Editing Muskox (section)

== Evolution ==

=== Extant relatives ===

The muskox is in the subtribe [[Ovibovina]] (or tribe Ovibovini) in the tribe [[Caprinae|Caprini]] (or subfamily Caprinae) of the subfamily [[Antilopinae]] in the family Bovidae. It is therefore more closely related to [[Domestic sheep|sheep]] and [[goat]]s than to [[ox]]en; it is placed in its own genus, ''Ovibos'' ([[Latin]]: "sheep-ox"). It is one of the two largest [[extant taxon|extant]] members of the caprines, along with the similarly sized [[Takin|Takin ''Budorcas'']].<ref name="Burnie">{{cite book|editor=Burnie D |editor2= Wilson DE |title= Animal: The Definitive Visual Guide to the World's Wildlife|publisher= DK Adult |year=2005 |isbn=0-7894-7764-5}}</ref> While the takin and muskox were once considered possibly closely related, the takin lacks common ovibovine features, such as the muskox's specialized horn morphology, and genetic analysis shows that their lineages actually separated early in caprine evolution. Instead, the muskox's closest living relatives appear to be the [[goral]]s of the genus ''[[Naemorhedus]]'', nowadays common in many countries of central and east Asia. The vague similarity between takin and muskox is therefore an example of [[convergent evolution]].<ref name="Lent1999">{{cite book |first=Peter C. |last=Lent |title=Muskoxen and Their Hunters: A History |url={{GBurl |id=KE2z-QFjj8kC}}|access-date= 2013-08-25|year= 1999|publisher=University of Oklahoma Press|isbn=0-8061-3170-5}}</ref>

=== Fossil history and extinct relatives ===
[[File:Preptoceras sinclairi.jpg|thumb|''[[Euceratherium]]'' skeleton (missing its ribs)]]
The modern muskox is the last member of a line of ovibovines that first evolved in temperate regions of Asia and adapted to a cold [[tundra]] environment late in its evolutionary history. Muskox ancestors with sheep-like high-positioned horns (horn cores being mostly over the plane of the [[frontal bone]]s, rather than below them as in modern muskoxen) first left the temperate forests for the developing grasslands of [[Central Asia]] during the [[Pliocene]], expanding into [[Siberia]] and the rest of northern [[Eurasia]]. Later migration waves of Asian ungulates that included high-horned muskoxen reached [[Europe]] and [[North America]] during the first half of the [[Pleistocene]]. The first well known muskox, the "shrub-ox" ''[[Euceratherium]]'', crossed to North America over an early version of the [[Bering Land Bridge]] two million years ago and prospered in the [[American southwest]] and [[Mexico]]. ''Euceratherium'' was larger yet more lightly built than modern muskoxen, resembling a giant sheep with massive horns, and preferred hilly grasslands.

A genus with intermediate horns, ''[[Soergelia]]'', inhabited Eurasia in the early Pleistocene, from [[Spain]] to Siberia, and crossed to North America during the [[Irvingtonian]] (1.8&nbsp;million years to 240,000 years ago), soon after ''Euceratherium''. Unlike ''Euceratherium'', which survived in America until the Pleistocene-[[Holocene]] [[Quaternary extinction event|extinction event]], ''Soergelia'' was a lowland dweller which disappeared fairly early, displaced by more advanced ungulates, such as the "giant muskox" ''[[Praeovibos priscus|Praeovibos]]'' (literally "before ''Ovibos''"). The low-horned ''Praeovibos'' was present in Europe and the [[Mediterranean]] 1.5&nbsp;million years ago, colonized [[Alaska]] and the [[Yukon]] one million years ago and disappeared half a million years ago. ''Praeovibos'' was a highly adaptable animal apparently associated with cold tundra ([[reindeer]]) and temperate woodland ([[red deer]]) faunas alike. During the [[Mindel glaciation]] 500,000 years ago, ''Praeovibos'' was present in the [[Kolyma river]] area in eastern Siberia in association with many [[Last Glacial Period|Ice Age]] [[megafauna]] that would later coexist with ''Ovibos'', in the Kolyma itself and elsewhere, including [[wild horse]]s, reindeer, [[woolly mammoth]] and [[Cervalces|stag-moose]]. It is debated, however, if ''Praeovibos'' was directly ancestral to ''Ovibos'', or both genera descended from a common ancestor, since the two occurred together during the middle Pleistocene. Defenders of ancestry from ''Praeovibos'' have proposed that ''Praeovibos'' evolved into ''Ovibos'' in one region during a period of isolation and expanded later, replacing the remaining populations of ''Praeovibos''.<ref name="Lent1999" />

Two more ''Praeovibos''-like genera were named in America in the 19th century, ''[[Bootherium]]'' and ''Symbos'', which are now identified as the male and female forms of a single, [[sexual dimorphism|sexually dimorphic]] species, the "woodland muskox", ''Bootherium bombifrons''. ''Bootherium'' inhabited open woodland areas of North America during the late Pleistocene, from Alaska to [[Texas]] and maybe even Mexico, but was most common in the [[Southern United States]], while ''Ovibos'' replaced it in the tundra-steppe to the north, immediately south of the [[Laurentian ice sheet]].<ref name="Lent1999" /><ref name="Wisconsinan Mammalian Faunas">{{cite web |url=http://www.kgs.ku.edu/Publications/Bulletins/GB5/Martin2/ |title=KGS--Guidebook 5--Wisconsinan Mammalian Faunas |work=ku.edu}}</ref>

Modern ''Ovibos'' appeared in [[Germany]] almost one million years ago and was common in the region through the Pleistocene. By the Mindel, muskoxen had also reached the [[British Isles]]. Both Germany and Britain were just south of the [[Scandinavian ice sheet]] and covered in tundra during cold periods, but Pleistocene muskoxen are also rarely recorded in more benign and wooded areas to the south like [[France]] and [[Green Spain]], where they coexisted with temperate ungulates like [[red deer]] and [[aurochs]]. Likewise, the muskox is known to have survived in Britain during warm [[interglacial]] periods.<ref name="Lent1999" />

Today's muskoxen are descended from others believed to have migrated from [[Siberia]] to [[North America]] between 200,000<ref name="WMAC">{{cite web|url=http://www.taiga.net/wmac/species/muskox/factsheet1_history.html |archive-url=https://web.archive.org/web/20041101113210/http://www.taiga.net/wmac/species/muskox/factsheet1_history.html |url-status=usurped |archive-date=2004-11-01 |title=Wildlife Management Advisory Council (North Slope) fact sheet|website= taiga.net}}</ref> and 90,000 years ago,<ref name="HWW">{{cite web |url=http://www.hww.ca/en/species/mammals/muskox.html |archive-url=https://web.archive.org/web/20130425074844/http://www.hww.ca/en/species/mammals/muskox.html |url-status=dead |title=Hinterland Who's Who |archive-date=April 25, 2013}}</ref> having previously occupied Alaska (at the time united to Siberia and isolated periodically from the rest of North America by the union of the Laurentide and [[Cordilleran Ice Sheet]]s during colder periods) between 250,000 and 150,000 years ago. After migrating south during one of the warmer periods of the [[Illinoian (stage)|Illinoian glaciation]], non-Alaskan American muskoxen would be isolated from the rest in the colder periods. The muskox was already present in its current stronghold of [[Banks Island]] 34,000 years ago, but the existence of other ice-free areas in the [[Canadian Arctic Archipelago]] at the time is disputed.<ref name="Lent1999" />

Along with the [[American bison|bison]] and the [[pronghorn]],<ref name="smithsonian">{{cite web|publisher=Smithsonian Institution|series= North American Mammals|url=http://www.mnh.si.edu/mna/image_info.cfm?species_id=7 |title=Pronghorn ''Antilocapra americana''}}</ref> the muskox was one of a few species of [[Pleistocene megafauna]] in North America to survive the Pleistocene/[[Holocene]] [[Quaternary extinction event|extinction event]] and live to the present day.<ref name="Switek">{{cite web|author=Switek, Brian|url=http://scienceblogs.com/laelaps/2010/03/10/of-all-the-mass-extinctions/ |title=Prehistoric DNA Reveals the Story of a Pleistocene Survivor, the Muskox|editor=''Laelaps'' blog |website=scienceblogs.com |date=10 March 2010 |access-date= 18 January 2013}}</ref> The muskox is thought to have been able to survive the [[last glacial period]] by finding ice-free areas ([[Refugium (population biology)|refugia]]) away from prehistoric peoples.<ref name="HWW" />

Fossil DNA evidence suggests that muskoxen were not only more geographically widespread during the Pleistocene, but also more [[genetic diversity|genetically diverse]].<ref name="SD">{{cite web |url=https://www.sciencedaily.com/releases/2005/10/051006085912.htm |title=Muskox Suffered Loss Of Genetic Diversity at Pleistocene/Holocene Transition |publisher=Science Daily |date=2005-10-06 |access-date=2011-03-03}}</ref> During that time, other populations of muskoxen lived across the Arctic, from the [[Ural Mountains]] to Greenland. By contrast, the current genetic makeup of the species is more homogenous. Climate fluctuation may have affected this shift in genetic diversity: research indicates colder periods in Earth's history are correlated with more diversity, and warmer periods with more homogeneity.<ref name="Switek" /> Muskox populations survived into the Holocene in Siberia, with their youngest records in the region being from the [[Taymyr Peninsula]], dating to around 2,700 years ago (~700 BC).<ref name=":1" />