Britannica Sources used in this answer

When did dinosaurs first appear and when did most dinosaurs become extinct?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Illustration showing examples of vertebrates: a turtle for reptiles, a songbird for birds, a bluegill fish, a salamander for amphibians, and two mammals-a whale and a groundhog. — Vertebrate The major groups of vertebrates include fishes, amphibians, reptiles, birds, and mammals.

Dinosaurs first appeared during the Triassic Period, which lasted from approximately 252.2 million to 201.3 million years ago. While pinpointing the exact moment of their origin is difficult due to the nature of the fossil record, paleontologists identify early dinosaur-like creatures in the Middle and Late Triassic epochs.123

Most dinosaurs became extinct 66 million years ago at the end of the Cretaceous Period. This mass extinction, known as the K-Pg (Cretaceous-Paleogene) extinction event, was triggered by a massive asteroid impact near the Yucatán Peninsula, which caused catastrophic global environmental changes and the collapse of many ecosystems.45

It is important to note that extinction is a natural, ongoing process in geologic time, and the history of dinosaurs throughout the Mesozoic Era was characterized by the continuous replacement of species as some died out and others evolved.4