Dinosaurs were the dominant vertebrate animals of terrestrial ecosystem for over 160 million years, from the late Triassic period (about 230 million years ago) to the end of the Cretaceous period (65 million years ago), when most of them became extinct in the Cretaceous–Tertiary extinction event.
The discovery in 1862 of Archaeopteryx first suggested a close relationship between dinosaurs and birds, as only the fossilized feathers of Archaeopteryx clearly distinguished it from contemporary small predatory dinosaurs such as Compsognathus. Research since the 1970s indicates that theropod dinosaurs are most likely the ancestors of bird; in fact, most paleontologists regard birds as the only surviving dinosaurs and some believe dinosaurs and birds should be put together under one biological class. Crocodilians are the other surviving close relatives of dinosaurs, and both groups are members of the Archosauria, a group of reptiles that first appeared in the very late Permian and became...
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