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Saurischia

From Academic Kids

Saurischia
Conservation status: Fossil

Saurischia pelvis structure
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Reptilia
Superorder:Dinosauria
Order:Saurischia
Groups

Sauropodomorpha
   Saturnalia
   Prosauropoda
   Sauropoda
Theropoda
   Eoraptor
   Herrerasauridae
   Ceratosauria
   Tetanurae

Saurischians (from the Greek Saurischia meaning "lizard hip") are one of the two orders/branches of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two great orders, based on their hip structure. Saurischians are distinguished from the Ornithischians by retaining the ancestral configuration of bones in the hip. All carnivorous dinosaurs (the theropods) are members of the Saurischians, as are one of the two great lineages of herbivorous dinosaurs, the sauropodomorphs. At the end of the Cretaceous Period, all non-avian Saurischians became extinct during the Cretaceous-Tertiary extinction event.

T.rex pelvis and thighbones, showing the saurischian pelvis. Picture taken at the
Enlarge
T.rex pelvis and thighbones, showing the saurischian pelvis. Picture taken at the Field Museum of Natural History

The Saurischians were differentiated from the Ornithischians in the Late Triassic Period. The Ornithischians evolved a new hip structure, with the pubis rotating to become parallel with the ischium. This hip structure is similar to that of birds, and so Ornithischians are termed "bird-hipped" dinosaurs, while the Saurischians are "lizard-hipped". Ironically, the true bird-hip possessed by modern birds evolved from the lizard-hipped theropods in the Jurassic Period, an example of convergent evolution.

While Seeley's classification has stood the test of time, there is a minority theory, first popularized by Robert Bakker in The Dinosaur Heresies that separates the theropods into their own group and places the two great groups of herbivorous dinosaurs (the sauropodomorphs and ornithischians) together in a separate group named as the Phytodinosauria ("plant dinosaurs") (Bakker), or Ornithischiformes (Cooper).de:Saurischia fa:کلپک‌ورکیان fr:Saurischia ko:용반류 he:בעלי אגן דמוי לטאה nl:Saurischia ja:竜盤類 pt:Saurischia

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