Dinosaurs (Greek <δεινόσαυρος,deinosavros> ) were the dominant vertebrate animals of terrestrial ecosystems 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 10,000 living species of birds have been classified as dinosaurs.

The discovery in 1861 of 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 since the 1970s indicates that theropod dinosaurs are most likely the ancestors of birds; 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 dominant in the mid-Triassic.

For about the first half of the 20th century, both scientists and the general public regarded dinosaurs as slow, unintelligent cold-blooded animals. However, the bulk of research since the 1970s has supported the view that they were active animals with elevated metabolisms, and often with adaptations for social interactions. This change of view was strongly influenced by evidence of the descent of birds from theropod dinosaurs.

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 among children. They have been featured in best-selling books and films (notably Jurassic Park), and new discoveries are regularly covered by the media.

The term "dinosaur" was first 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 were dinosaurs.

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.