Peaceful meaning for the silent bared-teeth displays of mandrills

We studied the meaning of silent bared-teeth displays in a captive group of mandrills (Mandrillus sphinx). We observed the displays mostly in positive interactions, in which case they could advertise the sender's peaceful intentions, though at times they also occurred as a response to aggression. We found no relationship between the direction of agonistic interactions and the display. Both variants of the display, with closed or open jaws, exhibited mostly symmetrical patterns. The evolutionary convergence of the closed and open bared-teeth displays might be related to the dominance style of mandrills.