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|See Dinosauria in Wikipedia, the free encyclopedia.|
Superorder Dinosauria, including birds, is the single most successful terrestrial vertebrate group in the history of life, and is defined as the common ancestor of orders Saurischia and Ornithischia and all its descendants. Dinosaurs belong to the class Sauropsida (reptiles) and the sublcass Diapsida. They existed during the Mesozoic era of earths prehistory, and went extinct around 65 million years ago as a result of one or more astroid impacts.
- Vomers reach caudally to the antorbital fenestra at least
- Three or more sacral vertebrae present
- Scapulocoracoidal glenoid oriented backward
- Deltopectoral crest low and 1/3 or 1/2 the length of the humerus
- Three of fewer phalanges in the fourth manual digit
- Acetabulum completely perforate
- Proximal head of femur fully offset, conferring parasagittal gait
- Fibula reduced
- Ascending process of the astragalus well developed
Origins and Evolution
Archosauromorpha is an infraclass of diapsids that likely descended from a single common ancestor about 260 to 250 million years ago. The Archosauriformes developed from archosauromorph ancestors about 250 million years ago. They include the family Proterosuchidae which gave rise to the Erythrosuchidae who in turn evolved into the Archosaurs about 250 to 245 million years ago. Ornithodira is a clade within Archosauria that existed from about 245 to 228 million years ago. Ornithodires diversified to produce dinosaurs about 230 million years ago. Many scientists once believed dinosaurs were polyphyletic with multiple groups of unrelated "dinosaurs" evolving due to similar pressures, but dinosaurs are now known to have formed a single group.
The dinosaurs began to occupy a prominent role in earth's ecosystem after the Triassic-Jurassic extinction event when most of the other groups of early archosaurs went extinct, which allowed the dinosaurs to evolve and fill the ecological niches left by the extinct archosaur species.
- Taylor, Mike (August 27, 2002). What is a dinosaur?. The dinosaur FAQ. Retrieved on 2008-04-14.
- Archosauromorpha. Wikipedia.
- Archosauriformes. Wikipedia.
- Proterosuchidae. Wikipedia.
- Erythrosuchidae. Wikipedia.
- Archosaur. Wikipedia.
- Ornithodira. Wikipedia.
- Archosauromorpha: Archosauria: Ornithodira. Palaeos. Retrieved 2008-04-15.