Land and/or Ice bridge formation and human immigration in the Japanese Island and their adjacent areas during the Quaternary: Multidisciplinary study among geology, paleontology, archaeology and anthropology

根据地质和古生物研究推断，第四纪在日本列岛内部和周围形成了3次陆桥，分别是1.2 Ma、0.6Ma和0.4Ma，冰桥仅在20ka时在津加鲁海峡形成。陆桥形成的频率和持续时间比以前认为的要少得多，也短得多。第四纪，特别是中更新世以来，哺乳动物向日本列岛的迁移受到限制，因此列岛的哺乳动物动物群与该时期的大陆有很大的不同。就考古学而言，在日本群岛上还没有发现晚更新世以前的旧石器时代的工具，而早更新世到晚更新世的工具在大陆上却大量存在。此外，最近的人类学修订表明，在日本大陆记录的许多“人类”化石中，只有少数人类化石是可靠的更新世人类，它们的年代是晚更新世的最后一部分。我们假设人类在更新世期间无法通过陆桥移民到日本群岛，因为陆桥形成的频率和持续时间相当有限。在晚更新世的寒冷时期，由于海平面下降，人类有可能通过渡船和漂流技术越过狭窄的海峡而移民。

On the basis of the geological and paleontological studies, it is inferred that land bridges were formed in and around the Japanese Islands, three times during the Quaternary, namely at 1.2 Ma, 0.6Ma and 0.4Ma, and ice bridges were formed only in the Tsugaru Strait at 20ka. The frequency and duration of the land bridge formation were fewer and much shorter than those previously considered. The immigrations of mammals into the Japanese Islands were limited during the Quaternary, especially since the Middle Pleistocene, and thus the mammalian faunas of the islands were considerably different from those of the continent during the period. As regards archaeology, Paleolithic tools prior to the Late Pleistocene have been unknown in the Japanese Islands, while those of the Early to Late Pleistocene have abundantly occurred in the continent. Moreover, the recent anthropological revision has revealed that only a few human fossils are reliable as Pleistocene humans among many "human" fossils recorded from the mainland of Japan, and they were dated as the last part of the Late Pleistocene. We assume that humans were not able to immigrate through the land bridges into the Japanese Islands during the Pleistocene, because the land bridge formation was quite limited in frequency and duration. It is possible that the humans immigrated by ferrying and rafting techniques across narrow straits formed by the drops of sea level during cold stages of the Late Pleistocene.