The artiodactyls include animals such as cattle, goats, deer, sheep, antelope, camels, llama, pigs, hoppopatmuses as well as numerous other groups.
Artiodactyls range in size from the mouse deer (or 'chevrotains') of Southeast Asia that are barely bigger than a rabbit, to the giant hippopotamus, which weighs some three tons. Giraffes, which are not so heavy as the giant hippopotamus, are indeed large in another way—what they lack in bulk they make up for in height, with some species reaching as much as 18 feet tall.
Social structure varies among artiodactyls. Some species, such as water deer of Southeast Asia, lead relatively solitary lives and only seek company during mating season. Other species, such as wildebeast, cape buffalo and American bison, form large heards.
Artiodactyls are a widespread group of mammals. They have colonized every contient except Antartica (although it should be noted humans introduced artiodactyls to Australia and New Zealand). Artiodactyls live in a variety of habitats including forests, deserts, grasslands, savanas, tundra and mountains.
The artiodactyles that inhabit open grasslands and savanas have evolved several key adaptations for life in those environments. Such adaptations include long legs (which enable swift running), keen eyesight, a good sense of smell and acute hearing. Together, these adaptations enable them to detect and evade predators with great success.
Many even-toed hoofed mammals grow large horns or antlers. Their horns or antlers are used most often when members of the same species come into conflict. Often, males use their horns when fighting each other to establish dominance during the mating season.
Most members of this order are herbivorous (that is, they consume a plant-based diet). Some artiodactyls have three- or four-chambered stomach which enables them to digest celloluse from the plant matter they eat with great efficiency. Pigs and peccaries have an omnivorous diet and this is refected in the physiology of their stomach which has only one chamber.
There are about 225 species of even-toed hoofed mammals. The group is divided into three basic subgroups based on the anatomy of their stomach. These include the ruminants (cattle, goats, deer, sheep and antelope), pseudo ruminants (camels, llama, alpaca, vicuna and guanaco) and the non-ruiminants (pigs, peccaries and hippopotamuses).
The three main groups of even-toed hoofed mammals arose by about 46 million years ago. At that time, even-toed hoofed mammals were by far outnumbered by their cousins the odd-toed hoofed mammals. Even-toed hoofed mammals survived on the fringes, in habitats that offered only hard-to-digest plant foods. That was when even-toed hoofed mammals became well-adapted herbivores and this dietary shift paved the way for their later diversification.
About 15 million years ago, during the Miocene, the climate changed and grasslands became the dominant habitat in many regions. Even-toed hoofed mammals, with their complex stomachs, were poised to take advantage of this shift in food availability and soon surpassed the odd-toed hoofed mammals in number and diversity.