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 and thrived during this time. The Mesozoic is divided into three periods: Triassic, Jurassic, and Cretaceous, each marked by significant changes in climate and life forms. During the Mesozoic, the continents were arranged differently than today, and the climate was generally warmer. This era saw the rise of not only dinosaurs but also 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 dinosaurs and paved the way for mammals to become the dominant land animals.