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{{Short description|Extinct family of dinosaurs}}
{{use American English|date= May 2022}}
{{good article}}
{{automatic taxobox
| name = Heterodontosaurids
| fossil_range = [[Early Jurassic]] – [[Early Cretaceous]], {{fossil range|earliest=210|200|140|latest=125}}<small>Possible Late Triassic record</small>
| image = Heterodontosaurus tucki cast - University of California Museum of Paleontology - Berkeley, CA - DSC04696.JPG
| image_alt = Holotype cast
| image_caption = Cast of specimen SAM-PK-K1332 of ''[[Heterodontosaurus tucki]]'', University of California Museum of Palaeontology
| taxon = Heterodontosauridae
| authority = [[Alfred Romer|Romer]], 1966 (Kuhn, [[1966 in paleontology|1966]])
| subdivision_ranks = Subgroups<ref name="sereno2012"/>
| subdivision = *{{extinct}}''[[Echinodon]]''
*{{extinct}}''[[Fruitadens]]''
*{{extinct}}''[[Geranosaurus]]''
*{{extinct}}''[[Tianyulong]]''
*{{extinct}}'''Heterodontosaurinae''' <small>Sereno, 2012</small><ref name="sereno2012"/>
** {{extinct}}''[[
** {{extinct}}''[[Heterodontosaurus]]''
** {{extinct}}''[[Lycorhinus]]''
** {{extinct}}''[[Manidens]]''
** {{extinct}}''[[
}}
Heterodontosaurids were
==Description==
[[File:Heterodontosauridae_Size_Comparison_by_PaleoGeek.svg|thumb|left|Size comparison of many heterodontosaurids]]
[[File:Fruitadens.jpg|thumb|Life restoration of ''[[Fruitadens]]'']]
Among heterodontosaurids, only ''[[Heterodontosaurus]]'' itself is known from a complete skeleton. Fragmentary skeletal remains of ''[[Abrictosaurus]]'' are known but have not been fully described, while most other heterodontosaurids are known only from jaw fragments and teeth. Consequently, most heterodontosaurid [[synapomorphy|synapomorphies]] (defining features) have been described from the teeth and jaw bones.<ref name="WW90">{{cite book |last=Weishampel |first=David B. |author-link=David B. Weishampel |author2=Witmer, Lawrence M. |editor1=Weishampel, David B. |editor2=Dodson, Peter |editor3=Osmólska, Halszka |title=The Dinosauria |year=1990 |publisher=University of California Press |___location=Berkeley |isbn=978-0-520-06727-1 |pages=486–497 |chapter=Heterodontosauridae }}</ref><ref name="DBNetal04">{{cite book |last1=Norman |first1=David B. |author1-link=David B. Norman |last2=Sues |first2=Hans-Dieter |last3=Witmer |first3=Lawrence M. |last4=Coria |first4=Rodolfo A. |author4-link=Rodolfo Coria |editor1=Weishampel, David B. |editor2=Dodson, Peter |editor3=Osmólska, Halszka |title=The Dinosauria |edition=Second |year=2004 |publisher=University of California Press |___location=Berkeley |isbn=978-0-520-24209-8 |pages=393–412 |chapter=Basal Ornithopoda}}</ref> ''Heterodontosaurus'' measured just over 1 meter (3.3 ft) in length,<ref name="SL80">{{cite journal |last=Santa Luca |first=Albert P. |year=1980 |title=The postcranial skeleton of ''Heterodontosaurus tucki'' (Reptilia, Ornithischia) from the Stormberg of South Africa |journal=Annals of the South African Museum |volume=79 |issue=7 |pages=159–211}}</ref> while the fragmentary remains of ''[[Lycorhinus]]'' may indicate a larger individual.<ref name="CEG90">{{cite journal |last=Gow |first=Christopher E. |year=1990 |title=A tooth-bearing maxilla referable to ''Lycorhinus angustidens'' Haughton, 1924 (Dinosauria, Ornithischia) |journal=Annals of the South African Museum |volume=99 |issue=10 |pages=367–380}}</ref>
''[[Tianyulong]]'' from China appears to preserve filamentous integument which has been interpreted to be a variant of the proto-feathers found in some theropods. These filaments include a crest along its tail. The presence of this filamentous integument has been used to suggest that both ornithischians and saurischians were [[endotherm]]ic.<ref name="XTZetal09">{{cite journal |last=Zheng |first=Xiao-Ting |author2=You, Hai-Lu |author3=Xu, Xing |author4=Dong, Zhi-Ming |date=19 March 2009 |title=An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures |journal=[[Nature (journal)|Nature]] |volume=458 |issue=7236 |pages=333–336 |doi=10.1038/nature07856 |pmid=19295609|bibcode=2009Natur.458..333Z |s2cid=4423110 }}</ref>
===Skull and teeth===
Both ''Abrictosaurus'' and ''Heterodontosaurus'' had very large [[eyes]]. Underneath the eyes, the [[jugal|jugal bone]] projected sideways, a feature also present in [[ceratopsia]]ns. As in the jaws of most ornithischians, the [[anatomical terms of ___location|anterior]] edge of the [[premaxilla]] (a bone at the tip of the upper jaw) was toothless and probably supported a [[keratin]]ous beak ([[rhamphotheca]]), although heterodontosaurids did have teeth in the [[anatomical terms of ___location|posterior]] section of the premaxilla. A large gap, called a [[diastema (dentistry)|diastema]], separated these premaxillary teeth from those of the [[maxilla]] (the main upper jaw bone) in many ornithischians, but this diastema was characteristically arched in heterodontosaurids. The [[mandible]] (lower jaw) was tipped by the [[predentary]], a bone unique to ornithischians. This bone also supported a beak similar to the one found on the [[premaxilla]]. All the teeth in the lower jaw were found on the [[dentary]] bone.<ref name="WW90" />
[[File:Heterodontosaur snouts.jpg|thumb|left|Snouts of ''Heterodontosaurus'' (A), ''[[Abrictosaurus]]'' (B), and ''Tianyulong'' (C)]]
Heterodontosaurids are named for their strongly [[heterodont]] [[dentition]]. There were three premaxillary teeth. In the [[Early Jurassic]] ''Abrictosaurus'', ''Heterodontosaurus'', and ''Lycorhinus'', the first two premaxillary teeth were small and conical, while the much larger third tooth resembled the canines of [[carnivora]]n [[mammal]]s and is often called the caniniform or 'tusk'. A lower caniniform, larger than the upper, took the first position in the dentary and was accommodated by the arched diastema of the upper jaw when the mouth was closed.<ref name="WW90" /> These caniniforms were serrated on both the anterior and posterior edges in ''Heterodontosaurus'' and ''Lycorhinus'', while those of ''Abrictosaurus'' bore serrations only on the anterior edge.<ref name="RAT70">{{cite journal |last=Thulborn |first=Richard A. |year=1970 |title=The systematic position of the Triassic ornithischian dinosaur ''Lycorhinus angustidens'' |journal=Zoological Journal of the Linnean Society |volume=49 |pages=235–245 |doi=10.1111/j.1096-3642.1970.tb00739.x |issue=3 }}</ref><ref name="JAH75">{{cite journal |last=Hopson |first=James A. |year=1975 |title=On the generic separation of the ornithischian dinosaurs ''Lycorhinus'' and ''Heterodontosaurus'' from the Stormberg Series (Upper Triassic) of South Africa |journal=South African Journal of Science |volume=71 |pages=302–305 }}</ref> In the [[Early Cretaceous]] ''Echinodon'', there may have been two upper caniniforms, which were on the maxilla rather than the premaxilla,<ref name="NB02">{{cite book |last1=Norman |first1=David B. |author1-link=David B. Norman |author2=Barrett, Paul M. |editor1=Milner, Andrew |editor2=Batten, David J. |chapter=Ornithischian dinosaurs from the Lower Cretaceous (Berriasian) of England |title=Life and Environments in Purbeck Times |series=''Special Papers in Palaeontology'' '''68''' |year=2002 |___location=London |publisher=Palaeontological Association |pages=161–189 |isbn=978-0-901702-73-9 }}</ref> and ''Fruitadens'' from the [[Late Jurassic]] may have had two lower caniniforms on each dentary.<ref name="PMG07">{{cite book |last=Galton |first=Peter M. |author-link=Peter Galton |editor1-last=Carpenter |editor1-first=Kenneth |chapter=Teeth of ornithischian dinosaurs (mostly Ornithopoda) from the Morrison Formation (Upper Jurassic) of the western United States. |title=Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs |year=2007 |___location=Bloomington |publisher=Indiana University Press |pages=17–47 |isbn=978-0-253-34817-3}}</ref><ref name="RJBetal10">{{cite journal |last=Butler |first=Richard J. |author2=Galton, Peter M. |author3=Porro, Laura B. |author4=Chiappe, Luis M. |author5=Henderson, D. M. |author6=Erickson, Gregory M. |year=2010 |title=Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America |journal=Proceedings of the Royal Society B |volume=277 |issue=1680 |pages=375–381 |doi=10.1098/rspb.2009.1494 |url= |pmc=2842649 |pmid=19846460}}</ref>
[[File:Heterodontosauridae evolution.jpg|thumb|Evolution of key masticatory specializations in heterodontosaurids, according to Sereno, 2012]]
Like the characteristic tusks, the cheek teeth of [[Synapomorphy|derived]] heterodontosaurids were also unique among early ornithischians. Small ridges, or denticles, lined the edges of ornithischian cheek teeth in order to crop vegetation. These denticles extend only a third of the way down the tooth crown from the tip in all heterodontosaurids; in other ornithischians, the denticles extend further down towards the root. Basal forms like ''Abrictosaurus'' had cheek teeth in both maxilla and dentary that were generally similar to other ornithischians: widely spaced, each having a low crown and a strongly-developed ridge (cingulum) separating the crown from the root. In more [[Synapomorphy|derived]] forms like ''Lycorhinus'' and ''Heterodontosaurus'', the teeth were chisel-shaped, with much [[hypsodont|higher crowns]] and no cingula, so that there was no difference in width between the crowns and the roots.<ref name="WW90" />
===Skeleton===
[[File:Tianyulong.jpg|thumb|Fossil of ''Tianyulong'', muzzle, hand, feet and tail framed in red]]
The postcranial anatomy of ''Heterodontosaurus tucki'' has been well-described, although ''H. tucki'' is generally considered the most derived of the Early Jurassic heterodontosaurids, so it is impossible to know how many of its features were shared with other species.<ref name="WW90" /> The forelimbs were long for a dinosaur, over 70% of the length of the hindlimbs. The well-developed deltopectoral crest (a ridge for the attachment of [[Pectoralis major muscle|chest]] and [[Deltoid muscle|shoulder]] muscles) of the [[humerus]] and prominent [[olecranon|olecranon process]] (where [[Triceps brachii muscle|muscles that extend the forearm]] were attached) of the [[ulna]] indicate that the forelimb was powerful as well. There were five digits on the [[manus (zoology)|manus]] ('hand'). The first was large, tipped with a sharply curved claw, and would rotate inwards when flexed; [[Robert Bakker]] called it the 'twist-thumb'.<ref name="RTB86">{{cite book |last=Bakker |first=Robert T. |author-link=Robert T. Bakker |title=The Dinosaur Heresies: New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction |year=1986 |publisher=William Morrow |___location=New York |isbn=978-0-14-010055-6 |page=453pp}}</ref> The second digit was the longest, slightly longer than the third. Both of these digits bore claws, while the clawless fourth and fifth digits were very small and simple in comparison. In the hindlimb, the [[tibia]] was 30% longer than the [[femur]], which is generally considered an adaptation for speed. The tibia and [[fibula]] of the lower leg were fused to the [[talus bone|astragalus]] and [[calcaneus|calcaneum]] of the ankle, forming a '[[tibiotarsus|tibiofibiotarsus]]' convergently with modern [[bird]]s. Also similarly to birds, the lower [[tarsus (skeleton)|tarsal]] (ankle) bones and [[metatarsus|metatarsals]] were fused to form a '[[tarsometatarsus]].' There are four digits in the [[pes (zoology)|pes]] (hindfoot), with only the second, third, and fourth contacting the ground. The tail, unlike many other ornithischians, did not have [[ossification|ossified]] [[tendon]]s to maintain a rigid posture and was probably flexible.<ref name="SL80" /> The fragmentary skeleton known for ''Abrictosaurus'' has never been fully described, although the forelimb and manus were smaller than in ''Heterodontosaurus''. Also, the fourth and fifth digits of the forelimb each bear one fewer [[phalanx bones|phalanx bone]].<ref name="RAT74">{{cite journal |last=Thulborn |first=Richard A. |year=1974 |title=A new heterodontosaurid dinosaur (Reptilia: Ornithischia) from the Upper Triassic Red Beds of Lesotho |journal=Zoological Journal of the Linnean Society |volume=55 |pages=151–175 |doi=10.1111/j.1096-3642.1974.tb01591.x |issue=2 }}</ref>
==Classification==
[[
South African [[paleontologist]] [[Robert Broom]] created the name ''[[Geranosaurus]]'' in 1911 for dinosaur jaw bones missing all of the teeth and some partial associated limb bones.<ref name="RB11">{{cite journal |last=Broom |first=Robert. |author-link=Robert Broom |year=1911 |title=On the dinosaurs of the Stormberg, South Africa |journal=Annals of the South African Museum |volume=7 |pages=291–308}}</ref> In 1924, ''Lycorhinus'' was named, and classified as a [[cynodont]], by [[Sidney Haughton]].<ref name="SHH24">{{cite journal |last=Haughton |first=Sidney H. |year=1924 |title=The fauna and stratigraphy of the Stormberg Series |journal=Annals of the South African Museum |volume=12 |pages=323–497}}</ref> ''Heterodontosaurus'' was named in 1962 and it, ''Lycorhinus'' and ''Geranosaurus'' were recognized as closely related ornithischian dinosaurs.<ref name="CC62">{{cite journal |last=Crompton |first=A.W. |author2=Charig, Alan |author2-link=Alan J. Charig |year=1962 |title=A new ornithischian from the Upper Triassic of South Africa |journal=Nature |volume=196 |pages=1074–1077 |doi=10.1038/1961074a0 |issue=4859|bibcode=1962Natur.196.1074C |s2cid=4198113 }}</ref> [[Alfred Romer]] named Heterodontosauridae in 1966 as a family of ornithischian dinosaurs including ''Heterodontosaurus'' and ''Lycorhinus''.<ref name="ASR66">{{cite book |last=Romer |first=Alfred S. |author-link=Alfred Sherwood Romer |title=Vertebrate Paleontology |edition=Third |year=1966 |publisher=University of Chicago Press |___location=Chicago |isbn=978-0-7167-1822-2 |page=[https://archive.org/details/vertebratepaleon0000carr/page/468 468 pp] |url=https://archive.org/details/vertebratepaleon0000carr/page/468 }}</ref> Kuhn independently proposed Heterodontosauridae in the same year and is sometimes cited as its principal author.<ref>{{Cite journal |last=Sereno |first=Paul |date=2012-03-10 |title=Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs |url=https://zookeys.pensoft.net/article/3152/ |journal=ZooKeys |language=en |issue=226 |pages=1–225 |doi=10.3897/zookeys.226.2840 |issn=1313-2970 |pmc=3491919 |pmid=23166462 |doi-access=free |archive-date=2021-02-03 |access-date=2022-08-18 |archive-url=https://web.archive.org/web/20210203120317/https://zookeys.pensoft.net/article/3152/ |url-status=live }}</ref> It was defined as a [[clade]] in 1998 by [[Paul Sereno]]<ref name="PCS98">{{cite journal |last=Sereno |first=Paul C. |author-link=Paul Sereno |year=1998 |title=A rationale for phylogenetic definitions, with application to the higher-level taxonomy of Dinosauria |journal=Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen |volume=210 |issue=1 |pages=41–83 |doi=10.1127/njgpa/210/1998/41 }}</ref> and redefined by him in 2005 as the stem clade consisting of ''Heterodontosaurus tucki'' and all species more closely related to ''Heterodontosaurus'' than to ''[[Parasaurolophus walkeri]]'', ''[[Pachycephalosaurus wyomingensis]]'', ''[[Triceratops horridus]]'', or ''[[Ankylosaurus magniventris]]''.<ref name="PCS05">{{cite web |url=http://www.taxonsearch.org/dev/file_home.php |title=Stem Archosauria—TaxonSearch |access-date=2007-02-24 |last=Sereno |first=Paul C. |author-link=Paul Sereno |date=2005-11-07 |url-status=dead |archive-url=https://web.archive.org/web/20070219102659/http://www.taxonsearch.org/dev/file_home.php |archive-date=2007-02-19 }}</ref> Heterodontosauridae was given a formal definition in the ''[[PhyloCode]]'' by Daniel Madzia and colleagues in 2021 as "the largest clade containing ''[[Heterodontosaurus tucki]]'', but not ''[[Iguanodon bernissartensis]]'', ''[[Pachycephalosaurus wyomingensis]]'', ''[[Stegosaurus stenops]]'', and ''[[Triceratops horridus]]''".<ref name="ReferenceA"/> Heterodontosaurinae is a [[stem-based taxon]] defined phylogenetically for the first time by [[Paul Sereno]] in 2012 as "the most inclusive [[clade]] containing ''[[Heterodontosaurus tucki]]'' but not ''[[Tianyulong confuciusi]]'', ''[[Fruitadens haagarorum]]'', ''[[Echinodon becklesii]]''."<ref name="sereno2012"/>
Heterodontosauridae includes the genera ''Abrictosaurus'', ''Lycorhinus'', and ''Heterodontosaurus'', all from South Africa. While [[Richard Thulborn]] once reassigned all three to ''Lycorhinus'',<ref name="RAT74"/> all other authors consider the three genera distinct.<ref name="JAH75"/> Within the family, ''Heterodontosaurus'' and ''Lycorhinus'' are considered [[sister taxa]], with ''Abrictosaurus'' as a basal member.<ref name="DBNetal04" /> ''Geranosaurus'' is also a heterodontosaurid, but is usually considered a ''[[nomen dubium]]'' because the type specimen is missing all its teeth, making it indistinguishable from any other genus in the family.<ref name="WW90" /> More recently, the genus ''Echinodon'' has been considered a heterodontosaurid in several studies.<ref name="NB02" /><ref name="PMG07" /> ''[[Lanasaurus]]'' was named for an upper jaw in 1975,<ref name="CEG75">{{cite journal |last=Gow |first=Christopher E. |year=1975 |title=A new heterodontosaurid from the Redbeds of South Africa showing clear evidence of tooth replacement |journal=Zoological Journal of the Linnean Society |volume=57 |pages=335–339 |doi=10.1111/j.1096-3642.1975.tb01895.x |issue=4 }}</ref> but more recent discoveries have shown that it belongs to ''Lycorhinus'' instead, making ''Lanasaurus'' a [[junior synonym]] of that genus.<ref name="CEG90" /> ''[[Dianchungosaurus]]'' was once considered a heterodontosaurid from [[Asia]],<ref name="CCY82">{{cite book |last=Young |first=C.C. |author-link=Yang Zhongjian |editor=Zhou M. |title=[Collected works of Yang Zhongjian] |year=1982 |publisher=Academica Sinica |___location=Beijing |language=zh |pages=38–42 |chapter=[A new genus of dinosaur from Lufeng County, Yunnan Province] }}</ref> but it has since been shown that the remains were a [[Chimera (paleontology)|chimera]] of [[prosauropod]] and [[mesoeucrocodylia]]n remains.<ref name="BX05">{{cite journal |last1=Barrett |first1=Paul M. |author2=Xu Xing |author2-link=Xu Xing (paleontologist) |year=2005 |title=A reassessment of ''Dianchungosaurus lufengensis'' Yang, 1982a, an enigmatic reptile from the Lower Lufeng Formation (Lower Jurassic) of Yunnan Province, People's Republic of China |journal=Journal of Paleontology |volume=79 |issue=5 |pages=981–986 |doi=10.1666/0022-3360(2005)079[0981:ARODLY]2.0.CO;2 |s2cid=89542580 |issn=0022-3360}}</ref> [[José Bonaparte]] also classified the South American ''[[Pisanosaurus]]'' as a heterodontosaurid at one time,<ref name="JFB76">{{cite journal |last=Bonaparte |first=Jose F. |author-link=Jose Bonaparte |year=1976 |title=''Pisanosaurus mertii'' Casamiquela and the origin of the Ornithischia |journal=Journal of Paleontology |volume=50 |pages=808–820}}</ref> but this animal is now known to be a more basal ornithischian.<ref name="WW90b">{{cite book |last=Weishampel |first=David B. |author-link=David B. Weishampel |author2=Witmer, Lawrence M. |editor1=Weishampel, David B. |editor2=Dodson, Peter |editor3=Osmólska, Halszka |title=The Dinosauria |edition=First |year=1990 |publisher=University of California Press |___location=Berkeley |isbn=978-0-520-06727-1 |pages=416–425 |chapter=''Lesothosaurus'', ''Pisanosaurus'', and ''Technosaurus''}}</ref>
[[File:Abrictosaurus.jpg|thumb|Skull of ''[[Abrictosaurus]]'']]
The membership of Heterodontosauridae is well-established in comparison to its uncertain [[phylogeny|phylogenetic]] position. Several early studies suggested that heterodontosaurids were very primitive ornithischians.<ref name="SL80" /><ref name="CC62"/> Due to supposed similarities in the morphology of the forelimbs, Robert Bakker proposed a relationship between heterodontosaurids and early [[sauropodomorph]]s like ''[[Anchisaurus]]'', bridging the orders [[Saurischia]] and [[Ornithischia]].<ref name="RTB86"/> The dominant hypothesis over the last several decades has placed heterodontosaurids as basal ornithopods.<ref name="WW90"/><ref name="DBNetal04" /><ref name="RAT70" /><ref name="PCS86">{{cite journal |last=Sereno |first=Paul C. |author-link=Paul Sereno |year=1986 |title=Phylogeny of the bird-hipped dinosaurs |journal=National Geographic Research |volume=2 |issue=2 |pages=234–256}}</ref> However, others have suggested that heterodontosaurids instead share a common ancestor with [[Marginocephalia]] ([[ceratopsians]] and [[pachycephalosaur]]s),<ref name="ZX83">{{cite journal |author=Zhao Xijin |author-link=Zhao Xijin |year=1983 |title=Phylogeny and evolutionary stages of Dinosauria |journal=Acta Palaeontologica Polonica |volume=28 |issue=1–2 |pages=295–306 }}</ref><ref name="MRC85">{{cite journal |last=Cooper |first=Michael A. |year=1985 |title=A revision of the ornithischian dinosaur ''Kangnasaurus coetzeei'' Haughton, with a classification of the Ornithischia |journal=Annals of the South African Museum |volume=95 |pages=281–317 }}</ref> a hypothesis that has found support in some early 21st century studies.<ref name="ZCX99">{{cite journal |doi=10.1080/02724634.1999.10011181 |author1=Zhao Xijin |author1-link=Zhao Xijin |author2=Cheng Zhengwu |author3=Xu Xing |author3-link=Xu Xing (paleontologist) |year=1999 |title=The earliest ceratopsian from the Tuchengzi Formation of Liaoning, China |journal=Journal of Vertebrate Paleontology |volume=19 |issue=4 |pages=681–691|bibcode=1999JVPal..19..681X }}</ref><ref name="YXW03">{{cite journal |author1=You Hailu |author2=Xu Xing |author2-link=Xu Xing (paleontologist) |author3=Wang Xiaolin |year=2003 |title=A new genus of Psittacosauridae (Dinosauria: Ornithopoda) and the origin and early evolution of marginocephalian dinosaurs |journal=Acta Geologica Sinica (English Edition) |volume=77 |issue=1 |pages=15–20 |doi=10.1111/j.1755-6724.2003.tb00105.x|bibcode=2003AcGlS..77...15Y |s2cid=89051352 }}</ref> The clade containing heterodontosaurids and marginocephalians has been named [[Heterodontosauriformes]].<ref name="XXetal06">{{cite journal |last1=Xu Xing |author2=Forster, Catherine A. |author3=Clark, James M. |author4=Mo Jinyou. |author-link=Xu Xing (paleontologist) |year=2006 |title=A basal ceratopsian with transitional features from the Late Jurassic of northwestern China |journal=Proceedings of the Royal Society B: Biological Sciences |volume=273 |pages=2135–2140 |doi=10.1098/rspb.2006.3566 |pmid=16901832 |first1=X |issue=1598 |pmc=1635516 }}</ref> Heterodontosaurids have also been seen as basal to both ornithopods and marginocephalians.<ref name="MO85">{{cite journal |last=Maryanska |first=Teresa |author-link1 = Teresa Maryańska |author2=Osmólska, Halszka. |year=1985 |title=On ornithischian phylogeny |journal=Acta Palaeontologica Polonica |volume=30 |pages=137–150 }}</ref><ref name="RMB05">{{cite journal |last=Butler |first=Richard J. |year=2005 |title=The 'fabrosaurid' ornithischian dinosaurs of the Upper Elliot Formation (Lower Jurassic) of South Africa and Lesotho |journal=Zoological Journal of the Linnean Society |volume=145 |issue=2 |pages=175–218 |doi=10.1111/j.1096-3642.2005.00182.x |doi-access=free }}</ref> In 2007, a [[cladistic]] analysis suggested that heterodontosaurids are basal to all known ornithischians except ''Pisanosaurus'', a result that echoes some of the very earliest work on the family.<ref name="BSN07">{{cite journal|author-link1=Richard J. Butler |last1=Butler |first1=Richard J. |last2=Smith |first2=Roger M.H. |last3=Norman |first3=David B. |author3-link=David B. Norman |title=A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithischia |journal=Proceedings of the Royal Society B: Biological Sciences |issue=published online |year=2007 |doi=10.1098/rspb.2007.0367 |volume=274 |pages=2041–6 |pmid=17567562 |pmc=2275175}}</ref><ref name="BUN08">{{cite journal |last=Butler |first=Richard J. |author2=Upchurch, Paul |author3=Norman, David B. |author3-link=David B. Norman |title=The phylogeny of the ornithischian dinosaurs |journal=Journal of Systematic Palaeontology |volume=6 |issue=1 |year=2008 |pages=1–40 |doi=10.1017/S1477201907002271|bibcode=2008JSPal...6....1B |s2cid=86728076 }}</ref> However, a study by Bonaparte found the Pisanosauridae to be synonymous with the Heterodontosauridae and not a separate family in its own right, thereby including ''[[Pisanosaurus]]'' as a heterodontosaur.<ref>Bonaparte, J.F. (1976). "Pisanosaurus mertii Casamiquela and the origin of the Ornithischia". Journal of Paleontology. 50 (5): 808–820. {{JSTOR|1303575}}.</ref> Butler et al. (2010) found the Heterodontosauridae to be the most basal known significant ornithischian radiation.<ref>R. J. Butler. 2010. The anatomy of the basal ornithischian dinosaur Eocursor parvus from the lower Elliot Formation (Late Triassic) of South Africa. Zoological Journal of the Linnean Society 160:648-684</ref>
The [[cladogram]] below shows the interrelationships within Heterodontosauridae, and follows the analysis by Sereno, 2012:<ref name="sereno2012 193-206">Sereno, P.C. (2012). pp. 193-206.</ref>
{{clade| style=font-size:100%;line-height:80%
|label1=Heterodontosauridae
|1={{clade
|1={{clade
|1=''[[Echinodon]]'' [[File:Cartography of Europe.svg|20px]]
|2=''[[Fruitadens]]'' [[File:Cartography of North America.svg|20px]]
|3=''[[Tianyulong]]'' [[File:Cartography of Asia.svg|20px]] }}
|label2=[[Heterodontosaurinae]]
|2={{clade
|1=''[[Lycorhinus]]'' [[File:Cartography of Africa.svg|20px]]
|2={{clade
|1={{clade
|1=''[[Pegomastax]]'' [[File:Cartography of Africa.svg|20px]]
|2=''[[Manidens]]'' [[File:Cartography of South America.svg|20px]] }}
|2={{clade
|1=''[[Abrictosaurus]]'' [[File:Cartography of Africa.svg|20px]]
|2=''[[Heterodontosaurus]]'' [[File:Cartography of Africa.svg|20px]] }} }} }} }} }}
A 2020 reworking of [[Cerapoda]] by Dieudonné and colleagues recovered the animals traditionally considered 'heterodontosaurids' as a basal grouping within Pachycephalosauria, paraphyletic with respect to the traditional, dome-headed pachycephalosaurs. This result was based on numerous skull characteristics including the [[teeth|dentition]], and also to account for the fact that [[pachycephalosaur]] fossils are completely unknown from the [[Jurassic]] period. Modern understanding of ornithischian phylogeny implies that Jurassic pachycephalosaurs must exist, because numerous Jurassic [[ceratopsian]]s have been found, yet no such pachycephalosaurs have been confidently identified. This analysis was done to elaborate on the findings of Baron and colleagues (2017), which found ''[[Chilesaurus]]'' to be a basal [[ornithischian]].<ref name=chilly>{{Cite journal|last1=Baron|first1=Matthew G.|last2=Barrett|first2=Paul M.|date=2018-03-01|title=Support for the placement of ''Chilesaurus'' within Ornithischia: a reply to Müller et al.|journal=Biology Letters|language=en|volume=14|issue=3|pages=20180002|doi=10.1098/rsbl.2018.0002|issn=1744-9561|pmid=29593075|pmc=5897612}}</ref> The phylogenetic analysis was conducted with ''Chilesaurus'' coded as an ornithischian, which also had implications for the phylogeny of [[ornithopod]]s.
The cladogram below is an abridged version of Dieudonne and colleagues' findings:<ref name="Dieudonne2020">{{cite journal |last1=Dieudonné |first1=P.E. |last2=Cruzado-Caballero |first2=P. |last3=Godefroit |first3=P. |last4=Tortosa |first4=T. |title=A new phylogeny of cerapodan dinosaurs |journal=Historical Biology |date=2020 |volume=33 |issue=10 |pages=2335–2355 |doi=10.1080/08912963.2020.1793979|doi-access=free }}</ref>
{{clade
|label1='''[[Ornithischia]]'''
|1={{clade
|1=''[[Chilesaurus]]'' [[File:Chilesasaurus.png|50px]]
|2={{clade
|1=''[[Laquintasaura]]'' <div style="{{mirrorH}}">[[File:Laquintasaura fixed by Tom Parker.png|50px]]</div>
|2={{clade
|state2=dotted
|2="Heterodontosauridae" (conventional position)
|1=''[[Lesothosaurus]]'' <div style="{{mirrorH}}">[[File:Lesothosaurus diagnosticus mirrored.png|50px]]</div>
|label3=[[Genasauria]]
|3={{clade
|1='''[[Thyreophora]]'''
|2={{clade
|1={{clade
|1=''[[Eocursor]]'' [[File:Eocursor BW.jpg|50px]]
|2={{clade
|1={{clade
|1=''[[Agilisaurus]]'' [[File:Agilisaurus life restoration.jpg|50px]]
|2=''[[Hexinlusaurus]]''
}}
|2={{clade
|1='''[[Ornithopoda]]'''
|label2=[[Marginocephalia]]
|2={{clade
|1='''[[Ceratopsia]]'''
|label2=[[Pachycephalosauria]]
|2={{clade
|grouplabel1="[[Heterodontosaurid]]s"<br>(paraphyletic)
|1={{clade |barbegin1=red
|1=''[[Fruitadens]]'' [[File:Fruitadens transparent.png|50px]] |bar1=red
|2={{clade
|1=''[[Lycorhinus]]'' |bar1=red
|2={{clade
|1=''[[Heterodontosaurus]]'' [[File:Heterodontosaurus restoration transparent.png|50px]] |bar1=red
|2=''[[Abrictosaurus]]'' [[File:Abrictosaurus dinosaur.png|50px]] |bar2=red
}}
}}
}}
|2={{clade
|1=''[[Tianyulong]]'' |bar1=red
|2={{clade
|1=''[[Echinodon]]'' |barend1=red
|2={{clade
|1=''[[Wannanosaurus]]'' [[File:Wannanosaurus for wiki review.jpg|50px]]
|2={{clade
|1=''[[Goyocephale]]''
|2={{clade
|1=''[[Prenocephale]]'' [[File:Prenocephale bickering (cropped + fix).jpg|50px]]
|2=''[[Homalocephale]]'' [[File:Homalocephale body.jpg|50px]]
|3=''[[Stegoceras]]'' [[File:Stegoceras validum.jpg|50px]]
|4=''[[Pachycephalosaurus]]'' [[File:Pachycephalosaurus Reconstruction.jpg|50px]]
}}
}}
}}
}}
}} }}
}} }} }}
}} }} }} }} }} }} }}
==Distribution==
[[File:Heterodontosauridae biogeography.jpg|thumb|left|[[Biogeographic]] distribution of heterodontosaurids in time]]
While originally known only from the Early Jurassic of southern Africa, heterodontosaurid remains are now known from four [[continent]]s. Early in heterodontosaurid history, the [[supercontinent]] [[Pangaea]] was still largely intact, allowing the family to achieve a near-worldwide [[Biogeography|distribution]].<ref name="NB02" /> The oldest known possible heterodontosaurid remains are a jaw fragment and isolated teeth from the [[Laguna Colorada Formation]] of [[Argentina]], which dates back to the [[Late Triassic]]. These remains have a derived morphology similar to ''Heterodontosaurus'', including a caniniform with serrations on both anterior and posterior edges, as well as high-crowned maxillary teeth lacking a cingulum.<ref name="BM01">{{cite journal |last=Báez |first=Ana Maria |author2=Marsicano, Claudia A. |year=2001 |title=A heterodontosaurid ornithischian dinosaur from the Upper Triassic of Patagonia |journal=Ameghiniana |volume=38 |issue=3 |pages=271–279}}</ref> Irmis ''et al.'' (2007) tentatively agreed that this fossil material represents a heterodontosaurid, but stated that additional material is needed to confirm this assignment because the specimen is poorly preserved,<ref>{{cite journal |author1=Randall B. Irmis |author2=William G. Parker |author3=Sterling J. Nesbitt |author4=Jun Liu |year=2007 |title=Early ornithischian dinosaurs: the Triassic record |journal=Historical Biology |volume=19 |issue=1 |pages=3–22 |doi=10.1080/08912960600719988|bibcode=2007HBio...19....3I |citeseerx=10.1.1.539.8311 |s2cid=11006994 }}</ref> while Sereno (2012) only stated that this material may represent an ornithischian or even specifically a heterodontosaurid.<ref name="sereno2012">{{cite journal |first1=Paul C. |last1=Sereno |year=2012 |title=Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs |journal=ZooKeys |issue=226 |pages=1–225 |doi=10.3897/zookeys.226.2840 |pmid=23166462 |pmc=3491919|doi-access=free }}</ref> [[Paul E. Olsen|Olsen]], Kent & Whiteside (2010) noted that the age of the Laguna Colorada Formation itself is poorly constrained, and thus it wasn't conclusively determined whether the putative heterodontosaurid from this formation is of Triassic or Jurassic age.<ref>{{cite journal |author1=Paul E. Olsen |author2=Dennis V. Kent |author3=Jessica H. Whiteside |year=2010 |title=Implications of the Newark Supergroup-based astrochronology and geomagnetic polarity time scale (Newark-APTS) for the tempo and mode of the early diversification of the Dinosauria |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |volume=101 |issue=3–4 |pages=201–229 |doi=10.1017/S1755691011020032 |bibcode=2010EESTR.101..201O |s2cid=16123732 }}</ref> The most diverse heterodontosaurid [[fauna]] comes from the Early Jurassic of southern Africa, where fossils of ''Heterodontosaurus'', ''Abrictosaurus'', ''Lycorhinus'', and the dubious ''Geranosaurus'' are found.<ref name="WW90" />
Undescribed Early Jurassic heterodontosaurids are also known from the [[United States]]<ref name="HDSetal94">{{cite book |last=Sues |first=Hans-Dieter |author2=Clark, James M. |author3=Jenkins, Farish A. |editor1=Fraser, Nicholas C. |editor2=Sues, Hans-Dieter |chapter=A review of the Early Jurassic tetrapods from the Glen Canyon Group of the American Southwest |title=In The Shadow of the Dinosaurs: Early Mesozoic Tetrapods |year=1994 |___location=Cambridge |publisher=Cambridge University Press |pages=285–294 |isbn=978-0-521-45899-3}}</ref> and [[Mexico]],<ref name="JMCetal94">{{cite book |last1=Clark |first1=James |last2=Montellano |first2=Marisol |last3=Hopson |first3=James A. |last4=Hernandez |first4=Rene |last5=Fastovsky |first5=David A. |editor1=Fraser, N.C. |editor2=Sues, H.-D. |chapter=An Early or Middle Jurassic tetrapod assemblage from the La Boca Formation, northeastern Mexico |title=In The Shadow of the Dinosaurs: Early Mesozoic Tetrapods |year=1994 |___location=Cambridge |publisher=Cambridge University Press |pages=295–302 |isbn=978-0-521-45899-3}}</ref> respectively. In addition, beginning in the 1970s, a great deal of fossil material was discovered from the Late Jurassic [[Morrison Formation]] near [[Fruita, Colorado|Fruita]], [[Colorado]] in the United States.<ref name="PMG07" /> Described in print in 2009, this material was placed in the genus ''[[Fruitadens]]''.<ref name="RJBetal10" /> Indeterminate heterodontosaurid teeth have been reported from the [[Middle Jurassic]] ([[Bathonian]]) [[Great Oolite Group]] of Great Britain,<ref>{{Cite journal |last1=Wills |first1=Simon |last2=Underwood |first2=Charlie J. |last3=Barrett |first3=Paul M. |date=3 September 2023 |title=A hidden diversity of ornithischian dinosaurs: U.K. Middle Jurassic microvertebrate faunas shed light on a poorly represented period |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2024.2323646 |journal=Journal of Vertebrate Paleontology |language=en |volume=43 |issue=5 |article-number=e2323646 |doi=10.1080/02724634.2024.2323646 |bibcode=2023JVPal..43E3646W |issn=0272-4634|url-access=subscription }}</ref> as well as the equivalently aged [[Itat Formation]] of [[Western Siberia]].<ref name=":2">{{Cite journal |vauthors=Averianov AO, Martin T, Skutschas PP, Danilov IG, Schultz JA, Schellhorn R, et al. |date=2016 |title=Middle Jurassic vertebrate assemblage of Berezovsk coal mine in western Siberia (Russia) |journal=Global Geology |volume=19 |issue=4 |pages=187–204 |doi=10.3969/j.issn.1673-9736.2016.04.01}}</ref> Heterodontosaurid teeth lacking a cingulum have also been described from Late Jurassic and Early Cretaceous formations in [[Spain]] and [[Portugal]].<ref name="BSHetal07">{{cite journal |last1=Sánchez-Hernández |first1=Barbara |last2=Benton |first2=Michael J. |author2-link=Michael J. Benton |last3=Naish |first3=Darren |year=2007 |title=Dinosaurs and other fossil vertebrates from the Late Jurassic and Early Cretaceous of the Galve area, NE Spain |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=249 |issue=1–2 |pages=180–215 |doi=10.1016/j.palaeo.2007.01.009 |bibcode=2007PPP...249..180S |url=http://doc.rero.ch/record/14854/files/PAL_E1992.pdf |archive-date=2024-04-15 |access-date=2023-01-16 |archive-url=https://web.archive.org/web/20240415050642/https://doc.rero.ch/record/14854/files/PAL_E1992.pdf |url-status=live }}</ref> The remains of ''Echinodon'' were redescribed in 2002, showing that it may represent a late-surviving heterodontosaurid from the [[Berriasian]] stage of the Early Cretaceous in southern England.<ref name="NB02" /> ''[[Dianchungosaurus]]'' from the Early Jurassic of China is no longer considered a heterodontosaurid; though one Middle-Late Jurassic Asian form is known (''[[Tianyulong]]'').<ref name="XTZetal09" /> Indeterminate cheek teeth possibly representing heterodontosaurids are also known from the [[Barremian]] aged [[Wessex Formation]] of southern England, which if confirmed would represent the youngest record of the group.<ref>{{Cite journal|last=Sweetman|first=Steven C.|date=March 2016|title=A comparison of Barremian–early Aptian vertebrate assemblages from the Jehol Group, north-east China and the Wealden Group, southern Britain: the value of microvertebrate studies in adverse preservational settings|url=http://link.springer.com/10.1007/s12549-015-0217-9|journal=Palaeobiodiversity and Palaeoenvironments|language=en|volume=96|issue=1|pages=149–167|doi=10.1007/s12549-015-0217-9|bibcode=2016PdPe...96..149S |s2cid=129956539 |issn=1867-1594|url-access=subscription}}</ref>
<!--
There exist a number of very bird-like footprint fossils from around the Triassic-Jurassic boundary, found in [[Argentina]] and [[South Africa]]. The [[ichnogenus]] ''Trisauropodiscus'' has been established for some of these; among those footprints some lack a [[hallux]] impression, while it is present in others. These fossil predate the oldest known [[avian]] [[theropod]], ''[[Archaeopteryx]]'', by up to 55 million years. Though the footprints have not been found associated directly with heterodontosaurid remains, these dinosaurs did occur in these locales at the right time. In addition, it is known that heterodontosaurids, due to their convergent foot morphology, must have left very bird-like tracks which, depending on the circumstances and substrate, sometimes had a small hallux impression and sometimes did not.-->
==Paleobiology==
[[File:Pegomastax africana reconstruction.jpg|left|upright|thumb|Restoration of ''[[Pegomastax]]'']]
Most heterodontosaurid fossils are found in [[geologic formation]]s that represent arid to semi-arid environments, including the [[Upper Elliot Formation]] of [[South Africa]] and the [[Purbeck Beds]] of southern England.<ref name="DBNetal04" /> It has been suggested that heterodontosaurids underwent seasonal [[estivation|aestivation]] or [[hibernation]] during the driest times of year. Due to the lack of replacement teeth in most heterodontosaurids, it was proposed that the entire set of teeth was replaced during this dormant period, as it seemed that continual and sporadic replacement of teeth would interrupt the function of the tooth row as a single chewing surface.<ref name="RAT74"/> However, this was based on a misunderstanding of heterodontosaurid jaw mechanics.<ref name="JAH80">{{cite journal |last=Hopson |first=James A. |year=1980 |title=Tooth function and replacement in early Mesozoic ornithischian dinosaurs: implications for aestivation |journal=Lethaia |volume=13 |issue=1 |pages=93–105 |doi=10.1111/j.1502-3931.1980.tb01035.x |bibcode=1980Letha..13...93H }}</ref> It was thought that heterodontosaurids actually did replace their teeth continually, though more slowly than in other [[reptile]]s, but [[computed tomography|CT scanning]] of skulls from juvenile and mature ''Heterodontosaurus'' shows no replacement teeth.<ref name="RJBetal08b">{{cite journal |last=Butler |first=Richard J. |author2=Porro, Laura B. |author3=Norman, David B. |year=2008 |title=A juvenile skull of the primitive ornithischian dinosaur ''Heterodontosaurus tucki'' from the 'Stormberg' of southern Africa |journal=Journal of Vertebrate Paleontology |volume=28 |issue=3 |pages=702–711 |doi=10.1671/0272-4634(2008)28[702:AJSOTP]2.0.CO;2 |s2cid=86739244 |issn=0272-4634 }}</ref> There is currently no evidence that supports the [[hypothesis]] of aestivation in heterodontosaurids,<ref name="WW90" /> but it cannot be rejected, based on the skull scans.<ref name="RJBetal08b" />
While the cheek teeth of heterodontosaurids are clearly adapted for grinding tough plant material, their diet may have been omnivorous. The pointed premaxillary teeth and sharp, curved claws on the forelimbs suggest some degree of predatory behavior. It has been suggested that the long, powerful forelimbs of ''Heterodontosaurus'' may have been useful for tearing into insect nests, similarly to modern [[anteater]]s. These forelimbs may have also functioned as digging tools, perhaps for [[root]]s and [[tuber]]s.<ref name="WW90" />
[[File:Tianyulong BW.jpg|thumb|''Tianyulong'' restoration]]
The length of the forelimb compared to the hindlimb suggests that ''Heterodontosaurus'' might have been partially [[quadruped]]al, and the prominent olecranon process and hyperextendable digits of the forelimb are found in many quadrupeds. However, the manus is clearly designed for grasping, not weight support. Many features of the hindlimb, including the long tibia and foot, as well as the fusion of the tibiofibiotarsus and tarsometatarsus, indicate that heterodontosaurids were adapted to run quickly on the hindlegs, so it is unlikely that ''Heterodontosaurus'' moved on all four limbs except perhaps when feeding.<ref name="SL80" />
The short tusks found in all known heterodontosaurids strongly resemble tusks found in modern [[musk deer]], [[peccary|peccaries]] and [[suidae|pigs]]. In many of these animals (as well as the longer-tusked [[walrus]] and [[Asian elephant]]s), this is a [[sexual dimorphism|sexually dimorphic]] trait, with tusks only found in males. The [[type specimen]] of ''Abrictosaurus'' lacks tusks and was originally described as a female.<ref name="RAT74"/> While this remains possible, the unfused [[sacrum|sacral]] [[vertebra]]e and short face indicate that this specimen represents a juvenile animal. A second, larger specimen originally proposed to belong to ''Abrictosaurus'' clearly possesses tusks, which was used to support the idea that tusks are found only in adults, rather than being a [[secondary sex characteristic|secondary sexual characteristic]] of males. These tusks could have been used for combat or [[Display (zoology)|display]] with members of the same species or with other species.<ref name="WW90" /> The absence of tusks in juvenile ''Abrictosaurus'' could also be another characteristic separating it from other heterodontosaurids as well, as tusks are known in juvenile ''Heterodontosaurus''. Other proposed functions for the tusks include defense and use in an occasionally omnivorous diet.<ref name="RJBetal08b" /> However, this specimen was alternatively reassigned to ''[[Lycorhinus]]'' by Sereno in 2012, which is already known to have possessed tusks and therefore their absence in ''Abrictosaurus'' may not have been a result of age.<ref name="sereno2012"/>
In 2005 a small complete fossilized heterodontosaurid skeleton more than 200 million years old was discovered in [[South Africa]]. In July 2016 it was scanned by a team of South African researchers using the [[European Synchrotron Radiation Facility]]; the scan of the dentition revealed palate bones less than a millimeter thick.<ref>{{cite web |url=http://www.news24.com/SouthAfrica/News/dinosaur-fossil-found-in-sa-finally-gives-up-its-secrets-20160727 |title=Dinosaur fossil found in SA finally gives up its secrets |access-date=2016-07-27 |date=2016-07-27 |archive-url=https://web.archive.org/web/20160728174918/http://www.news24.com/SouthAfrica/News/dinosaur-fossil-found-in-sa-finally-gives-up-its-secrets-20160727 |archive-date=2016-07-28 |url-status=live }}</ref>
==References==
{{Reflist|2}}
{{Ornithischia|H.}}
{{Taxonbar|from=Q131388}}
{{Portal bar|Dinosaurs}}
[[Category:Heterodontosauridae| ]]
[[Category:Dinosaur families]]
[[Category:Taxa named by Alfred Romer]]
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