The term equine refers to any member of this genus. "Equus" has many extinct species known only from fossils. The genus most likely originated in North America and spread quickly to the Old World. Equines are odd-toed ungulates with slender legs, long heads, relatively long necks, manes (erect in most subspecies) and long tails. All species are herbivorous, and mostly grazers with simpler digestive systems than ruminants. They can live on low-quality vegetation.