The age of the dinosaurs began about 215 million years ago and lasted for about 150 million years. They lived during what is known as the Mesozoic, or “middle life,” era in the history of life on Earth. Their ancestors—the fishes, amphibians, and early reptiles—had lived during the Palaeozoic, or “ancient life,” era. No dinosaurs live today, but during the Mesozoic era they were an amazingly successful group of animals. They dominated the land completely, and their relatives ruled the seas and the air. The word dinosaur means “terrible lizard,” and some of them must have been truly terrifying. The huge sauropods and ferocious, flesh-eating carnosaurs were awe-inspiring creatures. However, by the start of the Cenozoic, or “new life,” era, no dinosaurs remained. It is thought that dramatic changes in the world’s climate caused their extinction, and mammals then took over the land.