The role of bite force in the formation of orthodentine microwear in tree sloths (Mammalia: Xenarthra: Folivora): Implications for feeding ecology

•Hypothesize that tree sloth microwear features correlate with increasing bite forces.•Scratch width is the only feature to correlate to bite force and just in Choloepus.•Bradypus shows no significant correlation of microwear features with bite force.•Microwear creation is complex and requires more than just simple orthal closure.

ObjectivesThe purpose of this investigation was to explore the role and interplay that bite force has on the formation of microwear features upon the dentition of two- and three-fingered tree sloths (Choloepus and Bradypus, respectively), with the hypothesis that increasing relative bite force would correlate with an increase in frequency of microwear features.DesignMicrowear patterns were assessed by counting features (e.g. scratches, pits) seen within a standardized field of view on the mesio-labial facets casts of upper molariform series from sloth specimens using Scanning Electron Microscopy. Relative bite force was estimated using a geometric model to quantify the muscular inputs of the temporalis and masseter muscles with respect to the mandible at the centre of each lower tooth.ResultsAlthough relative bite force increases posteriorly along the toothrow, there is not a significant increase in frequency of scratches or pits in either sloth. Scratch width increases significantly as bite force increases in Choloepus.ConclusionsWe reject the hypothesis that higher magnitude of bite force is correlated with an increased number of microwear features in tree sloths. Results here suggest that other endogenous variables (such as chewing direction, manipulation of food during mastication, amount of food ingested) play a more significant role in the formation of microwear in sloths than orthal closure force. This further supports the formation of microwear on teeth as an intricate process that has multiple influences beyond the texture of food particles.