Equus (genus)
Equus is a genus of mammals in the family Equidae, which includes horses, donkeys, and zebras. Within Equidae, "Equus" is the only recognized extant genus, comprising seven living species. The term equine refers to any member of this genus, including horses. Like Equidae more broadly, "Equus" has numerous 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, but able to subsist on lower-quality vegetation.
Elk
Until recently, red deer and elk were considered to be one species, "Cervus elaphus". However, mitochondrial DNA studies, conducted on hundreds of samples in 2004 from red deer and elk subspecies as well as other species of the "Cervus" deer family, strongly indicate that elk, or wapiti, should be a distinct species, namely "Cervus canadensis". The previous classification had over a dozen subspecies under the "C. elaphus" species designation; DNA evidence concludes that elk are more closely related to Thorold's deer and even sika deer than they are to the red deer. Elk and red deer produce fertile offspring in captivity, and the two species have freely inter-bred in New Zealand's Fiordland National Park, where the cross-bred animals have all but removed the pure elk blood from the area.