# Trilophosaurus
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{{Short description|Extinct genus of reptiles}}
{{Automatic taxobox
| fossil_range = [Late Triassic](/source/Late_Triassic), {{fossil range|Carnian|Norian}}
| image = Trilophosaurus AMNH.jpg
| image_caption = Skeleton of ''[Trilophosaurus buettneri](/source/Trilophosaurus_buettneri)'' ([AMNH](/source/AMNH) 7502)
| taxon = Trilophosaurus
| authority = [Case](/source/Ermine_Cowles_Case), [1928](/source/1928_in_paleontology)
| type_species = {{extinct}}'''''Trilophosaurus buettneri'''''
| type_species_authority = Case, 1928
| subdivision_ranks = Species
| subdivision = * {{extinct}}''T. buettneri'' Case, 1928
* {{extinct}}?''T. dornorum'' Mueller & Parker, 2006
* {{extinct}}?''T. jacobsi'' Murry, 1987
([Junior synonym](/source/Junior_synonym) of ''[Spinosuchus](/source/Spinosuchus)''?)
* {{extinct}}''T. phasmalophos'' Kligman ''et al.'', 2020
| synonyms = {{collapsible list|bullets = true
|title=Genus synonymy
|''Chinleogomphius'' [Sues](/source/Hans-Dieter_Sues) & [Olsen](/source/Paul_E._Olsen), 1993
}}
{{collapsible list|bullets = true
|title='''Synonyms of ''T. buettneri''''':
|''[Malerisaurus](/source/Malerisaurus) langstoni'' Chatterjee, 1986
}}
{{collapsible list|bullets = true
|title='''Synonyms of ''T. jacobsi''''':
|''Chinleogomphius jacobsi'' (Murry, 1987)
|?''Trilophosaurus dornorum'' Mueller & Parker, 2006
}}
}}
[[File:Trilophosaurus3-Ghedo.JPG|left|thumb|Front of ''T. buettneri'' skeleton, [American Museum of Natural History](/source/American_Museum_of_Natural_History)]]
'''''Trilophosaurus''''' ([Greek](/source/Greek_language) for "[lizard](/source/lizard) with three [ridges](/source/ridges)") is a lizard-like [trilophosaurid](/source/trilophosaurid) [allokotosaur](/source/allokotosaur) known from the [Late Triassic](/source/Late_Triassic) of North America. It was a [herbivore](/source/herbivore) up to 2.5 m long.
== Description ==
''Trilophosaurus'' had a short, unusually heavily built skull, equipped with massive, broad flattened cheek teeth with sharp shearing surfaces for cutting up tough plant material. Teeth are absent from the [premaxilla](/source/premaxilla) and front of the lower jaw, which in life were probably equipped with a horny beak. Based on evidence derived from tooth wear patterns, ''Trilophosaurus'' was able to masticate labiolingually.[{{Cite journal |last=Mellett |first=Michael P. |last2=Kligman |first2=Ben T. |last3=Nesbitt |first3=Sterling J. |last4=Stocker |first4=Michelle R. |date=18 May 2023 |title=Masticatory mechanisms, dental function, and diet in Triassic trilophosaurids (Reptilia: Allokotosauria) |url=https://bioone.org/journals/Palaeodiversity/volume-16/issue-1/pale.v16.a4/Masticatory-mechanisms-dental-function-and-diet-in-Triassic-trilophosaurids-Reptilia/10.18476/pale.v16.a4.full |journal=Palaeodiversity |volume=16 |issue=1 |doi=10.18476/pale.v16.a4 |issn=1867-6294 |access-date=13 February 2025 |via=BioOne Digital Library|doi-access=free }}]
thumb|left|''T. buettneri'' compared to a human.
The skull is also unusual in that the lower [temporal opening](/source/temporal_fenestra) is missing, giving the appearance of a [euryapsid](/source/euryapsida) skull.{{Citation needed|date=July 2010}} Because of this, the trilophosaurs were once classified with [placodont](/source/placodont)s within [Sauropterygia](/source/Sauropterygia). [Carroll](/source/Robert_L._Carroll) (1988) suggested that the lower opening may have been lost to strengthen the skull.
== Taxonomy ==
thumb|Life reconstruction of ''Trilophosaurus buettneri''
''Trilophosaurus'' is traditionally thought to include two valid species: the typical ''T. buettneri'' and the more robust ''T. jacobsi''. In 1993, paleontologists [Hans-Dieter Sues](/source/Hans-Dieter_Sues) and [Paul E. Olsen](/source/Paul_E._Olsen) reassigned ''T. jacobsi'', as well as two additional trilophosaurids (''[Tricuspisaurus](/source/Tricuspisaurus)'' and ''[Variodens](/source/Variodens)''), to [Procolophonidae](/source/Procolophonidae) based on similarities between its tricuspid teeth and those of the newly described procolophonid ''[Xenodiphyodon](/source/Xenodiphyodon)''.[{{cite journal |last=Sues |first=H.-D. |author2=Olsen, P.E. |year=1993 |title=A new procolophonid and a new tetrapod of uncertain, possibly procolophonian affinities from the Upper Triassic of Virginia |journal=Journal of Vertebrate Paleontology |volume=13 |issue=3 |pages=282–286 |doi=10.1080/02724634.1993.10011510}}] This view persisted in subsequent publications[{{cite book |last=Fraser |first=N.C. |year=1997 |chapter=Assemblages of small tetrapods from British Late Triassic fissure deposits |title=In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods |url=https://archive.org/details/shadowdinosaurse00fras |url-access=limited |editor1=Fraser, N.C. |editor2=Sues, H.-D. |publisher= Cambridge University Press |location=Cambridge and New York |pages=[https://archive.org/details/shadowdinosaurse00fras/page/n217 214]–225 |isbn=9780521458993}}] until the cranial material of ''T. jacobsi'' was described by Heckert ''et al.'' (2006). The new material confirmed the originally classification that ''T. jacobsi'', as well as ''[Tricuspisaurus](/source/Tricuspisaurus)'' and ''[Variodens](/source/Variodens)'' based on similarities to it, are indeed [trilophosaurid](/source/trilophosaurid)s.[{{cite journal |last=Heckert |first=A.B. |author2=Lucas, S.G. |author3=Rinehart, L.F. |author4=Spielmann, J.A. |author5=Hunt, A.P. |author6= Kahle, R. |year=2006 |title=Revision of the archosauromorph reptile ''Trilophosaurus'', with a description of the first skull of ''Trilophosaurus jacobsi'', from the Upper Triassic Chinle Group, West Texas, USA |journal=Palaeontology |volume=49 |issue=3 |pages=621–640 |doi=10.1111/j.1475-4983.2006.00556.x|url=http://libres.uncg.edu/ir/asu/f/Heckert_Andrew_2006_Revision_of_the_Archosauromorph_orig.pdf.X.pdf |doi-access=free }}] Meanwhile, a third species of ''Trilophosaurus'', ''T. dornorum'', was named by Mueller & Parker (2006) based on teeth of a robust individual.[Müller, B. D. & Parker, W. G., 2006. [https://web.archive.org/web/20120328204346/http://www.nps.gov/pefo/upload/Mueller-Parker-2006-New-Species-of-Trilophosaurus.pdf A new species of ''Trilophosaurus'' (Diapsida: Archosauromorpha) from the Sonsela Member (Chinle Formation) of Petrified Forest National Park, Arizona]. ''Museum of Northern Arizona,'' Bulletin 62:119-125.] However, Spielmann ''et al.'' (2009) argued that the robustness of the new species is not sufficient to differentiate it from other ''Trilophosaurus'' species, especially in light of new robust specimens of ''T. jacobsi''. Therefore, they considered ''T. dornorum'' to be a [junior synonym](/source/junior_synonym) of ''T. jacobsi'',[Spielmann, J.A., Lucas, S.G., Heckert, A.B., Rinehart, L.F., and Richards, H.R., III. 2009. [http://www.palaeodiversity.org/pdf/02/Pal_2_14_283-314_gu_sw.pdf Redescription of ''Spinosuchus caseanus'' (Archosauromorpha: Trilophosauridae) from the Upper Triassic of North America]. ''Palaeodiversity'' 2:283-313.] a view that was maintained since in other publications.[{{cite journal |last1=Nesbitt |first1=S.J. |last2=Flynn |first2=J.J. |last3=Pritchard |first3=A.C. |last4=Parrish |first4=M.J. |last5=Ranivoharimanana |first5=L. |last6=Wyss |first6=A.R. |title=Postcranial osteology of Azendohsaurus madagaskarensis (?Middle to Upper Triassic, Isalo Group, Madagascar) and its systematic position among stem archosaur reptiles |journal=Bulletin of the American Museum of Natural History |issue=398 |year=2015 |doi=10.5531/sd.sp.15 |pages=1–126 |issn=0003-0090 |hdl=2246/6624 |hdl-access=free }}] Spielmann ''et al.'' (2006) redescribed the type material of ''[Malerisaurus](/source/Malerisaurus) langstoni'' and concluded that it's indistinguishable from ''T. buettneri'', and thus ''M. langstoni'' represents its synonym.[Spielmann, J.A., Lucas, S.G., Hunt, A.P., and Heckert. 2006. [https://libres.uncg.edu/ir/asu/f/Heckert_A_2006_37_Reinterpretation.pdf Reinterpretation of the holotype of ''Malerisaurus langstoni'', a diapsid reptile from the Upper Triassic Chinle Group of West Texas]. ''The Triassic-Jurassic Terrestrial Transition.'' New Mexico Museum of Natural History and Science, Bulletin 37:543-547.]
Nesbitt ''et al.'' (2015) performed a [phylogenetic analysis](/source/phylogenetic_analysis) focusing on relations within [Allokotosauria](/source/Allokotosauria) and recovered ''T. jacobsi'' to be more closely related to ''[Spinosuchus caseanus](/source/Spinosuchus_caseanus)'' than to the type species of ''Trilophosaurus''. To further test this possibility, the types of ''S. caseanus'' and ''T. jacobsi'' were scored separately from the referred the Kahle ''Trilophosaurus'' Quarry elements (referred to ''T. jacobsi'' by Spielmann ''et al.'' (2008) or to ''S. caseanus'' by Spielmann ''et al.'' (2009)). A phylogenetic analysis recovered the three in a [monophyletic](/source/monophyletic) clade to the exclusion of ''T. buettneri'' based on a single [autapomorphy](/source/autapomorphy). Furthermore, the types of ''S. caseanus'' and ''T. jacobsi'' as well as the Kahle Quarry material all scored identically, suggesting that ''T. jacobsi'' not only should be reassigned to ''Spinosuchus'', but in fact represents the junior synonym of its type and only species (''S. caseanus''). Nesbitt ''et al.'' (2015) refrained from officially synonymizing the two taxa pending further study of other advanced trilophosaurids.