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.
Caviinae
Caviinae is a subfamily uniting all living members of the family Caviidae with the exception of the maras, capybaras, and "Kerodon". The subfamily traditionally contained the guinea pig or cavy-like forms along with the cursorially adapted (running) "Kerodon". Molecular results suggest the Caviinae as so defined would be paraphyletic and "Kerodon" is more closely related to maras and capybaras than to other caviines. This led Woods and Kilpatrick (2005) to unite "Kerodon" and capybaras into the subfamily Hydrochoerinae within the Caviidae. These studies also suggest "Microcavia" and "Cavia" are more closely related to one another than either is to "Galea".