Ungulates are large grazing animals whose toenails have become enlarged into hooves. There are two orders of ungulates: Perissodactyla and Artiodactyla.
Animals in the order Artiodactyla have an even number of toes (usually two) that form a cloven hoof. This order is relatively diverse, containing 82 genera and several hundred species. There are nine families in this order, the most familiar of which are the pigs (Suidae), peccaries (Tayasuidae), hippopotamuses (Hippopotamidae), camels (Camelidae), deer (Cervidae), giraffes (Giraffidae), sheep, cattle, antelopes (Bovidae), and pronghorn antelopes (Antilocapridae).
Animals in the order Perissodactyla have an odd number of toes (usually one) that form a single, large hoof. Examples of this order include horses (family Equidae), tapirs (Tapiridae), and rhinos (Rhinocerotidae), together comprising six extant genera and 16 species.
At the time of the European discovery of North America, the native fauna of ungulates included bison (Bison bison), pronghorn antelope (Antilocapra americana), collared peccary (Tayassu tayacu), muskox (Ovibos moschatus), mountain goat (Oreanmnos americanus), and mountain and Dall sheep (Ovis canadensis and O. dalli). The North American Cervidae includes white-tailed deer and mule deer (Odocoileus virginianus and O. hemionus), wapiti or elk (Cervus elaphus), moose (Alces alces), and caribou (Rangifer tarandus).
About 8,000-10,000 years before Europeans first came to America, North America supported a substantially larger number of ungulate species, including 10 species of horses, four species of camels, a species of cow, two additional species of bison, and the saiga antelope (Saiga tatarica). There were also other large, now-extinct mammals, including four species of elephants, such as the mastodon (Mammut americanum) and mammoth (Mammuthus primigenius), a giant ground sloth (Gryptotherium listai), and large predators such as the sabertooth cat (Smilodon fatalis) and the American lion (Panthera leo atrox). These large mammals disappeared during a great wave of extinctions that occurred at the end of the last ice age (about 8-12 thousand years ago). These extinctions may have been caused by overhunting by the first human inhabitants of North America, migrants from Asia who colonized the continent at about that time.
Some species of ungulates that have been domesticated are important in agriculture and sometimes as draft animals. The most abundant domesticated ungulates are sheep (Ovis aries), goats (Capra hircus), cows (Bos taurus), zebu cows (B. indica), pigs (Sus scrofa), horses (Equus caballus), camels (Camelus dromedarius and C. bactrianus), and water buffalo (Bubalus bubalis).
Many of the wild species of ungulates have recently become endangered and some have become extinct as a result of human influences. The most important of the human activities that endanger wildlife are the habitat losses associated with extensive conversions of natural ecosystems into agricultural or urban lands, and overhunting for the meat, hide, horns, or antlers of these large animals. It is critical that these human influences be rigorously controlled, if there is to be room on Earth to sustain all living species of ungulates. Natural ecosystems would be severely impoverished if only domesticated species of ungulates used in agriculture were to survive, along with the few species tolerant of habitats created by humans.