Dinosaurs are a diverse group of animals of the clade Dinosauria. They first appeared during the Triassic period, approximately 230 million years ago, and were the dominant terrestrial vertebrates for 135 million years, from the beginning of the Jurassic (about 200 million years ago) until the end of the Cretaceous (65.5 million years ago), when the Cretaceous'Paleogene extinction event led to the extinction of most dinosaur groups at the close of the Mesozoic Era. . The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic Period, and consequently they are considered a subgroup of dinosaurs in modern classification systems. Some birds survived the extinction event that occurred 65 million years ago, and continue the dinosaur lineage to the present day.
Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints. Birds, at over 9,000 living species, are the most diverse group of vertebrates besides perciform fish. U