Cebids include some of the smallest primates and the smallest true monkeys, with pygmy marmosets averaging masses of 110 grams in males. Marmosets and tamarins (Callitrichinae) are generally smaller, with average mass ranging from 110 grams to 620 grams. Squirrel monkeys (Saimiriinae) are also small primates, with average mass ranging from 550 to 1250 grams. Capuchins (Cebinae) are more robust, with average masses ranging from 1.1 to 3.3 kg. In marmosets and tamarins, females are generally larger. In squirrel monkeys and capuchins, males are generally larger than females and males may have different head and body proportions than females.
Cebids are characterized by round heads with large, forward facing eyes and relatively short muzzles. All species are covered with fur, including the tail, ranging from short and dense in squirrel monkeys and capuchins to long and silky in tamarins and marmosets. Only capuchins have prehensile tails, although their tails are used mainly to steady themselves, rarely to grasp objects. All other cebid species have non-prehensile tails.
Cebids have long tails, generally longer than their body length. Squirrel monkeys range from 27.5 to 37 cm in body length and 14.2 to 17.8 cm in tail length. Capuchins are from 32 to 56 cm in body length and 38 to 56 cm in tail length. Marmosets and tamarins are from 14 to 29 cm head and body length and 20 to 40 cm in tail length. Fur color varies from white or buff through grays and browns to black. Some species of capuchins and marmosets and tamarins have tufts of fur on their heads, or longer hair on the head and shoulders, forming a mane or cape, as in golden lion tamarins.
Cebid hands have long, thin digits with flattened or curved nails. The thumbs are opposable in squirrel monkeys and capuchins and the first toe is large, well-developed and largely opposable in all species. Cebids possess bacula. The dental formula is i 2/2; c 1/1; pm 3/3; m 3/3, except in Leontopithecus, Saguinus, and Callithrix, in which third molars are lacking.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: female larger; male larger; sexes shaped differently