Editing Triceratops (section)

==Classification==

''Triceratops'' is the best-known genus of [[Ceratopsidae]], a family of large, mostly North American [[Ceratopsia|ceratopsians]]. The exact relationship of ''Triceratops'' among the other ceratopsids has been debated over the years. Confusion stemmed mainly from the combination of a short, solid frill (similar to that of [[Centrosaurinae]]), with long brow horns (more akin to [[Chasmosaurinae]]).<ref>{{cite web|url=http://dinosaurios.org/triceratops/|title=What is special about the Triceratops?|publisher=Dinosaurios.org|access-date=December 26, 2013|date=July 24, 2013|archive-date=May 31, 2020|archive-url=https://web.archive.org/web/20200531214022/http://dinosaurios.org/triceratops/|url-status=live}}</ref> In the first overview of ceratopsians, [[R. S. Lull]] hypothesized the existence of two lineages, one of ''[[Monoclonius]]'' and ''[[Centrosaurus]]'' leading to ''Triceratops'', the other with ''[[Ceratops]]'' and ''[[Torosaurus]]'', making ''Triceratops'' a centrosaurine as the group is understood today.<ref name="HML07">{{Cite book |title=The Ceratopsia |last1=Hatcher |first1=J. B. |last2=Marsh |first2=O. C. |last3=Lull |first3=R. S. |date=1907 |publisher=Government Printing Office |isbn=978-0-405-12713-7 |location=Washington, D.C.}}</ref> Later revisions supported this view when [[Lawrence Lambe]], in 1915, formally describing the first, short-frilled group as Centrosaurinae (including ''Triceratops''), and the second, long-frilled group as Chasmosaurinae.<ref name="RSL33">{{cite journal | last1 = Lull | first1 = R. S. | year = 1933 | title = A revision of the Ceratopsia or horned dinosaurs | url =https://archive.org/details/revisionofcerato33lull | journal = Memoirs of the Peabody Museum of Natural History | volume = 3 | issue = 3| pages = 1–175 |access-date=November 20, 2010 | doi=10.5962/bhl.title.5716}}</ref><ref name="LL15">{{cite book | last=Lambe | first=Lawrence M. | title=On Eoceratops canadensis, gen. nov., with remarks on other genera of Cretaceous horned dinosaurs | publisher= Geological Survey of Canada, Government Printing Bureau | publication-place=Ottawa | date=1915 | isbn=0-665-82611-7 | oclc=920394016}}</ref>

In 1949, [[Charles Mortram Sternberg]] was the first to question this position, proposing instead that ''Triceratops'' was more closely related to ''[[Arrhinoceratops]]'' and ''[[Chasmosaurus]]'' based on skull and horn features, making ''Triceratops'' a chasmosaurine ("ceratopsine" in his usage) genus.<ref name="CMS49">{{cite journal | last1 = Sternberg | first1 = C. M. | year = 1949 | title = The Edmonton fauna and description of a new ''Triceratops'' from the Upper Edmonton member; phylogeny of the Ceratopsidae | journal = National Museum of Canada Bulletin | volume = 113 | pages = 33–46 }}</ref> He was largely ignored, with [[John Ostrom]]<ref name="Ostrom66">{{cite journal|author=Ostrom, J. H.|year=1966| title=Functional morphology and evolution of the ceratopsian dinosaurs| journal=[[Evolution (journal)|Evolution]]| volume=20| issue=3 | pages = 290–308 | doi=10.2307/2406631|pmid=28562975|jstor=2406631}}</ref> and later David Norman placing ''Triceratops'' within the Centrosaurinae.<ref>{{cite book |last=Norman |first=David |title=The Illustrated Encyclopaedia of Dinosaurs |year=1985 |publisher=Salamander Books |location=London |isbn=978-0-517-46890-6}}</ref>

Subsequent discoveries and analyses, however, proved the correctness of Sternberg's view on the position of ''Triceratops'', with Thomas Lehman defining both subfamilies in 1990 and diagnosing ''Triceratops'' as "ceratopsine" on the basis of several morphological features. Apart from the one feature of a shortened frill, ''Triceratops'' shares no derived traits with centrosaurines.<ref name="TML90">{{Cite book |title=Dinosaur Systematics: Perspectives and Approaches |last=Lehman |first=T. M. |date=1990 |publisher=Cambridge University Press |isbn=978-0-521-36672-4 |editor-last=Carpenter |editor-first=K. |location=Cambridge |pages=211–229 |chapter=The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics |editor2-last=Currie |editor2-first=P. J.}}</ref> Further research by [[Peter Dodson]], including a 1990 [[cladistic]] analysis and a 1993 study using resistant-fit theta-rho analysis, or RFTRA (a [[morphometrics|morphometric technique]] which systematically measures similarities in skull shape), reinforces ''Triceratops''{{'}} placement as a chasmosaurine.<ref>{{Cite book |title=The Dinosauria |last1=Dodson |first1=P. |last2=Currie |first2=P. J. |date=1990 |publisher=University of California Press |isbn=978-0-520-06727-1 |editor-last=Weishampel |editor-first=D. B. |location=Berkeley |pages=593–618 |chapter=Neoceratopsia |author-link=Peter Dodson |editor2-last=Dodson |editor2-first=P. |editor3-last=Osmólska |editor3-first=H.}}</ref><ref>{{Cite journal |last=Dodson |first=P. |year=1993 |title=Comparative craniology of the Ceratopsia |url=http://earth.geology.yale.edu/~ajs/1993/11.1993.07Dodson.pdf |journal=American Journal of Science |volume=293 |pages=200–234 |doi=10.2475/ajs.293.A.200 |bibcode=1993AmJS..293..200D |access-date=January 21, 2007 |archive-date=August 19, 2018 |archive-url=https://web.archive.org/web/20180819045309/http://earth.geology.yale.edu/~ajs/1993/11.1993.07Dodson.pdf |url-status=live }}</ref>

[[File:2014 Triceratops horridus fossil.jpg|alt=An imposing Triceratops fossil on display, lit by blue and yellow light.|thumb|'Horridus', the most complete ''Triceratops'' fossil known, on display at the [[Melbourne Museum]]. Restored and prepared by the team at Pangea Fossils in Victoria British Columbia, Canada.]]
The cladogram below follows Longrich (2014), who named a new species of ''[[Pentaceratops]]'', and included nearly all species of chasmosaurine.<ref name="longrich15">{{Cite journal |last=Longrich |first=N. R. |year=2014 |title=The horned dinosaurs Pentaceratops and Kosmoceratops from the upper Campanian of Alberta and implications for dinosaur biogeography |journal=Cretaceous Research |volume=51 |pages=292–308 |doi=10.1016/j.cretres.2014.06.011|bibcode=2014CrRes..51..292L }}</ref>
{{clade| style=font-size:85%;line-height:85%
|label1=[[Chasmosaurinae]]
|1={{clade
 |1=''[[Mercuriceratops]]''
 |2={{clade
  |1=''[[Judiceratops]]''
  |2={{clade
   |1={{clade
    |1=''[[Chasmosaurus]]''
    |2=''[[Mojoceratops]]'' }}
   |2={{clade
    |1=''[[Agujaceratops]]''
    |2={{clade
     |1={{clade
      |1=''[[Pentaceratops aquilonius]]''
      |2=Williams Fork chasmosaur
      |3={{clade
       |1=''[[Pentaceratops sternbergii]]''
       |2=''[[Utahceratops]]'' }} }}
     |2={{clade
      |1=''[[Kosmoceratops]]''
      |2={{clade
       |1={{clade
        |1=''[[Anchiceratops]]''
        |2=Almond Formation chasmosaur }}
       |2={{clade
        |1={{clade
         |1=''[[Bravoceratops]]''
         |2=''[[Coahuilaceratops]]'' }}
        |2={{clade
         |1=''[[Arrhinoceratops]]''
         |label2=[[Triceratopsini]]
         |2={{clade
          |1=''[[Titanoceratops]]''
          |2={{clade
           |1=''[[Torosaurus]]''
           |2='''''Triceratops'''''}} }} }} }} }} }} }} }} }} }} }} }}
[[File:Laramie-skull.jpg|thumb|Skull of specimen DMNH 48617 from the [[Laramie Formation]] of eastern [[Colorado]]. Based on the age of the formation, it may be the oldest ''Triceratops'' known.]]
For many years after its discovery, the deeper evolutionary origins of ''Triceratops'' and its close relatives remained largely obscure. In 1922, the newly discovered ''[[Protoceratops]]'' was seen as its ancestor by [[Henry Fairfield Osborn]],<ref name="Dodhorned"/> but many decades passed before additional findings came to light. Recent years have been fruitful for the discovery of several antecedents of ''Triceratops''. ''[[Zuniceratops]]'', the earliest-known ceratopsian with brow horns, was described in the late 1990s, and ''[[Yinlong]]'', the first known [[Jurassic]] ceratopsian, was described in 2005.

These new finds have been vital in illustrating the origins of ceratopsians in general, suggesting an Asian origin in the Jurassic and the appearance of truly horned ceratopsians by the beginning of the Late Cretaceous in North America.<ref name="Dino2">{{Cite book |title=The Dinosauria |last1=Dodson |first1=P. |last2=Forster |first2=C. A. |last3=Sampson |first3=S. D. |date=2004 |publisher=University of California Press |isbn=978-0-520-24209-8 |editor-last=Weishampel |editor-first=D. B. |edition=second |location=Berkeley |pages=494–513 |chapter=Ceratopsidae |editor2-last=Dodson |editor2-first=P. |editor3-last=Osmólska |editor3-first=H.}}</ref>

In [[phylogenetics|phylogenetic taxonomy]], the genus ''Triceratops'' has been used as a reference point in the definition of Dinosauria. Dinosaurs have been designated as all descendants of the [[most recent common ancestor]] of ''Triceratops'' and [[Neornithes|modern bird]]s.<ref>{{cite journal | last1 = Gauthier | first1 = J. A. | year = 1986 | title = Saurischian monophyly and the origin of birds. The Origin of Birds and the Evolution of Flight, K. Padian (ed.) | journal = Memoirs of the California Academy of Sciences | volume = 8 | pages = 1–55 }}</ref> Furthermore, [[Ornithischia]] has been defined as those dinosaurs more closely related to ''Triceratops'' than to modern birds.<ref>{{cite journal | last1 = Sereno | first1 = P. C. | 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>