The Order Artiodactyla
  Even-toes hoofed mammals
One of the most numerous groups of mammals today, the even-toed ungulates rest their weight equally on the third and fourth toes of each foot and have an even number of functional toes. There are three sub-orders.
Sub-Order Suiformes
This group of primitive even-toed hoofed mammals do not chew the curd. There are three families.
Family Suidae
Pigs: 8 species
Pigs have a stocky body with a long head and mobile snout used for rooting, and sparse, bristly hair. They have a simple stomach, and eat both plant and animal food. Both their upper and lower tusk-like canine teeth point upwards. There are four toes on each foot, but the two central toes are the largest.
Family Tayassuidae
Peccaries: 2 species
Gregarious pig-like mammals from Central and South America, peccaries also have some ruminant characteristics: a fairly complex stomach, united third and fourth foot bones (these are separate in pigs) and tusk-like canines that point downwards and not upwards as in pigs.
Family Hippopotamidae
Hippopotamuses: 2 species
These animals are good swimmers and divers. Their large, heavy, short-legged bodies have a thick layer of fat under the skin, and their slightly webbed feet have four toes. The bulls fight, using their tusk-like lower canines as weapons.

Sub-Order Tylopoda
The animals forming this sub-order have complex stomachs and chew the cud, but have been separate from the ruminant sub-order for about 55 million years.
Family Camelidae
Camels: 3 wild species
Camels and llamas have only two functional toes, supported by expanded pads for walking on sand or snow. The slender snout bears a cleft upper lip.

Sub-Order Ruminantia
This is the most numerous and varied of the artiodactyl groups. All are ruminants (cud chewers) with three or, usually, four chambers in the stomach; their food is brought up from the first chamber and chewed while the animal is resting, before being swallowed a second time for complete digestion. Many have horns or antlers. There are five families.
Family Tragulidae
Chevrotains: 4 species
Chevrotains, also called mouse deer, are very small ruminants without horns. They have three-chambered stomachs, and the males have long, tusk-like canine teeth. They live in the tropical forests of Africa and southern Asia.
Family Cervidae
Deer: 40 species
Most male deer grow branched antlers - bony outgrowths of the skull covered with velvet (furry skin) during growth. Antler growth stops before the mating season and the velvet is then shed. Antlers are shed after the mating season. The smaller, more delicately built females do not generally have antlers.
Family Bovidae
Cattle and antelopes: 110 species
Bovids have horns with bony cores which grow hard sheaths of horny material. The horns, which are unbranched, are never shed; the sheath is constantly renewed from inside. Most bovids live in grasslands. They vary widely in body form. Examples include the yak, hartebeest, wild goat, bighorn sheep.
Family Antilocapridae
Pronghorns: 1 species
The pronghorn, Antilocapra americana, lives in North American grasslands. Both sexes have horns consisting of fused hairs sheathing a bony core; the sheath is shed each year.
Family Antilocapridae
Giraffes: 2 species
The two or three horns of the giraffe and okapi (absent in the female okapi) are bony growths covered by skin.

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