The tarpan or Eurasian wild horse, Equus caballus ferus or E. ferus, is an extinct wild horse related to the common domestic horse (E. caballus caballus) that roamed from southern France and Spain to central Russia, in steppe and forest environments. They stood approximately 140-145 centimetres (55-57 inches) tall at the shoulders, had a partly falling mane, a mouse-grey (grullo) coat color, dark legs and primitive markings, including a dorsal stripe and shoulder stripes. Smith (1866) described tarpans as mule-like, and making stronger sounds than domestic horses (Mass 2000-2013; Wikipedia 2014).
The name “tarpan” is Turkic for “wild horse,” and is distinguished from the feral horse (called Takja or Muzin). In modern use, the term has been loosely used to refer to the pre-domesticated ancestor of the modern horse, Equus ferus; to the pre-domestic subspecies believed to have lived into the historic era, Equus caballus ferus; and nonspecifically to all European primitive or "wild" horses in general (Wikipedia 2014). Other common synonyms for tarpans are Equus ferus ferus and E. c. gmelini.
Beginning in the 1930s, several attempts were made to genetically reconstruct horses that looked like tarpans through selective breeding, called “breeding back” by advocates. The breeds that resulted include the Heck horse, the Hegardt or Stroebel's horse, and a derivation of the Konik breed, all of which have a primitive appearance, particularly in having the grullo coat color. Some of these horses are now commercially promoted as "tarpans," although researchers discourage this use of the word, which they believe should only applied to the ancient E. caballus ferus (Castelli 2012).
Tarpans became extinct starting in Southern Europe, as a result of human hunting and a range decreasing in size with the increasing civilization of the Eurasian continent. They were persecuted because they caused damage to hay storages, often took domestic mares from pastures and because interbreeding with wild horses was an economic loss for farmers since the foals of such matings were intractable. Tarpans survived the longest in the southern parts of the Russian steppe. By 1880, when most “Tarpans” may have become hybrids, wild horses were very rare. In 1879 the last scientifically confirmed individual was killed. After that, only dubious sightings were documented. As the tarpan horse died out in the wild between 1875 and 1890, the last considered-wild mare was accidentally killed during an attempt at capture. The last captive individual believed to be a tarpan died in 1909 in a Russian zoo (Wikipedia 2014).
All extant wild horses belong to the subspecies Equus ferus przewalskii. The first visual account of Przewalski's-type wild horses date from more than 20,000 years ago. Rock engravings, paintings, and decorated tools dating from the late Gravetian to the late Magdalenian (20,000-9,000 BC), were discovered in caves in Italy, southern France, and northern Spain; 610 of these were horse figures (Leroi-Gourhan 1971). Many cave drawings in France show horses that look like Przewalskis Horse (Mohr 1971). In prehistoric times, the species probably roamed widely over the steppes of Central Asia, China, and Europe (Ryder 1990), although wild horses in Europe could have been Tarpans (Equus ferus gmelini).
The first written accounts of Przewalski's Horse originate from Tibet, recorded by the monk Bodowa, who lived around 900 AD. In the "Secret History of the Mongols", there is also a reference to wild horses that crossed the path of Chinggis Khaan during his campaign against Tangut in 1226, causing his horse to rear and throw him to the ground (Bokonyi 1974). That the wild horse was a prestigious gift, denoting its rarity or that it was difficult to catch, is shown by the presentation of a Przewalskis Horse to the emperor of Manchuria by Chechen-Khansoloj-Chalkaskyden, an important Mongolian, circa 1630 (Zevegmid and Dawaa 1973). In a Manchurian dictionary of 1771, Przewalskis Horse is mentioned as "a wild horse from the steppe" (Dovchin 1961).
Przewalski's Horse was not described in Linnaeus's "Systema Naturae" (1758) and remained largely unknown in the West until first mentioned by John Bell, a Scottish doctor who travelled in the service of Tsar Peter the Great in 1719-1722 (Mohr 1971). His account of the expedition, "A Journey from St Petersburg to Peking", was published in 1763. Bell and subsequent observers all located horses known at that time within the area of 85-97E and 43-50N (Chinese-Mongolian border). Wild horses were reported again from what is now China by Colonel Nikolai Mikailovich Przewalski, an eminent explorer, at the end of the 19th century. He made several expeditions by order of Tsar Alexander the Second of Russia to Central Asia, aiming to reach Tibet. While returning from his second expedition in Central Asia, he was presented with the skull and hide of a horse shot about 80 km north of Gutschen (in present-day China, around 40N, 90E). The remains were examined at the Zoological Museum of the Academy of Science in St Petersburg by I.S. Poliakov, who concluded that they were a wild horse, which he gave the official name Equus przewalskii (Poliakov 1881). Further reports came from the brothers Grigory and Michael Grum-Grzhimailo, who travelled through western China from 1889-1890. In 1889, they discovered a group in the Gashun area and shot four horses: three stallions and a mare. The four hides and the skulls of the three stallions, together with an incomplete skeleton, were sent back to the Zoological Museum in St. Petersburg. They were able to observe the horses from a short distance and gave the following account: "Wild horses keep in bands of no more than ten, each herd having a dominant stallion. There are other males, too, but they are young and, judging by the hide of the two-year old colt that we killed, the dominant male treats them very cruelly. In fact, the hide showed traces of numerous bites" (Grum-Grzhimailo 1982).
After the 'rediscovery' of the Przewalski's Horse for western science, western zoos and wild animal parks became interested in this species for their collections. Several long expeditions were mounted to catch animals. Some expeditions came back empty-handed and some had only seen a glimpse of wild Przewalski's Horses. It proved difficult to catch adult horses, because they were too shy and fast. Capture of foals was considered the best option as when chased they would become exhausted and lag behind their group (Hagenbeck 1909), although this may have involved killing adult harem members in the process (Bouman and Bouman 1994). Four expeditions that managed to catch live foals took place between 1897 and 1902. Fifty-three of these foals reached the west alive. Between the 1930s and the 1940s only a few Przewalski's Horses were caught and most died. One mare (Orlitza III) was caught as a foal in 1947 and was the last wild mare to contribute to the Przewalski's Horse gene pool in Europe. In Mongolia several Przewalski's Horses were captured and crossbred with domestic horses by the Mongolian War Ministry (Bouman and Bouman 1994).
In subsequent years the captive population increased, and since the 1990s reintroduction efforts have started in Mongolia and China; Mongolia was the first country where truly wild reintroduced populations existed within the historic range. Reintroductions in Mongolia began in the Great Gobi B Strictly Protected Area in the Dzungarian Basin (9,000 km2) and Hustai National Park in Mongol Daguur Steppe (570 km2) in 1994 (King and Gurnell 2005). A third reintroduction site, Khomintal, (2,500 km2), in the Great Lakes Depression, was established in 2004, as a buffer zone to the Khar Us Nuur National Park in Valley of the Lakes (C. Feh pers. comm.). Releases began in the Kalamaili Nature Reserve (17,330 km2), Xinjiang Province, China in 2001 and in the Dunhuang Xihu National Nature Reserve (6,600 km2), Gansu Province, China in 2010 (Liu et al. 2014), although almost all of these animals are corralled and fed in winter (Qing Cao pers. comm.). Further reintroduction sites are planned in Kazakhstan and Russia (W. Zimmerman pers. comm.).
Habitat and Ecology
Przewalski's Horse formerly inhabited steppe and semi-desert habitats. As most of this range became converted to agriculture, degraded or was increasingly occupied by livestock, the species became restricted to semi-desert habitats with limited water resources (Van Dierendonck and de Vries 1996). Lowland steppe vegetation was preferentially selected by horses at Hustai National Park and seasonal movements were affected by the availability of the most nutritious vegetation (King and Gurnell 2005). The breadth of species consumed and dietary overlap with other ungulates increased in winter, compared to summer, although forage did not appear to be limiting (Siestes et al. 2009). In the Gobi the Przewalski's Horses also selected for the most productive plant communities (Kaczensky et al. 2008).
The species is not territorial; home range sizes in Hustai NP varied from 120 to 2,400 ha and, in addition to grazing sites, included a permanent water source, patches of forest, and ridges with rocky outcrops (King and Gurnell 2005). In Great Gobi B SPA, home ranges of 150 to 825 km2 were reported (Kaczensky et al. 2008).
Because the historic range is not precisely known, there has been much debate about the areas in which Przewalski's Horses were last seen: was it merely a refuge or was it representative of the typical/preferred habitat? The Mongolia Takhi Strategy and Plan Work Group (MTSPWG 1993) concluded that the historic range may have been wider but that the Dzungarian Gobi, where they were last seen, was not a marginal site to which the species retreated as they had access to the rich habitats of mountain valleys and more oases than in the present time (Sokolov et al. 1990), due to these areas being occupied by herders and their livestock. Although grass and water are more available in other parts of Mongolia, these areas often have harsher winters. Subsequently, others provided evidence that the Gobi is an edge habitat, rather than an optimal habitat for Przewalski's Horses (Kaczensky et al. 2008), and certainly also subject to severe winters with devastating consequences for the population (Kaczensky et al. 2011). Studies of feral horses have shown that they are able to live and reproduce in semi-desert habitats but their survival and reproductive success is clearly sub-optimal compared to feral horses on more mesic grassland (Berger 1986). Van Dierendonck and de Vries (1996) suggest that the wild horse is primarily a steppe herbivore that can survive under arid conditions when there is access to waterholes.
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2011Endangered (EN)
- 2008Critically Endangered (CR)
- 1996Extinct in the Wild (EW)
Of the 53 animals recorded in the Studbook as having been brought into zoological collections in the west, fewer than 25% contributed any genes to the current living population. All Przewalski's Horses alive today are descended from 12 wild-caught individuals, and as many as four domestic horse founders described below, which were the nucleus of the captive breeding programme (Bowling and Ryder 1987). Eleven of the wild-caught individuals were brought into captivity between 1899 and 1902 with the last of them dying in 1939. The twelfth founder (Orlitza III) was captured as a foal in 1947. A thirteenth founder was born in 1906 in Halle (Germany) to a wild-caught stallion and a domestic Mongolian mare, and a fourteenth founder is a female born in Askania Nova (Ukraine) to a Przewalski's Horse stallion and a domestic female of a Tarpan type. In spite of the introgression of domestic horse blood, the current population is genetically very close to the original wild horses (Bowling et al. 2003).
As of 1 January 2014, the number of living captive and reintroduced animals in the International Studbook was 1,988 (883 males.1101 females.4 sex unknown). In addition to animals held in captivity and those already re-introduced, there have been a number of animals released into very large enclosures (reserves): Le Villaret, France (~4 km2; 2013: 18.18), Askania Nova, Ukraine (30 km2; 2014: 24.46), and Hortobgy National Park, Hungary (700 km2; 2014: 125.129). Bukhara, Uzbekistan (51 km2) had 19.17.1 horses in 2008 (W. Zimmermann pers. comm.) and 24 horses by 2013 (O. Pereladova pers. comm.). The unfenced Chernobyl exclusion zone (2,600 km2) in Ukraine contained 32.36 horses in 2008 (W. Zimmermann pers. comm.), and approximately 60 horses in early 2014 (T. Mousseau pers. comm.).
There are now approximately 387 free-ranging reintroduced and native-born Przewalski's Horses in Mongolia at three reintroduction sites (Zimmerman 2014). Between 1992 and 2004, 90 captive-born horses were transported to the Takhin Tal acclimatization site, from where they were released into the Great Gobi B Strictly Protected Area (SPA) (ITG International Takhi Group, Zimmermann 2008). A further three males were translocated from Hustai National Park to Takhin Tal in 2007 (Zimmermann 2008). In 2008 there were approximately 111 free-ranging horses in this subpopulation (Zimmerman 2008, Kaczensky and Walzer 2004). By December 2009 there were 138 individuals, but due to an extremely harsh winter (dzud) in 2009/2010 the population suffered extreme mortality: in April 2010 only 49 individuals remained (Kaczensky et al. 2011). By 2012 the population had increased to 71. By the end of 2013 there were 90 horses forming six harems and several bachelor groups. Sixteen foals were born in 2013; three of these foals died, and one adult male disappeared and is presumed dead (P. Kaczensky pers. comm.).
From 1992 to 2000, 84 horses were brought to Hustai National Park (NP) by the Foundation for the Preservation and Protection of the Przewalski Horse and Mongolian Association for Conservation of Nature and the Environment (MACNE) from reserves in Europe (King and Gurnell 2005). As of the middle of 2012 this population had approximately 275 individuals (Zimmerman 2014). By the end of 2013, there were 297 horses, of which 228 were members of 29 harems and the rest were bachelors. Sixty-four foals were born in 2013, with a 61% survival rate by years end: 25 foals, four yearlings, and seven adults died during 2013 (Usukhjargal 2013).
A third reintroduction site was started in 2004 at Seriin Nuruu in the Khomiin Tal buffer zone of the Khar Us Nuur National Park in western Mongolia (Association pour le Cheval de Przewalski: TAKH). Twenty-two individuals consisting of four pre-established families and one male bachelor group were brought from the reserve at Le Villaret, France between 2004 and 2005, and four horses from Prague Zoo were added in 2011 (Association TAKH, Zimmermann 2008). By the end of 2013 this population had 40 horses; eight foals were born in 2013 and 3threeof these died, as did two adult stallions (C. Feh pers. comm.).
In previous assessments of the reintroduced population in Mongolia, mature individuals were considered to be those that were born in the wild and five years of age. Individuals born in captivity were not counted as mature until they had reproduced in the wild, and produced offspring that were at least five years old (so potentially reproductive). The population grew from 55 mature individuals in the wild in 2006 (52: 26.26 in Hustai NP, 3: 1.2 in Gobi NP), to 79 in 2007 (Hustai NP: 33.35; Great Gobi B SPA: 3.8), 104 in 2008 (Hustai NP: 39.51; Great Gobi B SPA: 7.7), and 151 in 2009 (Hustai NP: 52.66; Great Gobi B SPA: 15.18). The winter of 2009/2010 was very severe and there was high mortality of Przewalski's Horses, particularly in the Gobi. In 2010, Hustai NP's mature population was 117 (53.64) and Great Gobi B SPA's number of mature individuals was reduced to 17 (8.9), giving a total population of 134 mature individuals. In 2012 the criterion for captive-born horses to be included as mature individuals was tightened to require them to have produced reproductively viable offspring (i.e., the reintroduced animal reproduced, and at least one of its offspring also reproduced); mature (5 years old) wild-born individuals continued to be included. Under these criteria, there were 178 mature individuals in the wild at the end of 2012: 153 (65.88) in Hustai NP, 23 (5.18) in Great Gobi B SPA, and 2 (1.1) in Khomiin Tal. Hence for a period of seven years, the mature population of Przewalski's Horses in Mongolia has been more than 50 individuals. Although this means that the Przewalski's Horse qualifies as Endangered (EN) it should be borne in mind that most of these individuals are from one reintroduction site and climatic perturbations like the extremely harsh winter in 2009/2010 can have very negative effects on small populations (Kaczensky et al. 2011). In China, the Wild Horse Breeding Centre (WHBC) in Xinjiang Province has established a large captive population of Przewalski's Horses (Liu et al. 2014). Since 2001 horses have been released into the nearby Kalamaili Nature Reserve (KNR), which had a population of 99 in 2012 and 121 in 2013. One harem group is roaming free on the Chinese side of the Dzungarian Gobi (Xinjiang); another 102 horses are roaming free during summer time but are returned to the acclimatization pen during the winter (Zimmermann et al. 2008; Qing Cao pers. comm.). The Gansu Endangered Species Research Center (GESRC) also has a captive breeding programme and has released at least seven horses into the Dunhuang Xihu National Nature Reserve (DXNNR) in 2010 and 2012 (Liu et al. 2014); all of these horses are fed in winter. A total of 59 foals have been born in the wild in China since 2009, with an estimated 19 individuals surviving in 2013 (Qing Cao pers. comm.). Until better data are available these animals are not known for sure to meet the criterion of mature individuals for a reintroduced species so have not been included in the species population size for this assessment.
For the reintroduced populations, small population size and limited spatial distribution is the primary threat, followed by potential hybridization with domestic horses and competition for resources with domestic horses and other livestock. Wherever Przewalski's Horses come into contact with domestic horses, there is the risk of hybridization and transmission of diseases. Recently, illegal mining in the protected areas is an additional threat to their viability. In Hustai NP it has been noted that overgrazing of the buffer-zone and continued pressure on the reserve are possible consequences of the enhanced economic activity in this area (Bouman 1998); however, the second phase of the project (1998-2003) paid much more attention to sustainable development of the buffer-zone. In the western section of the Great Gobi B SPA livestock grazing by nomads and military personnel continues, particularly in fall, winter and spring; however, the core zone is largely free from human influence all year round. Infectious diseases transmitted from domestic horses and their parasites, notably Babesia equi, B. caballi and strangles (infection by Streptococcus equi), are a major threat to small reintroduced populations originating from zoos (Roberts et al. 2005, King and Gurnell 2005). As was observed during 2009/2010, severe winters can result in significant mortality. While predation occurs naturally as for any wild ungulate, if excessive there could be impacts on this small population.
There is concern over loss of genetic diversity after being reduced to a very small population and maintained in captivity for several generations. Sixty per cent of the unique genes of the studbook population have been lost (Ryder 1994). Loss of founder genes is irretrievable and further losses must be minimized through close genetic management. Furthermore, inbreeding depression could become a population-wide concern as the population inevitably becomes increasingly inbred (Ballou 1994). However, correct management of the population can slow these losses significantly, as has been achieved since the organization of the regional captive-breeding programs. Fortunately, Przewalski's Horses have been shown to have both higher nuclear and mitochondrial nucleotide diversity than many domestic horse breeds in spite of the population bottlenecks they have experienced (Goto et al. 2011).
At the Endangered Wild Equid Workshop held in Ulaanbataar in 2010 the following threats were identified:Loss of population due to stochastic events (i.e. severe winter);
- Limited habitat and resources (pasture and water);
- Domestic horses (hybridization, disease, social stress);
- Lack of information, appreciation / awareness, lack of knowledge; and
- Exploitation of resources (i.e. mining).
Specific actions needed for each threat category were identified and described.
The following conservation actions are in place:
- An International Studbook was produced in 1959, followed in the 1970s by establishment of the North American Breeders Group, which developed into the Species Survival Plan for the Przewalski's Horse. The European Endangered Species Programme for this species was accepted in 1986. Many countries now cooperate in these programmes to minimize inbreeding and retain genetic diversity in their horse populations.
- There are three reintroduction sites in Mongolia, plus two in China.
- The Status and Action Plan for the Przewalski's Horse (Equus ferus przewalskii) was produced in 2002 (Wakefield et al. 2002), and provides a more detailed account of the history and ongoing conservation efforts surrounding the species.
- All three Mongolian reintroduction sites are monitoring their populations and are integrating community livelihood support into their projects (Ulambayar 2004).
- There have been several workshops of stakeholders involved in the reintroduction of Przewalski's Horse to Mongolia (Boyd 2009).
Conservation actions required:
- The health of wild and domestic horses should be monitored for disease (Roberts et al. 2005). Standardized techniques should be used to monitor health, fecundity, mortality, habitat utilization and social organization of all populations (Wakefield et al. 2002).
- Contact between Przewalski's Horses and domestic horses should be kept to a minimum.
- A single population management approach should be developed.
- Mongolia currently has the only sizeable wild population and an action plan is needed for the country.
- The genealogy of all horses in Mongolia should be established based on individual genotypes from micro-satellite data to monitor inbreeding levels, identify hybrids and plan for necessary movements of horses between reintroduction centres to maximize genetic diversity.
- An authoritative government protocol for hybrids should be developed, to be established before hybridization occurs, and to be made available in each re-introduction centre and to local people (King and Gurnell 2005).
- Further communication and cooperation between all re-introduction centres would be beneficial.
- Further training and post-graduate education of staff and biologists involved with this conservation work would be beneficial.
Websites for the reintroduction sites in Mongolia with further details and ways of supporting them are:
This species is one of a number which have been included in various “Pleistocene rewilding” plans. Pleistocene rewilding is the proposed practice of restoring ecosystems to their state in the Pleistocene, roughly 10,000 years ago. This contrasts the standard conservation benchmark, particularly in North America, of restoring ecosystems to their pre-Columbian or pre-industrial state. In both Eurasia and North America, the Pleistocene was characterized by much greater diversity and numbers of large herbivores and predators, including proboscidians, equids, camelids, and felidae (Donlan et al 2006; Zimov 2005). The process of restoration would involve the reintroduction of extant species in their historic range, as well as the introduction of ‘proxy organisms’ to replace the ecological functionality of extinct organisms (Donlan et al 2006).
There are three central theoretical goals to Pleistocene rewilding. In Siberia, a team led by Sergey Zimov is investigating the role of large herbivores as ecosystem engineers. It is thought that herbivory pressure could play a central role in maintaining a grass-dominated plant community, as opposed to either tree- or moss-dominated. Grasslands are known to be more stable carbon sinks than either mossy or forested tundra, due to the rapidity of their biogeochemical cycling (Zimov 2005). In principle, then, reintroducing Pleistocene fauna could have positive climate change mitigation effects. Proposals in North America have focused instead on the preservation of ecological dynamics. Proponents of Pleistocene rewilding argue that due to the strong ecological interactions of megafauna, it is likely that their extinction at the end of the Pleistocene would have caused cascading ecological disruptions lasting until the present time (Donlan et al 2006). Additionally, introduction programs could provide a new lease on life for extant, endangered megafauna species, such as cheetahs and Asian elephants (Rubenstein 2006).
Pleistocene rewilding, while headline-grabbing, is by no means the standard of modern conservation biology. There are a number of objections to the proposals of Pleistocene rewilders, summarized by Rubenstein et al (2006). The introduction of species which have been locally extinct for thousands of years, and more particularly the introduction of modern relatives of extinct species, carries many risks: the potential for invasive species, catastrophic disruption of existing ecosystems, inadvertent introduction of disease organisms, and unpredictable behavior of introduced species. Additionally, while paleoecology is a growing field, there is still a fair amount of uncertainty about the actual ecosystem functions of the Pleistocene.
Species which Zimov and his colleagues in Siberia are experimenting with bison, musk oxen, Przewalski’s horse, and Siberian tigers (Zimov 2005). Small-scale introductions have already begun in Yakutia. Donlan et al propose introducing Przewalski’s horse, Bolson tortoises, Bactrian camels, cheetahs, lions, and elephants into the Western United States (Donlan et al 2005). While some individuals of these species are present on privately owned land, there are no free-living populations in North America at this time.
The wild horse (Equus ferus) is a species of the genus Equus, which includes as subspecies the modern domesticated horse (Equus ferus caballus) as well as the undomesticated Tarpan (Equus ferus ferus), now extinct, and the endangered Przewalski's horse (Equus ferus przewalskii). The Przewalski's Horse was saved from the brink of extinction and reintroduced successfully to the wild. The Tarpan became extinct in the 19th century, though it was a possible ancestor of the domestic horse, and roamed the steppes of Eurasia at the time of domestication. However, other subspecies of Equus ferus may have existed and could have been the stock from which domesticated horses are descended. Since the extinction of the Tarpan, attempts have been made to reconstruct its phenotype, resulting in horse breeds such as the Konik and Heck horse. However, the genetic makeup and foundation bloodstock of those breeds is substantially derived from domesticated horses, and therefore these breeds possess domesticated traits.
The term "wild horse" is also used colloquially to refer to free-roaming herds of feral horses such as the Mustang in the United States, the Brumby in Australia, and many others. These feral horses are untamed members of the domestic horse subspecies (Equus ferus caballus), and should not be confused with the two truly "wild" horse subspecies.
Subspecies and their history
E. ferus had several subspecies. Three survived into modern times:
- The Domestic horse (Equus ferus caballus).
- The Tarpan or Eurasian Wild Horse (Equus ferus ferus), once native to Europe and western Asia. The Tarpan became effectively extinct in the late 19th century, and the last specimen died in captivity in an estate in Poltava Governorate, Russian Empire, in 1909.
- Przewalski's horse (Equus ferus przewalskii), also known as the Mongolian Wild Horse or Takhi, 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 and could have been the stock from which domesticated horses are descended.
Przewalski's Horse occupied the eastern Eurasian steppes, perhaps from the Urals to Mongolia, although the ancient border between Tarpan and Przewalski distributions has not been clearly defined. Przewalski's Horse was limited to Dzungaria and western Mongolia in the same period, and became extinct in the wild during the 1960s, but was re-introduced in the late 1980s to two preserves in Mongolia. Although researchers such as Marija Gimbutas theorized that the horses of the Chalcolithic period were Przewalski's, more recent genetic studies indicate that Przewalski's Horse is not an ancestor to modern domesticated horses.
Przewalski's Horse is still found today, though it is an endangered species and for a time was considered extinct in the wild. Roughly 1500 Przewalski's Horses are in zoos around the world. A small breeding population has been reintroduced in Mongolia. As of 2005, a cooperative venture between the Zoological Society of London and Mongolian scientists has resulted in a free-ranging population of 248 animals in the wild.
Przewalski's Horse has some biological differences from the domestic horse; unlike domesticated horses and the Tarpan, which both have 64 chromosomes, Przewalski's Horse has 66 chromosomes due to a Robertsonian translocation. However, the offspring of Przewalski and domestic horses are fertile, possessing 65 chromosomes.
Evolution and taxonomy
The horse family Equidae and the genus Equus evolved in North America, before the species moved into the Eastern Hemisphere. Studies using ancient DNA as well as DNA of recent individuals, shows the presence of two closely related horse species in North America, the Wild Horse and the "New World stilt-legged horse;" the latter is taxonomically assigned to various names.   Currently, three subspecies that lived during recorded human history are recognized. One subspecies is the widespread domestic horse (Equus ferus caballus), as well as two wild subspecies, the recently extinct Tarpan (Equus ferus ferus) and the endangered Przewalski's Horse (Equus ferus przewalskii).   Genetically, the pre-domestication horse, Equus ferus ferus, and domesticated horse, Equus ferus caballus, form a single homogeneous group (clade) and are genetically indistinguishable from each other.  The genetic variation within this clade shows only a limited regional variation, with a notable exception of Przewalski's Horse. Przewalski's Horse has several unique genetic differences that distinguishes it from the other subspecies, including 66 instead of 64 chromosomes,  unique Y-chromosome gene haplotypes,  and unique mtDNA haplotypes.  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 post-glacial times, the Tarpan and Przewalski's Horse. 
Scientific naming of the species
At present, the domesticated and wild horses are considered a single species, with the valid scientific name for the horse species being Equus ferus. The wild Tarpan subspecies is Equus ferus ferus, Przewalski's Horse is Equus ferus przewalskii, and the domesticated horse is Equus ferus caballus. The rules for the scientific naming of animal species are determined in the International Code of Zoological Nomenclature, which stipulates that the oldest available valid scientific name is used to name the species. Previously, when taxonomists considered domesticated and wild horse two subspecies of the same species, the valid scientific name was Equus caballus Linnaeus 1758, with the subspecies labeled Equus caballus caballus (domesticated horse), Equus caballus ferus Boddaert, 1785 (tarpan) and Equus caballus przewalskii Poliakov, 1881 (Przewalski's Horse). However, in 2003, the International Commission on Zoological Nomenclature decided that the scientific names of the wild species have priority over the scientific names of domesticated species, therefore mandating the use of Equus ferus for the horse, independent of the position of the domesticated horse.
Horses that live in an untamed state but have ancestors who have been domesticated are not truly "wild" horses; they are feral horses. For example, when the Spanish reintroduced the horse to the Americas beginning in the late 15th century, some horses escaped and formed feral herds, the best-known being the Mustang. The Australian equivalent to the Mustang is the Brumby, descended from horses strayed or let loose in Australia by English settlers. There are isolated populations of feral horses in a number of places, including Portugal, Scotland, and a number of barrier islands along the Atlantic coast of North America from Sable Island off Nova Scotia, to the Shackleford Banks of North Carolina. While these are often referred to as "wild" horses, they are not truly "wild" in the biological sense of having no domesticated ancestors.
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. It was speculated that the Riwoche horse might be a relict population of wild horses, but testing did not reveal genetic differences with domesticated horses, which is in line with news reports indicating that they are used as pack and riding animals by the local villagers. 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.
- Boyd, L. & King, S. R. B. (2011). "Equus ferus". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 18 January 2012.
- Grubb, P. (2005). "Order Perissodactyla". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. p. 630-631. ISBN 978-0-8018-8221-0. OCLC 62265494.
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