The silent bared-teeth face and the crest-raise of the mandrill (Mandrillus sphinx): a contextual analysis of signal function

Laidre, M.E. & Yorzinski, J.L. 2005. The silent bared-teeth face and the crest-raise of the mandrill (Mandrillus sphinx): a contextual analysis of signal function. Ethology 111(2): 143-157. PDF