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Fantastic asses

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Somali wild ass strikes the pose at Marwell Wildlife. Photo by Darren Naish. CC BY.

Come on, this is Tetrapod Zoology: you knew those asses would be of the equid kind, right? I don’t think there’s been much on Tet Zoo about equids yet, nor about perissodactyls at all (a crime, given my strong interest in fossil rhinos). See the links below, however. I’ve taken various wild ass photos at zoos over the years and today is a good chance to use a few of them.

Somali wild ass pair, photographed at Marwell Wildlife. Photo by Darren Naish. Image CC BY.

The nomenclature used for asses differs according to which source you consult. All of the African forms – sometimes termed asinines – are included in the species Equus asinus, and indeed domestic donkeys are extremely close relatives of both the Nubian wild ass E. a. africanus and Somali wild ass E. a. somaliensis. Somali wild asses differ obviously from Nubian wild asses and domestic donkeys in their striped legs. While the Nubian wild ass is probably extinct in the wild, the Somali wild ass is critically endangered and reduced to a population of less than 600. A third form – the Atlas wild ass E. a. atlanticus – seems to have become extinct in early historic times.

Domestic donkeys of the sort you see across northern Africa (these were photographed in Morrocco: they're hobbled and hence can't run fast). Photo by Darren Naish. CC BY.

Domestic donkeys belong to two genetic groups (termed Clade 1 and Clade 2) and it has sometimes been thought that both Nubian and Somali wild asses have contributed to the donkey gene pool, with the Somali wild asses contributing to the domestic donkey population in southern Europe (Clade 2) while donkeys elsewhere are mostly derived from the Nubian wild ass (Clade 1). Recent results indicate that Somali wild asses have little to no contribution to the donkey gene pool (Kimura et al. 2011), however. As with all stories of animal domestication, ideas on donkey domestication are hugely complex and I’m nowhere close to doing them justice here.

Incidentally, wild asses and donkeys are more like zebras than domestic horses in lacking ‘chestnuts’ (those weird, horny excrescences on the inside surfaces of the limbs) on the hindlimbs, an observation consistent with cladograms which show the caballine or caballid or caballoid lineage (domestic horses, European forest horses and so on) to be outside an ass + zebra clade. Nobody seems to know what the ‘chestnuts’ are: I’ve heard horsey people say that they’re vestigial remains of digits – Dent (1972) says this – but this can’t be true since they’re not associated with the metacarpus or metatarsus, the only places where digits occur.

Front cover of Dent (1972). A much treasured possession.

The history of the donkey and the variation that we’ve bred into its various forms is really interesting (there are dwarf donkeys, giant donkeys, shaggy-furred donkeys and so on). I recently got hold of Anthony Dent’s amusingly titled Donkey: the Story of the Ass from East to West (Dent 1972) after being in quest of it for some years. It’s there on the shelf next to Dent and Goodall’s A History of British Native Ponies.

The Asian wild asses are the Kulan, Onager and Kiang, grouped together as the hemionines or hemionids. Today, the Kulan and Onager are generally considered subspecies of the same species – E. hemionus – while the Kiang (also called the Tibetan wild ass, Khyang or Gorkhar) of the Tibetan Plateau is E. kiang. It’s the largest of the asses, reaching a shoulder height of 1.4 m (that’s 13.3 hands, apparently) and with big males weighing 400 kg. As is typical for equids from seasonally cool places, its summer coat is far shorter than the much darker winter one. Kiang are chestnut coloured dorsally and with a dark brown dorsal stripe, and white muzzle, legs and underparts. However, there’s quite some variation in how dark even the summer coat is. This has, combined with differences in body size, led to the idea that there are three Kiang subspecies: the Western kiang (E. k. kiang), Eastern kiang (E. k. holdereri) and Southern kiang (E. k. polyodon), the last of which is so rare that it was thought extinct prior to the reported rediscovery of about 100 animals in 1996. There’s some suspicion that the three forms grade into one another and simply represent a cline: molecular work is needed on the different populations.

Kiang male (left) and female at Edinburgh Zoo, photo by Darren Naish. Image CC BY.

Kiangs are steppe-dwelling animals that live in female-led herds that are famous for their cohesion, the animals walking or running in file and sticking tightly in a group even when panicking. A peculiarity of their behaviour compared to that of domestic horses is that they indulge in little allogrooming. Adult males live alone for much of the year but form all-male bands during the winter (Nowak 1999). Protracted, bloody battles have been recorded as stallions have fought to defend their harems. As you might predict from the social behaviour associated with this lifestyle, sexual dimorphism is pronounced. I recently photographed the animals you see above at Edinburgh Zoo. Note that the male (the larger animal on the left) has a blockier-shaped head, with a more strongly downturned nose.

Did I ever say that I love the artwork of Maurice Wilson? Seriously, big fan. Here's his illustration (from David Day's 1981 The Encyclopedia of Vanished Species) of the Syrian onager (E. hemionus hemippus), a tiny ass (90 cm tall at the shoulder) that was hunted to extinction some time round about 1930.

Kiang have become increasingly rare as their steppe habitat has been taken over for grazing by domestic horses, and also for agriculture and industry. Nowak (1999) says that there are only 52 captive Kiang outside of China. I’m not sure if there are Kiang x domestic donkey hybrids. Onagers have certainly been crossed with donkeys, despite the major chromosomal differences (in Onager, 2n = 54, in donkeys, 2n = 62). But then, hybridisation of just about any sort goes across Equidae: a review of this subject is in fact titled ‘Interspecific and extraspecific pregnancies in equids: anything goes’ (Allen & Short 1997).

Wild ass evolution is more interesting that you might think since there have been suggestions that the fossil species E. conversidens of the North American Pliocene and Pleistocene is especially close to the Kiang, in which case the Kiang lineage may have a distinct origin and history relative to those of the Onager and Kulan. This is inconsistent, however, with genetic data which indicates that E. hemionus and E. kiang are very close kin that only separated less than 500,000 years ago (Ryder & Chemnick 1990). If you’re wondering, molecular studies don’t find asinine and hemionine asses to group together: George & Ryder (1986) found E. hemionus to be closer to zebras than to African wild asses and Orlando et al. (2009) found the hemionine and asinine clades to be well separate. Then there are the fossil asses of Africa, some of which (like E. tabeti) have been regarded as closer to hemionines than to asinines by some authors. I’m not endorsing this, it might be erroneous (see Churcher 1982).

An equid montage: Grevy's zebra (top left), Kiang (bottom left), and New Forest pony (right). Photos by Darren Naish. CC BY.

Zebras? Don’t get me started: I’ve been trying to finish an article on them since 2006. ‘Stripes do not a zebra make’ (Bennett 1980), and while some studies do find zebras to form a clade (George & Ryder 1986), others find them scattered all about the equid tree (Bennett 1980, Orlando et al. 2009). Specifically, Orlando et al. (2009) found Grevy’s zebra E. grevyi to belong to a clade that also included the hemionines while Hartmann’s mountain zebra E. hartmannae belonged to a clade that also included asinines. The Quagga and plains zebras E. quagga were off on their own.

Oh, then there’s E. hydruntinus and the sussemiones. They’ll have to wait to another time – this was meant to be a quick picture-led post!

For previous Tet Zoo articles on perissodactyls, see…

Refs – -

Allen, W. R. & Short, R. V. 1997. Interspecific and extraspecific pregnancies in equids: anything goes.  The Journal of Heredity 88, 384-392.

Bennett, D. K. 1980. Stripes do not a zebra make, part I: A cladistic analysis of EquusSystematic Zoology 29, 272-287.

Churcher, C. S. 1982. Oldest ass recovered from Olduvai Gorge, Tanzania, and the origin of asses. Journal of Paleontology 56, 1124-1132.

Dent, A. 1972. Donkey: the Story of the Ass from East to West. George G. Harrap & Co., London.

George, M. & Ryder, O. A. 1986. Mitochondrial DNA evolution in the genus Equus. Molecular Biology and Evolution 3, 353-546.

Kimura, B., Marshall, F. B., Chen, S., Rosenbom, S., Moehlman, P. D., Tuross, N., Sabin, R. C., Peters, J., Barich, B., Yohannes, H., Kebede, F., Teclai, R., Beja-Pereira, A. & Mulligan, C. J. 2011. Ancient DNA from Nubian and Somali wild ass provides insights into donkey ancestry and domestication. Proceedings of the Royal Society B: Biological Sciences 1702, 50-57.

Nowak, R. M. 1999. Walker’s Mammals of the World, Volume II. The Johns Hopkins University Press, Baltimore and London.

Orlando, L., Metcalf, J. L. Alberdi, M. T., Telles-Antunes, M., Bonjean, D., Otte, M., Martin, F., Eisenmann, V., Mashkour, M., Morello, F., Prado, J. L., Salas-Gismondi, R., Shockey, B. J., Wrinn, P. J., Vasil’ev, S. K., Ovodov, N. D., Cherry, M. I., Hopwood, B., Male, D., Austin, J. J., Hänni, C. & Cooper, A. 2009. Revising the recent evolutionary history of equids using ancient DNA. Proceedings of the National Academy of Sciences 106, 21754-21759.

Ryder, O. A. & Chemnick, L. G. 1990. Chromosomal and molecular evolution in Asiatic wild asses. Genetica Dordrecht 83, 67-72.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at! Follow on Twitter @TetZoo.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Jerzy v. 3.0. 5:19 pm 09/5/2013

    Just in case – kiangs are doing fine in Tibetan plateau, and herds can be seen close to the major roads. They are also now much more common in Western zoos than 52 animals.

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  2. 2. Halbred 5:32 pm 09/5/2013

    So what would a modern equid cladogram look like? It sounds like horses are a lot more diverse than I’d thought. How far back in horse evolution do all these different animals go? That is, how far back do single-toed horses go?

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  3. 3. Heteromeles 6:12 pm 09/5/2013

    If horse hybridize as much as reported, one suspects that the Equid cladogram will look more like the Celtic Tree of Life (or the Triticeae cladogram) more than anything sensible.

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  4. 4. SWestfall 7:41 pm 09/5/2013

    “Chestnuts” in West Virginia parlance are “swimmers.”

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  5. 5. Dartian 1:53 am 09/6/2013

    this was meant to be a quick picture-led post!

    Aww, come on! No apologies needed. You know – and we know – that short, trivial articles just aren’t your thang. You might as well accept that fact and keep ‘em long and awesome. ;)

    By the way, you forgot to give the full reference for Bennett (1980). It is:

    Bennett, D.K. 1980. Stripes do not a zebra make, part I: A cladistic analysis of Equus. Systematic Zoology 29, 272-287.

    Too bad that part II was apparently never published. :(

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  6. 6. naishd 3:56 am 09/6/2013

    Oops, yes, forgot Bennett (1980), thanks. Will go add…


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  7. 7. Andreas Johansson 3:56 am 09/6/2013

    How does one pronounce “kiang”? One syllable or two?

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  8. 8. CS Shelton 7:22 am 09/6/2013

    And does the plural of kiang have no “s” or was that a typo? Those are flippin’ beautiful animals. Never heard of them.

    Also, you didn’t mention your recent tapir attack article on the Tet Zoo perissodactyl tip. I can remember that horrorshow quite distinctly.

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  9. 9. Chabier G. 8:08 am 09/6/2013

    There is an interesting debate about onagers here in Spain (well, yes, only in some circles). Equus hydruntinus has been found in Iron Age sites, and there are some descriptions of an enigmatic equid called “encebro”, “cebro” or “zebra” in medieval texts, the last mention of encebros dates from the early XVIIth century. Some people say encebro would be a feral horse or donkey, but looking at these old texts the species was regarded as a distinctive, wild game species, and I don’t think that medieval people, used to live aside with horses and donkeys, gave a different name to an animal which was simply a feral equid. Encebro could be the last surviving E. hydruntinus.
    Place names containing “cebro”, “cebra” and “encebro” are widely scattered across the Spanish and Portuguese geography. Moreover, the word “zebra” was adopted by the Portuguese sailors to name a new african equid that remembered them the original Iberian “zebra”, and this equid was much likely the almost stripeless Quagga, as sailing along African coast from Portugal the Cape shore could be the first territory sheltering zebras (I think Mountain Zebra doesn’t reach the Namib coast.
    The lack of Middle Age remains of onagers is argued against the identification Encebro-E. hydruntinus, but this lack can be explained: Medieval archaeozoology in Spain is all but nonexistent.

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  10. 10. naishd 8:25 am 09/6/2013

    Ha. I deliberately avoided a discussion of E. hydruntinus for fear of adding substantially to the article. The popular idea that this might be the same animal as the ‘Zebro’ referred to in historic texts has not been supported in recent studies, since the alleged 17th Century ‘E. hydruntinus‘ specimens from Portugal that’s key to this hypothesis turned out to be a misidentified domestic donkey. It also seems that other fossils and archaeological specimens referred to E. hydruntinus are actually assorted hemionines of diverse ancestry: the true E. hydruntinus (known from the fossil record of France) is a hemionine (perhaps even part of E. hemionus). Some specimens from Iran are nested deeply within E. hemionus (Orlando et al. 2009).

    Orlando et al. published a study devoted to the genetic of E. hydruntinus in 2006.

    Kiang: so far as I know, it’s pronounced kye-ang (with ‘kye’ rhyming with ‘eye’).


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  11. 11. josimo70 8:41 am 09/6/2013

    zebro < equiferus < Latin equus ferus

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  12. 12. Lars Dietz 12:42 pm 09/6/2013

    Have you seen Vilstrup et al. (2013)? Complete mitochondrial genomes support monophyly of zebras, but don’t really resolve their relation with asinines, hemiones and sussemiones. Of course, with such extensive hybridization, other genes may tell a different story.

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  13. 13. naishd 12:47 pm 09/6/2013

    Nope, news to me (thanks). Follow-up needed at some stage, obviously.


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  14. 14. Jerzy v. 3.0. 1:06 pm 09/6/2013

    Spanish encebro was almost certainly the wild horse (Equus ferus). Descriptions of this animal are consistent with the horse as opposed to a hemionine (grey, with striped legs, can be tamed and ridden).

    Interesting is that Spanish primitive horse Sorraya, historically extinct encebro and some cave paintings of horses all show stripes on legs. Perhaps striped legs were a common trait of SW European horses conserved across millenia.

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  15. 15. Dartian 1:48 pm 09/6/2013

    I don’t think that medieval people, used to live aside with horses and donkeys, gave a different name to an animal which was simply a feral equid

    Why not? It’s not unheard of that people distinguish feral from domestic animals by giving them different (vernacular) names. E.g. (just to take a few equid examples): mustang, brumby, konik.

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  16. 16. Yodelling Cyclist 4:09 pm 09/6/2013

    E. hydrunticus

    Am I being dense or shouldn’t that be E. hydruntinus ?

    If there’s smething new to learn here, I would love to be enlightened.

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  17. 17. naishd 5:37 pm 09/6/2013

    Dammit – that’s what happens when you’re lazy and use copy and paste. Yes, it’s hydruntinus (as used correctly in the body of the article). I’ll go correct, thanks.


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  18. 18. David Marjanović 5:42 pm 09/6/2013

    my strong interest in fossil rhinos

    Ooh! Opinions, please! Teleoceras and Metamynodon: hippo analogues or not? :-)

    this was meant to be a quick picture-led post!

    Why do you still bother trying :-)

    How does one pronounce “kiang”? One syllable or two?

    Judging from khyang, it’s one syllable, like the kyō of Tōkyō and Kyōto. Tibetan does that a lot. The h just means aspiration (it’s an English-style k, not a French-style one).

    zebro < equiferus < Latin equus ferus

    That’s a bit hard to imagine; such changes wouldn’t be entirely regular.

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  19. 19. CS Shelton 9:49 pm 09/6/2013

    Oh, you did mention the tapirs in the bottom part of the post. Sometimes I don’t make it through all that.

    I wonder if undiscovered fossils will ever reveal another perissodactyl as weird as chalicotheres. And further off topic, it seems like a shame all the creatures with that lifestyle are dead meat these days, except for limpin’ along pandas. Humans are not nice to slow-moving meaty herbivores.

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  20. 20. Chabier G. 2:44 am 09/7/2013

    Josimo70: as David Marjanovic says, equiferus > cebro is a very strange derivation for Iberian Romanic languages (compare Aquila > Águila, not “Acila”). But, even if that were true, it doesn’t proves anything, Medieval legal texts from Castile have a latin version, in which “cebro” is translated as “Onager”. :D
    Jerzy: There isn’t any ancient description depicting cebros with stripped legs, and the beast is always said to be untameable and far faster than horses. About Sorraia, it’s a Portuguese breed with a doubtful origin, to say the least, the result of zootecnics applying self idiosincratic ideas about primitive horses to a little herd of horses that was found in a remote area of Portugal, leg stripes were deliberately selected. I’ve seen leg stripes (very dense) in Przewalski’s horses at the Santillana del Mar Zoo. This is a recurrent caracter (atavic?) in horses and donkeys.
    Dartian: Touché!, but, even so, encebro was always regarded as a game piece,hunted by leather and meat, never as an animal worth to be captured and tamed, very strange in those times, when horses, mules and asses were essential and very expensive.
    I only think that the (attractive)hypothesis cebro = onager, matches with historical documents, but I know: there isn’t any solid, physical evidence, proving it.

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  21. 21. Jerzy v. 3.0. 8:27 am 09/7/2013

    Chabier G.:
    I saw a picture of some Spanish monk (or saint?) riding a cebro, so I think they could be tamed.

    Wild tarpans in Eastern Europe were also difficult to tame compared to a domestic horse, but it was possible. Tarpans were also usually hunted as game, rather than captured alive. Only the modern knowledge of tarpans comes mostly from the few individuals in captivity.

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  22. 22. Chabier G. 8:51 am 09/7/2013

    Jerzy: Well, you know, saints could ever tame a wolf, or expel all the snakes of Ireland,legends about miraculous beast taming are common. But even the authentic onager was domesticated by the Sumerians, and by nobody else later, AFAIK.
    I’m interested in that picture, please, Where was it?, How is it known the animal is a cebro?.

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  23. 23. Lars Dietz 10:28 am 09/7/2013

    “Medieval legal texts from Castile have a latin version, in which “cebro” is translated as “Onager”.”

    Yes, but “onager” was often used by medieval authors for wild horses, not only on the Iberian peninsula. Later, when most large ungulates had become more rare and there was a lot of confusion about names, it was also used for elks (not in Spain, of course). There’s even one gloss that translates “onager” as wisent! There’s a lot about this in the “Schelch” paper I linked to in another thread when possible Irish elk survival came up.

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  24. 24. Perisoreus 6:36 am 09/8/2013

    And please keep in mind that there were no species back in the middle ages: all kinds of phenetic forms might have been regarded as worthy of their own name, as is still visible in late naturalists’ works ob sexually dimorphic birds. And not only that, there are names that come with the use, age, habitat, occurence, number, rank, sex etc. of the animal. to think that monks in their chambers and peasants on their fields would adhere to something as empiricism or that they would have any interest in it is a misconception.

    It does not mean, however, that medieval knowledge is irrational or that it did not pertain to something we could reconstruct as a species that has since disappeared.

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  25. 25. naishd 7:33 am 09/8/2013

    Sorry, missed David’s comment (# 18) on fossil rhinos (“Teleoceras and Metamynodon: hippo analogues or not?”). My general feeling is, yes, both taxa were indeed amphibious: both are hippo-like in body shape and limb proportions (though note that Metamynodon should not be regarded as at all typical for Amynodontidae) and the taphonomic data (they are repeatedly discovered in channel-fill deposits across diverse locations) seems pretty compelling. Fossil rhinos: something else I need to cover appropriately at some stage…


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  26. 26. Jerzy v. 3.0. 8:18 am 09/8/2013

    Chabier G.:
    I saw the picture in some text concerning restoring large herbivores in Europe. I have a feeling it should be reasonably well known in Spain. I keep trying to find it… The problem is that unlike some people here I don’t write from where I have my library handy.

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  27. 27. Chabier G. 3:01 am 09/9/2013

    Lars and Perisoreus: many medieval erudites, mainly monks, wrote without never having seen a wild animal, and often tried to match latin and greek names with their homeland fauna,so,mistakes were common. About ancient and peasant knowledge, “taxonomic” categories are, I agree, rather weird for us, beavers were half-fish, for example. But medieval hunting laws were made with a practical purpose, and the animal names we find within these documents were real, existing game, only “cebro” can’t be identified properly. Then, only well done Archaeozoology could enlighten this question.

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  28. 28. David Marjanović 6:32 am 09/9/2013

    Yay! The numbers of comments are back on the main page! :-)

    and often tried to match latin and greek names with their homeland fauna

    Especially names that occurred in the Bible.

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  29. 29. gentle lemur 7:43 am 09/9/2013

    For the sake of completeness, it is probably worth mentioning the Indian and Mongolian wild asses, which are described as races of E. hemionus.

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  30. 30. vdinets 1:03 pm 09/9/2013

    As far as I remember, in most parts of Tibet the species name is pronounced “chyang”. Sounds a bit similar to “chang” (Tibetan beer).

    Some people who have worked on onager reintroduction project in Israel have told me that there could be some Syrian ssp. blood in those animals (although officially they are a mix of Iranian and Turkmenian ssp, which are almost identical). Indeed, they are clearly smaller than those in Turkmenistan.

    Somalian wild ass is now very difficult to find in Somaliland and Eritrea, and close to extinction, if not extinct, in the rest of Somalia and Djibouti. A few years ago I spent some time looking for it in Ethiopia. In Afar, local people said that a few were still around, but I didn’t see any. In Yangoudi-Rassa Nat’l Park, created specifically for this species, park rangers told me “we don’t have any wild donkeys, we have only problems”. I saw one animal in that park that looked like a wild ass, but it was too far to be sure.

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  31. 31. Frits B 4:15 pm 09/9/2013

    For what it is worth, the pronunciation is given here:
    Just click on the speaker symbol.

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  32. 32. Dartian 1:57 am 09/10/2013

    I’m not sure if there are Kiang x domestic donkey hybrids.

    According to St-Louis & Cóte (2009), there are. According to the same source, in captivity kiang have also produced hybrids with domestic horse, kulan/onager, and Burchell’s zebra. As you said, with equids anything goes. ;)

    St-Louis, A. & Cóte, S-D. 2009. Equus kiang. Mammalian Species 835, 1-11.

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  33. 33. Dartian 2:53 am 09/10/2013

    While I’m at it, I might as well update this piece of information too:

    Nowak (1999) says that there are only 52 captive Kiang outside of China.

    According to the above-quoted St-Louis & Cóte (2009), in 2008 there were 114 kiang in captivity worldwide. All of them belonged to the eastern subspecies, Equus kiang holdereri.

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  34. 34. Anthea Fleming 3:02 am 10/16/2013

    Hybrids between equine species are almost invariably sterile. For a mule (Male donkey/mare cross) to foal was counted a prodigy or omen in ancient Rome; it is very unusual. I have heard an unconfirmed report of a hinny(reverse cross)having a foal in Australia, but could not confirm it. The sire was said to be a Shetland or other small pony.

    Przhevalsky’s Horse is said to have a different chromosome number to the domestic horse, but hybrids are viable and have bedevilled Przhevalsky breeding programs. Its discoverer was not at all sure whether his new species was horse or a new onager-type ass.

    Onagers are stronger than domestic donkeys and in the Rann of Kutch (India) it was the practice to tether female donkeys in the desert in the hope of breeding onager hybrids. These would be sterile.

    I have seen Common Zebra/donkey hybrids in Melbourne Zoo. Grevy Zebra-horse hybrids were bred in East Africa. The sire’s stripes in both cases were superimposed on the dam’s colouring.

    Light-coloured mules can show donkey-stripes on the legs. Greek red-figure vase-paintings show them with exactly the same pattern as the Somali wild asses illustrated by Darren.

    Finally, the mediaeval Bestiary or Physiologus is mainly drawn from the Etymologies of St. Isidore of Seville, a 6th Century Spanish Bishop and encyclopaediast. After discussing the colours of horses, he says that the worst (lowest-status) is the dosinus (ass-coloured or ashen) “These originate from wild stock which we call equiferus and therefore cannot be used as city horses.” This is presumably the wild zabra or encebro, which is now known as the Sorraia – ash-dun with leg-stripes. Some specimens used to have stripes on the back, but this trait seems to have been bred out. Presumably early Portuguese explorers called the African equids after the striped equines they knew at home

    I found St Isidore on the Internet – of which he is apparently the patron saint.

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