Equus Temporal range: 5.33–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N Earliest Pliocene to recent[1]
Clockwise (from top left): plains zebra (E. quagga), domestic horse (E. f. caballus), onager (E. hemionus)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	Equidae
Subtribe:	Equina
Genus:	Equus Linnaeus, 1758
Type species
Equus caballus [2] Linnaeus, 1758
Extant species
E. africanus (African wild ass) E. caballus (domestic horse) E. ferus (wild horse) E. grevyi (Grévy's zebra) E. hemionus (onager) E. kiang (kiang) E. quagga (plains zebra) E. zebra (mountain zebra)

Equus (/ˈɛkwəs, ˈiːkwəs/)^[3] is a genus of mammals in the family Equidae, which includes horses, asses, and zebras. Within the Equidae, Equus is the only recognized extant genus, comprising seven living species. Like Equidae more broadly, Equus has numerous extinct species known only from fossils. The genus originated in North America and dispersed into the Old World and South America during the Early and Middle Pleistocene. Equines are odd-toed ungulates with slender legs, long heads, relatively long necks, manes (erect in most subspecies), and long tails. All species are herbivorous, and mostly grazers, with simpler digestive systems than ruminants but able to subsist on lower-quality vegetation.

While the domestic horse and donkey (along with their feral descendants) exist worldwide, wild equine populations are limited to Africa and Asia. Wild equine social systems are in two forms; a harem system with tight-knit groups consisting of one adult male or stallion/jackass, several females or mares/jennets, and their young or foals; and a territorial system where males establish territories with resources that attract females, which associate very fluidly. In both systems, females take care of their offspring, but males may play a role as well. Equines communicate with each other both visually and vocally. Human activities have threatened wild equine populations.

The word equus is Latin for "horse"^[4] and is cognate with the Greek ἵππος (hippos, "horse")^[5] and Mycenaean Greek i-qo /ikkʷos/, the earliest attested variant of the Greek word, written in Linear B syllabic script.^[6] Compare the alternative development of the Proto-Greek labiovelar in Ionic ἴκκος (ikkos).^[5][7]

Equus Zebras E. zebra E. quagga E. quagga chapmani †E. quagga quagga E. grevyi Wild asses E. kiang E. hemionus onager E. hemionus kulan Donkeys E. africanus africanus E. africanus somaliensis Horses E. caballus †E. ferus ferus E. ferus przewalskii

Cladogram of Equus after Vilstrup et al. (2013).[8]

The genus Equus was first described by Carl Linnaeus in 1758. It is the only recognized extant genus in the family Equidae.^[9] The first equids were small, dog-sized mammals (e.g. Eohippus) adapted for browsing on shrubs during the Eocene, around 54 million years ago (Mya). These animals had three toes on the hind feet and four on the front feet with small hooves in place of claws, but also had soft pads.^[10] Equids developed into larger, three-toed animals (e.g. Mesohippus) during the Oligocene and Miocene.^[9][10] From there, the side toes became progressively smaller through the Pleistocene until the emergence of the single-toed Equus.^[11]

The genus Equus, which includes all extant equines, is believed to have evolved from Dinohippus, via the intermediate form Plesippus. One of the oldest species is Equus simplicidens, described as zebra-like with a donkey-like head shape. The oldest material to date was found in Idaho, USA. The genus appears to have spread quickly into the Old World, with the similarly aged E. livenzovensis documented from western Europe and Russia.^[11] Molecular phylogenies indicate that the most recent common ancestor of all modern equines (members of the genus Equus) lived ~5.6 (3.9-7.8) Mya. Direct paleogenomic sequencing of a 700,000-year-old middle Pleistocene horse metapodial bone from Canada implies a more recent 4.07 Mya for the most recent common ancestor within the range of 4.0 to 4.5 Mya.^[12]

Mitochondrial evidence supports the division of Equus species into noncaballoid (which includes zebras and asses) and caballoids or "true horses" (which includes E. caballus and E. ferus przewalskii, alternatively E. przewalskii).^[8][13] Of the extant equine species, the lineage of the asses may have diverged first,^{[9][contradictory]} possibly as soon as Equus reached the Old World.^[13] Zebras appear to be monophyletic and differentiated in Africa, where they are endemic.^[8] Members of the subgenus Sussemionus were abundant during the Early and Middle Pleistocene of North America and Afro-Eurasia,^[14] but only a single species, Equus ovodovi survived into the Late Pleistocene and Holocene in south Siberia and China, with the youngest remains from China dating to around 3500 BP (1500 BC), during the Shang dynasty.^[15][16] Genetic data from E. ovodovi has placed the Sussemionus lineage as closer to zebras and asses than to caballine horses.^[16]

Molecular dating indicates the caballoid lineage diverged from the noncaballoids 4 Mya.^[8] Genetic results suggest that all North American fossils of caballine equines, as well as South American fossils traditionally placed in the subgenus E. (Amerhippus), belong to E. ferus.^[17] Remains attributed to a variety of species and lumped together as New World stilt-legged horses (including E. francisci, E. tau, and E. quinni) probably all belong to a second species that was endemic to North America.^[18] This was confirmed in a genetic study done in 2017, which subsumed all the specimens into the species E. francisci which was placed outside all extant horse species in the new genus Haringtonhippus^[19], although its placement as a separate genus was subsequently questioned.^[20] A separate genus of horse, Hippidion existed in South America.^[21] The possible causes of the extinction of horses in the Americas (about 12,000 years ago) have been a matter of debate. Hypotheses include climatic change and overexploitation by newly arrived humans.^[22][23] Horses only returned to the American mainland with the arrival of the conquistadores in 1519.^[24]

Subgenus	Image	Scientific name	Common name	Distribution
Equus		Equus ferus przewalskii / E. przewalskii and Equus caballus	(Przewalski's horse and domesticated horse)	Eurasia
Asinus		Equus africanus	African wild ass (includes domesticated donkey)	Horn of Africa, in Eritrea, Ethiopia and Somalia
		Equus hemionus	Onager, hemione, or Asiatic wild ass	Iran, Pakistan, India, and Mongolia, including in Central Asian hot and cold deserts of Kazakhstan, Uzbekistan, Turkmenistan, and China
		Equus kiang	Kiang	Tibetan Plateau
Hippotigris		Equus grevyi	Grévy's zebra	Kenya and Ethiopia
		Equus quagga	Plains zebra	south of Ethiopia through East Africa to as far south as Botswana and eastern South Africa
		Equus zebra	Mountain zebra	south-western Angola, Namibia and South Africa.

Many extinct prehistoric species of Equus have been described. The validity of some of these species is questionable and a matter of debate. For example, Equus niobrarensis is likely synonymous with Equus scotti, while Equus alaskae is most likely the same species as Equus lambei, which itself may be a North American form of the living Equus przewalskii.

DNA studies on American horse remains found frozen into permafrost have shown that several of the supposed American species, and the European Equus ferus, are actually one highly-variable widespread species. ,^[25] as if the evolutionary process of speciation was persistently being frustrated by large herds of the horses moving long distances and mixing, carrying their genes about with them.

• American species
  • Equus alaskae - Alaskan horse
  • Equus conversidens - Mexican horse
  • Equus fraternus
  • Equus francisi - now placed in a separate genus, Haringtonhippus^[26]
  • Equus giganteus - Giant horse
  • Equus lambei - Yukon horse
  • Equus neogeus - often placed in a separate genus, Amerhippus
  • Equus niobrarensis - Niobrara horse
  • Equus occidentalis - Western horse
  • Equus scotti - Scott's horse
  • Equus semiplicatus
  • Equus simplicidens - Hagerman horse

• Eurasian species
  • Equus altidens^{[citation needed]}
  • Equus dalianensis^{[citation needed]}
  • Equus lenensis - Siberian horse
  • Equus latipes^{[citation needed]}
  • Equus namadicus
  • Equus ovodovi^[27] - Ovodov's horse
  • Equus yunnanensis - Yunnan horse
  • Equus stenonis - Stenon zebra
  • Equus sivalensis - Indian horse

• African species
  • Equus algericus^{[citation needed]}
  • Equus capensis - Giant zebra
  • Equus mauritanicus - Saharan zebra

• Equus caballus - Domestic horse
• Equus asinus - Domestic donkey

Equine species can crossbreed with each other. The most common hybrid is the mule, a cross between a male donkey and a female horse. With rare exceptions, these hybrids are sterile and cannot reproduce.^[28] A related hybrid, a hinny, is a cross between a male horse and a female donkey.^[29] Other hybrids include the zorse, a cross between a zebra and a horse^[30] and a zonkey or zedonk, a hybrid of a zebra and a donkey.^[31] In areas where Grévy's zebras are sympatric with plains zebras, fertile hybrids do occur.^[32] Ancient DNA identifies the Bronze Age kunga as a cross between the Syrian wild ass and the donkey.

Equines have significant differences in size, though all are characterized by long heads and necks. Their slender legs support their weight on one digit (which evolved from the middle digits). Grévy's zebra is the largest wild species, standing up to 13.2 hands (54 inches, 137 cm) and weighing up to 405 kg (890 lb).^[33] Domesticated horses have a wider range of sizes. Heavy or draft horses are usually at least 16 hands (64 inches, 163 cm) high and can be as tall as 18 hands (72 inches, 183 cm) and weigh from about 700 to 1,000 kg (1,500 to 2,200 lb).^[34] Some miniature horses are no taller than 30 inches (76 cm) in adulthood.^[35] Sexual dimorphism is limited in equines. The penis of the male is vascular and lacks a bone (baculum). Equines are adapted for running and traveling over long distances. Their dentition is adapted for grazing; they have large incisors that clip grass blades and highly crowned, ridged molars well suited for grinding. Males have spade-shaped canines ("tushes"), which can be used as weapons in fighting. Equines have fairly good senses, particularly their eyesight. Their moderately long, erect ears are movable and can locate the source of a sound.^[9][36]

A dun-colored coat with primitive markings that include a dorsal stripe and often leg striping and transverse shoulder stripes reflect the wildtype coat and are observed in most wild extant equine species.^[37] Only the mountain zebra lacks a dorsal stripe.^[38] In domestic horses, dun color and primitive markings exist in some animals across many breeds.^[39] The purpose of the bold black-and-white striping of zebras has been a subject of debate among biologists for over a century, but 2014 evidence supports the theory that they are a form of protection from biting flies. These insects appear to be less attracted to striped coats, and compared to other wild equines, zebras live in areas with the highest fly activity.^[40] With the exception of the domestic horses, which have long manes that lay over the neck and long tail hair growing from the top of the tailhead or dock, most equines have erect manes and long tails ending in a tuft of hair.^[36] The coats of some equine species undergo shedding in certain parts of their range and are thick in the winter.^[40]

Zdroj:https://en.wikipedia.org?pojem=Equus_(subgenus)
Text je dostupný za podmienok Creative Commons Attribution/Share-Alike License 3.0 Unported; prípadne za ďalších podmienok. Podrobnejšie informácie nájdete na stránke Podmienky použitia.

---