I discussed when the ancestor of the Japanese macaques. Macaca fuscata, immigrated into the Japanese Islands based on the Japanese macaque fossils and the land bridge formation between the continent and the Japanese Islands.
The land bridges were formed at least twice in the Quaternary of Japan. Their ages are at the oxygen isotope stage 16, 0.63 million years ago (Ma) when Stegodon orientalis immigrated into the Japanese Islands and the stage 12, 0.43Ma when Palaeoloxodon naumanni did.
To date, the purported oldest fossil macaque in Japan is the isolated lower third molar unearthed from the fissure sediment at the Ando Quarry, Yamaguchi Prefecture. The associated fossil proboscideans are S. orientalis and P. naumanni. The age of the macaque fossil, therefore, remains elusive. A humerus fossil was found from Yarimizu, Chiba Prefecture. The associated proboscidean fossil was P. naumanni. Then the ancestor of the Japanese macaques immigrated into the Japanese Islands between 0.63Ma and 0.43Ma. At present, we cannot discuss whether the ancestor of the Japanese macaques immigrated into the Japanese Islands before 0.63Ma because of the paucity of the evidence.