Anatomy: This theropod dinosaur had a bulky body, a big head with powerful jaws, sharp teeth, and a stiff tail. Its front legs were tiny. T-rex was about 15 to 20 feet (4.6 to 6 m) tall and was about 40 feet (12.4 m) long. It weighed roughly 5 to 7 tons. T. rex probably had about 200 bones, roughly the same as us (no one knows exactly how many it had, since no complete T. rex skeletons have been found).