Are ancient dugong bones useful for analyses

The Ryukyu Archipelago of Japan is the northern limit of the distribution of the dugong (Dugong dugon), and populations in Japanese waters are small. Therefore, little biological information is available on local dugong, and new specimens or techniques are necessary to help shed light on the populations of this region. We assessed the suitability of using ancient dugong bones collected from ruins on Shimoji Island, in the Yaeyama Islands, for biological investigations. We collected more than 1,000 fragments of animal bone at the site. From these, we were able to reconstruct 91 dugong skulls, from which we estimated body length (124.2–301.2 cm) and age group compositions (43% adults, 29% adolescents, and 16% juveniles). Our estimation revealed a wide range of age groups, from neonates to mature adults. These results suggest that the ancient dugong population bred and spent all life stages along the coasts of the Yaeyama Islands. Moreover, our study shows that these ancient bones can be used for meaningful biological investigations on dugong, and should help to elucidate their historical distribution and population structure in this area.