Hidden population turnover of small odontocetes in the northwestern North Pacific during the Holocene

Despite numerous studies on the rise and fall of terrestrial megafauna in the Late Quaternary, knowledge about marine megafauna from this period remains limited. Here, we performed radiocarbon dating and partial mitochondrial DNA sequencing from the skeletal remains of three species of small odontocetes (Pacific white-sided dolphins, Dall’s porpoises, and harbour porpoises) excavated from prehistoric archaeological sites around the Japanese shore dating back to 8500 – 1000 years ago. Pacific white-sided dolphins that habituated the eastern coast of Hokkaido (a.k.a. ‘Aynu Mosir’) around 2000 years ago belonged to different maternal groups than those from over 5000 years ago and today. Furthermore, the species composition excavated from eastern Hokkaido sites varies between 5000 and 2000 years ago. These findings suggest two significant population turnovers of small odontocetes on the east coast of Hokkaido, a transitional zone between the coastal area of East Asia and the offshore North Pacific. Notably, the first turnover, occurring between 5000 and 2000 years ago, represents the oldest evidence of local population turnovers of marine megafauna during the Late Quaternary.