Editing Hyena (section)

==Evolution==

===Origins===
Hyenas originated in the jungles of [[Miocene]] Eurasia 22&nbsp;million years ago, when most early feliform species were still largely [[arboreal]]. The first ancestral hyenas were likely similar to the modern [[African civet]]; one of the earliest hyena species described, ''[[Plioviverrops]]'', was a lithe, civet-like animal that inhabited Eurasia 20–22&nbsp;million years ago, and is identifiable as a hyaenid by the structure of the [[middle ear]] and dentition. The lineage of ''Plioviverrops'' prospered, and gave rise to descendants with longer legs and more pointed jaws, a direction similar to that taken by canids in [[North America]].<ref name="mac119">{{Harvnb|Macdonald|1992|pp=119–144}}</ref>
Hyenas then diversified into two distinct types: lightly built dog-like hyenas and robust bone-crushing hyenas. Although the dog-like hyenas thrived 15&nbsp;million years ago (with one [[taxon]] having colonised North America), they became extinct after a change in climate, along with the arrival of canids into Eurasia. Of the dog-like hyena lineage, only the insectivorous [[aardwolf]] survived, while the bone-crushing hyenas (including the [[Extant taxon|extant]] spotted, [[brown hyena|brown]] and striped hyenas) became the undisputed top scavengers of Eurasia and Africa.<ref name="mac119" />

===Rise and fall of the dog-like hyenas===
[[File:Ictitherium viverrinum.JPG|left|thumb|Skull of ''Ictitherium viverrinum'', one of the "dog-like" hyenas. [[American Museum of Natural History]]]]
The descendants of ''Plioviverrops'' reached their peak 15&nbsp;million years ago, with more than 30 species having been identified. Unlike most modern hyena species, which are specialised bone-crushers, these dog-like hyenas were nimble-bodied, wolfish animals; one species among them was ''[[Ictitherium]] viverrinum'', which was similar to a [[jackal]]. The dog-like hyenas were numerous; in some Miocene fossil sites, the remains of ''Ictitherium'' and other dog-like hyenas outnumber those of all other carnivores combined. The decline of the dog-like hyenas began 5–7&nbsp;million years ago during a period of climate change, exacerbated by [[canid]]s crossing the [[Bering land bridge]] to Eurasia. One species, ''[[Chasmaporthetes|Chasmaporthetes ossifragus]]'', managed to cross the land bridge into North America, being the only hyena to do so. ''Chasmaporthetes'' managed to survive for some time in North America by deviating from the endurance-running and bone-crushing niches monopolized by canids, and developing into a [[cheetah]]-like sprinter. Most of the dog-like hyenas had died off by 1.5&nbsp;million years ago.<ref name="mac119" />

===Bone-crushing hyenas===
By 10–14&nbsp;million years ago, the hyena family had split into two distinct groups: dog-like hyenas and bone-crushing hyenas. The arrival of the ancestral bone-crushing hyenas coincided with the decline of the similarly built family [[Percrocutidae]]. The bone-crushing hyenas survived the changes in climate and the arrival of canids, which wiped out the dog-like hyenas, though they never crossed into North America, as their niche there had already been taken by the dog subfamily [[Borophaginae]]. By 5&nbsp;million years ago, the bone-crushing hyenas had become the dominant scavengers of Eurasia, primarily feeding on large herbivore carcasses felled by [[sabre-toothed cat]]s. One genus, ''[[Pachycrocuta]]'', was a {{cvt|110|kg}} mega-scavenger that could splinter the bones of [[elephant]]s.<ref name=Palmqvist_et_al_2011>{{cite journal|last1=Palmqvist|first1=P.|last2=Martinez-Navarro|first2=B.|last3=Pérez-Claros|first3=J. A.|last4=Torregrosa|first4=V.|last5=Figueiridio|first5=B.|last6=Jiménez-Arenas|first6=J. M.|last7=Patrocinio Espigares|first7=M.|last8=Ros-Montoya|first8=Sergio|last9=De Renzi|first9=M.|title=The giant hyena Pachycrocuta brevirostris: Modelling the bone-cracking behavior of an extinct carnivore|journal=Quaternary International|date=2011|volume=243|issue=#1|pages=61|doi=10.1016/j.quaint.2010.12.035|bibcode=2011QuInt.243...61P |hdl=10630/33571|hdl-access=free}}</ref><ref name="mac119" /> Starting in the early [[Chibanian|Middle Pleistocene]] ''Pachycrocuta'' was replaced by the smaller ''Crocuta'' and ''Hyena'', which corresponds to a general faunal change, perhaps in connection to the [[Mid-Pleistocene Transition|Mid-Pleistocene transition]].<ref>{{Cite journal |last1=Iannucci |first1=Alessio |last2=Mecozzi |first2=Beniamino |last3=Sardella |first3=Raffaele |last4=Iurino |first4=Dawid Adam |date=2021-11-15 |title=The extinction of the giant hyena Pachycrocuta brevirostris and a reappraisal of the Epivillafranchian and Galerian Hyaenidae in Europe: Faunal turnover during the Early–Middle Pleistocene Transition |url=https://www.sciencedirect.com/science/article/pii/S0277379121004479 |journal=Quaternary Science Reviews |volume=272 |pages=107240 |doi=10.1016/j.quascirev.2021.107240 |bibcode=2021QSRv..27207240I |issn=0277-3791}}</ref>

===Rise of modern hyenas===
[[File:Stripedspottedhyenas.jpg|thumb|right|upright|Skeletons of a [[striped hyena]] (left) and a [[spotted hyena]] (right), two species of the "bone-crushing" hyenas]]
The four extant species are the striped hyena (''Hyaena hyaena''), the brown hyena (''Parahyaena brunnea''), the spotted hyena (''Crocuta crocuta''), and the aardwolf (''Proteles cristata'').

The [[aardwolf]] can trace its lineage directly back to ''Plioviverrops'' 15&nbsp;million years ago, and is the only survivor of the dog-like hyena lineage. Its success is partly attributed to its insectivorous diet, for which it faced no competition from canids crossing from North America. It is likely that its unrivaled ability to digest the [[terpene]] excretions from soldier [[termite]]s is a modification of the strong digestive system its ancestors used to consume fetid carrion.<ref name="mac119" />

The [[striped hyena]] may have evolved from ''Hyaenictitherium namaquensis'' of [[Pliocene]] [[Africa]]. Striped hyena fossils are common in Africa, with records going back as far as the [[Villafranchian]]. As fossil striped hyenas are absent from the [[Mediterranean]] region, it is likely that the species is a relatively late invader to Eurasia, having likely spread outside Africa only after the extinction of [[spotted hyena]]s in Asia at the end of the [[Last Glacial Period|Ice Age]]. The striped hyena occurred for some time in [[Europe]] during the Pleistocene, having been particularly widespread in [[France]] and [[Germany]]. It also occurred in [[Montmaurin]], [[Hollabrunn]] in [[Austria]], the [[Furninha|Furninha Cave]] in [[Portugal]] and the Genista Caves in [[Gibraltar]]. The European form was similar in appearance to modern populations, but was larger, being comparable in size to the [[brown hyena]].<ref name="k66">{{Harvnb|Kurtén|1968|pp=66–68}}</ref>

The [[spotted hyena]] (''Crocuta crocuta'') diverged from the striped and brown hyena 10&nbsp;million years ago.<ref name="m1">{{Harvnb|Mills|Hofer|1998|p=1}}</ref> Its direct ancestor was the Indian ''Crocuta sivalensis'', which lived during the Villafranchian.<ref name="k69" /> Ancestral spotted hyenas probably developed social behaviours in response to increased pressure from rivals on carcasses, thus forcing them to operate in teams. Spotted hyenas evolved sharp [[carnassial]]s behind their crushing premolars, therefore they did not need to wait for their prey to die, and thus became pack hunters as well as scavengers. They began forming increasingly larger [[territory (animal)|territories]], necessitated by the fact that their prey was often migratory, and long chases in a small territory would have caused them to encroach into another [[Hyena clan|clan's]] turf.<ref name="mac119" /> Spotted hyenas spread from their original homeland during the [[Middle Pleistocene]], and quickly colonised a very wide area from Europe, to southern Africa and [[China]].<ref name="k69">{{Harvnb|Kurtén|1968|pp=69–72}}</ref> The eventual disappearance of the spotted hyena from Europe has traditionally been attributed to the end of the [[Last Glacial Period|last glacial period]] and a subsequent displacement of open grassland by closed forests, which favoured wolves and humans instead.<ref name="hyenawolf">{{cite web| url=http://www.u.arizona.edu/~mstiner/pdf/Stiner2004a.pdf| title=Comparative ecology and taphonomy of spotted hyenas, humans, and wolves in Pleistocene Italy| work=C. Stiner, Mary| publisher=Revue de Paléobiologie, Genève| access-date=2008-09-16| archive-date=2019-05-08| archive-url=https://web.archive.org/web/20190508135925/http://www.u.arizona.edu/~mstiner/pdf/Stiner2004a.pdf| url-status=dead}}</ref> However, analyses have shown that [[climate change]] alone is insufficient to explain the spotted hyena's disappearance from Europe, suggesting that other factors – such as human pressure – must have played a role.<ref>{{Cite journal |last1=Varela |first1=Sara |last2=Lobo |first2=Jorge M. |last3=Rodríguez |first3=Jesús |last4=Batra |first4=Persaram |date=2010-08-01 |title=Were the Late Pleistocene climatic changes responsible for the disappearance of the European spotted hyena populations? Hindcasting a species geographic distribution across time |url=https://www.sciencedirect.com/science/article/pii/S0277379110001265 |journal=Quaternary Science Reviews |volume=29 |issue=17 |pages=2027–2035 |doi=10.1016/j.quascirev.2010.04.017 |bibcode=2010QSRv...29.2027V |issn=0277-3791}}</ref> This suggests that the events must be seen within the broader context of [[Late Pleistocene extinctions|late-Quaternary extinctions]], as the late Pleistocene and early Holocene saw the disappearance of many primarily large mammals from Europe and the world.

Expansion or [[Gene duplication|duplication]] of the [[Olfactory receptor|olfatory receptor]] gene family has been found in all 4 extant species, which would have led to the evolution of the more specialised feeding habits of hyenas.<ref name=":0">{{Cite journal |last1=Westbury |first1=Michael V |last2=Le Duc |first2=Diana |last3=Duchêne |first3=David A |last4=Krishnan |first4=Arunkumar |last5=Prost |first5=Stefan |last6=Rutschmann |first6=Sereina |last7=Grau |first7=Jose H |last8=Dalén |first8=Love |last9=Weyrich |first9=Alexandra |last10=Norén |first10=Karin |last11=Werdelin |first11=Lars |last12=Dalerum |first12=Fredrik |last13=Schöneberg |first13=Torsten |last14=Hofreiter |first14=Michael |date=2021 |title=Ecological Specialization and Evolutionary Reticulation in Extant Hyaenidae |url=https://academic.oup.com/mbe/article/38/9/3884/6149117 |journal=Molecular Biology and Evolution |volume=38 |issue=9 |pages=3884–3897 |doi=10.1093/molbev/msab055 |issn=1537-1719 |pmc=8382907 |pmid=34426844}}</ref>

Expansion in immune-related gene families was also found in the spotted hyena, striped hyena and brown hyena, which would have led to the evolution of the [[scavenging]] in these species. Mutations and variants were also found in digestion-related genes (''ASH1L'', ''PTPN5'', ''PKP3'', ''AQP10''). One of these digestion-related genes has variants also related to enhanced bone mineralisation (''PTPN5''), while other have also a role in inflammatory skin responses (''PKP3'').<ref name=":0" />

In aardwolves, expansion of genes related to toxin response were found ([[Lipocalin]] and [[Glucuronosyltransferase|UDP Glucuronosyltransferase]] gene families), which would have led to the evolution of the feeding of termites [[Trinervitermes trinervoides|Trinervitermes]] in this species. Mutations and variants in genes related to craniofacial shape were also found (''GARS'', ''GMPR'', ''STIP1'', ''SMO'' and ''PAPSS2''). Another gene is related to protective epidermis function (''DSC1'').<ref name=":0" />

{{See also|Cave hyena}}