AskDefine | Define ornithischian

Dictionary Definition

ornithischian n : herbivorous dinosaur with a pelvis like that of a bird [syn: ornithischian dinosaur]

Extensive Definition

Ornithischia () or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos (ορνιθειος) meaning 'of a bird' and ischion (ισχιον) meaning 'hip joint'. They are known as the 'bird-hipped' dinosaurs because of their bird-like hip structure, even though birds actually descended from the 'lizard-hipped' dinosaurs (the saurischians). Being herbivores that sometimes lived in herds, they were more numerous than the saurischians. They were prey animals for the theropods and were smaller than the sauropods.

Characteristics

The Dinosauria superorder was divided into the two orders Ornithischia and Saurischia by Harry Seeley in 1887. This division, which has generally been accepted, is based on the evolution of the pelvis into a more bird-like structure (although birds did not descend from these dinosaurs), details in the vertebrae and armor and the possession of a 'predentary' bone. The predentary is an extra bone in the front of the lower jaw, which extends the dentary (the main lower jaw bone). The predentary coincides with the premaxilla in the upper jaw. Together they form a beak-like apparatus used to clip off plant material.
The ornithischian pubis bone points downward and toward the tail (backwards), parallel with the ischium, with a forward-pointing process to support the abdomen. This makes a four-pronged pelvic structure. In contrast to this, the saurischian pubis points downward and towards the head (forwards), as in ancestral lizard types. Ornithischians also had smaller holes in front of their eye sockets (antorbital fenestrae) than saurischians, and a wider, more stable pelvis. A bird-like pubis arrangement, parallel to the vertebral column, independently evolved three times in dinosaur evolution, namely in the ornithischians, the therizinosauroids and in bird-like dromaeosaurids.

Classification

Taxonomy

Linnaean ranks after Benton (2004),

Phylogeny

The ornithischians are divided in the two clades: the first are the Thyreophora and the second the Cerapoda. The Thyreophora include the Stegosauria (like the armored Stegosaurus) and the Ankylosauria (like Ankylosaurus). The Cerapoda include the Marginocephalia (Ceratopsia like the frilled ceratopsidae and Pachycephalosauria) and the Ornithopoda (among which duck-bills (hadrosaurs) such as Edmontosaurus). The Cerapoda are a relatively recent grouping (Sereno, 1986), and may conceivably be identical to (synonymous with) the older group, Ornithopoda: most of these divisions are not true by definition.
(basal Cerapoda after Butler, 2005)

References

  • Butler, R.J. 2005. The 'fabrosaurid' ornithischian dinosaurs of the Upper Elliot Formation (Lower Jurassic) of South Africa and Lesotho. Zoological Journal of the Linnean Society 145(2):175-218.
  • Sereno, P.C. 1986. Phylogeny of the bird-hipped dinosaurs (order Ornithischia). National Geographic Research 2(2):234-256.

External links

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ornithischian in Catalan: Ornitisqui
ornithischian in Czech: Ptakopánví
ornithischian in German: Vogelbeckensaurier
ornithischian in Spanish: Ornithischia
ornithischian in Esperanto: Ornitiskioj
ornithischian in Persian: پرنده‌ورکیان
ornithischian in French: Ornithischia
ornithischian in Galician: Ornithischia
ornithischian in Korean: 조반류
ornithischian in Italian: Ornithischia
ornithischian in Hebrew: בעלי אגן דמוי עוף
ornithischian in Luxembourgish: Vullebeckesaurier
ornithischian in Lithuanian: Paukščiadubeniai dinozaurai
ornithischian in Hungarian: Madármedencéjűek
ornithischian in Dutch: Ornithischia
ornithischian in Japanese: 鳥盤類
ornithischian in Norwegian: Ornithischia
ornithischian in Polish: Dinozaury ptasiomiedniczne
ornithischian in Portuguese: Ornitísquios
ornithischian in Russian: Птицетазовые
ornithischian in Simple English: Ornithischia
ornithischian in Slovak: Vtákopanvé dinosaury
ornithischian in Finnish: Linnunlantioiset
ornithischian in Swedish: Fågelhöftade dinosaurier
ornithischian in Ukrainian: Птахотазові
ornithischian in Volapük: Ornithischia
ornithischian in Chinese: 鳥臀目
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