An overlooked difference among Eurasian wild asses: length of the tail-tassel

Nobody seems previously to have noticed the intriguing variation in the length of the tail within the Eurasian wild ass (Equus hemionus).

The Mongolian wild ass (Equus hemionus hemionus, https://en.wikipedia.org/wiki/Mongolian_wild_ass) is similar in overall appearance to the Indian wild ass (Equus hemionus khur, https://en.wikipedia.org/wiki/Indian_wild_ass). This makes sense for two subspecies of the same widespread species.

However, for some strange reason the tail of the former (https://www.zoochat.com/community/media/equus-hemionus-hemionus-mongolian-wild-ass-female.209602/ and https://www.youtube.com/watch?v=mAesXpv3aKo and https://www.facebook.com/watch/?v=10155298731989759) is much longer than the tail of the latter (https://www.naturepl.com/stock-photo-indian-wild-ass-equus-hemionus-khur--wild-ass-sanctuary-little-rann-nature-image01643715.html and https://www.youtube.com/watch?v=rvbyM9AmGjs).

Puzzled by this finding, I scrutinised the tails of other ass-like, wild members of the genus Equus, namely the Somali wild ass (Equus africanus somaliensis), Grevy's zebra (Equus grevyi), and the two forms of mountain zebra (Equus hartmannae and E. zebra).

In all of these species, the tail is unremarkable, with the tassel reaching approximately to the hock. The species differ more in whether the tail is dark or pale than in whether the tassel is long or short.

The tail is indeed also unremarkable in the central subspecies of the Eurasian wild ass, namely Equus hemionus onager and E. hemionus kulan: https://www.naturepl.com/stock-photo-nature-image01508093.html and https://fineartamerica.com/featured/1-onager-equus-hemionus-eyal-bartov.html and https://stock.adobe.com/images/onager-also-known-as-hemione-or-kulan-or-asiatic-wild-ass-latin-name-equus-hemionus/241565734 and https://www.dreamstime.com/stock-photo-onager-equus-hemionus-brown-asian-wild-ass-who-famous-inhabitant-israeli-national-nature-reserve-park-near-eilat-image41151402 and https://www.dreamstime.com/royalty-free-stock-images-onager-wild-asian-ass-hai-bar-biblical-nature-reserve-km-north-eilat-israel-image30448629.

What this adds up to is the following: all the ass-like, wild species and subspecies in the genus Equus are similar in the length of the tail, except for the easternmost (tail long) and southernmost (tail short) subspecies of the Eurasian wild ass.

Although this variation remains unexplained in adaptive terms, taxonomists should add it to the list of features distinguishing the Mongolian wild ass from the Indian wild ass.

LONG TAIL

Equus hemionus hemionus

https://mongolia.wcs.org/Wildlife/Asiatic-Wild-Ass-Khulan.aspx

https://www.semanticscholar.org/paper/Remarks-on-the-Social-System-of-the-Mongolian-Wild-Neumann-Denzau-Denzau/808b7885b72d063ecea60ae41500b574e91c84de/figure/3

https://news.cgtn.com/news/3d3d414d79417a4d32457a6333566d54/index.html

https://www.zoochat.com/community/media/equus-hemionus-hemionus-mongolian-wild-ass-female.209600/

https://www.zoochat.com/community/media/equus-hemionus-hemionus-mongolian-wild-ass-female.209601/

https://www.biolib.cz/en/image/id374109/

https://zooinstitutes.com/animals/mongolian-wild-ass-dalian-forest-zoo-102717.html

https://www.pbase.com/cokesmith/image/149666436

https://www.fauna-flora.org/news/theres-something-exciting-happening-above-the-gobi-desert

https://twitter.com/TheWCS/status/1195079890514694144/photo/1

https://www.needpix.com/photo/download/736706/onager-donkey-asian-ass-zoo-equus-hemionus-livestock-mule-ungulate-exotic

https://pixabay.com/photos/onager-mule-zoo-ungulate-horse-1671296/

https://oneworldonehealth.wcs.org/news/ID/13617.aspx

https://www.biolib.cz/en/image/id315682/

https://www.zoochat.com/community/media/equus-hemionus-luteus-gobi-kulan-young-female.209611/

SHORT TAIL

Equus hemionus khur

https://www.alamy.com/stock-photo-onager-wild-donkey-equus-hemionus-also-khur-endangered-species-little-81556197.html

https://www.alamy.com/indian-wild-ass-equus-hemionus-khur-little-rann-of-kutch-gujarat-india-image157408211.html

https://static.wikia.nocookie.net/parody/images/b/ba/Indian_Wild_Ass.jpg/revision/latest?cb=20201107163829

https://www.jungledragon.com/image/36313/indian_wild_ass.html/zoom

https://www.flickr.com/photos/sarbhloh/33515960704

https://www.dreamstime.com/indian-wild-ass-indian-wild-ass-equus-hemionus-khur-ghudkhar-little-rann-kutch-gujarat-image102703294

https://www.alamy.com/stock-photo-asian-wild-ass-equus-hemionus-khur-128390815.html

https://www.dreamstime.com/indian-wild-ass-equus-hemionus-khur-also-called-ghudkhur-khur-indian-onager-close-up-indian-wild-ass-as-most-other-image116251495

MEDIUM-LENGTH TAIL

Equus africanus somaliensis

https://www.monaconatureencyclopedia.com/equus-africanus-somalicus/?lang=en

https://zooinstitutes.com/animals/somali-wild-ass-hai-bar-yotvata-2552.html

https://dissolve.com/stock-photo/Somali-wild-ass-equus-africanus-somaliensis-stands-arid-royalty-free-image/101-D869-39-320

https://www.dreamstime.com/stock-photo-somali-wild-donkey-equus-africanus-forefather-all-domestic-asses-species-extremely-rare-both-nature-image76340403

https://www.naturepl.com/stock-photo-nature-image01508002.html

Equus grevyi

https://www.alamy.com/stock-photo-grvys-zebra-with-her-three-week-old-foal-113614327.html

https://www.inaturalist.org/observations/68061066

https://www.inaturalist.org/observations/53931632

https://www.inaturalist.org/observations/68999700

https://www.inaturalist.org/observations/54908219

https://www.inaturalist.org/observations/38089842

https://www.inaturalist.org/observations/33945931

Equus hartmannae

https://www.inaturalist.org/observations/16019971

https://louisvillezoo.org/animalsandplants/hartmanns-mountain-zebra/

Fifth photo in http://dangerous-wild-animals.blogspot.com/2011/09/mountain-zebra.html

https://dewetswild.com/2018/07/10/hartmanns-mountain-zebra/#jp-carousel-36869

Equus zebra

https://videohive.net/item/grazing-cape-mountain-zebra/22472735

https://wildark.org/species/mountain-zebra/

https://www.dreamstime.com/stock-images-cape-mountain-zebra-equus-national-park-south-africa-image36456614

https://www.dreamstime.com/royalty-free-stock-photography-cape-mountain-zebra-standing-image21533027

Posted on October 22, 2021 09:42 AM by milewski milewski

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