Arctic Dinosaurs ( Documentary 2017 )

Dinosaurs are a diverse group of reptiles of the clade Dinosauria that first appeared during the Triassic period. Although the exact origin and timing of the evolution of dinosaurs is the subject of active research,[1] the current scientific consensus places their origin between 231 and 243 million years ago.[2] They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago. Their dominance continued through the Jurassic and Cretaceous periods and ended when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups 66 million years ago. The fossil record indicates that birds are modern feathered dinosaurs,[3] having evolved from theropod ancestors during the Jurassic Period.[4] As such, birds were the only dinosaur lineage to survive the mass extinction event.[5] Throughout the remainder of this article, the term "dinosaur" is sometimes used generically to refer to the combined group of avian dinosaurs (birds) and non-avian dinosaurs; at other times it is used to refer to the non-avian dinosaurs specifically, while the avian dinosaurs are sometimes simply referred to as "birds". This article deals primarily with non-avian dinosaurs.