Dental Topographic Analysis of Living and Fossil Lorisoids: Investigations into Markers of Exudate Feeding in Lorises and Galagos

Abstract

Studies integrating patterns of molar morphology and diet are particularly useful to address questions of evolutionary history and diet in extinct taxa. However, such studies are lacking among lorisoids compared with other primates. Lorisoidea is distinctive when considering diet as some taxa consume large quantities of gums or exudates, whereas others consume none. Although there has been previous study of the relationship between craniodental form and exudate feeding, little is known about how patterns of exudate feeding covary with variation in molar topography. We analyzed a sample (n = 52) of lorisoids representing 17 extant taxa and one extinct taxon (Karanisia clarki). We used dental topographic metrics to quantify functional aspects (i.e., curvature, complexity, and relief) of occlusal morphology. We also used ancestral state reconstruction to estimate topographic parameters for the last common ancestors (LCA) of Lorisoidea, Lorisidae, and Galagidae. As with previous studies, we found that higher topographic values characterize insectivores, whereas frugivores tend to have lower values. We reconstructed the LCA of Lorisoidea, Lorisidae, and Galagidae as insectivorous, with Lorisidae slightly more insectivorous, and potentially more exudativorous than Galagidae. Moreover, we identified a significant interaction between the primary dietary component (i.e., fruit or insects) and the level of exudate feeding in our sample, with exudate-feeding insectivores being associated with lower topographic values than exclusive insectivores. Finally, we reconstruct K. clarki as an insectivore, contrary to previous findings, although whether the animal fed on exudates remains ambiguous. Overall, our results provide a framework for testing ecological hypotheses about lorisoids and may point to a unique pattern of molar topography among exudativores.