Claim: Equidae includes species.

Equus is a genus of mammals in the family Equidae , which includes horses , asses , 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 -LRB- erect in most subspecies -RRB- and long tails . All species are herbivorous , and mostly grazers with simpler digestive systems than ruminants but able to subsist on lower quality vegetation .   While the domestic horse and donkey -LRB- along with their feral descendants -RRB- exist worldwide , wild equine populations are limited to Africa and Asia . Wild equine social systems come in two forms ; a harem system with tight-knit groups consisting of one adult male or stallion , several females or mares and their young or foals ; and a territorial system where males establish territories with resources that attract females , which associate very fluidly . In both systems , females take care of their offspring but males may play a role as well . Equines communicate with each other both visually and vocally . Human activities have threatened wild equine populations and out of the seven living species , only the plains zebra remains widespread and abundant .