This definition includes major groups such as ankylosaurians (armored herbivorous quadrupeds), stegosaurians (plated herbivorous quadrupeds), ceratopsians (bipedal or quadrupedal herbivores with neck frills), pachycephalosaurians (bipedal herbivores with thick skulls), ornithopods (bipedal or quadrupedal herbivores including ' duck-bills'), theropods (mostly bipedal carnivores and birds), and sauropodomorphs (mostly large herbivorous quadrupeds with long necks and tails). Both definitions result in the same set of animals being defined as dinosaurs: 'Dinosauria = Ornithischia + Saurischia'. It has also been suggested that Dinosauria be defined with respect to the MRCA of Megalosaurus and Iguanodon, because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria. Under phylogenetic nomenclature, dinosaurs are usually defined as the group consisting of the most recent common ancestor (MRCA) of Triceratops and modern birds (Neornithes), and all its descendants. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, and new discoveries are regularly covered by the media. The large sizes of some dinosaurs, as well as their seemingly monstrous and fantastic nature, have ensured their regular appearance in best-selling books and films, such as Jurassic Park. Since then, mounted fossil dinosaur skeletons have been major attractions at museums worldwide, and dinosaurs have become an enduring part of popular culture. The first dinosaur fossils were recognized in the early 19th century, with the name 'dinosaur' (meaning 'terrible lizard') being coined by Sir Richard Owen in 1842 to refer to these 'great fossil lizards'. Many dinosaurs were quite small, some measuring about 50 centimeters (20 inches) in length. The misconception that non-avian dinosaurs were uniformly gigantic is based in part on preservation bias, as large, sturdy bones are more likely to last until they are fossilized. While the dinosaurs' modern-day surviving avian lineage (birds) are generally small due to the constraints of flight, many prehistoric dinosaurs (non-avian and avian) were large-bodied-the largest sauropod dinosaurs are estimated to have reached lengths of 39.7 meters (130 feet) and heights of 18 m (59 ft) and were the largest land animals of all time.

Elaborate display structures such as horns or crests are common to all dinosaur groups, and some extinct groups developed skeletal modifications such as bony armor and spines. While dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, and some were able to shift between these stances. Evidence suggests that all dinosaurs were egg-laying, and that nest-building was a trait shared by many dinosaurs, both avian and non-avian.

Some were herbivorous, others carnivorous. Most research conducted since the 1970s, however, has indicated that dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction.

Through the first half of the 20th century, before birds were recognized as dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold-blooded. Dinosaurs are represented on every continent by both extant species (birds) and fossil remains. Using fossil evidence, paleontologists have identified over 900 distinct genera and more than 1,000 different species of non-avian dinosaurs. Birds, at over 10,700 living species, are among the most diverse groups of vertebrates. Dinosaurs can therefore be divided into avian dinosaurs-birds-and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.ĭinosaurs are varied from taxonomic, morphological and ecological standpoints. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. They first appeared during the Triassic period, between 245 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research. Birds are avian dinosaurs, and in phylogenetic taxonomy are included in the group Dinosauria.ĭinosaurs are a diverse group of reptiles of the clade Dinosauria.

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