Horse
The horse adapted to survive in areas of wide-open terrain with sparse vegetation, surviving in an ecosystem where other large grazing animals, especially ruminants, could not. Horses and other equids are odd-toed ungulates of the order Perissodactyla, a group of mammals that was dominant during the Tertiary period. In the past, this order contained 14 families, but only three—Equidae (the horse and related species), Tapiridae (the tapir), and Rhinocerotidae (the rhinoceroses)—have survived to the present day.
Wild horse
The horse family Equidae and the genus "Equus" evolved in North America, before the species moved into the Eastern Hemisphere. Studies using ancient DNA, as well as DNA of recent individuals, show the presence of two closely related horse species in North America, the wild horse and "Haringtonhippus francisci", the "New World stilt-legged horse"; the latter has been taxonomically assigned to various names.