Tyrannosaurus means ‘tyrant lizard’. It is the name of a group (genus) or related species of which the most famous is Tyrannosaurus rex (rex means ‘king’). The shortened version, T. rex, is often used (Note it is capital T, dot, small rex, not T-Rex or other spellings).

Tyrannosaurus was the most common large hunting dinosaur at the end of dinosaur times (68 to 65 million years ago), and this is probably why its bones were the first hunting dinosaur bones to be discovered.
Tyrannosaurus was covered with the pebbly scales common in most dinosaurs. Tyrannosaurus has two ‘fingers’ on its front limbs, but these limbs were tiny compared with its gigantic rear limbs. It also had a massive head.
It grew up to 13m long and was 4m tall at the hips (note that hip measurements are used to make it easier to compare different kinds of dinosaur). Like all dinosaurs, Tyrannosaurus pivoted around its hips, balancing the weight of its head with the weight of its tail. It weighed about 7 tonnes.
Like other dinosaurs, many of the bones were hollow, so reducing what would otherwise be an incredible weight of bone. The biggest T. rex head is 1.5m long. In this head, which was triangular, the eyes were set far apart and facing forwards giving it eyesight that was possibly as good as a modern hawk. That would be useful for spotting prey in the distance. The head ended in a narrow snout.
For much of the time, Tyrannosaurus may also have been a successful scavenger, as it had a very sensitive nose able to smell rotting carcasses from a long way off.
Tyrannosaurus may have been able to run when it was young, but as it grew up this would have become more and more difficult (picture ). Elephants have the same problem. But although they didn’t run, they ‘walked’ fast and may have reached 40km an hour. If so, they would have been the fastest large dinosaurs – much faster than their plant-eating prey.
T. rex could bite more powerfully than any other dinosaur. The backward-sloping teeth stopped any prey from slipping away.
T. rex grew ‘slowly’ at first, still being less than 2 tonnes at the age of 14. Then it put on a phenomenal spurt of growth, adding 600kg a year for the next four years, before slowing down as it reached adulthood.
Many T. rex seem to have died about 6 years after becoming fully grown, so the animal may not have had a long natural life.
Tarbosaurus is closely related to Tyrannosaurus, but lived and evolved in Mongolia after North America split away from Asia.