Editing Narwhal (section)

=== Tusk and dentition ===
[[File:Narwhal tusk, 1701-1930 Wellcome L0059030.jpg|thumb|Narwhal tusk|alt=The tusk of a male narwhal on display. The white tusk is long and shaped like a spiral.]]

The most conspicuous trait of male narwhals is a long, spiralled tusk, which is a [[canine tooth]] that projects from the left side of the upper jaw.<ref name=":20" /><ref name="Nweeia et al.">{{Cite journal |last1=Nweeia |first1=Martin T. |last2=Eichmiller |first2=Frederick C. |last3=Hauschka |first3=Peter V. |last4=Donahue |first4=Gretchen A. |last5=Orr |first5=Jack R. |last6=Ferguson |first6=Steven H. |last7=Watt |first7=Cortney A. |last8=Mead |first8=James G. |last9=Potter |first9=Charles W. |last10=Dietz |first10=Rune |last11=Giuseppetti |first11=Anthony A. |last12=Black |first12=Sandie R. |last13=Trachtenberg |first13=Alexander J. |last14=Kuo |first14=Winston P. |date=18 March 2014 |title=Sensory ability in the narwhal tooth organ system |url=https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.22886 |url-status=live |journal=The Anatomical Record |language=en |volume=297 |issue=4 |pages=599–617 |doi=10.1002/ar.22886 |issn=1932-8486 |pmid=24639076 |archive-url=https://web.archive.org/web/20240124201533/https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.22886 |archive-date=24 January 2024 |access-date=24 January 2024}}</ref> Both sexes have a pair of tusks embedded in the upper jaw, which in males erupt from the lip somewhere between two and three years of age.<ref name=":20" /> The tusk grows throughout the animal's life, reaching lengths of {{cvt|1.5|to|3|m}}.<ref>{{Cite journal |last1=Dietz |first1=Rune |last2=Desforges |first2=Jean-Pierre |last3=Rigét |first3=Frank F. |last4=Aubail |first4=Aurore |last5=Garde |first5=Eva |last6=Ambus |first6=Per |last7=Drimmie |first7=Robert |last8=Heide-Jørgensen |first8=Mads Peter |last9=Sonne |first9=Christian |date=10 May 2021 |title=Analysis of narwhal tusks reveals lifelong feeding ecology and mercury exposure |url=https://www.sciencedirect.com/science/article/pii/S0960982221002256 |url-status=live |journal=Current Biology |volume=31 |issue=9 |pages=2012–2019.e2 |bibcode=2021CBio...31E2012D |doi=10.1016/j.cub.2021.02.018 |issn=0960-9822 |pmid=33705717 |archive-url=https://web.archive.org/web/20240126170410/https://www.sciencedirect.com/science/article/pii/S0960982221002256 |archive-date=26 January 2024 |access-date=26 January 2024}}</ref><ref>{{Cite book |last=Dipper |first=Frances |url=https://books.google.com/books?id=lfYlEAAAQBAJ&dq=narwhal+weight&pg=PA436 |title=The Marine World: A Natural History of Ocean Life |date=8 June 2021 |publisher=Princeton University Press |isbn=978-0-691-23244-7 |pages=347 |language=en}}</ref><ref name=":1" /> It is hollow and weighs up to {{convert|7.45|kg|lb|abbr=on}}. Some males may grow two tusks, occurring when the right canine also protrudes through the lip.<ref name=":1">{{Cite journal |last1=Garde |first1=Eva |last2=Peter Heide-Jørgensen |first2=Mads |last3=Ditlevsen |first3=Susanne |last4=Hansen |first4=Steen H. |date=January 2012 |title=Aspartic acid racemization rate in narwhal (''Monodon monoceros'') eye lens nuclei estimated by counting of growth layers in tusks |url=https://polarresearch.net/index.php/polar/article/view/2584 |journal=Polar Research |language=en |volume=31 |issue=1 |pages=15865 |doi=10.3402/polar.v31i0.15865 |issn=1751-8369 |doi-access=free}}</ref><ref>{{Cite thesis |last=Lee |first=David S. |title=The ecological and social dynamics of Inuit narwhal foraging at Pond Inlet, Nunavut |date=2005 |degree=Doctor of Philosophy |publisher=McGill University |url=https://escholarship.mcgill.ca/concern/theses/q237hs40f |pages=7–13}}</ref> Females rarely grow tusks: when they do, the tusks are typically smaller than those of males, with less noticeable spirals.<ref name="WinterWhales" /><ref>{{Cite journal |last1=Garde |first1=Eva |last2=Heide-Jørgensen |first2=Mads Peter |date=3 June 2022 |title=Tusk anomalies in narwhals (Monodon monoceros) from Greenland |journal=Polar Research |volume=41 |doi=10.33265/polar.v41.8343 |issn=0800-0395 |doi-access=free}}</ref>

Current [[scientific consensus]] indicates that narwhal tusks are [[secondary sexual characteristics]] which indicate social status. Further functions of the narwhal tusk are debated: while some biologists suggest that narwhals use their tusks in fights, others argue that they may be of use in feeding.<ref name=":19">{{Citation |last1=Loch |first1=Carolina |title=Skulls, teeth, and sex |date=2023 |work=Sex in Cetaceans: Morphology, Behavior, and the Evolution of Sexual Strategies |pages=51–64 |editor-last=Würsig |editor-first=Bernd |editor-last2=Orbach |editor-first2=Dara N. |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-031-35651-3_3 |isbn=978-3-031-35651-3 |last2=Fordyce |first2=R. Ewan |last3=Werth |first3=Alexander |doi-access=free}}</ref> The tusk is also a highly [[innervate]]d [[sensory organ]] with millions of [[nerve ending]]s, allowing the narwhal to sense temperature variability in its surroundings.<ref name="Nweeia et al." /> These nerves may also be able to detect changes in particle concentration and water pressure.<ref name="Broad">{{Cite news |last=Broad |first=William |date=13 December 2005 |title=It's sensitive. Really. |url=https://www.nytimes.com/2005/12/13/science/its-sensitive-really.html?_r=0 |url-status=live |archive-url=https://web.archive.org/web/20240128091613/https://www.nytimes.com/2005/12/13/science/its-sensitive-really.html?_r=0 |archive-date=28 January 2024 |access-date=22 February 2017 |work=The New York Times}}</ref><ref name=":0">{{Cite web |last=Vincent, James |date=19 March 2014 |title=Scientists suggest they have the answer to the mystery of the narwhal's tusk |url=https://www.independent.co.uk/news/science/scientists-solve-the-mystery-of-the-narwhals-tusk-9202935.html |url-access=subscription |url-status=live |archive-url=https://ghostarchive.org/archive/20220618/https://www.independent.co.uk/news/science/scientists-solve-the-mystery-of-the-narwhals-tusk-9202935.html |archive-date=18 June 2022 |access-date=31 March 2014 |website=[[Independent.co.uk]]}}</ref> According to Martin Nweeia, male narwhals may rid themselves of encrustations on their tusks by rubbing them together, as opposed to posturing displays of aggressive male-to-male rivalry.<ref name="Broad" /><ref name=":0" /> [[Unmanned aerial vehicle|Drone]] footage from August 2016 in Tremblay Sound, [[Nunavut]], revealed that narwhals used their tusks to tap and [[wikt:stun#Verb|stun]] small [[Arctic cod]], making them easier to catch for feeding.<ref name=":19" /><ref>{{Cite news |date=17 May 2017 |title=Drone-shot video may have just solved 400-year debate over what narwhal tusks are used for |url=https://nationalpost.com/news/canada/drone-shot-video-may-have-just-solved-400-year-debate-over-what-narwhal-tusks-are-used-for |access-date=17 July 2024 |work=National Post}}</ref> Females, who usually do not have tusks, live longer than males, hence the tusk cannot be essential to the animal's survival. It is generally accepted that the primary function of the narwhal tusk is associated with [[sexual selection]].<ref name=":19" /><ref name=":13">{{Cite journal |last1=Kelley |first1=Trish C. |last2=Stewart |first2=Robert E. A. |last3=Yurkowski |first3=David J. |last4=Ryan |first4=Anna |last5=Ferguson |first5=Steven H. |date=April 2015 |title=Mating ecology of beluga (''Delphinapterus leucas'') and narwhal (''Monodon monoceros'') as estimated by reproductive tract metrics |url=https://onlinelibrary.wiley.com/doi/10.1111/mms.12165 |journal=Marine Mammal Science |language=en |volume=31 |issue=2 |pages=479–500 |bibcode=2015MMamS..31..479K |doi=10.1111/mms.12165 |issn=0824-0469}}</ref>

Alongside its tusk, the narwhal has a single pair of small [[vestigial]] teeth that reside in open [[tooth socket]]s in the upper jaw. These teeth, which differ in form and composition, encircle the exposed tooth sockets laterally, posteriorly, and ventrally.<ref name="Nweeia et al." /><ref name="smiths">{{Cite web |date=18 April 2012 |title=For a dentist, the narwhal's smile is a mystery of evolution |url=http://insider.si.edu/2012/04/for-dentist-the-narwhals-smile-is-a-mystery-of-evolution/ |url-status=live |archive-url=https://web.archive.org/web/20160914121508/http://insider.si.edu/2012/04/for-dentist-the-narwhals-smile-is-a-mystery-of-evolution/ |archive-date=14 September 2016 |access-date=6 September 2016 |publisher=Smithsonian Insider}}</ref> Vestigial teeth in male narwhals are commonly shed in the [[palate]]. The varied morphology and anatomy of small teeth indicate a path of evolutionary obsolescence.<ref name="Nweeia et al." /><ref>{{Cite journal |last1=Nweeia |first1=Martin T. |last2=Eichmiller |first2=Frederick C. |last3=Hauschka |first3=Peter V. |last4=Tyler |first4=Ethan |last5=Mead |first5=James G. |last6=Potter |first6=Charles W. |last7=Angnatsiak |first7=David P. |last8=Richard |first8=Pierre R. |last9=Orr |first9=Jack R. |last10=Black |first10=Sandie R. |date=30 March 2012 |title=Vestigial tooth anatomy and tusk nomenclature for ''Monodon Monoceros'' |url=http://dx.doi.org/10.1002/ar.22449 |journal=The Anatomical Record |volume=295 |issue=6 |pages=1006–1016 |doi=10.1002/ar.22449 |issn=1932-8486 |pmid=22467529}}</ref>