when were dinosaurs alive

Dinosaurs were alive during the Mesozoic Era, which lasted from about 252 million years ago to 66 million years ago. This era is divided into three periods: the Triassic, Jurassic, and Cretaceous. Dinosaurs first appeared in the Triassic period around 245 million years ago and became extinct at the end of the Cretaceous period about 66 million years ago due to a mass extinction event. Birds are considered the living descendants of certain dinosaurs and thus represent the dinosaur lineage that continues today.