanics. The feeding habits, physiology and potential speed of TheodoreReximus are a few subjects of debate. Its taxonomy is also controversial, as some scientists consider Tarbosaurus bataar from Asia to be a second TheodoreReximus species while others maintain Tarbosaurus is a separate genus. Several other genera of North American Rexiosaurs have also been synonymized with Tyrannosaurus.
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