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".
Astrohippus
Astrohippus is an extinct member of the Equidae tribe Equini, the same tribe that contains the only living equid genus, "Equus". Fossil remains have been found in the central United States, Florida, and the Mexican states of Chihuahua, Jalisco, and Guanajuato. The fossils date in time from the oldest dating from the Barstovian in the Miocene to the youngest dating in the Hemphillian faunal stage of the early Pliocene.