Tyrannosaurs (literally "Tyrant Lizard") was one of the very last dinosaurs. It was a giant carnivore (18 feet tall and 40 feet long) with a large head bearing enormous six-inch long teeth. If not actually the largest, it was among the largest carnivorous dinosaurs that ever lived.
Oddly, the forelimbs of Tyrannosaurs were very small in size and bore only two claws. It is difficult to imagine how the forearms were used, although massive muscle attachment sites on the arm bones suggest that the arms were strong and not merely functionless vestiges. One estimate suggests that the arm was strong enough to lift more than 450 pounds.
The hind limbs of Tyrannosaurs were powerful and were probably used not only for locomotion, but for grasping prey as well. The flexor tendons on the bottom of the feet were evidently very powerful, giving a grip similar to the talons of an eagle.
Tyrannosaurus was first discovered in 1902 by the famous paleontologist Barnum Brown. The bones were discovered in the Hell Creek region of Montana. Brown ultimately collected two skeletons, one in 1902 and a second, more complete specimen in 1908. The first specimen is the official scientific name-holder for the species Tyrannosaurus rex (rex = "king") and is now located in the Carnegie Museum in Pittsburgh. The second, more complete skeleton resides in New York, at the American Museum of Natural History. The New York specimen was originally mounted with a distinct upright posture, but the skeleton was later remounted to better reflect current scientific thinking. The remodeled skeleton has a shortened tail, which is borne off the ground.
A new, very complete skeleton of T. rex was found in 1990 in South Dakota. Nicknamed "Sue," this wonderful specimen can be seen on display at the Field Museum of Natural History in Chicago.
In addition to North America, Tyrannosaurus is also known from Mongolia. Specimens of Tyrannosaurus found there, were originally described under the scientific name Tarbosaurus. Apparently, these Mongolian specimens represent a different species of Tyrannosaurus, known as Tyrannosaurus bataar (bay-tar).