The geological era that extended from the end of the Palaeozoic era, about 251 million years ago, to the beginning of the Cenozoic era, about 66 million years ago. It comprises the Triassic, Jurassic, and Cretaceous periods. The Mesozoic era is often known as the Age of Reptiles as these animals, which included the dinosaurs, pterosaurs, and ichthyosaurs, became the dominant animal life form; most became extinct before the end of the era.