Diets of Pleistocene insular dwarf deer revealed by dental microwear texture analysis

Abstract

Microwear is defined as the microscopic scars left during mastication on the surfaces of teeth. Because microwear reflects the physical properties of the food eaten by animal, it has been used for reconstruction of the diets of extinct animals. We investigated the dental microwear of the extinct insular dwarf deer Cervus astylodon using materials excavated from Late Pleistocene archaeological sites on Okinawa Island (the Hananda-Gama Cave site and the Yamashita-cho Cave I site). We applied three-dimensional surface texture analysis to quantitatively evaluate microwear features. We analyzed 293 individual sika deer (Cervus nippon) from 15 populations in Japan with quantitative dietary data clarified by rumen contents or feces analyses, constructing one of the most comprehensive microwear databases of extant ruminants. We found that deer with a higher consumption of graminoids showed rougher tooth surfaces than those browsing on trees owing to the high content of abrasive silica in graminoid leaves. Using a regression equation relating surface roughness parameters and the percentage of graminoids in the diet, we estimated that C. astylodon from the Hananda-Gama Cave might have consumed a diet consisting of approximately 44% graminoids, whereas we estimate a predominantly graminoid-based diet (ca. 78%) for deer from the Yamashita-cho Cave. Therefore, contrary to the findings of mesowear and stable carbon isotope analysis, which indicated a browsing diet, we propose that C. astylodon were mixed feeders or possibly grazers. These findings provided an important implication of their peculiar evolution on islands.