Wild horse

Evidence supports E. ferus as having evolved in North America about 1.1 - 1.2 million years ago. Many American fossil horse species such as Equus lambei and Equus neogeus were formerly considered distinct species, but genetic and morphological analysis supports them as being conspecific with E. ferus. Around 800,000 - 900,000 years ago, E. ferus migrated west to Eurasia and North Africa via the Bering Land Bridge, and south to South America via the Isthmus of Panama as part of the Great American Interchange. By the mid-late Pleistocene, it had an extremely large range across the Americas, Eurasia, and North Africa, across which it was abundant.[13][14][15][16]

By the latest Pleistocene or early Holocene, American populations had disappeared as part of the Quaternary extinction event, leaving only the Old World populations. It remained widespread there and was ultimately also domesticated around 3600 B.C., but wild populations continued to decline. The last completely wild populations of the tarpan went extinct in Eastern Europe and the southern parts of Russia around the late 19th century, and the Przewalski's horse of Central Asia became extinct in the wild in 1969. However, over the past few centuries feral horses have been introduced to all continents except Antarctica, and Przewalski's horses have been reintroduced to their former habitats in Mongolia.[13]

In general, wild horses are grazers that prefer to inhabit open areas, such as steppes and grasslands. They may have seasonal food preferences, as seen in the Przewalski's subspecies.[17] Horses may fall prey to native predators where they live, such as wolves,[18] cougars,[19] and spotted hyenas.[20]

E. ferus has had several subspecies, only three of which have survived into modern times:[21]

• The domestic horse (Equus ferus caballus).
• The tarpan or Eurasian wild horse (Equus ferus ferus); was once native to Europe and western Asia before it became effectively extinct in the late 19th century. The last specimen died in 1909 whilst in captivity in an estate in Poltava Governorate, Russian Empire.
• Przewalski's horse (Equus ferus przewalskii); also known as the Mongolian wild horse or takhi, it is native to Central Asia and the Gobi Desert.

The latter two are the only never-domesticated "wild" groups that survived into historic times. However, other subspecies of Equus ferus may have existed.[8]

In the Late Pleistocene epoch, there were several other subspecies of E.ferus which have all since gone extinct. The exact categorization of Equus' remains into species or subspecies is a complex matter and the subject of ongoing work.[22]

Equus ferus fossil from 9100 BC found near Odense, at the Zoological Museum in Copenhagen

Probable European wild horse coat colors[23]

The horse family Equidae and the genus Equus evolved in North America during the Pliocene, before the species migrated across Beringia into the Eastern Hemisphere.[24] Studies using ancient DNA, as well as DNA of recent individuals, suggest the presence of two equine species in Late Pleistocene North America, a caballine species, suggested to be conspecific with the wild horse,[25][26] and Haringtonhippus francisci, the "New World stilt-legged horse"; the latter has been taxonomically assigned to various names, and appears to be outside the grouping containing all extant equines.[27] In South America there appear to have been several species of equine, Equus (Amerhippus) neogeus, which had previously thought to represent 5 taxa due to morphological variability,[28] and several species of Hippidion, which also lie outside the group containing all living horses.[29] (It had previously been suggested to have been nested within Equus based on incomplete sequence data[30])

Currently, three subspecies that lived during recorded human history are recognized.[21] One subspecies is the widespread domestic horse (Equus ferus caballus),[21] as well as two wild subspecies: the recently extinct tarpan (E. f. ferus) and the endangered Przewalski's horse (E. f. przewalskii).[5][6][21]

Genetically, the pre-domestication horse, E. f. ferus, and the domesticated horse, E. f. caballus, form a single homogeneous group (clade) and are genetically indistinguishable from each other.[25][30][31][32] The genetic variation within this clade shows only a limited regional variation, with the notable exception of Przewalski's horse.[25][30][31][32] Przewalski's horse has several unique genetic differences that distinguish it from the other subspecies, including 66 instead of 64 chromosomes,[5][33] unique Y-chromosome gene haplotypes,[34] and unique mtDNA haplotypes.[35][36]

Besides genetic differences, osteological evidence from across the Eurasian wild horse range, based on cranial and metacarpal differences, indicates the presence of only two subspecies in postglacial times, the tarpan and Przewalski's horse.[8][37]

Semi-feral Exmoor ponies. Though popularly called "wild" horses, feral and semi-feral horses are not truly wild; since their ancestors were domesticated.

Horses that live in an untamed state but have ancestors that have been domesticated are not truly "wild" horses; they are feral horses.[55] For instance, when the Spanish reintroduced the horse to the Americas, beginning in the late 15th century,[56] some horses escaped, forming feral herds; the best-known being the mustang.[57] Similarly, the brumby descended from horses strayed or let loose in Australia by English settlers.[58] Isolated populations of feral horses occur in a number of places, including Bosnia, Croatia, New Zealand, Portugal, Scotland and a number of barrier islands along the Atlantic coast of North America from Sable Island off Nova Scotia, to Cumberland Island, off the coast of Georgia.[59] Even though these are often referred to as "wild" horses, they are not truly "wild" in the biological sense of having no domesticated ancestors.[55]

In 1995, British and French explorers discovered a new population of horses in the Riwoche Valley of Tibet, unknown to the rest of the world, but apparently used by the local Khamba people.[60] It was speculated that the Riwoche horse might be a relict population of wild horses,[61] but testing did not reveal genetic differences with domesticated horses,[62] which is in line with news reports indicating that they are used as pack and riding animals by the local villagers.[63] These horses only stand 12 hands (48 inches, 122 cm) tall and are said to resemble the images known as "horse no 2" depicted in cave paintings alongside images of Przewalski's horse.[62]

• Horse behavior
• Evolution of the Horse