Cristid obliqua morphology as a correlate of diet in lorisoids

Methods for elucidating dietary patterns from dental morphology have provided much insight into molar form, function, and diet in extinct taxa. However, many methods rely on the collection of homologous landmarks (like shearing crest lengths), or computationally intensive and nuanced metrics that capture shape (like dental topography). Here, a new metric is proposed that is both simple to collect and that performs as well as other methods of linking tooth form and function. The angle at the cristid obliqua (ACO), a lower molar crest involved in the shearing phase of the power stroke, is measured as the angle between two lines derived from the hypoflexid to the middle of the cristid obliqua and then to the occlusal basin. The ACO was examined in a sample of extant lorisoid primates (N = 49 specimens) that have previously been examined using methods of dental topographic analysis. Results suggest that the ACO does not covary strongly with molar size or relative cristid obliqua length but is more strongly correlated with measures of dental topography such as relief and curvature. The ACO separates dietary groups (insectivores from exudativores and frugivores) almost as well as molar curvature and better than relief or cristid obliqua length. In general, insectivores have more strongly developed cristids obliquae for shearing insect carapaces and are therefore characterized by lower ACO values. Together, results suggest that the ACO provides further insight into molar form and function and this tool may be useful for examining dietary patterns in extinct primates and mammals more generally.