Equus (genus)

Equus Fossil range: 1.8–0 Ma PreЄ Є O S D C P T J K Pg N ↓ Early Pleistocene to Recent
Plains Zebras
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Perissodactyla Family: Equidae Gray, 1821 Genus: Equus Linnaeus, 1758
Species
E. asinus - Donkey E. africanus - African Wild Ass E. caballus - Domestic Horse E. ferus - Wild Horse E. grevyi - Grevy's Zebra E. hemionus - Onager E. kiang - Kiang E. quagga - Plains Zebra E. zebra - Mountain Zebra

Look up Equus, equus, or equine in Wiktionary, the free dictionary.

Equus is a genus of animals in the family Equidae that includes horses, donkeys, and zebras. Within Equidae, Equus is the only extant genus. Like Equidae more broadly, Equus has numerous extinct species known only from fossils. This article deals primarily with the extant species.

The term equine refers to any member of this genus, including any horse.

Classification

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Family Equidae (in addition to Equus, the family includes approximately 35 other genera, all extinct)

• Genus Equus
  • Subgenus Equus
    • Equus ferus Wild Horse^[1][2]
      • †Equus ferus ferus Tarpan
      • Equus ferus przewalskii Przewalski's Horse or Mongolian Wild Horse
      • Equus ferus caballus Domestic horse
  • Subgenus Asinus
    • Equus africanus African Wild Ass^[2][3]
      • Equus africanus africanus Nubian Wild Ass
      • †Equus africanus atlanticus Atlas Wild Ass
      • Equus africanus somalicus Somali Wild Ass
      • Equus africanus asinus Donkey or Burro
    • †Equus hydruntinus European Ass
    • Equus hemionus Onager or Asiatic Ass
      • Equus hemionus hemionus Mongolian Wild Ass
      • †Equus hemionus hemippus Syrian Wild Ass
      • Equus hemionus luteus Dziggetai or Gobi Kulan
      • Equus hemionus kulan Turkmenian Kulan
      • Equus hemionus khur Indian Wild Ass or Khur
      • Equus hemionus onager Persian Onager
    • Equus kiang Kiang
      • Equus kiang kiang Western Kiang
      • Equus kiang holdereri Eastern Kiang
      • Equus kiang polyodon Southern Kiang
      • Equus kiang chu Northern Kiang
    • †Equus cumminsii Cummin’s Ass
    • †Equus calobatus Stilt-legged Onager
    • †Equus tau Pygmy Onager
    • †Equus lambei Yukon Wild Ass (or Yukon Wild Horse)
  • Subgenus Dolichohippus
    • Equus grevyi Grevy's Zebra
  • Subgenus Hippotigris
    • Equus quagga Plains Zebra
      • †Equus quagga quagga Quagga
      • Equus quagga burchellii Burchell's Zebra
      • Equus quagga boehmi Grant's Zebra
      • Equus quagga borensis Selous' zebra
      • Equus quagga chapmani Chapman's Zebra
      • Equus quagga crawshayi Crawshay's Zebra
    • Equus zebra Mountain Zebra
      • Equus zebra zebra Cape Mountain Zebra
      • Equus zebra hartmannae Hartmann's Mountain Zebra
  • Subgenus †Amerhippus
    • †Equus scotti
    • †Equus niobrarensis
    • †Equus conversidens Mexican Horse
  • Subgenus †Parastylidequus
    • †Equus parastylidens Mooser’s Horse
  • incertae sedis
    • †Equus simplicidens Hagerman Horse (perhaps closest to Dolichohippus^[4])
    • †Equus occidentalis
    • †Equus complicatus
    • †Equus fraternus
    • †Equus excelsus (subgenus Equus?)
    • †Equus giganteus group
      • †Equus giganteus
      • †Equus pacificus
      • †Equus pectinatus
      • †Equus crinidens

Przewalski's horse, the only remaining type of "wild" horse that has never been domesticated	A domesticated horse	A donkey	An onager, one type of wild ass
A pair of kiangs	Quagga (now extinct)	Plains zebra	Grévy's zebra

Characteristics

Equines are medium to large mammals, with long heads, and necks with a mane. Their legs are slender and end in a single, unguligrade toe, protected by a horny hoof. They have long, slender, tails, either ending in a tuft, or entirely covered in flowing hair. They are adapted to generally open terrain, from plains and savannas, to mountains or deserts.

The range of equine monocular vision. Shaded areas represent blind spots.

The pinnae ("ears") of equines are mobile, enabling them to easily localise the origin of sounds. They have two-color, or dichromatic vision. Their eyes are set back far on the head, giving them a wide angle of view, without entirely losing binocular vision. Equines also have a vomeronasal organ, that allows males to use the flehmen, or 'lip-curling' response to assess the sexual state of potential mates.

Equines are herbivores, and feed predominantly on tough, fibrous food, such as grasses and sedges. When in need, they will also eat other vegetable matter, such as leaves, fruits, or bark, but are normally grazers, not browsers. Unlike ruminants, with their complex stomachs, equines break down cellulose in the "hindgut" or cecum, a part of the colon. Their dentition is almost complete, with cutting incisors to crop food, and grinding molars set well back behind a diastema. The dental formula for equines is:

A feral horse herd in the western United States

Eqines are social animals, living in herds or bands. Horses, along with Plains and Mountain Zebras, have permanent herds generally consisting of a single male and a band of females, with the remaining males forming small "bachelor" herds. The remaining species have temporary herds, lasting only a few months, which may be either single-sexed or mixed. In either case, there are clear hierarchies established amongst the individuals, usually with a dominant female controlling access to food and water resources and the lead male controlling mating opportunities.

Females, usually called mares in horses and zebras, or, in the case of asses and donkeys, jennys, usually bear a single foal, after a gestation period of approximately 11 months. Young equines are able to walk within an hour of birth, and are weaned after four to thirteen months (animals living in the wild naturally wean foals at a later date than those under domestication). Depending on species, living conditions and other factors, females in the wild may give birth every year or every other year.^[5][6]

Equines who are not in foal generally have a seasonal estrous cycle, from early spring into autumn. Most females enter an anestrus period during the winter and thus do not cycle in this period. The reproductive cycle is controlled by the photoperiod (length of the day), with estrus triggered when the days begin to lengthen. Anestrus prevents the female from conceiving in the winter months, as that would result in her foaling during the harshest part of the year, a time when it would be more difficult for the foal to survive.^[7] However, eqines who live near the equator, where there is less change in length of day from season to season, have no anestrus period, at least in theory.^[8] Further, for reasons that are not clear, about twenty percent of domestic mares in the Northern Hemisphere will cycle the year round.^[9]

Cross-breeds

Different species of Equus can crossbreed, though the ensuing offspring are usually infertile. Hybrids include:

a mule

• Mule, a cross between a male donkey and a female horse. Mules are the most common type of hybrid equine and are renowned for their toughness, surefootedness, and working ability.
• Hinny, a cross between a female donkey and a male horse. Considered a less desirable cross than a mule, generally smaller in size and not as hardy.
• Zeedonk or Zonkey, a cross between a donkey and a zebra.
• Zony, a zebra/pony cross.
• Zorse or zebrula, the offspring of a zebra stallion and a horse mare; the rarer reverse pairing is sometimes called a hebra.

Any equine with partial zebra ancestry is also called a zebroid.

See also

• Domestication of the horse

References

Sources

• Burke, et al. 2003. The systematic position of Equus hydruntinus, an extinct species of Pleistocene equid. Quaternary Research 59(3):459-469.
• Duncan, P. (ed.). 1992. Zebras, Asses, and Horses: an Action Plan for the Conservation of Wild Equids. IUCN/SSC Equid Specialist Group. IUCN, Gland, Switzerland.
• Equid Specialist Group 1996. Equus ferus. In: IUCN 2004. 2004 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 21 January 2006.
• Equid Specialist Group 1996. Equus ferus ssp. przewalskii. In: IUCN 2004. 2004 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 21 January 2006.
• Groves, C.P. & Bell, H.B. 2004. New investigations on the taxonomy of the zebras genus Equus, subgenus Hippotigris. Mammalian Biology. 69: 182-196.
• Higuchi et al. 1987. Mitochondrial DNA of the Extinct Quagga: Relatedness and Extent of Postmortem Change. Journal of Molecular Evolution 25:283-287.
• International Commission on Zoological Nomenclature. 2003. Opinion 2027 (Case 3010). Usage of 17 specific names based on wild species which are pre-dated by or contemporary with those based on domestic animals (Lepidoptera, Osteichthyes, Mammalia): conserved. Bull.Zool.Nomencl., 60:81-84.
• Moehlman, P.D. 2002. Equids. Zebras, Assess and Horses. Status Survey and Conservation Action Plan. IUCN/SSC Equid Specialist Group. IUCN, Gland, Switzerland. (http://www.iucn.org/themes/ssc/publications/actionplans.htm#Equids2002)
• Orlando, et al. 2006. Geographic distribution of an extinct equid (Equus hydruntinus : Mammalia, Equidae) revealed by morphological and genetical analyses of fossils. Molecular Ecology 15(8):2083-2093.

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