Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria.

They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period (about 230 million years ago) until the end of the Cretaceous (about 65 million years ago), when the Cretaceous–Paleogene extinction event led to the extinction of all non-avian dinosaurs at the close of the Mesozoic era.

The fossil record indicates that birds evolved within theropod dinosaurs during the Jurassic period. Some of them survived the Cretaceous–Paleogene extinction event, including the ancestors of all modern birds.

Consequently, in modern classification systems, birds are considered a type of dinosaur—the only group which survived to the present day