Hippidion (meaning pony) was a Welsh pony-sized horse that lived in South America during the Pleistocene epoch, between 2 million and 10,000 years ago. Hippidion has been considered a descendant of Merychippus, a genus of horses that migrated into the South American continent around 5 million years ago. Recent analysis of the DNA of Hippidion and other New World Pleistocene horses supports the novel hypothesis that Hippidion is actually descended from the living genus Equus, with a particularly close relationship to the domestic horse, Equus caballus (Weinstock et al., 2005). It stood about approximately 1.4 metres (4.6 ft) (also 13.2 hh) high at the shoulders and resembled a donkey. Evidence from the delicate structure of the nasal bones in the animal suggests that Hippidion evolved in isolation from the other horse species of North America. Hippidion and similar South American horses went extinct approximately 8000 years ago. Horses did not reappear there until the 1500s as a result of introduction by humans.