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Ornithischia
Ornithischia
(/ɔːrnɪˈθɪskiə/) is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure similar to that of birds.[2] The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek stem ornith- (ὀρνιθ-), meaning "of a bird", and ischion (ἴσχιον), plural ischia, meaning "hip joint". However, birds are only distantly related to this group as birds are theropod dinosaurs.[2] Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs (e.g. Triceratops), armored dinosaurs (Thyreophora) such as stegosaurs and ankylosaurs, pachycephalosaurids and the ornithopods.[2] There is strong evidence that certain groups of ornithischians lived in herds,[2][3] often segregated by age group, with juveniles forming their own flocks separate from adults.[4] 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,[5] Psittacosaurus,[6] and Kulindadromeus
Kulindadromeus
may have been primitive feathers.[7] Currently, the exact placement of Ornithischia
Ornithischia
within the dinosaur lineage is a contentious issue.[8] Traditionally, the group is considered sister to Saurischia
Saurischia
(which contains Theropoda
Theropoda
and Sauropodomorpha).[9] In the alternative evolutionary hypothesis for dinosaurs that was proposed by Baron, Norman & Barrett in the journal Nature in 2017, Ornithischia
Ornithischia
as well as Theropoda
Theropoda
were grouped together in the clade Ornithoscelida.[10][11] The work by Baron and colleagues was recently challenged by an international consortium of early dinosaur experts led by Max Langer. However, the data that supported the more traditional placement of Ornithischia, as sister-taxon of Saurischia, was found not to be statistically significant from the evidence that supported the Ornithoscelida hypothesis, in both the study by Langer et al. and the reply to the study by Baron et al.[12][13] A further 2017 study found some support for the previously abandoned Phytodinosauria
Phytodinosauria
model, which classifies ornithischians together with sauropodomorphs.[14]

Contents

1 Description

1.1 "Bird-hip" 1.2 Predentary 1.3 Other characteristics

2 Classification 3 Palaeoecology 4 See also 5 References 6 External links

Description[edit] In 1887, Harry Seeley
Harry Seeley
divided Dinosauria
Dinosauria
into two clades: Ornithischia and Saurischia. Ornithischia
Ornithischia
is a strongly supported clade with an abundance of diagnostic characters (common traits).[2] The two most notable traits are a "bird-like" hip and beak-like predentary structure though they shared other features as well.[2] "Bird-hip"[edit] The ornithischian pelvis is "opisthopubic", meaning that the pubis points down and back (posterior) parallel with the ischium (Figure 1a).[2] Additionally, the pelvis has a forward-pointing process to support the abdomen.[2] This results in a four-pronged pelvic structure. In contrast to this, the saurischian pelvis is "propubic", meaning the pubis points toward the head (anterior), as in ancestral reptiles (Figure 1b).[2] The opisthopubic pelvis independently evolved at least three times in dinosaurs (in ornithischians, birds and therizinosauroids).[15] Some argue that the opisthopubic pelvis evolved a fourth time in the clade Dromaeosauridae, but this is controversial, as other authors argue that dromeosaurids are mesopubic.[15] Predentary[edit] Ornithischians share a unique bone called the predentary (Figure 2).[2] This unpaired bone is found at the front of the lower jaws and presumably aided ornithischians in cropping vegetation. In 2017 Baron & Barrett suggested that Chilesaurus
Chilesaurus
may represent an early diverging ornithischian that had not yet acquired the predentary of all other ornithischians.[16][17]

Figure 1a - Ornithischian propisthopubic pelvic structure (left side)

Figure 1b - Saurischian propubic pelvic structure (left side)

Figure 2 - Heterodontosaurus
Heterodontosaurus
skull with palpebral bone (red), antorbital fenestra (yellow) and predentary (green) colored.

Other characteristics[edit]

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).[2] Ornithischians developed a narrow "eyebrow", or palpebral bone, across the outside of the eye socket.[2] Ornithischians had reduced, or even closed-off, antorbital fenestrae (the fenestra in front of the eye socket).[2] Ornithischian jaw joints were lowered below the level of the teeth, bringing the teeth into simultaneous occlusion.[2] Ornithischians had "leaf-shaped" cheek teeth.[2] 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.[2]

Classification[edit] Ornithischia
Ornithischia
is a branch-based taxon defined as all dinosaurs more closely related to Triceratops horridus
Triceratops horridus
Marsh, 1889 than to either Passer domesticus
Passer domesticus
(Linnaeus, 1758) or Saltasaurus loricatus
Saltasaurus loricatus
Bonaparte & Powell, 1980.[18] Genasauria comprises the clades Thyreophora and Neornithischia. Thyreophora
Thyreophora
includes Stegosauria
Stegosauria
(like the armored Stegosaurus) and Ankylosauria
Ankylosauria
(like Ankylosaurus). Neornithischia comprises several basal taxa, Marginocephalia
Marginocephalia
( Ceratopsia
Ceratopsia
and Pachycephalosauria), and Ornithopoda
Ornithopoda
(including duck-bills (hadrosaurs), such as Edmontosaurus). Cerapoda
Cerapoda
is a relatively recent concept (Sereno, 1986). The cladogram below follows a 2009 analysis by Zheng and colleagues. All tested members of Heterodontosauridae
Heterodontosauridae
form a polytomy.[19]

Ornithischia

Pisanosaurus
Pisanosaurus

Heterodontosauridae
Heterodontosauridae

Genasauria

Thyreophora

Lesothosaurus

Scutellosaurus
Scutellosaurus

Emausaurus

Scelidosaurus
Scelidosaurus

Stegosauria
Stegosauria

Ankylosauria
Ankylosauria

Neornithischia

Stormbergia

Agilisaurus
Agilisaurus

Hexinlusaurus

Cerapoda

Othnielia

Hypsilophodon
Hypsilophodon

Jeholosaurus

Yandusaurus

Orodromeus
Orodromeus

Zephyrosaurus

Ornithopoda
Ornithopoda

Marginocephalia

Pachycephalosauria
Pachycephalosauria

Ceratopsia
Ceratopsia

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

Ornithischia

Pisanosaurus
Pisanosaurus

Heterodontosauridae
Heterodontosauridae

Eocursor

Genasauria

Lesothosaurus

Thyreophora

Scutellosaurus
Scutellosaurus

Emausaurus

Scelidosaurus
Scelidosaurus

Stegosauria
Stegosauria

Ankylosauria
Ankylosauria

Neornithischia

Stormbergia

Agilisaurus
Agilisaurus

Hexinlusaurus

Othnielosaurus

Cerapoda

Ornithopoda
Ornithopoda

Marginocephalia

Pachycephalosauria
Pachycephalosauria

Ceratopsia
Ceratopsia

Palaeoecology[edit] Ornithischians shifted from bipedal to quadrupedal posture at least three times in their evolutionary history and it has been shown primitive members may have been capable of both forms of movement.[20] Most ornithischians were herbivorous.[2] In fact, most of the unifying characters of Ornithischia
Ornithischia
are thought to be related to this herbivory.[2] 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.[2] The smallest known Ornithischians are Fruitadens haagarorum.[21] The largest Fruitadens
Fruitadens
individuals reached just 65–75 cm. Previously, only carnivorous, saurischian theropods were known to reach such small sizes.[21] At the other end of the spectrum, the largest known ornithischians reach about 15 meters (smaller than the largest saurischians).[22] However, not all ornithischians were strictly herbivorous. Some groups, like the heterodontosaurids, were likely omnivores.[23] 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.[24] There is strong evidence that some ornithischians lived in herds.[2][3] This evidence consists of multiple bones beds with large numbers of the same species in different age classes who died simultaneously.[2][3] See also[edit]

Dinosaurs portal

References[edit]

^ Ferigolo, J.; Langer, M. C. (2007). "A Late Triassic
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 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
Ceratopsian
Dinosaur Psittacosaurus
Psittacosaurus
(early Cretaceous, People's Republic of China)". Palaeontology. 50 (5): 1023–1029. doi:10.1111/j.1475-4983.2007.00709.x. ISSN 1475-4983.  ^ 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. doi:10.1007/s00114-002-0339-6. ISSN 0028-1042. PMID 12435037.  ^ Godefroit, P.; Sinitsa, S.M.; Dhouailly, D.; Bolotsky, Y.L.; Sizov, A.V.; McNamara, M.E.; Benton, M.J.; Spagna, P. (2014). "A Jurassic ornithischian dinosaur from Siberia with both feathers and scales" (PDF). Science. 345 (6195): 451–455. doi:10.1126/science.1253351.  ^ Matthew G. Baron (2018). " Pisanosaurus
Pisanosaurus
mertii and the Triassic ornithischian crisis: could phylogeny offer a solution?". Historical Biology: An International Journal of Paleobiology. in press. doi:10.1080/08912963.2017.1410705.  ^ Seeley, H.G. (1888). "On the classification of the fossil animals commonly named Dinosauria". Proceedings of the Royal Society of London. 43: 165–171. doi:10.1098/rspl.1887.0117.  ^ 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.  ^ https://www.cam.ac.uk/research/news/new-study-shakes-the-roots-of-the-dinosaur-family-tree ^ Max C. Langer; Martín D. Ezcurra; Oliver W. M. Rauhut; Michael J. Benton; Fabien Knoll; Blair W. McPhee; Fernando E. Novas; Diego Pol; Stephen L. Brusatte (2017). "Untangling the dinosaur family tree". Nature. 551 (7678): E1–E3. doi:10.1038/nature24011.  ^ Matthew G. Baron; David B. Norman; Paul M. Barrett (2017). "Baron et al. reply". Nature. 551 (7678): E4–E5. doi:10.1038/nature24012.  ^ Luke A. Parry; Matthew G. Baron; Jakob Vinther (2017). "Multiple optimality criteria support Ornithoscelida". Royal Society Open Science. 4 (10): 170833. doi:10.1098/rsos.170833.  ^ a b Currie, Philip J.; Padian, Kevin (1997-10-06). Encyclopedia of Dinosaurs. Academic Press. pp. 537–538. ISBN 9780080494746.  ^ Baron, Matthew G.; Barrett, Paul M. (2017). "A dinosaur missing-link? Chilesaurus
Chilesaurus
and the early evolution of ornithischian dinosaurs". Biology Letters. The Royal Society. 13 (8). doi:10.1098/rsbl.2017.0220.  ^ http://www.cam.ac.uk/research/news/study-identifies-dinosaur-missing-link ^ Butler, Richard; Upchurch, Paul; Norman, David (2008). "The phylogeny of ornithischian dinosaurs". Journal of Systematic Palaeontology. 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. doi:10.1038/nature07856. PMID 19295609.  ^ 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. doi:10.1098/rspb.2009.1494. ISSN 0962-8452. PMC 2842649 . PMID 19846460.  ^ 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. doi:10.1111/j.1755-6724.2011.00378.x. ISSN 1755-6724.  ^ 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. 

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[edit]

Wikispecies
Wikispecies
has information related to Ornithischia

Ornithischia, from Palæos. (cladogram, characteristics)

v t e

Avemetatarsalians ( Dinosauromorpha
Dinosauromorpha
and relatives)

Kingdom: Animalia Phylum: Chordata Clade: Sauropsida Clade: Archosauria Clade: Avemetatarsalia

Dinosauromorpha Pterosauromorpha

Avemetatarsalia

Avemetatarsalia

†Scleromochlus

†Aphanosauria

Dongusuchus Spondylosoma Teleocrater Yarasuchus

Ornithodira

Dinosauromorpha

see below

†Pterosauromorpha

see below

Dinosauromorpha

†Lagerpetidae

Dromomeron Lagerpeton Ixalerpeton

Dinosauriformes

Marasuchus Lagosuchus Saltopus Nyasasaurus?

†Silesauridae

Agnosphitys Asilisaurus Diodorus Eucoelophysis Ignotosaurus Lewisuchus Lutungutali Pisanosaurus Pseudolagosuchus Silesaurus Sacisaurus Technosaurus?

Dinosauria (Dinosaurs)

†Ornithischia

see below

Saurischia

†Basal

Alwalkeria Teyuwasu?

Eusaurischia

†Eoraptor †Sauropodomorpha

see below

Theropoda

see below

†Pterosauromorpha

Scleromochlidae?

Scleromochlus?

Pterosauria

Eopterosauria

Peteinosaurus

Preondactylia

Austriadactylus Preondactylus

Eudimorphodontoidea

Raeticodactylidae

Raeticodactylus Caviramus

Eudimorphodontidae

Arcticodactylus Austriadraco

Eudimorphodontinae

Carniadactylus Eudimorphodon

Macronychoptera

Dimorphodontia

Dimorphodon Parapsicephalus

Novialoidea

Campylognathoididae

Campylognathoides Bergamodactylus

Breviquartossa

Rhamphorhynchidae Pterodactylomorpha

Sordes Allkaruen Monofenestrata

†Ornithischia

Basal ornithischians

Eocursor Fabrosaurus

Heterodontosauridae

Echinodon Fruitadens Tianyulong

Heterodontosaurinae

Lycorhinus Pegomastax Manidens Abrictosaurus Heterodontosaurus

Genasauria

Thyreophora

Scutellosaurus Emausaurus Tatisaurus

Scelidosauridae

Scelidosaurus

Eurypoda

Ankylosauria Stegosauria

Neornithischia

Lesothosaurus Agilisaurus Hexinlusaurus Othnielosaurus Kulindadromeus

Cerapoda

Ornithopoda

includes Iguanodontia

Marginocephalia

See Marginocephalia

†Sauropodomorpha

Sauropodomorpha

Pantydraco Thecodontosaurus Nambalia Efraasia Plateosauravus Ruehleia Buriolestes

Guaibasauridae

Guaibasaurus

Saturnaliinae

Saturnalia Chromogisaurus

Plateosauria

Sarahsaurus

Plateosauridae

Euskelosaurus Jaklapallisaurus Plateosaurus Unaysaurus

Riojasauridae

Eucnemesaurus Riojasaurus

Massospondylidae

Adeopapposaurus Coloradisaurus Glacialisaurus Leyesaurus Lufengosaurus Massospondylus Pradhania

Anchisauria

Anchisaurus Aardonyx Melanorosaurus Sefapanosaurus Leonerasaurus Lessemsaurus Antetonitrus Sauropoda

Theropoda

Theropoda

†Basal

Eodromaeus Daemonosaurus

†Herrerasauridae

Caseosaurus Chindesaurus Herrerasaurus Sanjuansaurus Staurikosaurus

Neotheropoda

Liliensternus Tachiraptor Zupaysaurus

†Coelophysoidea

Dracoraptor Dolichosuchus Gojirasaurus? Lophostropheus Podokesaurus Powellvenator Sarcosaurus Tawa

†Coelophysidae

Coelophysis Camposaurus Lucianovenator Panguraptor Procompsognathus Pterospondylus Segisaurus Lepidus

†Dilophosauridae

Cryolophosaurus? Dilophosaurus Dracovenator Shuangbaisaurus? Sinosaurus?

Averostra

†Ceratosauria

see Ceratosauria

Tetanurae

includes birds

Major clades underlined See also categories:

Archosaurs Dinosaurs Pterosaurs Ornithodirans

Cretaceous– Paleogene extinction event

Taxon identifiers

Wd: Q191488 EoL: 4530715 Fossilworks:

.