ABSTRACT
Marmosets and tamarins, the best-known platyrrhines, have been classified as Callitrichidae and Callitrichinae. The descriptions of primate behavior are arranged under four headings: ecology, sociality, life cycle, and cognition. Callitrich social units are highly variable in composition across taxa and time. Agonistic behavior is rare and usually happens during feeding. In a tamarin species changes in affiliative behaviors were correlated with fluctuations in urinary oxytocin. Mutual contact and grooming explained most of the variance in female oxytocin levels while sexual behavior explained most of the male variance. Callitrich gestation time is at the lower end of the platyrrhine range of variation. Aotus is the only living genus recognized in the Aotid family, but it has been divided into numerous species. Common names for the genus include douroucoulis, night monkeys, and owl monkeys. Owl monkeys, the only nocturnal anthropoids, are socially monogamous but display little affiliative behavior. Owl monkeys are small and sexual dimorphism is minimal.
