Pitheciids are small- to medium-sized monkeys. Callicebus is the smallest, followed by Pithecia, Chiropotes, and Cacajao. Both Chiropotes and Cacajao are sexually dimorphic in size, with males 20-23% larger than females. Sexual dichromatism is uncommon, but is found in Pithecia pithecia and P. aequatorialis.
It is most pronounced in Pithecia pithecia: males are solid black with a white face and black nose, while females are blackish-agouti with white stripes from under each eye to the corners of the mouth.
Other pitheciids range in color from dark agouti with paler hands and feet and sex-specific patterns of facial hair (Pithecia species), black with light to dark brown back and shoulders (Chiropotes satanas), silky black with a white nose (C. albinasus), reddish orange to orange, or white (Cacajao calvus), or black with a reddish brown to orange back, belly, and thighs (Cacajao melanocephalus). Callicebus is a very diverse genus in terms of coloration. The pelage ranges from black hands (Callicebus personatus), or black all over with yellow hands (Callicebus torquatus), while other species vary from agouti to roufous to grayish with various facial markings.
The four genera are quite distinct in appearance. Pithecia and Cacajao have long, coarse, fluffy hair, Callicebus has long, dense, fluffy hair, while Chiropotes is distinctive in having short body hair. Pithecia and Chiropotes have long, bushy, non-
prehensile tails, Callicebus has a long, thickly haired tail, and Cacajao is unique in having a short, bushy haired tail that measures only one-third the length of its body. Distinctive beards, bulbous temporal swellings, and distinctive pink scrotums in males and pink vaginal lips in females characterize bearded sakis (Chiropotes). The bald uakari (Cacajao calvus) is unique in having a bright red, naked face and a bald head
The major defining feature of pitheciids is a shared dental complex. Enormous laterally splayed canines that are functionally separated from the incisors by a diastema are used to open fruits protected by hard, thick husks. The incisors are inclined anteriorly for cropping fruit, and the lower ones are styliform. The molars have low occlusal relief and crenula-tions. Pitheciids have been characterized as "sclerocarpic foragers" because of their specialization for exploiting heavily protected fruit, such as species of the Brazil nut family (Lecythidaceae).
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