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Origin of dinosaurs

Origin of dinosaurs - Origin of dinosaurs Reptile skull...

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Origin of dinosaurs Reptile skull openings--facilitate jaw muscle action anapsid-- cotylosaurs and turtles parapsida--upper opening- ichthyosaurs euryapsida--upper--plesiosaurs synapsid(lower) --pelycosaurs, therapsids and their descendants thecodonts(a grade) and therapsids diverge in Permian Diapsids--two clades lepidosaurs(snakes, lizards) archosaurs ( include crocodilians, birds, dinosaurs)--share antorbital fenestra, loss of teeth on palate, shape of calcaneum. . Archosauriformes arise near the end of the Permian, and dinosaurs, crocodiles, and pterosaurs are present in the last third of the Triassic. Ornithodira = the noncroc. Archosaurs (Dinosauria and Pterosauria--both have erect posture with legs under body) Permian extinction--95 % of marine species--worst extinction since origin of life Origin of Dinosaurs In Britain, Owen, Buckland, & Mantell studied specimens prior to the naming of "dinosauria" Mantell worked on the first herbivorous dinosaur to be studied, Iguanodon. 1842-Sir Richard Owen named DINOSAURS 1887-H. G. Seeley named Ornithischia and Sauropoda. Classic differentiation has been on pelvis form, and this still works if you are looking at a mounted skeleton. In Ornithischia at least part of the pubis runs back along the lower edge of the ischium. Ornithischia usually have a predentary bone at the front of the lower jaw. Saurischia-pubis points anteriorly Dinoauria considered diphyletic until modern times when: 1974-Bakker and Galton united dinosaurs and added birds as a monophyletic group
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1986 J. Gautier of California Acad. of Sciences & Paul Serreno of U. of Chicago establish dinosaurs as a clade. Dinosaurs and pterosaurs may be descended from an animal like the archosaur Lagosuchus and its kin-- from the late Triassic of Argentina Paul Serreno has been digging out there and work will continue, so the "oldest" dinosaur is likely to change and be argued about in our lifetime-- Oldest dinosaur is a small, bipedal, insectivorous or carnivorous animal,
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