Abstract This study examined the form/function relationship in the dentitions of mammalian frugivores and faunivores. Total molar shearing was quantitatively examined in 17 species of small-bodied primates, marsupials, and micro-chiropterans. Ratios were constructed based on the sum of all shearing crests over the cubed root of body mass. Results demonstrated that at any given body mass, faunivorous taxa from all three orders have more well-developed molar shearing than any frugivorous species, thus representing three independent tests of this association in taxa with diverse phylogenetic histories. Aside from body mass, two other approximations of body size were examined, molar area and molar length. These particular body size surrogates were chosen because, unlike ratios based on body mass, these measures can be used to extrapolate this analysis to the fossil record. Ratios based on measures of molar shearing and these size estimates generally partitioned frugivores from faunivores; however, they were not as effective as the ratio based on mass, especially among primates. In many cases frugivores were found to have relatively smaller molars (both in area and length) than faunivores. Therefore, compared to the ratios based on mass, those corrected by molar area and length tend to overestimate the shearing potential of frugivores while underestimating the shearing potential of faunivores.