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Ornithischia

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Title: Ornithischia  
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Subject: Dinosaur, Thyreophora, Jeholosaurus, Alocodon, Serendipaceratops
Collection: Cretaceous Extinctions, Late Triassic First Appearances, Maastrichtian Extinctions, Ornithischians
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Ornithischia

Ornithischians
Temporal range:
Late TriassicLate Cretaceous, 231.4–66 Ma
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Edmontosaurus pelvis (showing ornithischian structure – left side) Oxford University Museum of Natural History
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Clade: Dinosauria
Order: Ornithischia
Seeley, 1888
Subgroups
Synonyms
  • Predentata[1] Marsh, 1894

Ornithischia ( )[2] or Predentata[1] 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.

Contents

  • Characteristics 1
  • Classification 2
    • Taxonomy 2.1
    • Phylogeny 2.2
  • References 3
  • External links 4

Characteristics

Ornithischian pelvic structure (left side)

The Dinosauria clade 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 down and towards 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 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, therizinosauroids and 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.[3]

Classification

Taxonomy

The simplified taxonomic list of ornithischian groups presented here follows a summary published by Thomas R. Holz, Jr. in 2011.[4]

Phylogeny

Genasaurian ornithischians are divided into two clades: the Thyreophora and the Cerapoda. Thyreophora includes the Stegosauria (like the armored Stegosaurus) and the Ankylosauria (like Ankylosaurus). Whereas Cerapoda includes the Marginocephalia (Ceratopsia like the frilled ceratopsidae and Pachycephalosauria) and the Ornithopoda (including duck-bills (hadrosaurs), such as Edmontosaurus). Cerapoda is 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.[5]

Ornithischia

Pisanosaurus



Heterodontosauridae

Genasauria
Thyreophora

Lesothosaurus



Scutellosaurus



Emausaurus



Scelidosaurus



Stegosauria


Ankylosauria






Neornithischia

Stormbergia



Agilisaurus



Hexinlusaurus

Cerapoda

Othnielia


Hypsilophodon


Jeholosaurus


Yandusaurus



Orodromeus


Zephyrosaurus



Ornithopoda

Marginocephalia

Pachycephalosauria


Ceratopsia









Cladogram after Butler et al., 2011. Ornithopoda includes Hypsilophodon, Jeholosaurus and others.[6]

Ornithischia

Pisanosaurus



Heterodontosauridae



Eocursor

Genasauria

Lesothosaurus

Thyreophora

Scutellosaurus



Emausaurus



Scelidosaurus



Stegosauria


Ankylosauria





Neornithischia

Stormbergia



Agilisaurus



Hexinlusaurus



Othnielosaurus

Cerapoda

Ornithopoda

Marginocephalia

Pachycephalosauria


Ceratopsia











References

  1. ^ a b Ferigolo, J.; Langer, M. C. (2007). "A Late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone". Historical Biology 19: 23.  
  2. ^ OED
  3. ^ Jeffrey A. Wilson; Claudia A. Marsicano; Roger M. H. Smith (2009-10-06). "PLOS ONE: Dynamic Locomotor Capabilities Revealed by Early Dinosaur Trackmakers from Southern Africa". PLOS ONE. 
  4. ^ Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix.
  5. ^ Zheng, Xiao-Ting; You, Hai-Lu; Xu, Xing; Dong, Zhi-Ming (19 March 2009). "An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures".  
  6. ^ Richard J. Butler, Jin Liyong, Chen Jun,  
  • 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

  • Ornithischia, from Palæos. (cladogram, characteristics)
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