Dinosaur

Dinosaurs were the dominant terrestrial vertebrate animals 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.

The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, and most paleontologists regard them as the only clade of dinosaurs to have survived until the present day.
Dinosaurs were a varied group of animals. Paleontologists have identified over 500 distinct genera and more than 1,000 different species of dinosaur, and remains have been found on every continent on Earth.Some dinosaurs were herbivorous, others carnivorous.

Some were bipedal, others quadrupedal, and others were able to shift between these body postures.

Many species developed elaborate skeletal modifications such as bony armor, horns or crests. Although generally known for their large size, many dinosaurs were human-sized or even smaller.

Most major groups of dinosaurs are known to have built nests and laid eggs, suggesting an oviparity similar to that of modern birds.
The term "dinosaur" was coined in 1842 by Sir Richard Owen and derives from Greek δεινός (deinos) "terrible, powerful, wondrous" + σαῦρος (sauros) "lizard". Through the first half of the twentieth century, most of the scientific community 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 numerous adaptations 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.

As a result, the word "dinosaur" has entered the vernacular, although its use and meaning in colloquial speech may be inconsistent with modern science.

In English, for example, "dinosaur" is commonly used to describe anything that is impractically large, slow-moving, obsolete, or bound for extinction.

General description

Using one of the above definitions, dinosaurs (aside from birds) can be generally described as terrestrial archosaurian reptiles with limbs held erect beneath the body, that existed from the Late Triassic (first appearing in the Carnian faunal stage) to the Late Cretaceous (going extinct at the end of the Maastrichtian).

Many prehistoric animals are popularly conceived of as dinosaurs, such as ichthyosaurs, mosasaurs, plesiosaurs, pterosaurs, and Dimetrodon, but are not classified scientifically as dinosaurs.

Marine reptiles like ichthyosaurs, mosasaurs, and plesiosaurs were neither terrestrial nor archosaurs; pterosaurs were archosaurs but not terrestrial; and Dimetrodon was a Permian animal more closely related to mammals.

Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic, especially the Jurassic and Cretaceous.

Other groups of animals were restricted in size and niches; mammals, for example, rarely exceeded the size of a cat, and were generally rodent-sized carnivores of small prey.

One notable exception is Repenomamus giganticus, a triconodont weighing between 12 kilograms (26 lb) and 14 kilograms (31 lb) that is known to have eaten small dinosaurs like young Psittacosaurus.
Dinosaurs were an extremely varied group of animals;

according to a 2006 study, over 500 dinosaur genera have been identified with certainty so far, and the total number of genera preserved in the fossil record has been estimated at around 1850, nearly 75% of which remain to be discovered.

An earlier study predicted that about 3400 dinosaur genera existed, including many which would not have been preserved in the fossil record.

As of September 17, 2008, 1047 different species of dinosaurs have been named.Some were herbivorous, others carnivorous. Some dinosaurs were bipeds, some were quadrupeds, and others, such as Ammosaurus and Iguanodon, could walk just as easily on two or four legs.

Many had bony armor, or cranial modifications like horns and crests. Although known for large size, many dinosaurs were human-sized or smaller. Dinosaur remains have been found on every continent on Earth, including Antarctica.No dinosaurs are known to have lived in marine or aerial habitats, although it is possible some feathered theropods were flyers.