Baboons are primates comprising the genus Papio, one of the 23 genera of Old World monkeys, in the family Cercopithecidae. There are six species of baboon: the hamadryas baboon, the Guinea baboon, the olive baboon, the yellow baboon, the Kinda baboon and the chacma baboon. Each species is native to one of six areas of Africa and the hamadryas baboon is also native to part of the Arabian Peninsula. Baboons are among the largest non-hominoid primates and have existed for at least two million years. Baboons vary in size and weight depending on the species. The smallest, the Kinda baboon, is in length and weighs only , while the largest, the chacma baboon, is up to in length and weighs . All baboons have long, dog-like muzzles, heavy, powerful jaws with sharp canine teeth, close-set eyes, thick fur except on their muzzles, short tails, and nerveless, hairless pads of skin on their protruding buttocks called ischial callosities that provide for sitting comfort. Male hamadryas baboons have large white manes. Baboons exhibit sexual dimorphism in size, colour and/or canine teeth development. Baboons are diurnal and terrestrial, but sleep in trees, or on high cliffs or rocks at night, away from predators. They are found in open savannas and woodlands across Africa. They are omnivorous and their diet consists of a variety of plants and animals. Their principal predators are Nile crocodiles, leopards, lions and hyenas. Most baboons live in hierarchical troops containing harems. Baboons can determine from vocal exchanges what the dominance relations are between individuals. In general, each male can mate with any female; the mating order among the males depends partly on their social rank. Females typically give birth after a six-month gestation, usually to one infant. The females tend to be the primary caretaker of the young, although several females may share the duties for all of their offspring. Offspring are weaned after about a year. They reach sexual maturity around five to eight years.