Horse
Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus".
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.