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(tīrăn´´ōsôr´ s, tĭr—)
[Gr.,=tyrant lizard], member of a family, Tyrannosauridae, of bipedal carnivorous saurischian dinosaurs characterized by having strong hind limbs, a muscular tail, and short forelimbs. Tyrannosaurids are theropods, having three toes on the hind feet. The oldest known tyrannosaurids lived approximately 120 million years ago. Fossilized bones have been found in Asia and North America. The family includes Albertosaurus, Tarbosaurus, and Tyrannosaurus.The best known species is the huge North American Tyrannosaurus rex, which lived around 70 million years ago. The largest were an estimated 39 ft (12 m) in total length and weighed around 10 tons. They had an elongated skull and large, spike-shaped teeth in jaws that could open to a 4-ft (122-cm) gape. Like the other tyrannosaurids, the short forelimbs had two fingers armed, like the three digits of the powerful hind limbs, with sharp, curved claws; on the foot was a spurred toe not reaching to the ground. A ferocious terrestrial carnivore, T. rex is believed to have existed only for a short time in the late Cretaceous period and to have dominated the North American continent at that time; fossil remains have been found in the W United States.For many years T. rex was believed to be the largest carnivorous dinosaur, but this honor was challenged by the 1995 discovery of the 42.6-ft (13-m) Giganotosaurus carolinii in Patagonia and the 1996 discovery of the 45-ft (13.7-m) Carcharodontosaurus saharicus in the Moroccan Sahara. Remains of a second Tyrannosaurus species, T. bataar, have been found in Mongolia. It was a contemporary of T. rex, but was somewhat smaller and had a comparatively smaller head and shorter arms.
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