Dinosaurs (Greek δεινόσαυρος, deinosauros) were the dominant vertebrate animals of terrestrial ecosystems for over 160 million years, from the late Triassic period (about 230 million years ago) until the end of the Cretaceous period (65 million years ago), when most of them became extinct in the Cretaceous–Tertiary extinction event. The 10 000 living species of birds have been classified as dinosaurs.

The term "dinosaur" was coined in 1842 by Sir Richard Owen and derives from Greek δεινός (deinos) "terrible, powerful, wondrous" + σαῦρος (sauros) "lizard". It is sometimes used informally to describe other prehistoric reptiles, such as the pelycosaur Dimetrodon, the winged pterosaurs, and the aquatic ichthyosaurs, plesiosaurs and mosasaurs, although none of these animals were dinosaurs. Through the first half of the 20th century, most of the scientific community believed dinosaurs to have been slow, unintelligent cold-blooded animals. Most research conducted since the 1970s, however, has supported the view that dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. The resulting transformation in the scientific understanding of dinosaurs has gradually filtered into popular consciousness.

The 1861 discovery of the primitive bird Archaeopteryx first suggested a close relationship between dinosaurs and birds. Aside from the presence of fossilized feather impressions, Archaeopteryx was very similar to the contemporary small predatory dinosaur Compsognathus. Research has since identified theropod dinosaurs as the most likely direct ancestors of birds; most paleontologists today regard birds as the only surviving dinosaurs, and some suggest that dinosaurs and birds should be grouped into one biological class. Aside from birds, crocodilians are the only other close relatives of dinosaurs to have survived until the present day. Like dinosaurs and birds, crocodilians are members of Archosauria, a group of reptiles that first appeared in the very late Permian and came to predominate in the mid-Triassic.

Since the first dinosaur fossils were recognized in the early nineteenth century, mounted dinosaur skeletons have become major attractions at museums around the world. Dinosaurs have become a part of world culture and remain consistently popular. They have been featured in best-selling books and films (notably Jurassic Park), and new discoveries are regularly covered by the media.

Etymology

The taxon Dinosauria was formally named in 1842 by English palaeontologist Richard Owen, who used it to refer to the "distinct tribe or sub-order of Saurian Reptiles" that were then being recognized in England and around the world. The term is derived from the Greek words δεινός (deinos meaning "terrible", "powerful", or "wondrous") and σαύρα (saura meaning "lizard" or "reptile"). Though the taxonomic name has often been interpreted as a reference to dinosaurs' teeth, claws, and other fearsome characteristics, Owen intended it merely to evoke their size and majesty. In colloquial English "dinosaur" is sometimes used to describe an obsolete or unsuccessful thing or person, despite the dinosaurs' 160 million year reign and the global abundance and diversity of their descendants, the birds.