• communicative complexity
• bared-teeth
• Tonkean macaques
• facial expressions
• FACS

The thesis project aims to study the complexity of facial communication in the Tonkeana macaque (Macaca tonkeana), one of the seven endemic species of macaque present in the island of Sulawesi, Indonesia.
Particular attention is given to the so-called "bared-teeth" expressions (i.e. bared teeth), on which due to poorly objective study methods, there is ambiguity in the literature, especially as regards the actual number of different displays present.
The analysis of facial expressions is done using the FACS (Facial Action Coding System, Ekman & Freisen 1978), i.e. a relatively recent method developed to quantitatively (and therefore more objectively) describe facial expressions, on the basis of the muscles activated for produce the display.
Thanks to this method I objectively classified the various "bared-teeth expressions", and I investigated other aspects related to the communicative complexity(e.g. the flexibility in contextual usage; combination with other facial expressions)
The aim of the study is to produce more objective and less ambiguous data than those currently present in the literature, which can lay the foundations for future comparative studies aimed at studying the evolution of this behavior in macaques, and in general throughout the order of primates.