Squirrel monkeys live in the tropical rainforests of South America, except in the southeastern coastal forests of Brazil. Squirrel monkeys prefer primary and secondary forest, gallery forest and forest edge. They prefer the intermediate forest levels, but they can sometimes be found on the ground or in upper canopy levels. They occupy many different types of forests. Squirrel monkeys are up to 12.5 inches long (body length), with a tail of approximately 16 inches. They have a slender, lithe build, with a short greyish coat and bright yellow legs. Their non-prehensile tail often curls over one shoulder when they are resting. They have 36 teeth, and their teeth are sexually dimorphic in that males have large upper canines. Squirrel monkesy possess nails instead of claws, and they have been called 'small, nervous primates'. They are the smallest of the Primate family Cebidae. Squirrel monkey groups may be made up of as many as 300 individuals. In the non-mating season, subgroups form within the main group based on, for instance, age, sex or family roles. These subgroups are abandoned during the mating season. Group size is affected by habitat. Squirrel monkeys are very agile; they often run throughout the forest on branches. Squirrel monkeys display female dominance, with the females forming the central core of the group, or troop. Some temporary relationships may form between a mother with no infant and another female's infant. These older females become "aunts". Males have a "subadult" period in while they still play with other juveniles. Males also display a clear dominance hierarchy. Males at the top of their hierarchy are not always the most successful in mating; it is unclear what the advantage of social position is. There are no territorial disputes, groups tend to mutually avoid one another. Groups may sometimes be found together, but not for long and perhaps only to search for food. Squirrel monkeys are diurnal, and activities are usually centered around a source of water. Squirrel monkeys eat mainly fruit and some insects; they also consume some leaves and seeds. The first hour or so of the day is spent searching and collecting fruit. From then on, they look also for spiders and insects. A group spreads throughout the forest in all canopy levels to search for food.