There have been a couple of posts on here before on this subject. A good long time ago now I put up a post on intraspecific variation and the implications for taxonomy, and I also had a post on variation in coat colour in deer. Fine though that was, colour is not the best example to use when talking about vertebrate palaeontology, some kind of nice osteological feature is what you really want.
And here is one – horns of the addax, taken at Marwell zoo. Horns can be notoriously screwy in captive animals and you can see whole herds of things like bongo with barely a one having the ‘normal’ horn shape for the species. While that effect is probably a bit at play here you can see variation in the curvature of the horns between the different animals, not to mention the one with a really screwy (and presumably trimmed) horn.
Plus, well, I like addax and hadn’t managed to include them in the zoo review.