Tyrannosaurus, from the Greek meaning "tyrant lizard" because of its size, large teeth and claws also known colloquially as T-Rex and "The King of the Dinosaurs", was a giant carnivorous theropod dinosaur from the Upper Maastrichtian, the last stage of the Cretaceous period, or about 70 million years ago. Over thirty skulls have been located and identified, all of them in North America. T-Rex was one of the largest land carnivores of all time, with a length of forty to forty-three feet, a heigth of approximately sixteen feet and weighing in at around 17,000 pounds. Unlike many other species, many of T-Rex's bones were fused together, preventing movement between them. The bones themselves were much more massive than was typical of a theropod, and the serrated teeth, far from being bladelike, were massive and oval in cross-section. Heavy wear, and the bite marks found on bones of other dinosaurs, indicate that those teeth could bite into solid bone. The teeth were often worn or broken at the tips from heavy use but, unlike mammals, were continually grown and shed throughout the life of the animal. Tyrannosaurus' brain was long and close to cylindrical, and it was probably among the most intelligent carnosaurs.