Topics: Dinosaur, Dinosaurs, Triassic Pages: 13 (3685 words) Published: February 1, 2013
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For other uses, see Dinosaur (disambiguation).
Temporal range: Middle Triassic–Present, 231.4–0 Ma (range includes birds) PreЄ
A collection of fossil dinosaur skeletons. Clockwise from top left: Microraptor gui (a winged theropod), Apatosaurus louisae (a giant sauropod), Stegosaurus stenops (a plated stegosaur), Triceratops horridus (a horned ceratopsian), Edmontosaurus regalis (a duck-billed ornithopod), Gastonia burgei (an armored ankylosaur). Scientific classification e

Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauriformes
Clade: Dinosauria
Owen, 1842
Major groups


Dinosaurs are a diverse group of animals of the clade Dinosauria. They first appeared during the Triassic period, approximately 230 million years ago, and were the dominant terrestrial vertebrates for 135 million years, from the beginning of the Jurassic (about 200 million years ago) until the end of the Cretaceous (66 million years ago), when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups at the close of the Mesozoic Era. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic Period and, consequently, they are considered a subgroup of dinosaurs in most modern classification systems.[1][2] Some birds survived the extinction event that occurred 66 million years ago, and their descendants continue the dinosaur lineage to the present day.[3]

Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints. Birds, at over 9,000 living species, are the most diverse group of vertebrates besides perciform fish.[4] Using fossil evidence, paleontologists have identified over 500 distinct genera[5] and more than 1,000 different species of non-avian dinosaurs.[6] Dinosaurs are represented on every continent by both extant species and fossil remains.[7] Some are herbivorous, others carnivorous. Most dinosaurs have been bipedal,[not verified in body] though many extinct groups included quadrupedal species, and some were able to shift between these body postures. Many species possess elaborate display structures such as horns or crests, and some prehistoric groups developed skeletal modifications such as bony armor and spines. Birds have been the planet's dominant flying vertebrate since the extinction of the pterosaurs, and evidence suggests that egg laying and nest building is a trait shared by all dinosaurs. Many prehistoric dinosaurs were large animals—the largest sauropods may have achieved a length of 58 meters (190 feet) and a height of 9.25 meters (30 feet 4 inches)[8]—but the idea that non-avian dinosaurs were uniformly gigantic is a misconception based on preservation bias; large, sturdy bones are more likely to last until they are fossilized. Many dinosaurs were quite small; Xixianykus, for example, was only about 50 cm (20 in) long.

Although the word dinosaur means "terrible lizard", the name is somewhat misleading, as dinosaurs are not lizards. Rather, they represent a separate group of reptiles with a distinct upright posture not found in lizards, and many extinct forms did not exhibit traditional reptilian characteristics. Additionally, many prehistoric animals, including mosasaurs, ichthyosaurs, pterosaurs, plesiosaurs, and Dimetrodon, are popularly conceived of as dinosaurs, but are not classified as dinosaurs. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the scientific community believed dinosaurs to be sluggish and cold-blooded. Most research...
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