SUMMARY: Two captive groups of the brown capuchin, Cebuts apella, were observed for approximately 146 hours, with particular attention paid to the facial expressions of this species. Seven discrete facial expressions having the properties of ritualized displays were observed. These were classified as follows according to motivational, status indication, and social functional criteria: (I) Open Mouth Bared Teeth - threat, (2) Open Mouth Staccato Beep - probably defensive threat, (3) Bared Teeth Scream - appeasement, maternal solicitation, (4) Grin - probably appeasement and reassurance, (5) Lipsmacking - reassurance, leads to passive contact, (6) Forehead Raise - affinitive, leads to active contact, and (7) Relaxed Open Mouth - play face, possibly play reassurance. An examination of the intention movements and the behaviors temporally associated with the facial expressions strongly suggests the brown capuchins studied here are providing accurate motivational information to other group members. Facial expressions morphologically similar to those observed in capuchins are also given by many species of Ceropithecinae, especially Macaca and Papio, with similar expressions occurring in similar social contexts. The presence of ritualized appeasement gestures in Cebus, Macaca, and Papio may be a function of the diversity of diet and the resulting spatial distribution of food items.
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