Editing Walrus (section)

==Taxonomy and evolution==
[[File:Fossil walrus skull (Odobenus rosmarus).jpg|thumb|Fossil walrus (''O. rosmarus'') skull, collected off the coast of [[New Jersey]] in 1938. At the [[American Museum of Natural History|AMNH]]. ]]
The walrus is a mammal in the [[Order (biology)|order]] [[Carnivora]]. It is the sole surviving member of the [[family (biology)|family]] Odobenidae, one of three lineages in the [[suborder]] [[Pinnipedia]] along with true seals ([[Phocidae]]) and eared seals ([[Otariidae]]). While there has been some debate as to whether all three lineages are [[monophyletic]], i.e. descended from a single ancestor, or [[diphyletic]], recent genetic evidence suggests all three descended from a [[caniform]] ancestor most closely related to modern bears.<ref name=Lento1995>{{cite journal | vauthors = Lento GM, Hickson RE, Chambers GK, Penny D | title = Use of spectral analysis to test hypotheses on the origin of pinnipeds | journal = Molecular Biology and Evolution | volume = 12 | issue = 1 | pages = 28–52 | date = January 1995 | pmid = 7877495 | doi = 10.1093/oxfordjournals.molbev.a040189 | doi-access = free }}</ref> Recent multigene analysis indicates the odobenids and otariids diverged from the phocids about 20–26 million years ago, while the odobenids and the otariids separated 15–20 million years ago.<ref name=Arnason06>{{cite journal | vauthors = Arnason U, Gullberg A, Janke A, Kullberg M, Lehman N, Petrov EA, Väinölä R | title = Pinniped phylogeny and a new hypothesis for their origin and dispersal | journal = Molecular Phylogenetics and Evolution | volume = 41 | issue = 2 | pages = 345–54 | date = November 2006 | pmid = 16815048 | doi = 10.1016/j.ympev.2006.05.022 | bibcode = 2006MolPE..41..345A }}</ref><ref name=Higdon07>{{cite journal | vauthors = Higdon JW, Bininda-Emonds OR, Beck RM, Ferguson SH | title = Phylogeny and divergence of the pinnipeds (Carnivora: Mammalia) assessed using a multigene dataset | journal = BMC Evolutionary Biology | volume = 7 | pages = 216 | date = November 2007 | issue = 1 | pmid = 17996107 | pmc = 2245807 | doi = 10.1186/1471-2148-7-216 | doi-access = free | bibcode = 2007BMCEE...7..216H }}</ref> Odobenidae was once a highly diverse and widespread family, including at least twenty species in the subfamilies Imagotariinae, Dusignathinae and Odobeninae.<ref>{{cite journal| vauthors = Kohno N |year = 2006|title = A new Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan, and its implications for odobenid phylogeny|journal = Journal of Vertebrate Paleontology|volume = 26|issue = 2|pages = 411–421|doi = 10.1671/0272-4634(2006)26[411:ANMOMC]2.0.CO;2| s2cid=85679558 }}</ref> The key distinguishing feature was the development of a squirt/suction feeding mechanism; tusks are a later feature specific to Odobeninae, of which the modern walrus is the last remaining ([[Relict (biology)|relict]]) species.

Two subspecies of walrus are widely recognized: the Atlantic walrus, ''O. r. rosmarus'' (Linnaeus, 1758) and the Pacific walrus, ''O. r. divergens'' (Illiger, 1815). Fixed genetic differences between the Atlantic and Pacific subspecies indicate very restricted gene flow, but relatively recent separation, estimated at 500,000 and 785,000 years ago.<ref name= Hoelzel2002>{{cite book|veditors = Hoelzel AR|year = 2002|title = Marine mammal biology: an evolutionary approach|location = Oxford|publisher = Blackwell Publishing|isbn = 978-0-632-05232-5|url = {{google books |plainurl=y |id=OwF05MfTag}}}}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> These dates coincide with the hypothesis derived from fossils that the walrus evolved from a tropical or subtropical ancestor that became isolated in the Atlantic Ocean and gradually adapted to colder conditions in the Arctic.<ref name=Hoelzel2002/>

The modern walrus is mostly known from Arctic regions, but a substantial breeding population occurred on isolated [[Sable Island]], {{cvt|100|mi}} southeast of [[Nova Scotia]] and {{cvt|500|mi}} due east of [[Portland, Maine]], until the early Colonial period.<ref>{{cite journal| vauthors = Allen G |year = 1930|title = The Walrus in New England |journal = Journal of Mammalogy |volume = 11|issue = 2 |pages = 139–145 |doi = 10.2307/1374062 | jstor=1374062 }}</ref><ref>{{cite web| url= https://www.cbc.ca/news/canada/nova-scotia/sable-island-horses-walruses-1.3335467 |title = Sable Island horses, walruses to be discussed at meeting | website = cbc.ca| date =  November 25, 2015| first= Jennifer | last = Henderson | accessdate = July 1, 2023}}</ref> Abundant walrus remains have also been recovered from the southern North Sea dating to the [[Eemian]] interglacial period, when that region would have been submerged as it is today, unlike the intervening glacial lowstand when the shallow North Sea was dry land.<ref>{{cite web |url= https://libstore.ugent.be/fulltxt/RUG01/003/008/245/RUG01-003008245_2021_0001_AC.pdf| publisher= Ghent University| first1 = Hendrik | last1 = Plas |year= 2021| title= Walrus fossils from Het Scheur off the Belgian coast: remains of a late Pleistocene colony?}}</ref> Fossils known from [[San Francisco]], [[Vancouver]], and the Atlantic US coast as far south as [[North Carolina]] have been referred to glacial periods.<ref>{{cite journal | first1 = CR | last1 = Harington | first2 = Graham | last2 = Beard |name-list-style = vanc |year = 1992|title = The Qualicum walrus: a Late Pleistocene walrus (Odobenus rosmarus) skeleton from Vancouver Island, British Columbia, Canada |journal = Annales Zoologici Fennici |volume = 28|issue = 3/4 |pages = 311–319 | jstor = 23735455 |url = http://www.jstor.org/stable/23735455 }}</ref>

An isolated population in the [[Laptev Sea]] was considered by some authorities, including many Russian biologists and the canonical ''Mammal Species of the World'',<ref name= msw3/> to be a third subspecies, ''O. r. laptevi'' (Chapskii, 1940), but has since been determined to be of Pacific walrus origin.<ref>{{cite web| url= https://nammco.no/wp-content/uploads/2018/10/higdon-stewart-2018-1.pdf|publisher=WWF Arctic Programme| first1 = Jeff W. | last1 = Higdon | first2 = D. Bruce | last2 = Stewart |name-list-style = vanc |year=2018|title=State of Circumpolar Walrus Populations : Odobenus rosmarus|pages = 6}}</ref>