The horse (Equus ferus caballus) is a domesticated one-toed hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of Equus ferus. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature, Eohippus, into the large, single-toed animal of today. Humans began domesticating horses around 4000 BC, and their domestication is believed to have been widespread by 3000 BC. Horses in the subspecies caballus are domesticated, although some domesticated populations live in the wild as feral horses. There are four widely recognized extant species of tapir, all of the family Tapiridae; three are in the genus Tapirus, and a fourth in the genus Acrocodia. They are the South American tapir, the Malayan tapir, Baird's tapir, and the mountain tapir.