Dinosaurs lived during a massive stretch of Earth’s history known as the Mesozoic Era, which began about 252 million years ago and ended around 66 million years ago. This era is often called the Age of Dinosaurs because dinosaurs were the dominant animals on land for most of this time.

The Mesozoic Era is divided into three periods. First came the Triassic Period, when the very first dinosaurs appeared. Next was the Jurassic Period, when dinosaurs grew larger and more diverse, including some of the most famous giants. Finally, the Cretaceous Period saw the rise of advanced dinosaurs, flowering plants, and eventually the sudden event that wiped out most dinosaurs.

Dinosaurs didn’t all live at the same time. Some species lived millions of years apart and would never have met. When the Age of Dinosaurs ended about 66 million years ago—likely due to a massive asteroid impact—most dinosaurs went extinct, but their legacy continued through birds.