Donkey
Donkeys can interbreed with other members of the family Equidae, and are commonly interbred with horses. The hybrid between a jack and a mare is a mule, valued as a working and riding animal in many countries. Some large donkey breeds such as the Asino di Martina Franca, the Baudet de Poitou and the Mammoth Jack are raised only for mule production. The hybrid between a stallion and a jenny is a hinny, and is less common. Like other inter-species hybrids, mules and hinnies are usually sterile. Donkeys can also breed with zebras in which the offspring is called a zonkey (among other names).
Mustang
The taxonomic horse family "Equidae" evolved in North America 55 million years ago. By the late Pleistocene era, there were two species of the family remaining there, the caballine (stout legged) and stilt-legged, which recent DNA studies have indicated represent different genera; ""Equus"" and ""Haringtonhippus,"" respectively. "Haringtonhippus" went extinct, and "Equus" was extirpated from the Americas at the end of the last ice age, possibly due to a changing climate or the impact of newly arrived human hunters. Thus at the beginning of the Columbian Exchange, there were no equids in the Americas.