Dinosaurs (from Greek: δεινός terrible or potent, and σαύρα lizard) are a diverse group of animals that 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 most dinosaur species 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.
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