Dinosaurs predominantly lived during the Mesozoic Era, which is often referred to as the "Age of Reptiles." This era spanned approximately 180 million years and is divided into three major periods: the Triassic, Jurassic, and Cretaceous. The Mesozoic Era began around 252 million years ago and ended about 66 million years ago with the mass extinction event that wiped out the dinosaurs, along with many other species. During this time, dinosaurs evolved into various shapes and sizes, adapting to different environments and filling ecological niches as the dominant terrestrial vertebrates.