Dinosauria (Dinosaurs)

• Main Author: Carpenter, Kenneth
• Format: Other/Unknown Material
• Language: English
• Published: Wiley 2011
• Subjects: Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1002/9780470015902.a0001545.pub2; https://onlinelibrary.wiley.com/doi/pdf/10.1002/9780470015902.a0001545.pub2; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/9780470015902.a0001545.pub2

Abstract Dinosaurs are a group of extinct vertebrates that lived from 230 to 65 million years ago (Ma). They originated in southern Pangaea during the Middle Triassic from a small, meter‐long bipedal archosaur (the group that includes crocodiles and pterosaurs). Within a few million years dinosaurs rapidly diversified into two major groups (Ornithischia and Saurischia) based on pelvic structure and three main clades or subgroups (Ornithischia, Sauropodomorpha and Theropoda). Further diversification resulted in the various dinosaur classic types, such as tyrannosaurs, apatosaurs, stegosaurs, ankylosaurs and ceratopsians. These various types reflect the two locomotor styles, bipedal and quadrupedal, as well as the three dietary groups, herbivorous, carnivorous and omnivorous. Dinosaurs spread globally and by the Jurassic appear on all the continents, including ice‐free Antarctica. They also spread into a variety of niches, including flight. The extinction of this seemingly successful group 65 Ma is still the subject of much debate. Hypothetical causes include disease, volcanism, sea level drop, asteroid impact, or a combination of these. The only survivor of the ‘Great Extinction’ are the birds, or avian dinosaurs. Key Concepts: Dinosaurs appeared in the Late Triassic of South America 230 Ma and survive today as birds. Dinosaurs underwent dramatic diversification within a few million years after their appearance so that most varieties were present by the Middle Jurassic. Dinosaurs also spread globally, occurring on all continents and in a variety of environments. Although an asteroid impact apparently marks the end of the Cretaceous, there is still no uniform agreement that it was the cause for the extinction of nonavian dinosaurs. Modern birds are believed to be descendants of small, feathered theropods.