Tooth Function of the Northern Raccoon (Procyon lotor) and Adaptations to Omnivory in the Order Carnivora

The raccoon (Procyon lotor) is an omnivorous carnivoran, with a diet that consists of plant material such as acorns, corn, fruits and berries, as well as animal matter including insects, crustaceans and vertebrates. While the morphology of the teeth of P. lotor is well known, the occlusal functions of crown features of the cheek dentition have not been studied in detail. The aim of this study is to describe the tooth function of the raccoon. Of the 26 raccoon skulls studied, 19 were used in a wear facet analysis and seven were included in a dentine exposure series. Additionally, an Occlusal Fingerprint Analyser (OFA) analysis was performed. The results showed that the power stroke of P. lotor consists of two phases, both with a large horizontal component. This suggests that grinding plays a major role in its tooth function, which is corroborated by the presence of grinding facets on the buccal sides of the P4 hypocone, M1 protocone and metaconule and M2 protocone, as well as on the antagonistic surfaces on the lower molars. Abrasion on multiple cusps of the upper and lower cheek teeth and their antagonistic basins shows that crushing is also an important component of raccoon tooth function, and crushing basins exist on the lower as well as upper teeth. The OFA analysis furthermore revealed an occlusal relationship between the enlarged M1 metaconule and the trigonid basin of the m2, while the hypocone of the M1 is shifted lingually with respect to that of the P4, indicating that the M1 metaconule replaces the function of the hypocone. The observed functional replacement of the hypocone by the metaconule on the M1 has not been recorded previously in Carnivora and opens up new questions about the tooth evolution of P. lotor and other procyonids.