Tyrannosaurus Rex

(Lat., "tyrant-lizard king"), large, bipedal, carnivorous DINOSAUR, (q.v.) of the family Tyrannosauridae, of the latter part of the Mesozoic era. About 14 m (about 45 ft) long, about 5 m (about 19 ft) tall, and weighing more than 4 metric tons, Tyrannosaurus was well equipped for preying on the large herbivorous dinosaurs of 70 million years ago. Its long skull had powerful jaws with sharp, doubly serrated teeth, some of which were 15 cm (6 in) long. The tiny forelimbs, out of proportion to the rest of the massive body, each bore two sharp claws; the powerful hind limbs each were armed with three forward-pointing claws, well suited for tearing flesh, and a fourth, backward-pointing claw. Fossils found in North America (Montana and South Dakota) and Mongolia in strata of Upper Cretaceous age (see Cretaceous Period) indicate that the species came into being and became extinct in the relatively short space of a few million years. In 1996 fossils were found in Thailand of a much smaller tyrannosaur, about 6 m (about 21 feet) from nose to tail, that lived some 50 million years before Tyrannosaurus rex; this discovery suggests that tyrannosaurs may have evolved in Asia and spread to North America over a land bridge across the Bering Sea.