Equus (genus) and pioneer spirit of the West" under the Wild and Free-Roaming Horses and Burros Act of 1971, and in "Kleppe v. New Mexico", the United States Supreme Court ruled that the animals so designated were, as a matter of law, wildlife. 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
Equus niobrarensis Equus niobrarensis Equus niobrarensis (or commonly, Niobrara horse) is an extinct species of "Equus", the genus that includes the horse. "E. niobrarensis" may be synonymous with "Equus scotti". It was "stout-legged" and belonged to the "big horses" category as defined by M. C. Winans. The skull of the horse was noted as being broader than Equus caballus. "E. niobrarensis" was native to North America and commonly found in western North America and dates to the late Pleistocene. Fossils of "E. niobrarensis" were discovered at Dry Cave in Wisconsin. Another mention of an "E. niobrarensis" discovery was in Skeleton Cave, Oregon.