Dinosaurs are a diverse group of raptiles of the clade Dinosauria. They first appeared during the triassic period between 243 and 233.23 million years ago , although the exact origin and timing of the evolutions of dinausaures is the subject of active research. They became the dominant terrestrial vertebrates after the triassic event 201.3 million years ago; their dominance continued through the jurassic and cretaceaux periods. The fossile record demonstrates that birds are modern feathered dinausaures , having evolved from earlier theropodes during the late jurassica epoch. As such, birds were the only dinosaur lineage to survive theevent approximately 66 million years ago. Dinosaurs can therefore be divided into avian dinosaurs, or birds; and non-avian dinosaurs, which are all dinosaurs other than birds. This article deals primarily with non-avian dinosaurs.
Dinosaurs are a varied group of animals from taxonomic morphological and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish. Using fossil evidence, have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both extant species (birds) and fossil remains. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold blooded. however, has indicated that all dinosaurs were active animals with elevated numerous adaptations for social interaction. Evidence suggests that all dinosaurs were egg laying ; and nest-building was a trait shared by many dinosaurs, both avian and non-avian.
While dinosaurs were ancestrally bipedal many groups included species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, and some extinct groups developed skeletal modifications such as bony. 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 dinosaurs are estimated to have reached lengths of 39.7 meters (130 feet) and heights of 18 meters (59 feet) and were the largest land animals of all time. Still, the idea that non-avian dinosaurs were uniformly gigantic is a misconception based in part on preservation bias, as large, sturdy are more likely to last until they are fossilized. Many dinosaurs were quite small: for example, was only about 50 cm (20 in) long.