The Artist

Until the late 20th century, all groups of dinosaurs were believed to be extinct. The fossil record, however, indicates that birds, which are now termed "avian dinosaurs,"[3] are the modern descendants of feathered dinosaurs,[4] having evolved from theropod ancestors during the Jurassic Period.[5] As such, birds were the only dinosaur lineage to survive the mass extinction event.[6] Throughout the remainder of this article, the term "dinosaur" is sometimUntil the late 20th century, all groups of dinosaurs were believed to be extinct. The fossil record, however, indicates that birds, which are now termed "avian dinosaurs,"[3] are the

While dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal 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 armor and spines. 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)[12] and heights of 18 meters (59 feet)[13] 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 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.