Seasonal dietary flexibility in the omnivorous raccoon dog (Nyctereutes procyonoides, Canidae) revealed by dental microwear texture analysis: Implications for paleoecology of canids

Dental microwear texture analysis (DMTA) is widely applied to reconstruct diets in herbivorous and carnivorous mammals, but its applicability to omnivorous canids remains insufficiently tested. Because omnivores consume foods with highly variable mechanical properties, it remains unclear whether DMTA can reliably detect seasonal and ontogenetic dietary variation in such taxa. Here, we evaluate the utility of DMTA in the raccoon dog ( Nyctereutes procyonoides ), a wild omnivorous canid inhabiting cool-temperate Japan. Three-dimensional enamel surface textures were analyzed from lower molars of road-killed individuals of known age and sex. Surface roughness varied seasonally, with smoother textures during periods of increased insect consumption and rougher textures during seasons characterized by greater fruit and vertebrate intake. Correlation analyses with independent fecal dietary data supported these trends, suggesting that DMT primarily reflects variation in the mechanical properties of dominant seasonal food resources. Age-related differences were also detected, as adults exhibited significantly rougher surfaces than juveniles, likely reflecting ontogenetic differences in bite force and feeding behavior. No significant sex-related differences were observed. These results demonstrate that DMTA can detect ecologically meaningful dietary variation in a wild omnivorous canid under natural conditions. By providing a modern ecological framework for interpreting dietary flexibility, this study supports the application of DMTA to fossil and archaeological canids and offers comparative insights into dietary transitions associated with environmental change, human proximity, and domestication processes.