Striping on neck suggests that extinct quagga is different species from Burchell's zebra

@tonyrebelo Many thanks for pointing out failed links. The above is a copy of a photo-email I sent, about 5.5 years ago, to Colin Groves, the authority on the taxonomy of zebras. Colin Groves has since died, and items have vanished from the Web. I will replace the failed links with working ones. However, the main point of interest is that Colin Groves acknowledged, in response, that be had never noticed these differences, and he expressed regret for having assumed that quagga was merely the southernmost subspecies of the plains zebra. Because Groves is well-known to be a 'splitter', the implication is that, had he spotted this difference himself, he would have kept quagga as a separate species. Regardless of taxonomic decisions, however, the difference of kind, as opposed to degree, may help to explain why it has proved so hard to 'rebreed' the extinct quagga from a ssp. of the plains zebra. The 'Rau quagga' standards are not actually sufficient for claiming any true, overall, reinstatement of the phenotype of the extinct form. The rebreeding projects have produced fascinating results, but it is a stretch to claim that they have 'rebred' anything. What has been produced is the palest form of plains zebra, as opposed to a semblance of the extinct quagga, not so?

@tonyrebelo Is your quote from an item in the literature?

Not quite on this topic, but have you seen what water does to zebra stripes: only the vertical stripes show. Why is that? (part of it is that the non-vertical stripes are on top and dont reflect, but why the hindquarters?)
https://www.inaturalist.org/observations/133454966
https://www.inaturalist.org/observations/133454958
Perhaps Zebra stripes are not for lions and hyenas but for crocodiles?

@tonyrebelo @jeremygilmore

Differences between extinct quagga and Equus quagga burchellii:

The following (http://l450v.alamy.com/450v/c797mt/zebra-in-hluhluwe-umfolozi-game-reserve-kwazulu-natal-south-africa-c797mt.jpg) shows an adolescent individual of Equus quagga burchellii, in Hluhluwe-IMfolozi reserve in Zululand.

It shows the maximum ‘darkness’ of this subspecies, in the sense that here we have the maximum breadth of the dark striping.

Note that, in this individual, a) the mane is, overall, as much dark-striped as pale-striped, and b) there is narrow dark-rimming on the front-of-ear.

However, the overall point is that, even when this subspecies expresses is ‘maximum darkness’, a) the pale striping on the mane remains whitish rather than fawn, and b) this applies also to the anterior part of the cheek.

Also note the length of the mane and forelock, which look about double the length seen in any museum specimen of the extinct quagga.

Some individuals of E. q. burchellii are darker than others. However, this darkness is not associated with any shortening of mane or forelock. Furthermore, the fawn tinge in the pale areas between the dark striping never seems to extend on to the cheeks, as it does in the extinct quagga.

All specimens of the extinct quagga, without exception, have the pale ‘ground-colour’ on the anterior part of the cheeks fawn, not whitish. Furthermore, I have yet to find a single individual of E. q. burchellii that has the ‘ground colour’ of the anterior part of the cheeks fawn, as opposed to whitish.

Although this individual of E. q. burchellii is particularly ‘dark’ for its subspecies, there is nothing ‘quagga-like’ about it, not so?

What this all seems to add up to:

One can select for darkness in burchellii, or one can select for stripelessness in burchellii. However, neither extrapolation is likely to approach the phenotype of the extinct quagga.

This is because no amount of darkening in burchellii ever seems a) to extend on to the ‘ground colour’ of the cheeks, b) to darken the pale striping on the mane, and c) to bring any shortening of mane and forelock.

By following the trend of stripelessness (as done in all the ‘re-breeding programmes), one is again frustrated. This is because no amount of extension of the shadow striping in the anterior direction (ultimately on to even the cheeks) seems to bring overall darkness. Equus quagga burchellii retains the paleness of its ‘ground colour’, even as its shadow striping is multiplied.

So, contrary to any previous tacit assumption, the darkness of the ‘ground colour’ in the extinct quagga is not the result of the accentuation and spreading of shadow striping.

The ‘re-breeding’ programmes have essentially tried to cover the animal in shadow striping, so extreme that it ‘fills in’ the pale areas of the pelage.

However, this has not worked, because the ‘ground colour’ - particularly on the head and mane - remains whitish, no matter how shadow-striped the individual may be, in burchellii.

Equus quagga burchellii in Zululand, showing pale masseter area:
  
The following (https://thumb1.shutterstock.com/display_pic_with_logo/364990/364990,1311717883,34/stock-photo-zebras-at-hluhluwe-umfolozi-game-reserve-located-km-north-of-durban-is-the-oldest-proclaimed-81699373.jpg) of Equus quagga burchellii in Zululand (Hluhluwe-iMfolozi) shows the tendency to pale stripelessness on the masseter area, a tendency that occurs also in the intensely striped E. q. crawshayi. I have yet to see such a tendency expressed in any museum specimen of the extinct quagga. By the way, also note that the shadow striping extends as far to the anterior as the posterior-most part of the neck.

Jaques-Laurent Agasse (https://en.wikipedia.org/wiki/Jacques-Laurent_Agasse) was a competent painter with a particularly keenneye for equids.

Here is his depiction of a captive specimen of the extinct quagga, painted from life: https://commons.wikimedia.org/wiki/File:Agasse_Quagga.jpg

One can see from another depiction by Agasse (https://www.alamy.com/jacques-laurent-agasse-zebra-image367348337.html?imageid=EBC5D4C0-A4FF-4A38-9A81-A20D8DBE0F10&p=726102&pn=1&searchId=b09cd93958705b5d852dd2db560d38fc&searchtype=0) that he paid attention to detail on the posterior surface of the ear pinna.

It is obvious that Agasse erred by depicting the heads of quagga and mountain zebra as smaller than they really are. This is understandable in view of his the extremely 'refined' breeds of the domestic horse, which do indeed have heads smaller than those of any wild species in the genus Equus.

Agasse showed the back-of-ear of this individual of the extinct quagga as an irregular, medium-tone brown, with dark distally, and perhaps a spot of pale at the very tip.

https://commons.wikimedia.org/wiki/File:Plains_Zebra_%28Equus_quagga_burchellii%29_foal_%2832549106614%29.jpg