Horse
The horse adapted to survive in areas of wide-open terrain with sparse vegetation, surviving in an ecosystem where other large grazing animals, especially ruminants, could not. Horses and other equids are odd-toed ungulates of the order Perissodactyla, a group of mammals that was dominant during the Tertiary period. In the past, this order contained 14 families, but only three—Equidae (the horse and related species), Tapiridae (the tapir), and Rhinocerotidae (the rhinoceroses)—have survived to the present day.
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.