Zebra black and white at birth. Plains and mountain zebra foals are protected by their mothers, as well as the head stallion and the other mares in their group. Grévy's zebra foals have only their mother as a regular protector, since, as noted above, Grévy's zebra groups often disband after a few months. Attempts have been made to train zebras for riding, since they have better resistance than horses to African diseases. While occasionally successful, most of these attempts failed due to the zebra's more unpredictable nature and tendency to panic under stress. For this reason, zebra-mules or zebroids (crosses between
Grévy's zebra Abyssinia. Traditionally, this species was classified in the subgenus "Dolichohippus" with plains zebra and mountain zebra in "Hippotigris". Fossils of zebra-like equids have been found throughout Africa and Asia in the Pliocene and Pleistocene deposits. Notable examples include "E. sanmeniensis" from China, "E. cautleyi" from India, "E. valeriani" from central Asia and "E. oldowayensis" from East Africa. The latter, in particular is very similar to the Grévy's zebra and may have been its ancestor. The modern Grévy's zebra arose in the early Pleistocene. Zebras appear to be a monophyletic lineage and recent (2013) phylogenies have placed Grevy's zebra in a