The Mesozoic Era is a geological time period that lasted from about 252 to 66 million years ago. It is often called the "Age of Reptiles" because it was dominated by dinosaurs, which evolved during this time. The era is divided into three periods: the Triassic, Jurassic, and Cretaceous. During the Mesozoic, the continents were arranged differently than today, and the climate was generally warmer. This era saw the rise of many other species, including the first mammals and birds. The Mesozoic ended with a mass extinction event, likely caused by an asteroid impact, which led to the decline of the dinosaurs.