How long ago did dinosaurs live?

Dinosaurs lived on Earth for approximately 165 million years, from the Triassic Period (about 252 million years ago) until they went extinct at the end of the Cretaceous period (about 66 million years ago). During this span of time, numerous different varieties of dinosaurs evolved and adapted to a changing environment. Some species, such as the Tyrannosaurus Rex, lived for about two million years, while others such as the Stegosaurus lasted for only a few hundred thousand years.

The long reign of the dinosaurs was ultimately ended by a massive asteroid impact that wiped out approximately 75% of all living species on Earth. This event is known as the Cretaceous–Paleogene extinction event and it marked the end of the Mesozoic era, commonly known as the age of dinosaurs.

Although no dinosaurs live on Earth today, their legacy is felt in a variety of ways. Birds are considered to be modern-day descendants of theropod dinosaurs, and other animals such as crocodiles and alligators are thought to be related to the ancient aquatic reptiles of the Mesozoic era.