text: About 12-13 m (39-43 ft) in length, 5 m (16 ft) tall and estimated to be from 4 tonnes [6] to 8 tonnes in weight, T. rex was one of the largest land carnivores of all time. Compared to other carnivorous dinosaurs, the skull of Tyrannosaurus is heavily modified. Many of the bones are fused together, preventing movement between them. The bones themselves are much more massive than is typical of a theropod, and the serrated teeth, far from being bladelike, are massive and oval in cross-section. Heavy wear, and the bite marks found on bones of other dinosaurs, indicate that these teeth could bite into solid bone. The teeth are 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 theropods, as measured by EQ. The neck was short and muscular, to support the head. The arms of T. rex were very small, perhaps to make up for the weight of its enormous head, but were very sturdy. They may have been used for grasping during mating or as aids in rising from a lying position, or perhaps to pin meat against the body while dragging a carcass to prevent it swinging around. The legs were relatively long and slender for an animal of its size. To compensate for its immense bulk, the interior of many bones was hollow. This considerably reduced the weight of the skeleton while maintaining much of the strength of the bones.