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).
Pliohippus
Pliohippus (Greek πλεῖον (pleion, "more") and ἵππος (ippos, "horse")) is an extinct genus of Equidae, the "horse family". "Pliohippus" arose in the middle Miocene, around 15 million years ago. It was similar in appearance to "Equus", but had two long extra toes on both sides of the hoof, externally barely visible as callused stubs. The long and slim limbs of "Pliohippus" reveal a quick-footed steppe animal.