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Ornithischia

January 01, 1970

Ornithischia (/ˌɔːrnəˈθɪski.ə/) is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds.[6] The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek stem ornith- (ὀρνιθ-), meaning "bird", and ischion (ἴσχιον)[a], meaning "hip".[7] However, birds are only distantly related to this group as birds are theropod dinosaurs.[6] Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs (e.g. Triceratops), the pachycephalosaurs or "thick-headed" dinosaurs, the armored dinosaurs (Thyreophora) such as stegosaurs and ankylosaurs, and the ornithopods.[6] There is strong evidence that certain groups of ornithischians lived in herds,[6][8] often segregated by age group, with juveniles forming their own flocks separate from adults.[9] 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,[10] and Kulindadromeus may have been primitive feathers.[11]

Ornithischia
Temporal range:
Early Jurassic–Late Cretaceous, 200.91–66 Ma (Possible Triassic record)
A collection of ornithischian fossil skeletons. Clockwise from upper left: Heterodontosaurus (Heterodontosauridae), Nipponosaurus (Ornithopoda), Borealopelta (Ankylosauria), Triceratops (Ceratopsia), Stegoceras (Pachycephalosauria), and Stegosaurus (Stegosauria).
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Seeley, 1888[1]
Subgroups
Synonyms[5]

Description edit

Ornithischia is a very large and diverse group of dinosaurs, with members known from all continents, habitats, and a very large range of sizes. They are primarily herbivorous browsers or grazers, but some members may have also been opportunistic omnivores.[12] Ornithischians are united by multiple features of the skull, teeth, and skeleton, including especially the presence of a predentary and palpebral, an increased number of sacral vertebrae, the absence of gastralia, and an opisthopubic pubis.[13] Early ornithischians ranged around 1–2 m (3.3–6.6 ft) in length, with them increasing in size over time so that the largest armoured ornithischians were around 7.5 m (25 ft) and 9 t (8.9 long tons; 9.9 short tons), the largest horned ornithischians were around 8.5 m (28 ft) and 11 t (11 long tons; 12 short tons), and the largest crested ornithischians were around 15 m (49 ft) and 13.5 t (13.3 long tons; 14.9 short tons).[12]

 
Skull of Lesothosaurus, an early ornithischian

Much of the knowledge of early ornithischian anatomy comes from Lesothosaurus, which is a taxon known from multiple skulls and skeletons from the Early Jurassic of Lesotho. The rear of its skull is box-like, while the snout tapers to a point. The nasal opening is small, the antorbital fossa that opens from the side of the skull into the palate is large, shallow and triangular, the orbit is large and round and has a palpebral creating a brow, and the lower jaw has a large mandibular fenestra.[14]

The skulls of Emausaurus and Scelidosaurus, two early members of the armoured group Thyreophora, show similarities in the box-like skull that tapers to the front. The antorbital fossa is smaller and forming an elongate oval in both taxa, and the palpebral which is elongate and slender in Lesothosaurus is widened in Emausaurus and completely incorporated into the skull as a flat bone in Scelidosaurus.[14][15] Skulls in members of the thyreophoran group Stegosauria are much longer and lower, with the width at the back being greater than the height in Stegosaurus. The snout and lower jaw are long and deep, and in some genera the premaxilla does not have any teeth. As in Scelidosaurus, the palpebral forms the top border of the orbit as a flat brow bone, but the antorbital fossa is reduced to the point of absence in some genera.[16]

Ankylosaurs, the other group of armoured ornithischians, have very robust, immobile skulls, with three significant features that separate them from other groups. The antorbital fossa, supratemporal fenestra and mandibular fenestra are all closed, the sutures separating skull bones are almost completely obliterated by surface texturing, and there is bony armour above the orbits, and at the top and bottom corners of the back of the skull. Teeth are sometimes absent from the premaxilla, and both the upper and lower jaws have deeply inset teeth creating large cheeks. Ankylosaurs also have very extensive and complicated network of sinuses, formed by bone growth in the palate.[17]

The skulls are known from many early ornithopods and some heterodontosaurids, showing similar general features. Skulls are relatively tall with shorter snouts, but the snout is elongated in some later taxa like Thescelosaurus. The orbit and antorbital fossa are large, but the nasal opening is small, and while teeth are present in the premaxilla, there is a toothless front tip that likely formed a keratinous beak. The premaxillary teeth and the first lower tooth in Heterodontosaurus are enlarged into sizeable canines.[18] In later ornithopods, the skulls are more elongate and sometimes fully rectangular, with a very large nasal opening, and a thin, elongate palpebral that can extend the entire way across the orbit. Teeth are almost always absent from the premaxilla, the antorbital fossa is reduced and round to slit-like, the tip of the snout is sometimes flared to form a broad beak.[19] Members of the ornithopod family Hadrosauridae show further adaptations, including the formation of dental batteries where teeth are continuously replaced, and in many genera the development of prominent cranial crests formed by multiple different bones of the skull.[20]

Pachycephalosauria, at one time thought to be close to ornithopods and know known to be related instead to ceratopsians, show very unique skull anatomy that is unlike any other ornithischian. The bones of the top of the skull are thickened and in many taxa expanded significantly to form round bony domes as the top of the head, as well as possessing small nodes or elongate spikes along the back edge of the skull. Many taxa are only known from these thick skull domes, which are fused from the frontal and parietal bones. As in many other ornithischians, the snout is short and tapering, the nasal opening is small, the antorbital fossa is sometimes absent, and there are premaxillary teeth, though only three. The two palpebrals are also incorporated into the skull roof as in thyreophorans, rather than free.[21]

Ceratopsians, the sister group to pachycephalosaurs, also display many cranial adaptations, most importantly the evolution of a bone called the rostral that forms the top beak opposite the predentary. The jugal bones flare to the sides to create a pentagonal skull seen from above, the nasal opening is closer to the top of the snout than the teeth, and while the snout tapers in some taxa, it is very deep and short in Psittacosaurus. The ceratopsian palpebral is generally triangular, and the back edge of the skull roof forms a flat frill that is enlarged in more derived ceratopsians.[22] The ceratopsian family Ceratopsidae progresses on these features with the addition of horns above each orbit and on the top of the snout, as well as substantial elongation of the frill and in many genera the development of two large parietal fenestrae forming holes in the frill. The skull and frill elongation makes the skulls of Torosaurus and Pentaceratops the largest of any known terrestrial vertebrate, at over 2 m (6.6 ft) long.[23]

Early ornithischians were relatively small dinosaurs, averaging about 1–2 meters in body length, with a triangular skull that had large circular orbits on the sides. This suggests that early ornithischians had relatively huge eyes that faced laterally. The forelimbs of early ornithischians are considerably shorter than their hindlimbs. A small forelimb such as those present in early ornithischians would not have been useful for locomotion, and it is evident that early ornithischians were bipedal dinosaurs. The entire skeleton was lightly built, with a largely fenestrated skull and a very stout neck and trunk. The tail is nearly half of the dinosaurs' overall length. The long tail presumably acted as a counterbalance and as a compensating mechanism for shifts in the creature's center of gravity. The hindlimbs of early ornithischians show that the tibia is considerably longer than the femur, a feature that suggests that early ornithischians were adapted for bipedality, and were fast runners.[24]

"Bird-hip" edit

The ornithischian pelvis was "opisthopubic", meaning that the pubis pointed down and backwards (posterior), parallel with the ischium (Figure 1a).[6] Additionally, the ilium had a forward-pointing process (the preacetabular process) to support the abdomen.[6] This resulted in a four-pronged pelvic structure. In contrast to this, the saurischian pelvis was "propubic", meaning the pubis pointed toward the head (anterior), as in ancestral reptiles (Figure 1b).[6]

The opisthopubic pelvis independently evolved at least three times in dinosaurs (in ornithischians, birds and therizinosauroids).[25] Some argue that the opisthopubic pelvis evolved a fourth time, in the clade Dromaeosauridae, but this is controversial, as other authors argue that dromaeosaurids are mesopubic.[25] It has also been argued that the opisthopubic condition is basal to maniraptorans (including among others birds, therizinosauroids and dromaeosaurids), with some clades having later experienced a reversal to the propubic condition.[26]

Classification edit

History edit

 
 
The general pelvis of Ornithischia (left) and Saurischia (right) illustrating the differences highlighted by Seeley (1888) as justifying their independent evolution

The first recognition of an herbivorous group of dinosaurs was named Orthopoda in 1866 by Edward Drinker Cope,[27] a name that is now recognized as a synonym of Ornithischia.[28] Discussions on the taxonomy of dinosaurs by Othniel Charles Marsh identified two major groups of herbivorous dinosaurs, Ornithopoda and Stegosauria,[29] containing genera from a broad geographic and stratigraphic distribution.[13] While often these groups were placed within Dinosauria, Harry Govier Seeley suggested instead in 1888 that ornithopods and stegosaurs, which shared many features in the skull, limbs, and hip, were unrelated to other dinosaurs, and so he proposed that Dinosauria was an unnatural grouping of two independently-evolved suborders, Saurischia and Ornithischia. It is from the anatomy of the hip that Seeley chose the name Ornithischia, referencing the bird-like anatomy of the ischium bone.[1] Many researchers did not follow the division of Seeley at first, with Marsh naming the group Predentata to unite ornithopods, stegosaurs, and Ceratopsia within Dinosauria,[30] but with additional work and new discoveries the unnatural nature of Dinosauria came to be accepted, and the names Seeley proposed found common use.[31] After further decades, in 1974 Robert T. Bakker and Peter M. Galton provided new evidence in support of the grouping of ornithischians and saurischians together within a natural Dinosauria,[32] which has been supported since.[13]

The first cladistic studies on Ornithischia were published simultaneously in 1984 by David B. Norman, Andrew R. Milner, and Paul C. Sereno. These studies differed somewhat in their results, but found that Iguanodon was closer to hadrosaurs than other ornithopods, followed by Dryosaurus, Hypsilophodon and then Lesothosaurus and its relatives.[33][34][35][36][13] While the study of Norman placed ceratopsians between Hypsilophodon and more derived ornithopods,[34] the study of Sereno placed ceratopsians with ankylosaurs and stegosaurs.[36] It has since been recognized by that ceratopsians are closer to ornithopods than the armoured ankylosaurs and stegosaurs,[4] but the relationships of some groups are still in states of change, with some more consistent results than others.[37][3] An early study that looked at the relationships within Ornithischia with greater detail was that of Sereno in 1986, who provided features that supported the evolution of all ornithischian groups and shared similarities with earlier studies. Sereno found that Lesothosaurus was the most primitive ornithischian, with all other ornithischians united within the clade Genasauria, which has two subgroups. The first subgroup, Thyreophora, unites ankylosaurs and stegosaurs along with more primitive taxa like Scelidosaurus, while the second subgroup, Cerapoda, contained ornithopods, ceratopsians, pachycephalosaurs, and small primitive forms.[4] One group of the small primitive forms considered to be cerapodans by Sereno, Heterodontosauridae, has since been found to be a group of very early ornithischians of similar evolutionary status as Lesothosaurus,[37] although this result is not definitive.[38]

The first large-scale numerical analysis of the phylogenetics of Ornithischia was published in 2008 by Richard J. Butler and colleagues, including many primitive ornithischians and members from all of the major subgroups, to test some of the hypotheses given previously about ornithischian evolution and the relationships of the groups. Thyreophora was found to be a supported group, as well as the clade of pachycephalosaurs and ceratopsians that Sereno named Marginocephalia in 1986. Some taxa considered earlier to be ornithopods, like heterodontosaurids, Agilisaurus, Hexinlusaurus and Othnielia, were instead found to be outside of both Ornithopoda and Ceratopsia, but still closer to those two groups than thyreophorans. The early Argentinian taxon Pisanosaurus was found to be the most primitive ornithischian, but while overall results agreed with earlier studies and showed some stability, areas of the evolutionary tree were found to be problematic, and with potential for later change.[37] In 2021, a new phylogenetic study was published authored by Paul-Emile Dieudonné and colleagues that instead found Heterodontosauridae to nest alongside Pachycephalosauria within Marginocephalia, changing the early evolution of ornithopods considerably, and showing that the evolution of ornithischians was far from definitive.[38] Below are the cladograms of Sereno, Butler and colleagues, and Dieudonné and colleagues, restricted to the major clades of Ornithischia, Heterodontosauridae, Lesothosaurus and Pisanosaurus.

Sereno, 1986[4]

Butler et al., 2008[37]

Dieudonné et al., 2021[38]

Subgroups edit

When Ornithischia was first named, Seeley united the orders Ornithopoda and Stegosauria of Marsh's taxonomy within the new group.[1] Ceratopsia was then recognized as a unique group related to ornithopods and stegosaurs by Marsh by 1894, with each of the three suborders still being recognized as distinct groups today.[13][30] Ceratopsians are recognized as group that grew in diversity later in the Cretaceous after evolving in the Late Jurassic, encompassing a diverse array of bodyforms from the small, bipedal Psittacosaurus up to the very large, quadrupedal, horned and frilled ceratopsids like Torosaurus, which has the longest skull of any terrestrial vertebrate.[22][23] Ornithopods, which range from the Early Jurassic in some studies until the end of the Cretaceous with continuous diversity, are generally bipedal and unarmoured, though some later groups like Hadrosauridae evolved complex dental anatomy in the form of batteries of teeth.[18][20] Stegosaurs are comparatively limited, restricted to a primarily Jurassic group of moderate to large, quadrupedal herbivores with two rows of vertical plates ornamenting their spine, which possibly did not go extinct until the Late Cretaceous, though at the time of Marsh Stegosauria was used for all armored and quadrupedal taxa, many of which are now separated into Ankylosauria.[16][17] Ankylosaurs were only recognized as a distinct group from stegosaurs in the 1920s despite many members being known for decades before, with the group now encompassing a broad array of heavy, quadrupedal ornithischians with extensive armour covering their body and skull.[17] The fifth recognized major subgroup of ornithischians is Pachycephalosauria,[13] which was first named in 1974 after being confused for a long time with the theropod Troodon on account of their similarly omnivorous and unique teeth.[39][21] Pachycephalosaurians are unique for their tall, thickened skulls and small, bipedal bauplan, suggesting that their domes were for sexual display or combat in the form of head-butting or flank-butting.[21] Some taxa, particularly those at one point groupt together in the ornithopod family Hypsilophodontidae, are now recognized to not fall within any of the major ornithischian groups, and either be outside Genasauria, or on the basal stem of Neornithischia outside Cerapoda.[37]

Following the publication of the PhyloCode to provide rules and regulations on the use of taxonomic names for groups, the internal classification of Ornithischia was revised by Daniel Madzia and colleagues in 2021 to provide a framework of definitions and taxa for other studies to follow and modify from. They names the new clade Saphornithischia to unite heterodontosaurids with more derived ornithischians to encompass the concept of the well-supported clear ornithischians, as the origins of the group and the relationships of primitive taxa like Pisanosaurus and members of Silesauridae may sometimes be found to be ornithischians outside this core grouping. Madzia and colleagues also provided a composite cladogram of Ornithischia to illustrate the consensus of internal divisions, which can be seen below. Ornithischia has been defined as all taxa closer to Iguanodon than Allosaurus or Camarasaurus. Genasauria has been defined as the smallest clade containing Ankylosaurus, Iguanodon, Stegosaurus, and Triceratops.[3]

Ornithischia

Heterodontosaurus tucki (Heterodontosauridae)  

Genasauria
Thyreophora
Neornithischia

Jeholosaurus shangyuanensis (Jeholosauridae)

Hypsilophodon foxii (Hypsilophodontidae)  

Cerapoda
Marginocephalia
Ornithopoda

Multiple taxa within Ornithischia fall around the origin of the group, or cannot be classified definitively. Lesothosaurus and Laquintasaura have been found as basal thyreophorans or basal ornithischians, Chilesaurus is either a theropod or a basal ornithischian, Pisanosaurus has been found as a basal ornithischian or a non-ornithischian silesaurid, Eocursor has been a basal ornithischian or a basal member of Neornithischia, Serendipaceratops cannot be classified beyond Ornithischia as it is either an ankylosaur or a ceratopsian, and Alocodon, Fabrosaurus, Ferganocephale, Gongbusaurus, Taveirosaurus, Trimucrodon and Xiaosaurus are dubious ornithischians of uncertain basal classification.[3][2][40][14][41] Depending on the phylogenetic results, Silesauridae could either be a clade within Ornithischia, its members could form an evolutionary gradient, or some members found form a clade while others are part of a gradient.[2][42]

Evolution edit

 
Skull of Revueltosaurus, a genus originally considered an early ornithischian based on its teeth[43]

For a long time, the only understanding of the origins of Ornithischia came from Lesothosaurus and Pisanosaurus, which together represented the best-known Early Jurassic and Triassic ornithischians respectively. Many suggestions of taxa and specimens that could be referred to Ornithischia from the Triassic were based on teeth and jaw bones, as they showed similar adaptations for herbivory. The genera Revueltosaurus, Galtonia, Pekinosaurus, Tecovasaurus, Lucianosaurus, Protecovasaurus, Crosbysaurus, and Azendohsaurus were all at one time considered to be Triassic ornithischians with only their teeth known, but are now recognized to be completely unrelated.[44] The only early ornithischians that were considered to be diagnostic in a 2004 review by Norman and colleagues were Lesothosaurus, Pisanosaurus and Technosaurus, limiting the early ornithischian record to only two Triassic genera from Argentina and the USA and one Early Jurassic genus from South Africa, with all the tooth taxa being considered undiagnostic.[14] Referrals of isolated teeth to Ornithischia based on herbivorous features began to be extensively questioned by William G. Parker and colleagues in 2005 after the discovery of skull and skeleton material clearly from Revueltosaurus showing that the "ornithischian-like" teeth were from an animal more closely related to crocodiles than birds, and there were multiple occurrences of herbivory throughout Triassic reptiles.[44][43] Removing the list of Triassic tooth taxa from Ornithischia, the early diversity of the group was substantially reduced, especially in comparison to the known Triassic diversity of theropods and sauropodomorphs. If Pisanosaurus represented the earliest ornithischian, there would be at least a 20 million year gap in the evolution of Ornithischia until Lesothosaurus and heterodontosaurids. It is possible that the limited early record of ornithischians is due to them inhabiting environments that were less conducive to fossilization, or that the phylogenetics of the group were incorrect and that early ornithischians were already known but identified as members of other groups.[44]

Possible evolutionary relationships of Ornithischia[2]

First noted in the 2003 naming of the early taxon Silesaurus, some taxa generally considered non-dinosaurs show similarities to ornithischians in the teeth and jaw anatomy.[45][5] These basal taxa, which were then grouped within Silesauridae and commonly as the sister group to Dinosauria, may instead be the earliest ornithischians. They show adaptations for the evolution of herbivory, and can fill in the gap in early evolution of ornithischians that were otherwise only clearly known since the beginning of the Jurassic. This hypothesis has found support in multiple different phylogenetic analyses,[46][47] but the results are not yet accepted as definitive enough to contradict other possible evolutionary strategies of dinosaurs. Alternatively, and more in line with earlier studies on dinosaur evolution, silesaurids may be the sister taxa to the Saurischia-Ornithischia split, or even other arrangements of the three main dinosaur groups Ornithischia, Sauropodomorpha, and Theropoda.[2] The 2017 phylogenetic study of Matthew G. Baron and colleagues suggested that instead of a Saurischia-Ornithischia split, ornithischians were instead closest to theropods in the clade Ornithoscelida, with sauropodomorphs being outside the grouping. Under this case, the omnivory in the earliest sauropodomorphs and ornithischians would be the ancestral condition for dinosaurs, along with the grasping abilities seen in the earliest ornithischians and theropods.[48] While Ornithoscelida is a possible hypothesis for the evolution of dinosaurs and the close relationships of Ornithischia, follow-up studies have not found it statistically more likely than the traditional dichotomy of Ornithischia and Saurischia, or the third alternative, Phytodinosauria, where ornithischians and sauropodomorphs are closer to each other than theropods.[49][50][51]

Along with Pisanosaurus, which was supported as the earliest ornithischian for a time before being considered just as likely to be a silesaur rather than an ornithischian, an additional problematic taxon is Chilesaurus from the Late Jurassic of Chile. While it was originally named as a derived theropod with unique anatomy, it was found in studies based on Baron and colleagues results to instead be either the basalmost ornithischian, or a sauropodomorph. As the earliest ornithischian, Chilesaurus tied multiple details of ornithischian and theropod anatomy together supporting their union in Ornithoscelida, though when it is not the basalmost ornithischian, a traditional Saurischia is recovered. The problematic nature of Chilesaurus requires further revisiting of its anatomy, but the details of vertebral air pockets, pelvis shape, and hand support it as a theropod.[2] Daemonosaurus, typically a theropod or close relative of herrerasaurs, has also been found as the basalmost ornithischian at times when Ornithoscelida is recovered, but it does not share any unique features with ornithischians and redescribing its anatomy found it fairly confidently to be a basal dinosaur not related closely to Ornithischia.[52]

The phylogenetic analysis of Norman and colleagues in 2022 recovered the members of Silesauridae as forming an ancestral grade within Ornithischia even with the inclusion of Chilesaurus, supporting the earlier results of Müller and Garcia and their evolutionary trends for early ornithischian anatomy. Norman and colleagues used Prionodontia over both Saphornithischia and Genasauria, since all were recovered as encompassing the same node.[2] The earliest ornithischians under this reconstruction were faunivorous, as seen by Lewisuchus, which has typical teeth like theropods. Serrations on teeth become larger for taxa more derived than Asilisaurus, the development of a cingulum in teeth is seen in Technosaurus and later ornithischians, the lower jaw becomes more elongate in taxa above Silesaurus, and core ornithischians are united by the pubic bone angling backwards, and the modification of the ankle joint.[47]

 
Lower jaws and teeth of (top to bottom) Kwanasaurus, Asilisaurus, Eucoelophysis, Technosaurus, Sacisaurus, Silesaurus, Diodorus scytobrachion and Soumyasaurus

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.[53]

Most ornithischians were herbivorous.[6] In fact, most of the unifying characters of Ornithischia are thought to be related to this herbivory.[6] 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 more effectively digest plant matter.[6] The smallest known ornithischian is Fruitadens haagarorum.[54] The largest Fruitadens individuals reached just 65–75 cm. Previously, only carnivorous, saurischian theropods were known to reach such small sizes.[54] At the other end of the spectrum, the largest known ornithischians reach about 15 meters (smaller than the largest saurischians).[55]

However, not all ornithischians were strictly herbivorous. Some groups, like the heterodontosaurids, were likely omnivores.[56] 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.[57] The members of Genasauria were primarily herbivores.[58] Genasaurians most often had their head at the level of one meter, which suggests they were feeding primarily on “ground-level plants such as ferns, cycads, and other herbaceous gymnosperms."[59]

There is strong evidence that some ornithischians lived in herds.[6][8] This evidence consists of multiple bone beds where large numbers of individuals of the same species and of different age groups died simultaneously.[6][8]

See also edit

Notes edit

  1. ^ plural ischia

References edit

  1. ^ a b c Seeley, H.G. (1888). "On the classification of the fossil animals commonly named Dinosauria". Proceedings of the Royal Society of London. 43 (258–265): 165–171. doi:10.1098/rspl.1887.0117.
  2. ^ a b c d e f g h Norman, D.B.; Baron, M.G.; Garcia, M.S.; Müller, R.T. (2022). "Taxonomic, palaeobiological and evolutionary implications of a phylogenetic hypothesis for Ornithischia (Archosauria: Dinosauria)". Zoological Journal of the Linnean Society. 196 (4): 1273–1309. doi:10.1093/zoolinnean/zlac062.
  3. ^ a b c d Madzia, D.; Arbour, V.M.; Boyd, C.A.; Farke, A.A.; Cruzado-Caballero, P.; Evans, D.C. (2021). "The phylogenetic nomenclature of ornithischian dinosaurs". PeerJ. 9: e12362. doi:10.7717/peerj.12362. PMC 8667728. PMID 34966571.
  4. ^ a b c d Sereno, P.C. (1986). "Phylogeny of the Bird-Hipped Dinosaurs (Ornithischia)". National Geographic Research. 2 (2): 234–256.
  5. ^ 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 (1): 23–33. Bibcode:2007HBio...19...23F. doi:10.1080/08912960600845767.
  6. ^ a b c d e f g h i j k l Fastovsky, David E.; Weishampel, David B. (2012). Dinosaurs: A Concise Natural History. Cambridge: Cambridge University Press. ISBN 978-1107276468.
  7. ^ Colbert, Edwin H. (Edwin Harris); Knight, Charles Robert (1951). The dinosaur book: the ruling reptiles and their relatives. New York: McGraw-Hill. p. 152.
  8. ^ a b c Qi, Zhao; Barrett, Paul M.; Eberth, David A. (2007-09-01). "Social Behaviour and Mass Mortality in the Basal Ceratopsian Dinosaur Psittacosaurus (early Cretaceous, People's Republic of China)" (PDF). Palaeontology. 50 (5): 1023–1029. Bibcode:2007Palgy..50.1023Q. doi:10.1111/j.1475-4983.2007.00709.x. ISSN 1475-4983. S2CID 128781816.
  9. ^ Zhao, Q. (2013). "Juvenile-only clusters and behaviour of the Early Cretaceous dinosaur Psittacosaurus". Acta Palaeontologica Polonica. doi:10.4202/app.2012.0128.
  10. ^ 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. Bibcode:2002NW.....89..361M. doi:10.1007/s00114-002-0339-6. ISSN 0028-1042. PMID 12435037. S2CID 17781405.
  11. ^ Godefroit, P.; Sinitsa, S.M.; Dhouailly, D.; Bolotsky, Y.L.; Sizov, A.V.; McNamara, M.E.; Benton, M.J.; Spagna, P. (2014). (PDF). Science. 345 (6195): 451–455. Bibcode:2014Sci...345..451G. doi:10.1126/science.1253351. hdl:1983/a7ae6dfb-55bf-4ca4-bd8b-a5ea5f323103. PMID 25061209. S2CID 206556907. Archived from the original (PDF) on 2019-02-09. Retrieved 2016-08-28.
  12. ^ a b Paul, G.S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press. pp. 261–373. ISBN 978-0-691-23157-0.
  13. ^ a b c d e f Weishampel, D.B. (2004). "Ornithischia". In Weishampel, D.B.; Osmólska, H.; Dodson, P. (eds.). The Dinosauria (2nd ed.). University of California Press. pp. 323–324. ISBN 0-520-24209-2.
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Wikispecies has information related to Ornithischia.
  • , from Palæos. (cladogram, characteristics)

January 01, 1970
ornithischia, ɔːr, extinct, clade, mainly, herbivorous, dinosaurs, characterized, pelvic, structure, superficially, similar, that, birds, name, bird, hipped, reflects, this, similarity, derived, from, greek, stem, ornith, ὀρνιθ, meaning, bird, ischion, ἴσχιον,. Ornithischia ˌ ɔːr n e ˈ 8 ɪ s k i e is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds 6 The name Ornithischia or bird hipped reflects this similarity and is derived from the Greek stem ornith ὀrni8 meaning bird and ischion ἴsxion a meaning hip 7 However birds are only distantly related to this group as birds are theropod dinosaurs 6 Ornithischians with well known anatomical adaptations include the ceratopsians or horn faced dinosaurs e g Triceratops the pachycephalosaurs or thick headed dinosaurs the armored dinosaurs Thyreophora such as stegosaurs and ankylosaurs and the ornithopods 6 There is strong evidence that certain groups of ornithischians lived in herds 6 8 often segregated by age group with juveniles forming their own flocks separate from adults 9 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 10 and Kulindadromeus may have been primitive feathers 11 OrnithischiaTemporal range Early Jurassic Late Cretaceous 200 91 66 Ma PreꞒ Ꞓ O S D C P T J K Pg N Possible Triassic record A collection of ornithischian fossil skeletons Clockwise from upper left Heterodontosaurus Heterodontosauridae Nipponosaurus Ornithopoda Borealopelta Ankylosauria Triceratops Ceratopsia Stegoceras Pachycephalosauria and Stegosaurus Stegosauria Scientific classification Domain Eukaryota Kingdom Animalia Phylum Chordata Clade Dinosauria Clade OrnithischiaSeeley 1888 1 Subgroups Chilesaurus Pisanosaurus Parapredentata Norman et al 2022 2 Silesauridae paraphyletic Prionodontia Owen 1874 2 Saphornithischia Madzia et al 2021 3 Eocursor Laquintasaura Lesothosaurus Heterodontosauridae Genasauria Sereno 1986 4 Thyreophora Neornithischia Dubious genera Alocodon Fabrosaurus Ferganocephale Gongbusaurus Notoceratops Serendipaceratops Taveirosaurus Trimucrodon Xiaosaurus Synonyms 5 Predentata Marsh 1894 Contents 1 Description 1 1 Bird hip 2 Classification 2 1 History 2 2 Subgroups 2 3 Evolution 3 Palaeoecology 4 See also 5 Notes 6 References 7 External linksDescription editOrnithischia is a very large and diverse group of dinosaurs with members known from all continents habitats and a very large range of sizes They are primarily herbivorous browsers or grazers but some members may have also been opportunistic omnivores 12 Ornithischians are united by multiple features of the skull teeth and skeleton including especially the presence of a predentary and palpebral an increased number of sacral vertebrae the absence of gastralia and an opisthopubic pubis 13 Early ornithischians ranged around 1 2 m 3 3 6 6 ft in length with them increasing in size over time so that the largest armoured ornithischians were around 7 5 m 25 ft and 9 t 8 9 long tons 9 9 short tons the largest horned ornithischians were around 8 5 m 28 ft and 11 t 11 long tons 12 short tons and the largest crested ornithischians were around 15 m 49 ft and 13 5 t 13 3 long tons 14 9 short tons 12 nbsp Skull of Lesothosaurus an early ornithischian Much of the knowledge of early ornithischian anatomy comes from Lesothosaurus which is a taxon known from multiple skulls and skeletons from the Early Jurassic of Lesotho The rear of its skull is box like while the snout tapers to a point The nasal opening is small the antorbital fossa that opens from the side of the skull into the palate is large shallow and triangular the orbit is large and round and has a palpebral creating a brow and the lower jaw has a large mandibular fenestra 14 The skulls of Emausaurus and Scelidosaurus two early members of the armoured group Thyreophora show similarities in the box like skull that tapers to the front The antorbital fossa is smaller and forming an elongate oval in both taxa and the palpebral which is elongate and slender in Lesothosaurus is widened in Emausaurus and completely incorporated into the skull as a flat bone in Scelidosaurus 14 15 Skulls in members of the thyreophoran group Stegosauria are much longer and lower with the width at the back being greater than the height in Stegosaurus The snout and lower jaw are long and deep and in some genera the premaxilla does not have any teeth As in Scelidosaurus the palpebral forms the top border of the orbit as a flat brow bone but the antorbital fossa is reduced to the point of absence in some genera 16 Ankylosaurs the other group of armoured ornithischians have very robust immobile skulls with three significant features that separate them from other groups The antorbital fossa supratemporal fenestra and mandibular fenestra are all closed the sutures separating skull bones are almost completely obliterated by surface texturing and there is bony armour above the orbits and at the top and bottom corners of the back of the skull Teeth are sometimes absent from the premaxilla and both the upper and lower jaws have deeply inset teeth creating large cheeks Ankylosaurs also have very extensive and complicated network of sinuses formed by bone growth in the palate 17 The skulls are known from many early ornithopods and some heterodontosaurids showing similar general features Skulls are relatively tall with shorter snouts but the snout is elongated in some later taxa like Thescelosaurus The orbit and antorbital fossa are large but the nasal opening is small and while teeth are present in the premaxilla there is a toothless front tip that likely formed a keratinous beak The premaxillary teeth and the first lower tooth in Heterodontosaurus are enlarged into sizeable canines 18 In later ornithopods the skulls are more elongate and sometimes fully rectangular with a very large nasal opening and a thin elongate palpebral that can extend the entire way across the orbit Teeth are almost always absent from the premaxilla the antorbital fossa is reduced and round to slit like the tip of the snout is sometimes flared to form a broad beak 19 Members of the ornithopod family Hadrosauridae show further adaptations including the formation of dental batteries where teeth are continuously replaced and in many genera the development of prominent cranial crests formed by multiple different bones of the skull 20 Pachycephalosauria at one time thought to be close to ornithopods and know known to be related instead to ceratopsians show very unique skull anatomy that is unlike any other ornithischian The bones of the top of the skull are thickened and in many taxa expanded significantly to form round bony domes as the top of the head as well as possessing small nodes or elongate spikes along the back edge of the skull Many taxa are only known from these thick skull domes which are fused from the frontal and parietal bones As in many other ornithischians the snout is short and tapering the nasal opening is small the antorbital fossa is sometimes absent and there are premaxillary teeth though only three The two palpebrals are also incorporated into the skull roof as in thyreophorans rather than free 21 Ceratopsians the sister group to pachycephalosaurs also display many cranial adaptations most importantly the evolution of a bone called the rostral that forms the top beak opposite the predentary The jugal bones flare to the sides to create a pentagonal skull seen from above the nasal opening is closer to the top of the snout than the teeth and while the snout tapers in some taxa it is very deep and short in Psittacosaurus The ceratopsian palpebral is generally triangular and the back edge of the skull roof forms a flat frill that is enlarged in more derived ceratopsians 22 The ceratopsian family Ceratopsidae progresses on these features with the addition of horns above each orbit and on the top of the snout as well as substantial elongation of the frill and in many genera the development of two large parietal fenestrae forming holes in the frill The skull and frill elongation makes the skulls of Torosaurus and Pentaceratops the largest of any known terrestrial vertebrate at over 2 m 6 6 ft long 23 Early ornithischians were relatively small dinosaurs averaging about 1 2 meters in body length with a triangular skull that had large circular orbits on the sides This suggests that early ornithischians had relatively huge eyes that faced laterally The forelimbs of early ornithischians are considerably shorter than their hindlimbs A small forelimb such as those present in early ornithischians would not have been useful for locomotion and it is evident that early ornithischians were bipedal dinosaurs The entire skeleton was lightly built with a largely fenestrated skull and a very stout neck and trunk The tail is nearly half of the dinosaurs overall length The long tail presumably acted as a counterbalance and as a compensating mechanism for shifts in the creature s center of gravity The hindlimbs of early ornithischians show that the tibia is considerably longer than the femur a feature that suggests that early ornithischians were adapted for bipedality and were fast runners 24 Bird hip edit The ornithischian pelvis was opisthopubic meaning that the pubis pointed down and backwards posterior parallel with the ischium Figure 1a 6 Additionally the ilium had a forward pointing process the preacetabular process to support the abdomen 6 This resulted in a four pronged pelvic structure In contrast to this the saurischian pelvis was propubic meaning the pubis pointed toward the head anterior as in ancestral reptiles Figure 1b 6 The opisthopubic pelvis independently evolved at least three times in dinosaurs in ornithischians birds and therizinosauroids 25 Some argue that the opisthopubic pelvis evolved a fourth time in the clade Dromaeosauridae but this is controversial as other authors argue that dromaeosaurids are mesopubic 25 It has also been argued that the opisthopubic condition is basal to maniraptorans including among others birds therizinosauroids and dromaeosaurids with some clades having later experienced a reversal to the propubic condition 26 Classification editHistory edit nbsp nbsp The general pelvis of Ornithischia left and Saurischia right illustrating the differences highlighted by Seeley 1888 as justifying their independent evolution The first recognition of an herbivorous group of dinosaurs was named Orthopoda in 1866 by Edward Drinker Cope 27 a name that is now recognized as a synonym of Ornithischia 28 Discussions on the taxonomy of dinosaurs by Othniel Charles Marsh identified two major groups of herbivorous dinosaurs Ornithopoda and Stegosauria 29 containing genera from a broad geographic and stratigraphic distribution 13 While often these groups were placed within Dinosauria Harry Govier Seeley suggested instead in 1888 that ornithopods and stegosaurs which shared many features in the skull limbs and hip were unrelated to other dinosaurs and so he proposed that Dinosauria was an unnatural grouping of two independently evolved suborders Saurischia and Ornithischia It is from the anatomy of the hip that Seeley chose the name Ornithischia referencing the bird like anatomy of the ischium bone 1 Many researchers did not follow the division of Seeley at first with Marsh naming the group Predentata to unite ornithopods stegosaurs and Ceratopsia within Dinosauria 30 but with additional work and new discoveries the unnatural nature of Dinosauria came to be accepted and the names Seeley proposed found common use 31 After further decades in 1974 Robert T Bakker and Peter M Galton provided new evidence in support of the grouping of ornithischians and saurischians together within a natural Dinosauria 32 which has been supported since 13 The first cladistic studies on Ornithischia were published simultaneously in 1984 by David B Norman Andrew R Milner and Paul C Sereno These studies differed somewhat in their results but found that Iguanodon was closer to hadrosaurs than other ornithopods followed by Dryosaurus Hypsilophodon and then Lesothosaurus and its relatives 33 34 35 36 13 While the study of Norman placed ceratopsians between Hypsilophodon and more derived ornithopods 34 the study of Sereno placed ceratopsians with ankylosaurs and stegosaurs 36 It has since been recognized by that ceratopsians are closer to ornithopods than the armoured ankylosaurs and stegosaurs 4 but the relationships of some groups are still in states of change with some more consistent results than others 37 3 An early study that looked at the relationships within Ornithischia with greater detail was that of Sereno in 1986 who provided features that supported the evolution of all ornithischian groups and shared similarities with earlier studies Sereno found that Lesothosaurus was the most primitive ornithischian with all other ornithischians united within the clade Genasauria which has two subgroups The first subgroup Thyreophora unites ankylosaurs and stegosaurs along with more primitive taxa like Scelidosaurus while the second subgroup Cerapoda contained ornithopods ceratopsians pachycephalosaurs and small primitive forms 4 One group of the small primitive forms considered to be cerapodans by Sereno Heterodontosauridae has since been found to be a group of very early ornithischians of similar evolutionary status as Lesothosaurus 37 although this result is not definitive 38 The first large scale numerical analysis of the phylogenetics of Ornithischia was published in 2008 by Richard J Butler and colleagues including many primitive ornithischians and members from all of the major subgroups to test some of the hypotheses given previously about ornithischian evolution and the relationships of the groups Thyreophora was found to be a supported group as well as the clade of pachycephalosaurs and ceratopsians that Sereno named Marginocephalia in 1986 Some taxa considered earlier to be ornithopods like heterodontosaurids Agilisaurus Hexinlusaurus and Othnielia were instead found to be outside of both Ornithopoda and Ceratopsia but still closer to those two groups than thyreophorans The early Argentinian taxon Pisanosaurus was found to be the most primitive ornithischian but while overall results agreed with earlier studies and showed some stability areas of the evolutionary tree were found to be problematic and with potential for later change 37 In 2021 a new phylogenetic study was published authored by Paul Emile Dieudonne and colleagues that instead found Heterodontosauridae to nest alongside Pachycephalosauria within Marginocephalia changing the early evolution of ornithopods considerably and showing that the evolution of ornithischians was far from definitive 38 Below are the cladograms of Sereno Butler and colleagues and Dieudonne and colleagues restricted to the major clades of Ornithischia Heterodontosauridae Lesothosaurus and Pisanosaurus Sereno 1986 4 Ornithischia Lesothosaurus Genasauria Thyreophora Stegosauria Ankylosauria Cerapoda Marginocephalia Pachycephalosauria Ceratopsia Euornithopoda Heterodontosauria OrnithopodaButler et al 2008 37 Ornithischia Pisanosaurus Heterodontosauridae Genasauria Thyreophora Lesothosaurus Stegosauria Ankylosauria Neornithischia Cerapoda Ornithopoda Marginocephalia Pachycephalosauria CeratopsiaDieudonne et al 2021 38 Ornithischia Lesothosaurus Thyreophora Stegosauria Ankylosauria Cerapoda Ornithopoda Marginocephalia Ceratopsia Pachycephalosauria incl heterodontosaurids Subgroups edit When Ornithischia was first named Seeley united the orders Ornithopoda and Stegosauria of Marsh s taxonomy within the new group 1 Ceratopsia was then recognized as a unique group related to ornithopods and stegosaurs by Marsh by 1894 with each of the three suborders still being recognized as distinct groups today 13 30 Ceratopsians are recognized as group that grew in diversity later in the Cretaceous after evolving in the Late Jurassic encompassing a diverse array of bodyforms from the small bipedal Psittacosaurus up to the very large quadrupedal horned and frilled ceratopsids like Torosaurus which has the longest skull of any terrestrial vertebrate 22 23 Ornithopods which range from the Early Jurassic in some studies until the end of the Cretaceous with continuous diversity are generally bipedal and unarmoured though some later groups like Hadrosauridae evolved complex dental anatomy in the form of batteries of teeth 18 20 Stegosaurs are comparatively limited restricted to a primarily Jurassic group of moderate to large quadrupedal herbivores with two rows of vertical plates ornamenting their spine which possibly did not go extinct until the Late Cretaceous though at the time of Marsh Stegosauria was used for all armored and quadrupedal taxa many of which are now separated into Ankylosauria 16 17 Ankylosaurs were only recognized as a distinct group from stegosaurs in the 1920s despite many members being known for decades before with the group now encompassing a broad array of heavy quadrupedal ornithischians with extensive armour covering their body and skull 17 The fifth recognized major subgroup of ornithischians is Pachycephalosauria 13 which was first named in 1974 after being confused for a long time with the theropod Troodon on account of their similarly omnivorous and unique teeth 39 21 Pachycephalosaurians are unique for their tall thickened skulls and small bipedal bauplan suggesting that their domes were for sexual display or combat in the form of head butting or flank butting 21 Some taxa particularly those at one point groupt together in the ornithopod family Hypsilophodontidae are now recognized to not fall within any of the major ornithischian groups and either be outside Genasauria or on the basal stem of Neornithischia outside Cerapoda 37 Following the publication of the PhyloCode to provide rules and regulations on the use of taxonomic names for groups the internal classification of Ornithischia was revised by Daniel Madzia and colleagues in 2021 to provide a framework of definitions and taxa for other studies to follow and modify from They names the new clade Saphornithischia to unite heterodontosaurids with more derived ornithischians to encompass the concept of the well supported clear ornithischians as the origins of the group and the relationships of primitive taxa like Pisanosaurus and members of Silesauridae may sometimes be found to be ornithischians outside this core grouping Madzia and colleagues also provided a composite cladogram of Ornithischia to illustrate the consensus of internal divisions which can be seen below Ornithischia has been defined as all taxa closer to Iguanodon than Allosaurus or Camarasaurus Genasauria has been defined as the smallest clade containing Ankylosaurus Iguanodon Stegosaurus and Triceratops 3 Ornithischia Heterodontosaurus tucki Heterodontosauridae nbsp Genasauria Thyreophora Stegosauria Huayangosaurus taibaii Huayangosauridae Stegosaurus stenops Stegosauridae nbsp Ankylosauria Mymoorapelta maysi Nodosauridae Polacanthus foxii Polacanthinae nbsp Nodosaurinae Nodosaurus textilis Panoplosaurus mirus Panoplosaurini Struthiosaurus austriacus Struthiosaurini Ankylosauridae Hylaeosaurus armatus Shamosaurinae Gobisaurus domoculus Shamosaurus scutatus Ankylosaurinae Pinacosaurus grangeri Saichania chulsanensis Ankylosaurus magniventris Ankylosaurini nbsp Neornithischia Jeholosaurus shangyuanensis Jeholosauridae Thescelosauridae Orodromeus makelai Orodrominae Thescelosaurus neglectus Thescelosaurinae Hypsilophodon foxii Hypsilophodontidae nbsp Cerapoda Marginocephalia Pachycephalosauria Stegoceras validum nbsp Pachycephalosaurinae Sphaerotholus goodwini Pachycephalosaurus wyomingensis Pachycephalosaurini Ceratopsia Psittacosaurus mongoliensis Chaoyangsaurus youngi Chaoyangsauridae Neoceratopsia Leptoceratops gracilis Leptoceratopsidae Coronosauria Protoceratops andrewsi Protoceratopsidae nbsp Ceratopsidae Ceratops montanus Chasmosaurinae Chasmosaurus belli Anchiceratops ornatus nbsp Arrhinoceratops brachyops Triceratops horridus Triceratopsini Centrosaurinae Nasutoceratops titusi Nasutoceratopsini Eucentrosaura Centrosaurus apertus Centrosaurini nbsp Pachyrhinosaurini Achelousaurus horneri Pachyrhinosaurus canadensis Ornithopoda Elasmaria Gasparinisaura cincosaltensis nbsp Macrogryphosaurus gondwanicus Talenkauen santacrucensis Iguanodontia Rhabdodontidae Rhabdodon priscus Zalmoxes robustus Tenontosaurus tilletti nbsp Dryomorpha Dryosaurus altus Dryosauridae Ankylopollexia Camptosaurus dispar Camptosauridae nbsp Styracosterna Hypselospinus fittoni Hadrosauriformes Iguanodon bernissartensis Iguanodontidae nbsp Hadrosauroidea Probactrosaurus gobiensis Hadrosauridae Hadrosaurus foulkii Hadrosaurinae Saurolophus osborni Saurolophinae nbsp Lambeosaurus lambei Lambeosaurinae Multiple taxa within Ornithischia fall around the origin of the group or cannot be classified definitively Lesothosaurus and Laquintasaura have been found as basal thyreophorans or basal ornithischians Chilesaurus is either a theropod or a basal ornithischian Pisanosaurus has been found as a basal ornithischian or a non ornithischian silesaurid Eocursor has been a basal ornithischian or a basal member of Neornithischia Serendipaceratops cannot be classified beyond Ornithischia as it is either an ankylosaur or a ceratopsian and Alocodon Fabrosaurus Ferganocephale Gongbusaurus Taveirosaurus Trimucrodon and Xiaosaurus are dubious ornithischians of uncertain basal classification 3 2 40 14 41 Depending on the phylogenetic results Silesauridae could either be a clade within Ornithischia its members could form an evolutionary gradient or some members found form a clade while others are part of a gradient 2 42 Evolution edit nbsp Skull of Revueltosaurus a genus originally considered an early ornithischian based on its teeth 43 For a long time the only understanding of the origins of Ornithischia came from Lesothosaurus and Pisanosaurus which together represented the best known Early Jurassic and Triassic ornithischians respectively Many suggestions of taxa and specimens that could be referred to Ornithischia from the Triassic were based on teeth and jaw bones as they showed similar adaptations for herbivory The genera Revueltosaurus Galtonia Pekinosaurus Tecovasaurus Lucianosaurus Protecovasaurus Crosbysaurus and Azendohsaurus were all at one time considered to be Triassic ornithischians with only their teeth known but are now recognized to be completely unrelated 44 The only early ornithischians that were considered to be diagnostic in a 2004 review by Norman and colleagues were Lesothosaurus Pisanosaurus and Technosaurus limiting the early ornithischian record to only two Triassic genera from Argentina and the USA and one Early Jurassic genus from South Africa with all the tooth taxa being considered undiagnostic 14 Referrals of isolated teeth to Ornithischia based on herbivorous features began to be extensively questioned by William G Parker and colleagues in 2005 after the discovery of skull and skeleton material clearly from Revueltosaurus showing that the ornithischian like teeth were from an animal more closely related to crocodiles than birds and there were multiple occurrences of herbivory throughout Triassic reptiles 44 43 Removing the list of Triassic tooth taxa from Ornithischia the early diversity of the group was substantially reduced especially in comparison to the known Triassic diversity of theropods and sauropodomorphs If Pisanosaurus represented the earliest ornithischian there would be at least a 20 million year gap in the evolution of Ornithischia until Lesothosaurus and heterodontosaurids It is possible that the limited early record of ornithischians is due to them inhabiting environments that were less conducive to fossilization or that the phylogenetics of the group were incorrect and that early ornithischians were already known but identified as members of other groups 44 Possible evolutionary relationships of Ornithischia 2 Silesauridae Dinosauria Saurischia Sauropodomorpha Theropoda Ornithischia Silesauridae Dinosauria Theropoda Phytodinosauria Sauropodomorpha Ornithischia Silesauridae Dinosauria Sauropodomorpha Ornithoscelida Theropoda Ornithischia Dinosauria Saurischia Sauropodomorpha Theropoda Ornithischia silesaurs traditional ornithischians First noted in the 2003 naming of the early taxon Silesaurus some taxa generally considered non dinosaurs show similarities to ornithischians in the teeth and jaw anatomy 45 5 These basal taxa which were then grouped within Silesauridae and commonly as the sister group to Dinosauria may instead be the earliest ornithischians They show adaptations for the evolution of herbivory and can fill in the gap in early evolution of ornithischians that were otherwise only clearly known since the beginning of the Jurassic This hypothesis has found support in multiple different phylogenetic analyses 46 47 but the results are not yet accepted as definitive enough to contradict other possible evolutionary strategies of dinosaurs Alternatively and more in line with earlier studies on dinosaur evolution silesaurids may be the sister taxa to the Saurischia Ornithischia split or even other arrangements of the three main dinosaur groups Ornithischia Sauropodomorpha and Theropoda 2 The 2017 phylogenetic study of Matthew G Baron and colleagues suggested that instead of a Saurischia Ornithischia split ornithischians were instead closest to theropods in the clade Ornithoscelida with sauropodomorphs being outside the grouping Under this case the omnivory in the earliest sauropodomorphs and ornithischians would be the ancestral condition for dinosaurs along with the grasping abilities seen in the earliest ornithischians and theropods 48 While Ornithoscelida is a possible hypothesis for the evolution of dinosaurs and the close relationships of Ornithischia follow up studies have not found it statistically more likely than the traditional dichotomy of Ornithischia and Saurischia or the third alternative Phytodinosauria where ornithischians and sauropodomorphs are closer to each other than theropods 49 50 51 Along with Pisanosaurus which was supported as the earliest ornithischian for a time before being considered just as likely to be a silesaur rather than an ornithischian an additional problematic taxon is Chilesaurus from the Late Jurassic of Chile While it was originally named as a derived theropod with unique anatomy it was found in studies based on Baron and colleagues results to instead be either the basalmost ornithischian or a sauropodomorph As the earliest ornithischian Chilesaurus tied multiple details of ornithischian and theropod anatomy together supporting their union in Ornithoscelida though when it is not the basalmost ornithischian a traditional Saurischia is recovered The problematic nature of Chilesaurus requires further revisiting of its anatomy but the details of vertebral air pockets pelvis shape and hand support it as a theropod 2 Daemonosaurus typically a theropod or close relative of herrerasaurs has also been found as the basalmost ornithischian at times when Ornithoscelida is recovered but it does not share any unique features with ornithischians and redescribing its anatomy found it fairly confidently to be a basal dinosaur not related closely to Ornithischia 52 The phylogenetic analysis of Norman and colleagues in 2022 recovered the members of Silesauridae as forming an ancestral grade within Ornithischia even with the inclusion of Chilesaurus supporting the earlier results of Muller and Garcia and their evolutionary trends for early ornithischian anatomy Norman and colleagues used Prionodontia over both Saphornithischia and Genasauria since all were recovered as encompassing the same node 2 The earliest ornithischians under this reconstruction were faunivorous as seen by Lewisuchus which has typical teeth like theropods Serrations on teeth become larger for taxa more derived than Asilisaurus the development of a cingulum in teeth is seen in Technosaurus and later ornithischians the lower jaw becomes more elongate in taxa above Silesaurus and core ornithischians are united by the pubic bone angling backwards and the modification of the ankle joint 47 nbsp Lower jaws and teeth of top to bottom Kwanasaurus Asilisaurus Eucoelophysis Technosaurus Sacisaurus Silesaurus Diodorus scytobrachion and Soumyasaurus Dinosauria Saurischia Herrerasauridae Daemonosaurus Chindesaurus Tawa hallae Eodromaeus Sauropodomorpha Theropoda Faunivorous Ornithischia Lewisuchus Soumyasaurus Asilisaurus Sulcimentisauria Diodorus scytobrachion Technosaurus Parapredentata Ignotosaurus Silesaurus Sacisaurus Lutungutali Kwanasaurus Eucoelophysis Pisanosaurus Laquintasaura Prionodontia Thyreophora Neornithischia HerbivorousPalaeoecology editOrnithischians 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 53 Most ornithischians were herbivorous 6 In fact most of the unifying characters of Ornithischia are thought to be related to this herbivory 6 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 more effectively digest plant matter 6 The smallest known ornithischian is Fruitadens haagarorum 54 The largest Fruitadens individuals reached just 65 75 cm Previously only carnivorous saurischian theropods were known to reach such small sizes 54 At the other end of the spectrum the largest known ornithischians reach about 15 meters smaller than the largest saurischians 55 However not all ornithischians were strictly herbivorous Some groups like the heterodontosaurids were likely omnivores 56 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 57 The members of Genasauria were primarily herbivores 58 Genasaurians most often had their head at the level of one meter which suggests they were feeding primarily on ground level plants such as ferns cycads and other herbaceous gymnosperms 59 There is strong evidence that some ornithischians lived in herds 6 8 This evidence consists of multiple bone beds where large numbers of individuals of the same species and of different age groups died simultaneously 6 8 See also edit nbsp Dinosaurs portalNotes edit plural ischiaReferences edit a b c Seeley H G 1888 On the classification of the fossil animals commonly named Dinosauria Proceedings of the Royal Society of London 43 258 265 165 171 doi 10 1098 rspl 1887 0117 a b c d e f g h Norman D B Baron M G Garcia M S Muller R T 2022 Taxonomic palaeobiological and evolutionary implications of a phylogenetic hypothesis for Ornithischia Archosauria Dinosauria Zoological Journal of the Linnean Society 196 4 1273 1309 doi 10 1093 zoolinnean zlac062 a b c d Madzia D Arbour V M Boyd C A Farke A A Cruzado Caballero P Evans D C 2021 The phylogenetic nomenclature of ornithischian dinosaurs PeerJ 9 e12362 doi 10 7717 peerj 12362 PMC 8667728 PMID 34966571 a b c d Sereno P C 1986 Phylogeny of the Bird Hipped Dinosaurs Ornithischia National Geographic Research 2 2 234 256 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 1 23 33 Bibcode 2007HBio 19 23F doi 10 1080 08912960600845767 a b c d e f g h i j k l Fastovsky David E Weishampel David B 2012 Dinosaurs A Concise Natural History Cambridge Cambridge University Press ISBN 978 1107276468 Colbert Edwin H Edwin Harris Knight Charles Robert 1951 The dinosaur book the ruling reptiles and their relatives New York McGraw Hill p 152 a b c Qi Zhao Barrett Paul M Eberth David A 2007 09 01 Social Behaviour and Mass Mortality in the Basal Ceratopsian Dinosaur Psittacosaurus early Cretaceous People s Republic of China PDF Palaeontology 50 5 1023 1029 Bibcode 2007Palgy 50 1023Q doi 10 1111 j 1475 4983 2007 00709 x ISSN 1475 4983 S2CID 128781816 Zhao Q 2013 Juvenile only clusters and behaviour of the Early Cretaceous dinosaur Psittacosaurus Acta Palaeontologica Polonica doi 10 4202 app 2012 0128 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 Bibcode 2002NW 89 361M doi 10 1007 s00114 002 0339 6 ISSN 0028 1042 PMID 12435037 S2CID 17781405 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 Bibcode 2014Sci 345 451G doi 10 1126 science 1253351 hdl 1983 a7ae6dfb 55bf 4ca4 bd8b a5ea5f323103 PMID 25061209 S2CID 206556907 Archived from the original PDF on 2019 02 09 Retrieved 2016 08 28 a b Paul G S 2024 The Princeton Field Guide to Dinosaurs 3rd ed Princeton University Press pp 261 373 ISBN 978 0 691 23157 0 a b c d e f Weishampel D B 2004 Ornithischia In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 323 324 ISBN 0 520 24209 2 a b c d Norman D B Witmer L M Weishampel D B 2004 Basal Ornithischia In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 325 334 ISBN 0 520 24209 2 Norman D B Witmer L M Weishampel D B 2004 Basal Thyreophora In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 335 342 ISBN 0 520 24209 2 a b Galton P M Upchurch P C 2004 Stegosauria In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 343 362 ISBN 0 520 24209 2 a b c Vickaryous M K Maryanska T Weishampel D B 2004 Ankylosauria In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 363 392 ISBN 0 520 24209 2 a b Norman D B Sues H D Witmer L M Coria R A 2004 Basal Ornithopoda In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 393 412 ISBN 0 520 24209 2 Norman D B 2004 Basal Iguanodontia In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 413 437 ISBN 0 520 24209 2 a b Horner J R Weishampel D B Forster C A 2004 Hadrosauridae In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 438 463 ISBN 0 520 24209 2 a b c Maryanska T Chapman R E Weishampel D B 2004 Pachycephalosauria In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 464 477 ISBN 0 520 24209 2 a b You H Dodson P Weishampel D B 2004 Basal Ceratopsia In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 478 494 ISBN 0 520 24209 2 a b Dodson P Forster C A Sampson S D 2004 Ceratopsidae In Weishampel D B Osmolska H Dodson P eds The Dinosauria 2nd ed University of California Press pp 494 513 ISBN 0 520 24209 2 Colbert E H 1981 A primitive ornithischian dinosaur from the Kayenta Formation of Arizona Museum Northern Arizona Bull 53 1 61 a b Currie Philip J Padian Kevin 1997 10 06 Encyclopedia of Dinosaurs Academic Press pp 537 538 ISBN 9780080494746 Holtz T R and Osmolska H 2004 Saurischia In Weishampel Dodson and Osmolska eds The Dinosauria second edition Berkeley University of California Press Cope E D 1866 The anomalous relations existing between the tibia and fibula in certain of the Dinosauria Proceedings of the Academy of Natural Sciences of Philadelphia 18 316 317 Kuhn O 1946 Das System der fossilen und rezenten Amphibien und Reptilien Bericht der Naturforschenden Gesellschaft in Bamberg 29 49 67 Marsh O C 1881 Principal characters of the American Jurassic Dinosaurs American Journal of Science 21 3 417 423 a b 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3 556 574 Bibcode 2003JVPal 23 556D doi 10 1671 A1097 Cabreira S F Kellner A W A Dias da Silva S da Silva L R Bronzati M Marsola J C A Muller R T Bittencourt J S Batista B J A Raugust T Carrilho R Brodt A Langer M C 2016 A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet Current Biology 26 22 3090 3095 Bibcode 2016CBio 26 3090C doi 10 1016 j cub 2016 09 040 PMID 27839975 a b Muller R T Garcia M S 2020 A paraphyletic Silesauridae as an alternative hypothesis for the initial radiation of ornithischian dinosaurs Biology Letters 16 8 1 5 doi 10 1098 rsbl 2020 0417 PMC 7480155 PMID 32842895 Baron M G Norman D B Barrett P M 2017 A new hypothesis of dinosaur relationships and early dinosaur evolution Nature 543 7646 501 506 Bibcode 2017Natur 543 501B doi 10 1038 nature21700 PMID 28332513 Langer M C Ezcurra M D Rauhut O W M Benton M J Knoll F McPhee B W Novas F E Pol D Brusatte S L 2017 Untangling the dinosaur family tree Nature 551 7678 E1 E3 Bibcode 2017Natur 551E 1L doi 10 1038 nature24011 hdl 1983 d088dae2 c7fa 4d41 9fa2 aeebbfcd2fa3 PMID 29094688 Baron M G Norman D B Barrett P M 2017 Baron et al reply Nature 551 7678 E4 E5 Bibcode 2017Natur 551E 4B doi 10 1038 nature24012 PMID 29094705 Parry L A Baron M G Vinther J 2017 Multiple optimality criteria support Ornithoscelida Royal Society Open Science 4 10 170833 Bibcode 2017RSOS 470833P doi 10 1098 rsos 170833 PMC 5666269 PMID 29134086 Nesbitt S J Sues H D 2021 The osteology of the early diverging dinosaur Daemonosaurus chauliodus Archosauria Dinosauria from the Coelophysis Quarry Triassic Rhaetian of New Mexico and its relationships to other early dinosaurs Zoological Journal of the Linnean Society 191 1 150 179 doi 10 1093 zoolinnean zlaa080 Jeffrey A Wilson Claudia A Marsicano Roger M H Smith 6 October 2009 Dynamic Locomotor Capabilities Revealed by Early Dinosaur Trackmakers from Southern Africa PLOS ONE 4 10 e7331 Bibcode 2009PLoSO 4 7331W doi 10 1371 journal pone 0007331 PMC 2752196 PMID 19806213 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 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 Bibcode 2011AcGlS 85 58J doi 10 1111 j 1755 6724 2011 00378 x ISSN 1755 6724 S2CID 85351874 Barrett P M Rayfield E J 2006 Ecological and evolutionary implications of dinosaur feeding behaviour PDF Trends in Ecology amp Evolution 21 4 217 224 doi 10 1016 j tree 2006 01 002 PMID 16701088 Ji Q Wu X Cheng Y Ten F Wang X Ji Y 2016 Fish hunting ankylosaurs Dinosauria Ornithischia from the Cretaceous of China Journal of Geology 40 2 Barrett P M amp Rayfield E J 2006 Ecological and evolutionary implications of dinosaur feeding behaviour Trends in Ecology amp Evolution 21 4 217 224 Fastovsky D E amp Weishampel D B 2012 Dinosaurs a concise natural history 2nd ed Cambridge New York Cambridge University Press External links edit nbsp Wikispecies has information related to Ornithischia Ornithischia from Palaeos cladogram characteristics Retrieved from https en wikipedia org w index php title Ornithischia amp oldid 1222847330, wikipedia, wiki, book, books, library,

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