Late Triassic–Late Cretaceous, 231.4–66 Ma
|Edmontosaurus pelvis (showing ornithischian structure – left side) Oxford University Museum of Natural History|
Ornithischia (// or-ni-THISS-kee-ə) or Predentata is an extinct clade 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.
The clade Dinosauria was divided into the two orders Ornithischia and Saurischia by Harry Seeley in 1887. This division, which has generally been accepted, is based in part on the evolution of the pelvis into a more bird-like structure (although birds did not descend from ornithischian dinosaurs), details in the vertebrae and armor, and the possession of a predentary bone. The predentary is a single toothless bone that lies in the front of the dentaries, extending the lower jaw. 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 (posterior), 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 (anterior), as in ancestral reptiles. Ornithischians also typically possess smaller antorbital fenestra (openings in the skull 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.
The simplified taxonomic list of ornithischian groups presented here follows a summary published by Thomas R. Holz, Jr. in 2011.
- Heterodontosauridae – (strong-snouted dinosaurs)
- Thyreophora – (armored dinosaurs)
- Pachycephalosauria – (boneheaded dinosaurs)
Ornithischia is a branch-based taxon defined as all dinosaurs more closely related to Triceratops horridus Marsh, 1889 than to either Passer domesticus (Linnaeus, 1758) or Saltasaurus loricatus Bonaparte & Powell, 1980. Genasauria comprises the clades Thyreophora and Neornithischia. Thyreophora includes Stegosauria (like the armored Stegosaurus) and Ankylosauria (like Ankylosaurus). Neornithischia comprises several basal taxa, Marginocephalia (Ceratopsia and Pachycephalosauria), and Ornithopoda (including duck-bills (hadrosaurs), such as Edmontosaurus). Cerapoda is a relatively recent concept (Sereno, 1986).
- 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. doi:10.1080/08912960600845767.
- 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.
- Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix.
- Butler, Richard; Upchurch, Paul; Norman, David (2008). "The phylogeny of ornithischian dinosaurs". Journal of Systematic Paleontology 6 (1): 1–40. doi:10.1017/S1477201907002271.
- 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.
- 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.
|Wikispecies has information related to: Ornithischia|
- Ornithischia, from Palæos. (cladogram, characteristics)