When did dinosaurs become extinct? July 30, 2020 by Pamela Landy Dinosaurs lived during the Mesozoic era, 225 million to 65 million years ago. By the end of that era, all Archosauria (or “ruling reptiles”), except crocodiles, had died. Related Answers Why was the National Rail Passenger Corporation Amtrak founded in 1970? How old is the species of fish known as the coelacanth? What is the earliest era of geologic time? In what geologic era did man evolve? When did the dodo become extinct? When did the passenger pigeon become extinct in the U.S.?