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ORNITHISCHIA (/ɔːrnᵻˈθɪskiə/ or-ni-THISS-kee-ə ) is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure similar to that of birds . The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek ornitheos (ορνιθειος) meaning "of a bird" and ischion (ισχιον) meaning "hip joint". Birds are members of the saurischian , or "lizard-hipped", dinosaurs.

Ornithischia
Ornithischia
is well-supported as one of the two major groups in the Dinosauria. Many characteristics define the group though most are thought to be linked to herbivory.

Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs (e.g. Triceratops
Triceratops
), armored dinosaurs ( Thyreophora ) such as stegosaurs and ankylosaurs , pachycephalosaurids and the ornithopods . There is strong evidence that certain groups of ornithischians lived in herds, often segregated by age group, with juveniles forming their own flocks separate from adults.

Some were at least partially covered in filamentous (hair- or feather- like) pelts, and there is much debate over whether these filaments found in specimens of Tianyulong , Psittacosaurus
Psittacosaurus
, and Kulindadromeus may have been primitive feathers . In the alternative evolutionary hypothesis for dinosaurs that was proposed by Baron, Norman & Barrett in the journal Nature in 2017, the presence of such features in Ornithischia
Ornithischia
as well as Theropoda was interpreted as possible evidence for feathers being an ancestral condition of the clade Ornithoscelida
Ornithoscelida
.

CONTENTS

* 1 Anatomy & Diagnostic Characters

* 1.1 "Bird-hip" * 1.2 Predentary * 1.3 Other characteristics

* 2 Ecology

* 3 Classification

* 3.1 Taxonomy * 3.2 Phylogeny

* 4 References * 5 External links

ANATOMY "> FIGURE 1A - ORNITHISCHIAN PROPISTHOPUBIC PELVIC STRUCTURE (LEFT SIDE) FIGURE 1B - SAURISCHIAN PROPUBIC PELVIC STRUCTURE (LEFT SIDE) FIGURE 2 - HETERODONTOSAURUS SKULL WITH PALPEBRAL BONE (RED), ANTORBITAL FENESTRA (YELLOW) AND PREDENTARY (GREEN) COLORED.

OTHER CHARACTERISTICS

* Ornithischians had paired premaxillary bones that were toothless and roughened at the tip of the snout (presumably due to the attachment of a keratinous beak). * Ornithischians developed a narrow "eyebrow", or palpebral bone, across the outside of the eye socket. * Ornithischians had reduced, or even closed-off, antorbital fenestrae (the fenestra in front of the eye socket). * Ornithischian jaw joints were lowered below the level of the teeth, bringing the teeth into simultaneous occlusion. * Ornithischians had "leaf-shaped" cheek teeth. * Ornithischian backbones were stiffened near the pelvis by the ossification of tendons above the sacrum. Additionally, ornithischians had at least five sacral vertebrae attaching to the pelvis.

ECOLOGY

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.

Most ornithischians were herbivorous. In fact, most of the unifying characters of Ornithischia
Ornithischia
are thought to be related to this herbivory. For example, the shift to an opisthopubic pelvis is thought to be related to the development of a large stomach or stomachs and gut which would allow ornithischians to digest plant matter better. The smallest known Ornithischians are Fruitadens haagarorum. The largest Fruitadens
Fruitadens
individuals reached just 65–75 cm. Previously, only carnivorous, saurischian theropods were known to reach such small sizes. At the other end of the spectrum, the largest known ornithischians reach about 15 meters (smaller than the largest saurischians).

However, not all ornithischians were strictly herbivorous. Some groups, like the heterodontosaurids , were likely omnivores . At least one species of ankylosaurian , Liaoningosaurus paradoxus , appears to have been at least partially carnivorous , with hooked claws, fork-like teeth, and stomach contents suggesting that it may have fed on fish.

There is strong evidence that some ornithischians lived in herds. This evidence consists of multiple bones beds with large numbers of the same species in different age classes who died simultaneously.

CLASSIFICATION

TAXONOMY

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

* ORNITHISCHIA

* Eocursor * Fabrosaurus * Pisanosaurus
Pisanosaurus
* Taveirosaurus * Trimucrodon * Heterodontosauridae – (strong-snouted dinosaurs)

* THYREOPHORA – (armored dinosaurs)

* STEGOSAURIA

* Huayangosauridae * Stegosauridae

* ANKYLOSAURIA

* Nodosauridae * Ankylosauridae

* NEORNITHISCHIA

* ORNITHOPODA

* Thescelosauridae – (last primitive beaked dinosaurs)

* IGUANODONTIA

* Rhabdodontidae – (advanced European beaked dinosaurs) * Dryosauridae – (small advanced beaked dinosaurs) * Camptosauridae – (mid-sized advanced beaked dinosaurs) * Hadrosauridae – (duckbilled dinosaurs)

* MARGINOCEPHALIA

* Pachycephalosauria – (boneheaded dinosaurs)

* CERATOPSIA

* Chaoyangsauridae – (early parrot-beaked dinosaurs) * Psittacosauridae – (parrot dinosaurs)

* NEOCERATOPSIA

* Leptoceratopsidae – (small-frilled dinosaurs) * Bagaceratopsidae – (lump-nosed frilled dinosaurs) * Protoceratopsidae – (deep-tailed frilled dinosaurs) * Ceratopsidae
Ceratopsidae
– (horned dinosaurs)

PHYLOGENY

Ornithischia
Ornithischia
is a branch-based taxon defined as all dinosaurs more closely related to Triceratops
Triceratops
horridus Marsh, 1889 than to either Passer domesticus (Linnaeus, 1758) or Saltasaurus loricatus Bonaparte padding:0;">

Pisanosaurus
Pisanosaurus

Heterodontosauridae

Genasauria

Thyreophora

Lesothosaurus

Scutellosaurus
Scutellosaurus

Emausaurus

Scelidosaurus

STEGOSAURIA

ANKYLOSAURIA

Neornithischia

Stormbergia

Agilisaurus

Hexinlusaurus

Cerapoda

Othnielia
Othnielia

Hypsilophodon
Hypsilophodon

Jeholosaurus

Yandusaurus

Orodromeus

Zephyrosaurus

ORNITHOPODA

Marginocephalia

PACHYCEPHALOSAURIA

CERATOPSIA

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

ORNITHISCHIA

Pisanosaurus
Pisanosaurus

Heterodontosauridae

Eocursor

Genasauria

Lesothosaurus

Thyreophora

Scutellosaurus
Scutellosaurus

Emausaurus

Scelidosaurus

STEGOSAURIA

ANKYLOSAURIA

Neornithischia

Stormbergia

Agilisaurus

Hexinlusaurus

Othnielosaurus
Othnielosaurus

Cerapoda

ORNITHOPODA

Marginocephalia

PACHYCEPHALOSAURIA

CERATOPSIA

REFERENCES

* ^ Ferigolo, J.; Langer, M. C. (2007). "A Late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone". Historical Biology. 19: 23–33. doi :10.1080/08912960600845767 . * ^ A B C D E F G H I J K L M N O P Q R S T U V Fastovsky, David E.; Weishampel, David B. (2012). Dinosaurs: A Concise Natural History. Cambridge: Cambridge University Press. ISBN 1107276462 . * ^ A B C Qi, Zhao; Barrett, Paul M.; Eberth, David A. (2007-09-01). "Social Behaviour and Mass Mortality in the Basal Ceratopsian Dinosaur
Dinosaur
Psittacosaurus
Psittacosaurus
(early Cretaceous, People\'s Republic of China)". Palaeontology. 50 (5): 1023–1029. ISSN 1475-4983 . doi :10.1111/j.1475-4983.2007.00709.x . * ^ Zhao, Q. (2013). "Juvenile-only clusters and behaviour of the Early Cretaceous
Cretaceous
dinosaur Psittacosaurus". Acta Palaeontologica Polonica. doi :10.4202/app.2012.0128 . * ^ A B Richard J. Butler, Jin Liyong, Chen Jun, Pascal Godefroit (May 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 . CS1 maint: Multiple names: authors list (link ) * ^ Mayr, Gerald; Peters, Stefan D.; Plodowski, Gerhard; Vogel, Olaf (2002-08-01). "Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus". Naturwissenschaften. 89 (8): 361–365. ISSN 0028-1042 . PMID 12435037 . doi :10.1007/s00114-002-0339-6 . * ^ Godefroit, P.; Sinitsa, S.M.; Dhouailly, D.; Bolotsky, Y.L.; Sizov, A.V.; McNamara, M.E.; Benton, M.J.; Spagna, P. (2014). "A Jurassic
Jurassic
ornithischian dinosaur from Siberia with both feathers and scales" (PDF). Science. 345 (6195): 451–455. doi :10.1126/science.1253351 . * ^ Baron, M.G.; Norman, D.B.; Barrett, P.M. (2017). "A new hypothesis of dinosaur relationships and early dinosaur evolution". Nature. 543: 501–506. doi :10.1038/nature21700 . * ^ A B Currie, Philip J.; Padian, Kevin (1997-10-06). Encyclopedia of Dinosaurs. Academic Press. pp. 537–538. ISBN 9780080494746 . * ^ Jeffrey A. Wilson; Claudia A. Marsicano; Roger M. H. Smith (6 October 2009). "Dynamic Locomotor Capabilities Revealed by Early Dinosaur
Dinosaur
Trackmakers from Southern Africa". PLoS ONE. PLOS ONE. 4: e7331. doi :10.1371/journal.pone.0007331 . * ^ A B Butler, Richard J.; Galton, Peter M.; Porro, Laura B.; Chiappe, Luis M.; Henderson, Donald M.; Erickson, Gregory M. (2010-02-07). "Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic
Jurassic
heterodontosaurid from North America". Proceedings of the Royal Society of London B: Biological Sciences. 277 (1680): 375–381. ISSN 0962-8452 . PMC 2842649  . PMID 19846460 . doi :10.1098/rspb.2009.1494 . * ^ Yannan, Ji; Xuri, Wang; Yongqing, Liu; Qiang, Ji (2011-02-01). "Systematics, Behavior and Living Environment of Shantungosaurus Giganteus (Dinosauria: Hadrosauridae)". Acta Geologica Sinica - English Edition. 85 (1): 58–65. ISSN 1755-6724 . doi :10.1111/j.1755-6724.2011.00378.x . * ^ Barrett, P. M.; Rayfield, E. J. (2006). "Ecological and evolutionary implications of dinosaur feeding behaviour". Trends in Ecology & Evolution. 21 (4): 217–224. doi :10.1016/j.tree.2006.01.002 . * ^ Ji, Q.; Wu, X.; Cheng, Y.; Ten, F.; Wang, X.; Ji, Y. (2016). "Fish-hunting ankylosaurs (Dinosauria, Ornithischia) from the Cretaceous
Cretaceous
of China". Journal of Geology. 40: 2. * ^ Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur
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
Cretaceous
heterodontosaurid dinosaur with filamentous integumentary structures". Nature . 458 (7236): 333–336. PMID 19295609 . doi :10.1038/nature07856 .

* 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. doi :10.1111/j.1096-3642.2005.00182.x . * Sereno, P.C. (1986). "Phylogeny of the bird-hipped dinosaurs (order Ornithischia)". National Geographic Research. 2 (2): 234–256.

EXTERNAL LINKS

Wikispecies
Wikispecies
has information related to: ORNITHISCHIA

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