Taxonomy: 2 genera: Cebus (organ-grinder or capuchin monkeys) and saimiri (squirrel monkeys)
Biogeography: Widely distributed in neotropical forests
Body size & anatomy: Small (saimiri = 1 kg) to medium (cebus = 4 kg). Cebus has the largest brain compared to its body size for any new world monkey.
Diet: Frugivore-insectivores, but some will eat anything available.
Society: Multimale-multifemale societies. Squirrel monkeys have a short breeding system and females are dominant.
This is the grab-bag subfamily- has a lot of odds and ends.
Taxonomy: 5 genera: Aotus (night monkey), callicebus (titi), pithecia, chiropotes, and cacajao (uakari), which may be the ugliest new world monkey. They have bright red faces, and are bald.
Biogeography: Pithecia, cacajao (who like to live in flooded forests so haven't been studied too much since they're hard to get to), and chiropotes restricted to Amazonia; Aotus distributed widely; Callicebus dispersed patchily.
Body size & Anatomy: Medium size, 2-4 kg, but aotus and callicebus about 1 kg
Diet: Frugivores, 'seed predators;' uakari eats unripe fruit- really just opens it to get the seeds
Society: Pithecia, cacajao and chiropotes variable; aotus and callicebus monogamous. Aotus (night monkey) is the only nocturnal monkey.
Taxonomy: A single genus alouatta. There are lots of species. These are the howler monkeys. They're pretty common. More often heard than seen.
Biogeography: Found in all regions, they're the most widely dispersed of all the platyrrinni.
Body size & Anatomy: Large (7-8 kg), with an enlarged hyoid bone (in throat) and very deep mandible (related to howling). Long hind gut (related to folivory) because leaves take a long time to digest. Howlers are the analogues of colobinae in old world. Prehensile tails, used for support during feeding.
Society: Social organization variable, multi-male to single-male groups. Unusual to have such variation within a subfamily. Since they're so common and are easy to identify and slow-moving, they're often studied.
Subfamily Atelinae (wooly monkeys and spider monkeys)
Taxonomy: 3 genera: Ateles (spider monkey), brachyteles (wooly spider monkey aka mariki), and lagothrix (wooly monkey). An interesting physiological fact about these guys: the female's clitoris is bigger than the male's penis! This makes them hard to sex.
Biogeography: Ateles: all areas except SE brazil. Brachyteles: endangered and rare; a few hundred individuals only SE Brazil. Lagothrix: limited to upper Amazon.
Body size & Anatomy: Large; up to 9.5 kg. They are long-limbed, with prehensile tails used in feeding and locomotion (rapid brachiation).
Diet: Frugivorous, but brachyteles folivorous
Society: Ateles has a fission-fusion social system; A group shares a boundary and defends it but they don't usually hang out together. Brachyteles has multimale groups but not much overcompetition, so the females mate with lots of guys. For a male to beat out the others, he just needs to put in more sperm per session, so they have ended up with really big testes. Also there are multifemale groups.