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 lambei of the modern wild horse, including the domestic horse, "Equus caballus". Controversy still surrounds "E. lambei" and the divergence of other similar extinct horse species. Through examinations of the bones and teeth of "Equus lambei", many similarities can be seen with the modern horse "Equus caballus". There is also a strong resemblance to "E. lambei" in the metapodials of "E. caballus przewalskii" and the phalanges of "E. caballus lenensis" "." Metrical and morphological studies of horse teeth from the Bluefish Caves confirm the close similarity between "Equus lambei" with wild and domestic horses alive today. "E. lambei" is a "caballus"