Until fairly recently Tyrannosaurus Rex was thought to be the largest meat eating hunter ever to have stalked the Earth. The discovery of Carcharodontosaurus, Giganotosaurus and Tarbosaurus have changed it's status as 'king of the tyrant lizards'. Strangely, thought, Tyrannosaurus is still the dinosaur we think of when asked to name a gigantic meat eater. Typically, it had a very large head with powerful jaws and huge saw-edged teeth capable of crunching through bones. The head was 1.5m (5ft) long and the biggest teeth are 30cm (1 ft) from the point to the base to the root. T - Rex has been described as the most efficient killer to have appeared in the fossil record. There are beautiful exhibits at the Natural History Museum in New York and the Field museum in Chicago. In the Field Museum, 'Sue', the most expensive dinosaur ever, is on display. In 1997, she was bought for $8.4 million ($8.4,000,000) at sotheby's in New York. The exhibits in New York and Chicago show how well balanced Tyrannosaurus was and how threatening it would have been to even the largest, best - amoured dinosaurs. Massive scars on Tyrannosaurus bones were probably the result of Tyrannosaurids fighting among themselves. Even the dung of T - Rex was on a giant scale: a fossil dropping 43 cm (17 in) long was discovered in Saskatchewan, Canada, in 1998.