Labiolingual thickness and cross-sectional area in callitrichid incisors

Several species of primate rely on tree exudates as a component of their diet, with taxa ranging from opportunistic exudativores to intensive exudativores. To access these exudates, many taxa make use of modified anterior teeth to gouge into tree bark to stimulate the flow of saps or gums. Recent efforts have identified several "dental signatures" of exudativory among primates, including differences in the robustness and bending resistance of the strepsirrhine toothcomb. The relative size and the labiolingual thickness of the lower incisors have also been cited as a difference between gouging and non-gouging callitrichids, with the former predicted to have relatively larger (in cross-sectional area) and labiolingually thicker lower incisors. However, along with methodological issues, these predictions have generally only been tested in a small sample of callitrichid taxa. Here, these predictions are tested in a sample of seven extant callitrichid species (N = 185 specimens), representing five genera. The results suggest that gouging callitrichids are not characterized by relatively larger incisors, contrary to previous results. However, the gougers are characterized by labiolingually thicker lower incisors compared to the non-gougers, which hypothetically helps resist bending stress during gouging. Having relatively taller incisors, as well as more highly decussated enamel, larger tooth roots, and differences in enamel distribution, along with the labiolingually thicker lower incisors may explain why the gouging taxa are not characterized by relatively larger incisors. This pattern of incisor morphology serves as another signal for primate gouging and may provide insight into gouging behavior in the fossil record and other extant taxa such as the exudativorous lorisoids.