What key difference exists between the wild ancestor of the donkey and the onager regarding shoulder markings?

Answer

The ancestral African wild ass commonly features shoulder stripes, similar to its dorsal stripe

While the onager often appears more uniform in its pale coat, the ancestral African wild ass commonly features a dark dorsal stripe along with shoulder stripes.

What key difference exists between the wild ancestor of the donkey and the onager regarding shoulder markings?
DonkeyOnager