Evans, Susan E. Department of Anatomy and Developmental Biology, University College London, London, United Kingdom.
- Skull morphology
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A group of reptiles characterized by two pairs of lateral skull openings (fenestrae) and a suborbital fenestra in the palate below the eye. This group includes living and extinct lizards, snakes, tuatara, and crocodiles, as well as a range of extinct Late Paleozoic and Mesozoic lineages including rhynchosaurs, protorosaurs, younginiforms, choristoderes, dinosaurs, and pterosaurs. In addition, most workers would now include the so-called parapsid or euryapsid reptiles (defined as possessing a single upper-skull fenestra; Fig. 1c), with the view that the ancestral lower temporal fenestra was secondarily reduced or closed in the aquatic nothosaurs, plesiosaurs, pliosaurs, ichthyosaurs, and placodonts. Perhaps more surprisingly, some authors also consider the anapsid (no skull fenestrae) turtles to be diapsid derivatives, and this idea, while still contentious, has received support from many molecular phylogenetic studies, which use deoxyribonucleic acid (DNA) sequence data to determine evolutionary relationships. Birds evolved from bipedal theropod dinosaurs and are also part of the diapsid radiation, although older, traditional classifications place them in a separate class, Aves. See also: Anapsida; Animal evolution; Aves; Dinosauria
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