Estimation of diet in extinct raccoon dog species by the molar ratio method

Estimation of the dietary habits of extinct species using morphological traits has been attempted in numerous studies; however, previous methods have encountered several difficulties, such as requiring specialized equipment. In this study, we describe an easy quantitative method for estimating the dietary habits, and apply it to extinct raccoon dogs (Nyctereutes) species (Carnivora, Mammalia). The method is based on the lower molar ratios (M₂/M₁ size) that reflect the species diet (carnivorous and omnivorous tendencies) in Canidae. Among the species statistically compared, Nyctereutes sinensis showed a lower M₂/M₁ score similar to that of Nyctereutes procyonoides albus (Hokkaido, Japan), whereas Nyctereutes tingi had a higher M₂/M₁ score similar to that of Nyctereutes procyonoides viverrinus (Honshu and Kyushu, Japan). These scores suggest that the diets of N. sinensis and N. tingi were similar to those of N. p. albus (relatively carnivorous) and N. p. viverrinus (relatively omnivorous), respectively. Other extinct raccoon dogs also showed varied M₂/M₁ score, suggesting dietary difference. These results suggest that raccoon dogs underwent dietary transitions or exhibited dietary plasticity during evolution, while their range of diets might have remained the same as those of different populations of extant species Nyctereutes procyonoides.