Hyena

                    Hyenas Hyenasorhyaenas(fromGreek"ὕαινα" —hýaina[1]) are the animals of the familyHyaenidae/haɪˈɛnɨdiː/of thefeliforuborderof theCarnivora. With only four species, it is the fourth-smallestbiological familyin the Carnivora, and one of the smallest in the classMammalia.[2]Despite their low diversity, hyenas are unique and vital components to mostAfricanand someAsianecosystems.[3]Althoughphylogeneticallyclose tofelinesandviverrids, hyenas are behaviourally and morphologically similar tocaninesinseveral aspects; both hyenas and canines are nonarboreal,cursorialhunters that catch prey with their teeth rather than claws. Both eat food quickly and may store it, and their calloused feet with large, blunt, nonretractable nails are adapted for running and making sharp turns. However, the hyenas' grooming, scent marking, defecating habits, mating, and parental behaviour are consistent with the behaviour of other feliforms.[4]Although long reputed to be cowardly scavengers, hyenas, especiallyspotted hyenas, kill as much as 95% of the foodthey eat,[5]and have been known to drive off leopards or lionesses from their kills. Hyenas are primarily nocturnal animals, but may venture from their lairs in the early-morning hours. With the exception of the highly social spotted hyena, hyenas are generally notgregariousanimals, though they may live in family groups and congregate at kills.[6]Hyenas first arose in Eurasia during theMioceneperiod from viverrid-like ancestors, and developed into two distinct branches; the lightlybuilt dog-like hyenas and the robust bone-crushing hyenas. Although the dog-like hyenas thrived 15 million years ago (with onetaxonhaving colonised North America), they died out after a change in climate along with the arrival ofcanidsinto Eurasia. Of the dog-likehyena lineage, only the insectivorousaardwolfsurvived, while the bone-crushing hyenas (whoseextantmembers are thespotted,brownandstriped hyenas) became the undisputed topscavengers of Eurasia and Africa.[7]Hyenas feature prominently in the folklore and mythology of human cultures with which they aresympatric. Hyenas are mostly viewed with fear and contempt, as well as being associated with witchcraft, as their body parts are used as ingredients intraditional medicine. Among the beliefs held by some cultures, hyenas are thought to influence people’s spirits, rob graves,and steal livestock and children.[8]EvolutionOriginsHyenas originated in the jungles ofMioceneEurasia 22 million years ago, when most early feliform species were still largelyarboreal. Thefirst ancestral hyenas were likely similar to the modernbanded palm civet; one of the earliest hyena species exhumed,Plioviverrops, was a lithe, civet-like animal that inhabited Eurasia 20–22 million years ago, and is identifiable as a hyaenid by the structure of themiddle earand dentition. The lineage ofPlioviverropsprospered, and gave rise to descendants with longer legs and more pointed jaws, a direction similar to that taken by canids inNorth America.[7]Rise and fall of the dog-like hyenasSkull ofIctitherium viverrinum, one of the"dog-like" hyenas.American Museum of Natural HistoryThe descendants ofPlioviverropsreached their peak 15 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 wasIctitheriumviverrinum, whichwas similar to ajackal. The dog-like hyenas were very numerous; in some Miocene fossil sites, the remains ofIctitheriumand other dog-like hyenas outnumber those of all other carnivores combined. The decline of the dog-like hyenas began 5–7 million years ago during a period of climate change, which was exacerbated whencanidscrossed theBering land bridgeto Eurasia. One species,Chasmaporthetes ossifragus, managed to cross the land bridge into North America, being the only hyena to do so.Chasmopothertesmanagedto survive for some time in North America by deviating from thecursorialand bone-crushing niches monopolised by canids, and developing into acheetah-like sprinter. Most of the dog-like hyenas had died off by 1.5 million years ago.[7]Bone-crushing hyenasBy 10–12 million years ago, the hyena family had split into two distinct groups; that of the dog-like hyenas and the bone-crushing hyenas. The arrival of the ancestral bone-crushing hyenas coincided with the decline of the similarly built but unrelatedPercrocutidaefamily. The bone-crushing hyenas survived the devastating changes in climate and the arrival ofcanids, which wiped out the dog-like hyenas, though they never crossed into North America, as their niche there had already been taken by theBorophaginaefamily. By 5 million years ago, the bone-crushing hyenas became the dominant scavengers of Eurasia, primarily feeding on large herbivore carcasses felled bysabre-toothed cats. One genus,Pachycrocuta, was a 200 kg (440 lb) mega-scavenger that couldsplinter the bones ofelephants. With the decline of large herbivores by the late ice age,Pachycrocutawas replaced by the smallerCrocuta.[7]Rise of modern hyenasTheaardwolfcan trace its lineage directly back toPlioviverrops15 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. Its unrivaled ability to digest theterpeneexcretions from soldiertermitesis likely a modification of the strong digestive system its ancestors used to digest fetid carrion.[7]Skeletons of astriped hyenaand aspotted hyena, two species of the "bone-crushing" hyenas.Muséum national d'histoire naturelleThestriped hyenamay have evolved fromH. namaquensisofPlioceneAfrica. Striped hyena fossils are common in Africa, with records goingback as far as the MiddlePleistoceneand even to the Villafranchian. As fossil striped hyenas are absent from theMediterraneanregion, it is likely that the species is a relatively late invaderto Eurasia, having likely spread outside Africa only after the extinction ofspotted hyenasin Asia at the end of theIce Age. The striped hyena occurred for some time inEuropeduring the Pleistocene, having been particularly widespread inFranceandGermany. It also occurred inMontmaurin,HollabrunninAustria,the Furninha Cave inPortugaland the Genista Caves inGibraltar. The European form was similar in appearance to modern populations, but was larger, being comparable in size to thebrown hyena.[9]Thespotted hyenadiverged from the striped and brown hyena 10 million years ago.[10]Its direct ancestor was the IndianCrocuta sivalensis, which lived during the Villafranchian.[11]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 sharpcarnassialsbehind their crushing premolars, therefore they did not need to wait for their prey to die, as is the case for brown and striped hyenas, and thus became pack hunters as well as scavengers. They began forming increasingly largerterritories, 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 clan's turf.[7]Spotted hyenas spread from their original homeland during theMiddle Pleistocene, and quickly colonised a verywide area from Europe, to southern Africa andChina.[11]With the decline of grasslands 12,500 years ago, Europe experienced a massive loss of lowland habitats favoured by spotted hyenas, and a corresponding increase inmixed woodlands. Spotted hyenas, under these circumstances, would have been outcompeted bywolvesandhumans, who were as much at home in forests as in open lands—and in highlands as in lowlands. Spotted hyena populations began to shrink after roughly 20,000 years ago, completely disappearing fromWestern Europebetween 11 and 14 thousand years ago, and earlier in some areas.[12]Genera of the Hyaenidae (extinct and recent)Reconstruction ofPachycrocutabrevirostrisAspotted hyenaof subfamily HyaeninaeThe list follows McKenna and BellsClassificationof Mammalsfor prehistoric genera (1997)[13]and Wozencraft (2005) in Wilson and ReedersMammal Species of the Worldfor extant genera.[14]The Percrocutids are, in contrast toMcKenna and Bell's classification, not included as a subfamily into the Hyaenidae, but as the separate familyPercrocutidae. Furthermore, the living brown hyena and its closest extinct relatives are not included in the genusPachycrocuta, but in the genusHyaena. TheProtelinae(Aardwolves) are not treated as a separate subfamily, but included in theHyaeninae.*.Family Hyaenidae*.*.†Tongxinictis(Middle Miocene of Asia)*.†Subfamily Ictitheriinae*.†Herpestides(Early Miocene of Africa and Eurasia)*.†Plioviverrops(includingJordanictis,Protoviverrops,Mesoviverrops; Early Miocene to Early Pliocene of Europe, Late Miocene of Asia)*.†Ictitherium(=Galeotherium; includingLepthyaena,Sinictitherium,Paraictitherium; Middle Miocene of Africa, Late Miocene to Early Pliocene of Eurasia)*.†Thalassictis(includingPalhyaena,Miohyaena,Hyaenictitherium,Hyaenalopex; Middle to Late Miocene of Asia, Late Miocene of Africa and Europe)*.†Hyaenotherium(Late Miocene to Early Pliocene of Eurasia)*.†Miohyaenotherium(Late Miocene of Europe)*.†Lychyaena(Late Miocene of Eurasia)*.†Tungurictis(Middle Miocene of Africa and Eurasia)*.†Proictitherium(Middle Miocene of Africaand Asia, Middle to Late Miocene of Europe)*.Subfamily Hyaeninae*.†Palinhyaena(Late Miocene of Asia)*.†Ikelohyaena(Early Pliocene of Africa)*.Hyaena(=Euhyaena, =Hyena; includingbrown Hyena,Pliohyaena,Pliocrocuta,Anomalopithecus) Early Pliocene (?MiddleMiocene) to Recent of Africa, Late Pliocene (?Late Miocene) to Late Pleistocene of Europe, Late Pliocene to recent in Asia*.†Hyaenictis(Late Miocene of Asia?, Late Miocene of Europe, Early Pliocene (?Early Pleistocene) of Africa)*.†Leecyaena(Late Miocene and/or Early Pliocene of Asia)*.†Chasmaporthetes(=Ailuriaena; includingLycaenops,Euryboas; Late Miocene to Early Pleistocene of Eurasia, Early Plioceneto Late Pliocene or Early Pleistocene of Africa, Late Pliocene to Early Pleistocene of North America)*.†Pachycrocuta(Pliocene and Pleistocene of Eurasia and Africa)*.†Adcrocuta(Late Miocene of Eurasia)*.Crocuta(=Crocotta; includingEucrocuta; Late Pliocene to recent of Africa, Late Pliocene to Late Pleistocene of Eurasia)*.Subfamily Protelinae*.Proteles(=Geocyon; Pleistocene to Recent of Africa)CharacteristicsBuildFurther information:Spotted hyena#Physical description,Striped hyena#Physical description,Aardwolf#Physical characteristics, andBrown hyena#DescriptionStriped hyena skull. Note the disproportionately large carnassials and premolars adapted for bone consumptionAardwolf skull. Note the greatly reduced molars and carnassials, rendered redundant from insectivoryHyenas have relatively short torsos and are fairly massive and wolf-like in build, but have lower hind quarters, high withers and their backs slope noticeably downward toward their croups. The forelegs are high, while the hind legs are very short and their necks are thick andshort. Their skulls superficially resemble those of large canids, but are much larger and heavier, with shorter facial portions. Hyenas aredigitigrade, with the fore and hind paws having four digits each and sporting bulging pawpads.[15]Like canids, hyenas have short, blunt, non-retractable claws.[16]Theirpelageis sparse and coarse with poorly developed or absent underfur. Most species have a rich maneof long hair running from the withers or from the head.[15]With the exception of the spotted hyena, hyaenids have striped coats, which they likely inherited from their viverrid ancestors.[7]Their ears are large and have simple basal ridges and no marginal bursa.[16]Theirvertebral column, including thecervical regionare of limited mobility. Hyenas have nobaculum.[17]Hyenas have an additional pair of ribs than canids, and their tongues are rough like those of felids and viverrids.[18]Males in most hyena species are larger than females,[19]though the spotted hyena is exceptional, as it is the female of the species that outweighs and dominates the male. Also, unlike other hyenas, thefemale spotted hyena's external genitaliaclosely resembles that of the male.[20]Theirdentitionis similar to that of theFelidae, but is more specialised for consuming coarse food and crushing bones. Thecarnassials, especially the upper, are very powerful and are shifted far back to the point of exertion of peak pressure on the jaws. The other teeth, save for the underdeveloped uppermolars, are powerful, with broad bases and cutting edges. Thecaninesare short, but thick and robust.[17]Labiolingually, theirmandiblesare much stronger at the canine teeth than in canids, reflecting the fact that hyenas crack bones with both their anterior dentition and premolars, unlike canids, which do so with their post-carnassial molars.[21]The strength of their jaws is such that both striped and spotted hyenas have been recorded to kill dogs with a single bite to the neck without breaking the skin.[22][23]The spotted hyena is renowned for its strong bite proportional to its size, but a number of other animals (including theTasmanian devil) are proportionately stronger.[24][25]The aardwolf has greatly reduced cheek teeth, sometimes absent in the adult, butotherwise has the same dentition as the other three species.[26]Thedental formulafor all hyena species is:3.1.4.13.1.3.1Hyenas lackperinealscent glands, but have a large pouch of naked skin located at the anal opening. Large anal glands open into it from above theanus. Severalsebaceous glandsare present between the openings of the anal glands and above them.[16]These glands produce a white, creamy secretion the hyenas paste onto grass stalks. The odour ofthis secretionis very strong, smelling of boiling cheapsoapor burning, and can be detected by humans several metres downwind.[27]The secretions are primarily used forterritorial marking, though both the aardwolf[7]and the striped hyena[28]willspraythem when attacked.BehaviourSee also:Spotted hyena#Behaviour,Brown hyena#Behavior,Striped hyena#Behavior, andAardwolf#BehaviorSpotted hyena cubs at their denBrown hyena cub standing on a path of stonesHyenas groom themselves often like felids and viverrids, and their way oflicking their genitalsis very cat-like (sitting on the lower back, legs spread with one leg pointing vertically upward). However, unlike other feliforms, they do not"wash" their faces. They defecate in the same manner as other Carnivora, though they neverraise their legs as canids do when urinating, as urination serves no territorial function for them. Instead, hyenasmark their territoriesusing their anal glands, a trait found also inviverridsandmustelids, but not canids andfelids.[29]When attacked by lions or dogs, striped[30]and brown hyenas[31]willfeign death, though the spotted hyena will defend itself ferociously.[23]The spotted hyena is very vocal, producing a number of different sounds consisting of whoops, grunts, groans, lows, giggles, yells, growls, laughs and whines.[29]The striped hyena is comparatively silent, its vocalisations being limited to a chattering laugh and howling.[32]Matingbetween hyenas involves a number of short copulations with brief intervals, unlike canids, who generallyengage in a single, drawn out copulation.[29]Spotted hyena cubs are next