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#REDIRECT [[Ornithischia]]
{{Automatic taxobox
| name = Genasaurs
| fossil_range = [[Early Jurassic]]-[[Late Cretaceous]], {{fossilrange|199.6|66.5}}
| image =
| image_caption =
| authority = [[Paul Sereno|Sereno]], 1986
| subdivision_ranks = Subgroups
| subdivision =
* {{extinct}}''[[Serendipaceratops]]''
* {{extinct}}'''[[Neornithischia]]'''
* {{extinct}}'''[[Thyreophora]]'''
| synonyms =Pachypoda <small>[[Ernst Haeckel|Haeckel]], 1895</small>
}}

'''Genasauria''' is a clade of extinct beaked, primarily [[herbivorous]] [[dinosaurs]]. [[Paleontologist]] [[Paul Sereno]] first named Genasauria in 1986.<ref name="sereno1986">Sereno, Paul C. (1986). Phylogeny of the bird-hipped dinosaurs (Order Ornithischia). National Geographic Research, 2(2), 234–256.</ref> The name Genasauria is derived from the Latin word ''gena'' meaning ‘cheek’ and the Greek word ''saúra'' (σαύρα) meaning ‘lizard.’ Genasauria is the most inclusive clade within the order [[Ornithischia]]. According to Sereno (1986), Genasauria represents all ornithischians except for the most primitive ornithischian, ''[[Lesothosaurus]]''. Sereno’s formal definition is, “''[[Ankylosaurus]]'', ''[[Triceratops]]'', their most recent common ancestor and all descendants.”<ref name="sereno1986" /> It is hypothesized that Genasauria had diverged from ''Lesothosaurus'' by the Early Jurassic.<ref name="sereno1991">Sereno, Paul C. (1991). Lesothosaurus,“fabrosaurids,” and the early evolution of Ornithischia. Journal of Vertebrate Paleontology, 11(2), 168–197.</ref> Cranial features that characterize Genasauria include a medial offset of the maxillary dentition, a sprout-shaped mandibular symphysis, moderately sized coronoid process, and an edentulous (without teeth) anterior portion of the premaxilla.<ref name="sereno1986" /> A distinguishing postcranial feature of Genasauria is a pubic peduncle of the ilium that is less robust than the ischial peduncle.<ref name="sereno1986" />
Genasauria is commonly divided into [[Neornithischia]] and [[Thyreophora]]. Neornithischia is characterized by asymmetrical distributions of enamel covering the crowns of the cheek teeth, an open acetabulum, and a laterally protruding ischial peduncle of the ilium. Neornithischia includes ornithopods, pachycephalosaurs, and ceratopsians. Thyreophora is characterized by body armor and includes stegosaurs, ankylosaurs, ''[[Scelidosaurus]]'', and ''[[Scutellosaurus]]''.<ref name="sereno1986" />

==Distinguishing characteristics==

===Cranial characteristics===
Genasauria contains a medial offset of the maxillary dentition (buccal emargination), which is commonly referred to as the ‘ornithischian cheek.'<ref>Padian, K. (1997). Encyclopedia of dinosaurs. San Diego: Academic Press.</ref> Other characteristics of the ornithischian cheek include “a deep-set position of the tooth rows, away from the sides of the face, a spout-shaped front to the mandibles, and reduction in the size of the opening on the outside of the lower jaw (the external mandibular foramen)."<ref>Fastovsky, D. E., & Weishampel, D. B. (2012). Dinosaurs: a concise natural history (2nd ed). Cambridge ; New York: Cambridge University Press.</ref> The ornithischian cheek is largely inferred to be evidence for the possession of muscular cheeks that were used for complex chewing behavior and is a fundamentally Genasaurian characteristic.<ref name="galton1973">Galton, P. M. (1973). The cheeks of ornithischian dinosaurs. Lethaia, 6(1), 67–89. http://doi.org/10.1111/j.1502-3931.1973.tb00873.x</ref> Galton (1973) also suggests that the ornithischian cheek was found between the maxillary and dentary ridges to prevent the loss of food through the jaws. It may have consisted of connective tissue and skin, rather than muscle fibers, which meant that the tongue was used to move food that had accumulated between the teeth and the cheek, back to the tongue side of the cheek so that it could be further broken down by the teeth.<ref name="galton1973" /> The ornithischian cheek is absent or only weakly developed in ''Lesothosaurus'', which supports its placement as a sister group to Genasauria.<ref name="sereno1986" />
In Genasauria, the mandibular symphysis is shaped like a spout and forms at an acute angle.<ref name="sereno1986" /> The mandibular symphysis is the point of fusion between the two lateral dentary bones. The mandible of Genasauria is also characterized by the possession of a coronoid process that is longer than 50 percent of the depth of the midlength of the dentary.<ref>Weishampel, D. B., Dodson, P., & Osmólska, H. (2004). The dinosauria. Univ of California Press.</ref> The coronoid process is a thin anterior projection of bone from the dentary, which serves as a site for the attachment of muscles that aid in chewing behavior.<ref>Holliday, C. M. (2009). New Insights Into Dinosaur Jaw Muscle Anatomy. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 292(9), 1246–1265. http://doi.org/10.1002/ar.20982</ref>

===Post-cranial characteristics===
Post-cranial characteristics include reduced relative size of the pubic peduncle of the ilium and a fourth trochanter that is shifted distally on the shaft of the femur.<ref name="sereno1986" /> The pubic peduncle of the ilium is an anterior extension of the ilium, which joins with the pubis. In Genasauria, the relative size of the public peduncle, compared to the size of the ilium, is reduced. The fourth trochanter is a process (extension) of the femur that serves as an attachment point for tail muscles, mainly for attachment of the ''Musculus caudofemoralis longus''.<ref>Benton, M. (2009). Vertebrate Palaeontology. Wiley. Retrieved from https://books.google.com/books?id=VThUUUtM8A4C</ref>

==Feeding behavior==
The members of Genasauria were primarily herbivores with some exceptions, like the omnivorous [[heterodontosaurid]]s.<ref>Barrett, P. M., & Rayfield, E. J. (2006). Ecological and evolutionary implications of dinosaur feeding behaviour. Trends in Ecology & Evolution, 21(4), 217–224.</ref> 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."<ref name="fastovsky">Fastovsky, D. E., & Weishampel, D. B. (2012). Dinosaurs: a concise natural history (2nd ed). Cambridge ; New York: Cambridge University Press.</ref>

==Major divisions==

===Thyreophora===
[[Thyreophora]] are defined as representing all taxa more closely related to ''[[Ankylosaurus]]'' than to ''[[Triceratops]]'' and are characterized by extensive dorsal body armor scutes.<ref name="sereno1991" /><ref>Nopcsa, F. (1915). Die Dinosaurier der siebenbürgischen Landesteile Ungarns: Von Franz Baron Nopcsa. Mit Tafel I-IV und 3 Figuren im Texte.[Umschlagtitel.]. Buchdruckerei des Franklin-Vereins.</ref> The group spanned about 100 million years, beginning in the early Jurassic though the late Cretaceous.<ref>Thompson, R. S., Parish, J. C., Maidment, S. C. R., & Barrett, P. M. (2012). Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora). Journal of Systematic Palaeontology, 10(2), 301–312. http://doi.org/10.1080/14772019.2011.569091</ref> During their time on earth, they gave rise to over 50 different species. They contain the groups [[Ankylosauria]] and [[Stegosauria]], as well as, a number of basal forms such as ''[[Scelidosaurus]]'',<ref>Owen, R. (1861). Palaeontology or a systematic summary of extinct animals and their geological relations. Black.</ref> ''Emausaurus'',<ref>Haubold, H. (1990). Dinosaurs and fluctuating sea levels during the mesozoic. Historical Biology, 4(2), 75–106. http://doi.org/10.1080/08912969009386535</ref> and ''Scutellosaurus''.<ref>Colbert, E. H. (1981). A primitive ornithischian dinosaur from the Kayenta Formation of Arizona. Museum of Northern Arizona Press.</ref> Fossils of Thyreophora have been primarily found in the northern hemisphere.<ref name="fastovsky" /> Thyreophora can be distinguished from Neornithischia based on: transversely broad process of the jugal and parallel rows of keeled scutes on the dorsal surface of the body.<ref name="fastovsky" />

===Neornithischia===
[[Neornithischia]] is a clade containing [[Ornithopoda]] and [[Marginocephalia]], which is a node-based clade that contains [[Ceratopsia]] and [[Pachycephalosauria]].<ref name="fastovsky" /> Neornithischia was previously labeled as [[Cerapoda]]. However, this name has been more recently given a less inclusive definition.<ref name="sereno1986" /> Neorniththischia evolved during the Jurassic period and persisted until the late Cretaceous period. Their fossils have only been found in the northern hemisphere.<ref name="fastovsky" /> Neornithischia can be distinguished from the Thyreophora by the following derived characteristics: significant diastem between premaxillary and maxillary teeth, five or fewer maxillary teeth, and finger-like anterior trochancter.<ref name="fastovsky" />

==Classification==

===Taxonomy===
This version of taxonomic classification is from ''The Dinosauria''.
* Genasauria
** [[Thyreophora]]
*** ''[[Scutellosaurus]]''
*** [[Ankylosauria]]
*** [[Stegosauria]]
** [[Neornithischia]]
*** [[Ornithopoda]]
*** [[Marginocephalia]]
**** [[Ceratopsia]]
**** [[Pachycephalosauria]]

===Phylogeny===
There is debate as to the placement of ''Lesothosaurus'' as a sister group to Genasauria as or as a basal member of Genasauria. Sereno (1986) argues that ''Lesothosaurus'' does not contain the defining Genasaurian synapomorphies of a medial offset of the maxillary dentition, a sprout-shaped mandibular symphysis, moderately sized coronoid process, and an edentulous (without teeth) anterior portion of the premaxilla, and a pubic peduncle of the ilium that is less robust than the ischial peduncle.<ref name="sereno1986" /> Butler (2011) argues that the synapomorphies that should exclude ''Lesothosaurus'' from Genasauria have been described in ''Lesothosaurus'' specimens. Butler writes “The position of ''Lesothosaurus'' within Neornithischia is supported by three unequivocal characters: reduction of the forelimb to less than 40% of the hind-limb length, presence of a dorsal groove on the ischium, and a strongly reduced, splint-like meta-tarsal one.” The following two cladograms illustrate the two opinions.<ref>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. http://doi.org/10.1111/j.1096-3642.2005.00182.x</ref>

The following is a cladogram based on the paper by Sereno (1986) that originally defined Genasauria.

{{clade| style=font-size:85%;line-height:80%
|label1='''Genasauria'''
|1={{clade
|label1=[[Thyreophora]]
|1={{clade
|1=''[[Scutellosaurus]]''
|label2=[[Thyreophoroidea]]
|2={{clade
|1=''[[Scelidosaurus]]''
|label2=[[Eurypoda]]
|2={{clade
|1=[[Stegosauria]]
|2=[[Ankylosauria]] }} }} }}
|label2=[[Neornithischia]]
|2={{clade
|1=[[Euornithopoda]]
|label2=[[Marginocephalia]]
|2={{clade
|1=[[Pachycephalosauria]]
|2=[[Ceratopsia]] }} }} }} }}

The following is a more recent cladogram based on an analysis by Butler et al. (2011).

{{clade| style=font-size:85%;line-height:80%
|label1='''Genasauria'''
|1={{clade
|1=''[[Lesothosaurus]]''
|label2=[[Thyreophora]]
|2={{clade
|1=''[[Scutellosaurus]]''
|2={{clade
|1=''[[Emausaurus]]''
|2={{clade
|1=''[[Scelidosaurus]]''
|label2=[[Eurypoda]]
|2={{clade
|1='''[[Stegosauria]]'''
|2='''[[Ankylosauria]]''' }} }} }} }}
|label3=[[Neornithischia]]
|3={{clade
|1=''[[Stormbergia]]''
|2={{clade
|1=''[[Agilisaurus]]''
|2={{clade
|1=''[[Hexinlusaurus]]''
|2={{clade
|1=''[[Othnielosaurus]]''
|label2=[[Cerapoda]]
|2={{clade
|1='''[[Ornithopoda]]'''
|label2=[[Marginocephalia]]
|2={{clade
|1='''[[Pachycephalosauria]]'''
|2='''[[Ceratopsia]]''' }} }} }} }} }} }} }} }}

==References==
{{reflist}}

==External links==
* [http://www.geol.umd.edu/~tholtz/G104/handouts/104GenasauriaPhyl.pdf One definition of Genasauria]
* {{Cite NIE|wstitle=Orthopoda|year=1905 |short=x}} An obsolete order that embraced at least two of its groups.

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{{Ornithodira|O.}}
{{Taxonbar|from=Q2605453}}

[[Category:Ornithischians]]

Latest revision as of 18:55, 4 May 2024

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