Ornithischia

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Ornithischians
Temporal range:
Late TriassicLate Cretaceous, 231.4–66Ma
Edmontosaurus pelvis (showing ornithischian structure – left side) Oxford University Museum of Natural History
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Seeley, 1888
Subgroups

Ornithischia (/ɔrnɨˈθɪskiə/ or-ni-THISS-kee-ə)[1] 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 belong to the 'lizard-hipped' dinosaurs (the saurischians).

Some commonly known Ornithischians include the horned dinosaurs (ceratopsians), armored dinosaurs (stegosaurs and ankylosaurs), Iguanodon, and the "duck-billed" dinosaurs (hadrosaurids). Being herbivores that sometimes lived in herds, they were more numerous than the saurischians. Many were prey animals for the theropods and were usually smaller than the sauropods.

Characteristics[edit]

Ornithischian pelvic structure (left side)

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 toward the head (forwards), as in ancestral lizard types. Ornithischians also had smaller antorbital fenestrae (holes in front of their eye sockets) than did saurischians, and a wider, more stable pelvis. A bird-like pubis arrangement, parallel to the vertebral column, evolved independently three times in dinosaur evolution, namely in the ornithischians, in the therizinosauroids and in bird-like dromaeosaurids.

Ornithischians shifted from bipedal to quadrupedal posture at least three times in their evolutionary history and have been shown to have been capable of adopting both postures early in their evolutionary history.[2]

Classification[edit]

Taxonomy[edit]

The simplified taxonomic list of ornithischian groups presented here follows a summary published by Thomas R. Holz, Jr. in 2011.[3]

Phylogeny[edit]

Genasaurian ornithischians are divided into two clades: the Thyreophora and 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 (including duck-bills (hadrosaurs) such as Edmontosaurus). The Cerapoda are a relatively recent concept (Sereno, 1986).

The cladogram below follows a 2009 analysis by Zheng and colleagues. All tested members of Heterodontosauridae form a polytomy.[4]

Ornithischia

Pisanosaurus Pisanosaurus.jpg




Heterodontosauridae Fruitadens.jpg


Genasauria
Thyreophora

Lesothosaurus




Scutellosaurus Scutellosaurus.jpg




Emausaurus




Scelidosaurus Scelidosaurus2.jpg




Stegosauria Stegosaurus BW.jpg



Ankylosauria Edmontonia dinosaur.pngAnkylosaurus dinosaur.png







Neornithischia

Stormbergia




Agilisaurus Agilisaurus2.jpg




Hexinlusaurus


Cerapoda

Othnielia



Hypsilophodon Hypsilophodon.jpg



Jeholosaurus



Yandusaurus




Orodromeus Orodromeus.jpg



Zephyrosaurus




Ornithopoda Parasaurolophuspic steveoc.jpg


Marginocephalia

Pachycephalosauria Pachycephalosauria jmallon.jpg



Ceratopsia Psittacosaurus mongoliensis whole BW.jpgTriceratops BW.jpg










Cladogram after Butler et al., 2011. Ornithopoda includes Hypsilophodon, Jeholosaurus and others.[5]

Ornithischia

Pisanosaurus Pisanosaurus.jpg




Heterodontosauridae Fruitadens.jpg




Eocursor


Genasauria

Lesothosaurus


Thyreophora

Scutellosaurus Scutellosaurus.jpg




Emausaurus




Scelidosaurus Scelidosaurus2.jpg




Stegosauria Stegosaurus BW.jpg



Ankylosauria Edmontonia dinosaur.pngAnkylosaurus dinosaur.png






Neornithischia

Stormbergia




Agilisaurus Agilisaurus2.jpg




Hexinlusaurus




Othnielosaurus


Cerapoda

Ornithopoda Parasaurolophuspic steveoc.jpg


Marginocephalia

Pachycephalosauria Pachycephalosauria jmallon.jpg



Ceratopsia Psittacosaurus mongoliensis whole BW.jpgTriceratops BW.jpg












References[edit]

  1. ^ OED
  2. ^ http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0007331;jsessionid=CE8F3EE637FFD712F6BF85FF02711889
  3. ^ Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix.
  4. ^ Zheng, Xiao-Ting; You, Hai-Lu; Xu, Xing; Dong, Zhi-Ming (19 March 2009). "An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures". Nature 458 (7236): 333–336. doi:10.1038/nature07856. PMID 19295609. 
  5. ^ Richard J. Butler, Jin Liyong, Chen Jun, Pascal Godefroit (2011). "The postcranial osteology and phylogenetic position of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, north-eastern China". Palaeontology 54 (3): 667–683. doi:10.1111/j.1475-4983.2011.01046.x. 
  • 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[edit]