| Dinosaurs first appeared during the Triassic period, approximately 237 million years ago, and were the dominant terrestrial vertebrates for 135 million years until the end of the Cretaceous (66 million years ago), when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic Period.
Although the word dinosaur means "terrible lizard", the name is somewhat misleading, as dinosaurs are not lizards. Instead, they represent a separate group of reptiles which, like many extinct forms, did not exhibit characteristics traditionally seen as reptilian, such as a sprawling limb posture or ectothermy.
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