Atypical tooth wear found in fossil hominins also present in a Japanese macaque population

Objectives Atypical tooth wear, including macroscopically visible striations on anterior teeth and within root grooves on posterior teeth, are often regarded as evidence of non-masticatory, tool use behavior in fossil hominins. Both these types of dental tissue loss are often considered unique to the genus Homo and suggested to be the earliest evidence of human cultural habits. The aim of this study was to describe similar tooth wear found in a wild primate population and to conduct a differential diagnosis of this atypical tissue loss. Materials and Methods The focus of this study was a sample of wild Japanese macaques from Koshima Island, Japan. Individuals were provisioned regularly on the beach as part of one of the longest running primate field sites. Tooth wear and fractures in this group were compared to two other non-provisioned populations. Information on diet and behavior were obtained from extensive literature and on-going field observations. Results All Koshima Island individuals analyzed showed atypical tooth wear. Large macroscopic striations were visible on many teeth, with sub-vertical striations prominent on the labial surfaces of incisors. Root grooves on posterior teeth were observed in half of the individuals, some showing clear directional striations similar to those reported in "toothpick" grooves in fossil hominins. Tool use and the habitual insertion of non-masticatory items in the mouth has not been observed in this population. Discussion Accidental ingestion of sand and oral processing of marine mollusks likely creates these atypical wear patterns. Implications for similar wear that has been associated with tool-use in fossil hominin samples were discussed.