Equus caballus; Print; The horse (Equus ferus caballus) is one of two extant subspecies of Equus ferus. It is an odd-toed ungulate mammal belonging to the taxonomic family Equidae. 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. These feral populations are not true wild horses; as this term is used to describe horses that have never been domesticated; such as the endangered Przewalski's horse; a separate subspecies; and the only remaining true wild horse. There is an extensive; specialized vocabulary used to describe equine-related concepts; covering everything from anatomy to life stages; size; colors; markings; breeds; locomotion; and behavior.; enterolite