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Birds are thus considered to be dinosaurs and dinosaurs are, therefore, not extinct. Barrett in 2017 suggested a radical revision of dinosaurian systematics. recovered the Ornithischia as being closer to the Theropoda than the Sauropodomorpha, as opposed to the traditional union of theropods with sauropodomorphs.
Birds are classified as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs. They resurrected the clade Ornithoscelida to refer to the group containing Ornithischia and Theropoda.
Dinosauria itself was re-defined as the last common ancestor of Triceratops horridus, Passer domesticus, Diplodocus carnegii, and all of its descendants, to ensure that sauropods and kin remain included as dinosaurs.
Many prehistoric animal groups are popularly conceived of as dinosaurs, such as ichthyosaurs, mosasaurs, plesiosaurs, pterosaurs, and pelycosaurs (especially Dimetrodon), but are not classified scientifically as dinosaurs, and none had the erect hind limb posture characteristic of true dinosaurs.
Birds are now recognized as being the sole surviving lineage of theropod dinosaurs.
The large sizes of some dinosaur groups, as well as their seemingly monstrous and fantastic nature, have ensured dinosaurs' regular appearance in best-selling books and films, such as Jurassic Park.
Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, and new discoveries are regularly covered by the media.
Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic, especially the Jurassic and Cretaceous periods.
Other groups of animals were restricted in size and niches; mammals, for example, rarely exceeded the size of a domestic cat, and were generally rodent-sized carnivores of small prey.