Tyrannosaurus Rex, whose name means "tyrant lizard king", had a large, sturdy head and long hind legs and a tail. In comparison, its arms were very short with two-fingered hands. It is believed that T-Rex was able to balance skilfully and moved around on its two hind legs. Dinosaurs lived about 225 million years ago. It is thought likely that the dinosaurs were wiped out around 65 million years ago, when many plants and animals died as a result of climatic changes brought about by a meteor striking the earth, but no one knows what really happened.