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Dinosaur
Dinosaurs are a diverse group of reptiles. They 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 period (about 65 million years ago), when the Cretaceous–Tertiary extinction event caused the extinction of most dinosaur species, except for some birds. The fossil recordindicates that birds evolved from theropod dinosaurs during the Jurassic period, and most paleontologists regard them as the only group of dinosaurs to have survived until the present day.[1]
Dinosaurs are a diverse and varied group of animals; birds, at over 9,000 species, are the most diverse group of vertebrate besides perciform fish.[2] Paleontologists have identified over 500 distinct genera[3] andmore than 1,000 different species of non-avian dinosaurs.[4] Dinosaurs are represented on every continent by both extant species and fossil remains.[5] Some dinosaurs are or were herbivorous, others carnivorous. Some have been bipedal, others quadrupedal, and others have been able to shift between these body postures. Many non-avian species developed elaborate skeletal modifications such as bonyarmor, horns or crests. Avian dinosaurs have been the planet's dominant flying vertebrate since the extinction of the pterosaurs. Although generally known for the large size of some species, most dinosaurs were human-sized or even smaller. Most groups of dinosaurs are known to have built nests and laid eggs.
The term "dinosaur" was coined in 1842 by the English paleontologist Richard Owen, andderives from Greek δεινός (deinos) "terrible, powerful, wondrous" + σαῦρος (sauros) "lizard". Through the first half of the twentieth century, most of the scientific community mistakenly believed dinosaurs to have been sluggish, unintelligent cold-blooded animals. Most research conducted since the 1970s, however, has indicated that dinosaurs were active animals with elevated metabolisms and numerousadaptations for social interaction.
Since the first dinosaur fossils were recognized in the early nineteenth century, mounted dinosaur skeletons have been major attractions at museums around the world, and dinosaurs have become a part of world culture. They have been featured in best-selling books and films such as Jurassic Park, and new discoveries are regularly covered by the media. Theoutdated image of dinosaurs as maladapted extinct monsters has led to the word "dinosaur" entering the vernacular to describe anything that is impractically large, slow-moving, obsolete, or bound for extinction.

Natural history
Origins and early evolution
For a long time many scientists thought dinosaurs were polyphyletic with multiple groups of unrelated "dinosaurs" evolving due to similarpressures,[27][28][29] but dinosaurs are now known to have formed a single group.[11][30]
Dinosaurs diverged from their archosaur ancestors approximately 230 million years ago during the Middle to Late Triassic period, roughly 20 million years after the Permian–Triassic extinction event wiped out an estimated 95% of all life on Earth.[31][32] Radiometric dating of the rock formation that containedfossils from the early dinosaur genus Eoraptor establishes its presence in the fossil record at this time. Paleontologists believe Eoraptor resembles the common ancestor of all dinosaurs;[33] if this is true, its traits suggest that the first dinosaurs were small, bipedal predators.[34] The discovery of primitive, dinosaur-like ornithodirans such as Marasuchus and Lagerpeton in Argentinian MiddleTriassic strata supports this view; analysis of recovered fossils suggests that these animals were indeed small, bipedal predators.
When dinosaurs appeared, terrestrial habitats were occupied by various types of basal archosaurs and therapsids, such as aetosaurs, cynodonts, dicynodonts, ornithosuchids, rauisuchias, and rhynchosaurs. Most of these other animals became extinct in the Triassic, in one...