Editing Triceratops (section)

===Functions of the horns and frill===

[[File:UCMP Triceratops right.JPG|left|thumb|Juvenile and adult skulls—the juvenile skull is about the size of an adult human head]]
There has been much speculation over the functions of ''Triceratops''{{'}} head adornments. The two main theories have revolved around use in combat and in courtship display, with the latter now thought to be the most likely primary function.<ref name="Dino2"/>

Early on, Lull postulated that the frills may have served as anchor points for the jaw muscles to aid chewing by allowing increased size and power for the muscles.<ref>{{cite journal | last1 = Lull | first1 = R. S. | year = 1908 | title = The cranial musculature and the origin of the frill in the ceratopsian dinosaurs | url = https://zenodo.org/record/1450156 | journal = American Journal of Science | volume = 4 | issue = 25 | pages = 387–399 | doi = 10.2475/ajs.s4-25.149.387 | bibcode = 1908AmJS...25..387L | access-date = June 12, 2019 | archive-date = November 15, 2019 | archive-url = https://web.archive.org/web/20191115184638/https://zenodo.org/record/1450156 | url-status = live }}</ref> This has been put forward by other authors over the years, but later studies do not find evidence of large muscle attachments on the frill bones.<ref name="Forster90">{{cite thesis|last=Forster|first= C. A. |date=1990|title= The cranial morphology and systematics of ''Triceratops'', with a preliminary analysis of ceratopsian phylogeny|degree= Ph.D. Dissertation|publisher= University of Pennsylvania|location= Philadelphia|pages= 227 }}</ref>

''Triceratops'' were long thought to have used their horns and frills in combat with large predators, such as ''[[Tyrannosaurus]]'', the idea being discussed first by [[Charles Hazelius Sternberg|Charles H. Sternberg]] in 1917 and 70 years later by Robert Bakker.<ref name="RTB86"/><ref>{{cite book|last=Sternberg|first= C. H. |publisher=C. H. Sternberg{{--}}The World Company Press |date=1917|title=Hunting Dinosaurs in the Badlands of the Red Deer River, Alberta, Canada|location= Lawrence, Kansas|pages= 261 |doi=10.5962/bhl.title.159811 }}</ref> There is evidence that ''Tyrannosaurus'' did have aggressive head-on encounters with ''Triceratops'', based on partially healed tyrannosaur tooth marks on a ''Triceratops'' brow horn and [[squamosal]]. The bitten horn is also broken, with new bone growth after the break. Which animal was the aggressor, however, is unknown.<ref name="JH08">{{Cite book |title=Tyrannosaurus rex, the Tyrant King (Life of the Past) |last=Happ |first=J. |publisher=Indiana University Press |year=2008 |isbn=978-0-253-35087-9 |editor-last=Larson |editor-first=P. |location=Bloomington |pages=355–368 |chapter=An analysis of predator-prey behavior in a head-to-head encounter between ''Tyrannosaurus rex'' and ''Triceratops'' |editor2-last=Carpenter |editor2-first=K.}}</ref>  Paleontologist Peter Dodson estimates that, in a battle against a bull ''Tyrannosaurus'', the ''Triceratops'' had the upper hand and would successfully defend itself by inflicting fatal wounds to the ''Tyrannosaurus'' using its sharp horns. ''Tyrannosaurus'' is also known to have fed on ''Triceratops'', as shown by a heavily tooth-scored ''Triceratops'' [[ilium (bone)|ilium]] and [[sacrum]].<ref name="erickson1996">{{Cite journal |last1=Erickson |first1=Gregory M. |last2=Olson |first2=Kenneth H. |date=March 19, 1996 |title=Bite marks attributable to Tyrannosaurus rex: Preliminary description and implications |journal=Journal of Vertebrate Paleontology |volume=16 |issue=1 |pages=175–178 |doi=10.1080/02724634.1996.10011297 |bibcode=1996JVPal..16..175E |issn=0272-4634 |url=https://zenodo.org/record/3732430 |access-date=June 3, 2020 |archive-date=October 19, 2021 |archive-url=https://web.archive.org/web/20211019153802/https://zenodo.org/record/3732430 |url-status=live }}</ref> 

In addition to combat with predators using its horns, ''Triceratops'' are popularly shown engaging each other in combat with horns locked. While studies show that such activity would be feasible, if unlike that of present-day horned animals,<ref>{{cite journal | last=Farke | first=A. A. | year=2004 | title=Horn Use in ''Triceratops'' (Dinosauria: Ceratopsidae): Testing Behavioral Hypotheses Using Scale Models | url=http://www.nhm.ac.uk/hosted_sites/pe/2004_1/horn/horn.pdf | access-date=November 20, 2010 | journal=Palaeo-electronica | volume=7 | issue=1 | pages=1–10 | archive-date=March 3, 2016 | archive-url=https://web.archive.org/web/20160303204748/http://www.nhm.ac.uk/hosted_sites/pe/2004_1/horn/horn.pdf | url-status=live }}</ref> there is disagreement about whether they did so. Although pitting, holes, lesions, and other damage on ''Triceratops'' skulls (and the skulls of other ceratopsids) are often attributed to horn damage in combat, a 2006 study finds no evidence for horn thrust injuries causing these forms of damage (with there being no evidence of infection or healing). Instead, non-pathological [[bone resorption]], or unknown bone diseases, are suggested as causes.<ref name="TF06">{{cite book|last1=Tanke|first1= D. H. |last2= Farke|first2= A. A. |date=2006|chapter= Bone resorption, bone lesions, and extracranial fenestrae in ceratopsid dinosaurs: a preliminary assessment|editor-last= Carpenter|editor-first= K. |title=Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs|publisher= Indiana University Press|location= Bloomington|pages= 319–347|isbn=978-0-253-34817-3}}</ref> A 2009 study compared incidence rates of skull lesions and [[periosteal reaction]] in ''Triceratops'' and ''[[Centrosaurus]]'', showing that these were consistent with ''Triceratops'' using its horns in combat and the frill being adapted as a protective structure, while lower pathology rates in ''Centrosaurus'' may indicate visual use over physical use of cranial ornamentation or a form of combat focused on the body rather than the head.<ref>{{cite journal | last1 = Farke | first1 = A.A. | last2 = Wolff | first2 = E.D.S. | last3 = Tanke | first3 = D.H. | last4 = Sereno | first4 = Paul| year = 2009 | title = Evidence of Combat in ''Triceratops'' | journal = PLOS ONE | volume = 4 | issue = 1| page = e4252 | doi = 10.1371/journal.pone.0004252 | editor1-last = Sereno | editor1-first = Paul | bibcode = 2009PLoSO...4.4252F | pmid=19172995 | pmc=2617760| doi-access = free }} {{open access}}</ref><ref>{{Cite magazine |last=Wall |first=Michael |date=January 27, 2009 |title=Scars Reveal How Triceratops Fought |url=https://www.wired.com/2009/01/dinofight/ |archive-url=https://web.archive.org/web/20140820071319/https://www.wired.com/2009/01/dinofight/ |archive-date=August 20, 2014 |access-date=December 13, 2024 |magazine=Wired |language=en-US |issn=1059-1028}}</ref><ref>{{Cite web |last=Switek |first=Brian |date=February 5, 2009 |title=Triceratops v. Triceratops |url=https://www.smithsonianmag.com/science-nature/triceratops-v-triceratops-38373087/ |archive-url=https://web.archive.org/web/20140416192132/https://www.smithsonianmag.com/science-nature/triceratops-v-triceratops-38373087/ |archive-date=April 16, 2014 |access-date=December 13, 2024 |website=Smithsonian Magazine |language=en}}</ref> The frequency of injury was found to be 14% in ''Triceratops''.<ref>{{cite journal | last1 = Peterson | first1 = JE | last2 = Dischler | first2 = C | last3 = Longrich | first3 = NR | year = 2013 | title = Distributions of Cranial Pathologies Provide Evidence for Head-Butting in Dome-Headed Dinosaurs (Pachycephalosauridae) | journal = PLOS ONE | volume = 8 | issue = 7| page = e68620 | doi = 10.1371/journal.pone.0068620 | pmid=23874691 | pmc=3712952| bibcode = 2013PLoSO...868620P | doi-access = free }} {{open access}}</ref> The researchers also concluded that the damage found on the specimens in the study was often too localized to be caused by bone disease.<ref>{{cite magazine |url=https://www.wired.com/wiredscience/2009/01/dinofight/ |title=Scars Reveal How Triceratops Fought – |magazine=Wired |date=January 27, 2009 |access-date=August 3, 2010 |first=Michael |last=Wall |archive-date=January 12, 2014 |archive-url=https://web.archive.org/web/20140112143952/http://www.wired.com/wiredscience/2009/01/dinofight/ |url-status=live }}</ref> Histological examination reveals that the frill of ''Triceratops'' is composed of fibrolamellar bone.<ref>{{Cite book |title=Encyclopedia of Dinosaurs |last=Reid |first=R.E.H. |date=1997 |publisher=Academic Press |editor-last=Currie |editor-first=P. J. |location=San Diego, CA. |pages=329–339 |chapter=Histology of bones and teeth |editor2-last=Padian |editor2-first=K.}}</ref> This contains [[fibroblast]]s that play a critical role in wound healing and is capable of rapidly depositing bone during remodeling.<ref>{{cite journal | last1 = Horner | first1 = JR | last2 = Goodwin | first2 = MB | year = 2009 | title = Extreme Cranial Ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus | journal = PLOS ONE | volume = 4 | issue = 10| page = e7626 | doi = 10.1371/journal.pone.0007626 | pmid = 19859556 | pmc=2762616| bibcode = 2009PLoSO...4.7626H | doi-access = free }}</ref><ref>{{cite journal | last1 = Horner | first1 = JR | last2 = Lamm | first2 = E | year = 2011 | title = Ontogeny of the parietal frill of Triceratops: a preliminary histological analysis | journal = Comptes Rendus Palevol | volume = 10 | issue = 5–6| pages = 439–452 | doi=10.1016/j.crpv.2011.04.006}}</ref>

[[File:Triceratops lesions.jpg|thumb|Examples of [[Periosteal reaction|periosteal reactive]] bone in selected specimens of ''Triceratops'']]
One skull was found with a hole in the [[Jugal bone#In dinosaurs|jugal bone]], apparently a puncture wound sustained while the animal was alive, as indicated by signs of healing. The hole has a diameter close to that of the distal end of a ''Triceratops'' horn. This and other apparent healed wounds in the skulls of ceratopsians have been cited as evidence of non-fatal intra-specific competition in these dinosaurs.<ref name="farlowanddodson1975">{{cite journal | last1 = Farlow | first1 = J. O. | last2 = Dodson | first2 = P. | year = 1975 | title = The behavioral significance of frill and horn morphology in ceratopsian dinosaurs | journal = Evolution | volume = 29 | issue = 2| pages = 353–361 | doi=10.2307/2407222| pmid = 28555861 | jstor = 2407222 }}</ref><ref>{{cite book|last=Martin|first= A. J.|date=2006|title= Introduction to the Study of Dinosaurs|edition= Second|location= Oxford|publisher= Blackwell Publishing|pages= 299–300|isbn=978-1-4051-3413-2}}</ref> Another specimen, referred to as "Big John", has a similar fenestra to the squamosal caused by what appears to be another ''Triceratops'' horn and the squamosal bone shows signs of significant healing, further vindicating the hypothesis that this ceratopsian used its horns for intra-specific combat.<ref>{{cite journal |last1=D’Anastasio |first1=Ruggero |last2=Cilli |first2=Jacopo |last3=Bacchia |first3=Flavio |last4=Fanti |first4=Federico |last5=Gobbo |first5=Giacomo |last6=Capasso |first6=Luigi |title=Histological and chemical diagnosis of a combat lesion in Triceratops |journal=Scientific Reports |date=April 7, 2022 |volume=12 |issue=1 |pages=3941 |doi=10.1038/s41598-022-08033-2 |pmid=35393445 |pmc=8990019 |bibcode=2022NatSR..12.3941D |language=en |issn=2045-2322}}</ref>

The large frill also may have helped to increase body area to [[thermoregulation|regulate body temperature]].<ref>{{Cite journal |last=Wheeler |first=P.E. |year=1978 |title=Elaborate CNS cooling structures in large dinosaurs |journal=[[Nature (journal)|Nature]] |volume=275 |issue=5679 |pages=441–443 |bibcode=1978Natur.275..441W |doi=10.1038/275441a0 |pmid=692723|s2cid=4160470 }}</ref> A similar theory has been proposed regarding the plates of ''[[Stegosaurus]]'',<ref>{{Cite journal |last1=Farlow |first1=J. O. |last2=Thompson |first2=C. V. |last3=Rosner |first3=D. E. |year=1976 |title=Plates of the dinosaur ''Stegosaurus'': Forced convection heat loss fins? |journal=[[Science (magazine)|Science]] |volume=192 |issue=4244 |pages=1123–5 |bibcode=1976Sci...192.1123F |doi=10.1126/science.192.4244.1123 |pmid=17748675|s2cid=44506996 }}</ref> although this use alone would not account for the bizarre and extravagant variation seen in different members of [[Ceratopsidae]], which would rather support the sexual display theory.<ref name="Dino2"/>

The theory that frills functioned as a sexual display was first proposed by Davitashvili in 1961 and has gained increasing acceptance since.<ref name="TML90"/><ref name="Forster90"/><ref name="Davitashvili61">{{cite book|title=Teoriya Polovogo Otbora (Theory of Sexual Selection)|year=1961|author=Davitashvili, L. Sh.|page=538|publisher=Izdatel'stvo Akademii nauk SSSR}}</ref> Evidence that visual display was important, either in courtship or other social behavior, can be seen in the ceratopsians differing markedly in their adornments, making each species highly distinctive. Also, modern living creatures with such displays of horns and adornments use them similarly.<ref name="farlowanddodson1975" /> A 2006 study of the smallest ''Triceratops'' skull, ascertained to be that of a juvenile, shows the frill and horns developed at a very early age, predating sexual development. That would suggest they were probably important for visual communication and species recognition in general.<ref>{{cite journal| author1=Goodwin, M.B.| author2=Clemens, W.A.| author3=Horner, J.R.| author4=Padian, K.| name-list-style=amp| url=http://www.ucmp.berkeley.edu/people/mbg/Goodwin_et_al_2006.pdf| title=The smallest known ''Triceratops'' skull: new observations on ceratopsid cranial anatomy and ontogeny| journal=Journal of Vertebrate Paleontology| volume=26| issue=1| pages=103–112| doi=10.1671/0272-4634(2006)26[103:TSKTSN]2.0.CO;2| year=2006| s2cid=31117040| issn=0272-4634| access-date=January 21, 2007| archive-url=https://web.archive.org/web/20151105200947/http://www.ucmp.berkeley.edu/people/mbg/Goodwin_et_al_2006.pdf| archive-date=November 5, 2015| url-status=dead}}</ref> However, the use of the exaggerated structures to enable dinosaurs to recognize their own species has been questioned, as no such function exists for such structures in modern species.<ref>{{Cite journal |last1=Hone |first1=D. W. E. |last2=Naish |first2=D. |date=2013 |title=The 'species recognition hypothesis' does not explain the presence and evolution of exaggerated structures in non-avialan dinosaurs |journal=Journal of Zoology |volume=290 |issue=3 |pages=172–180 |doi=10.1111/jzo.12035|doi-access=free }}</ref>