Retrospective isotope analysis of ancient remains to distinguish between tamed and wild animals

The origin and process of the domestication of wild animals have long fascinated scientists. However, there are no reliable methods to distinguish between tamed and wild animals. Here, we present a new method to identify tamed and wild juvenile brown bears (Ursus arctos) using retrospective isotope analysis of the femur. We used femurs from the nine bear cubs and the tibia from one domesticated dog excavated from the Nijibetsu Shuwan Kumaokuriba site, Hokkaido Islands, Japan (late 19th century–1939 AD). These bears were potentially tamed by indigenous Ainu people, and the domesticated dog was used as a reference of a tamed animal. We subdivided these bones into 10 sections along the growing axis, extracted collagen and measured the stable nitrogen isotope ratios (δ¹⁵N). The bone sections of the domesticated dog had constant δ¹⁵N values that were as high as that of salmon, suggesting that tamed animals exclusively consumed a marine diet fed to them by the Ainu. Notably, two of nine brown bear cubs showed a temporal elevation of δ¹⁵N to the similar isotope ratios of the dog tibia, which is unlikely to occur in the wild condition, strongly suggesting that they were tamed and fed by the Ainu people.