Equidae
Equidae (sometimes known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, donkeys, and zebras, and many other species known only from fossils. All extant species are in the genus "Equus". Equidae belongs to the order Perissodactyla, which includes the extant tapirs and rhinoceros, and several extinct families.
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.