Many primates habitually feed on tree gums and saps. Some of these tree exudate feeders actively elicit exudate flow by biting trees with their anterior teeth. Many researchers hypothesize that this tree gouging behavior involves relatively large jaw forces and jaw gapes. Further, some scientists argue that gougers have skulls adapted to these jaw forces and gapes. In reality, we know almost nothing about the jaw forces and gapes during gouging. The researchers will quantify the jaw forces and gapes that common marmosets (Callithrix jacchus) use during gouging using an apparatus they designed to record these data. They will analyze the magnitude and timing of jaw forces and gapes during gouging of different tree types in a male and female marmoset. This will allow them to assess the relative magnitude of the gouging data by comparing gouging jaw forces to the forces marmosets create during transducer biting and gapes during gouging to gapes during chewing. Their results will provide the first empirical data on primate jaw forces and gapes during gouging. The pilot data collected on these two animals will be used to demonstrate the feasibility of the approach and justify collecting data on a larger marmoset sample. The results will be applied to test hypotheses of skull adaptations to gouging in marmosets.