What is a dinosaur ?

Dinosaurs are a group of reptiles called archosaurian. For 160 million years, dinosaurs dominated the land in the late Triassic period until a meteor wiped them all out 230 million years ago. Modern birds nowadays are from a line of dinosaurs that survived the extinction. They were part of the major wave biodiversity that occured after the catastrophic event of extinction.

Dinosaurs, including birds, belong to a group called superorder dinosaurian. Birds’ closest relatives are pterosaurs or the flying reptiles. Dinosaurs and pterosaurs are members of unranked archosaurs called Orniithodira. Aside from birds, the order crocodilian like alligators, crocodiles and caimans are the only surviving achosaurs.

Dinosaurs are all edscendants of the normal ancestor of the Triceratops dinosaur and modern birds. This common ancestor lined in the period of Triassic, so the dinosaurs covers a huge group. Modern birds and triceratops are chosen because they are indistinctly related in some way; as some evidence suggest that the descendants of their ancestors cover all dinosaurs.

Dinosaurs are grouped according to their hip structure – as ornithischids (bird-hipped) and as saurischids (lizard-hipped). The lizard-hipped dinosaurs includes the theropods, tyrannosaurus rex, sauropodomorphs and mostly bipedal carnivorous dinosaurs. The bird-hipped dinosaurs include a wide range of herbivores, such as ceratopsians.

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