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

根据地质学和古生物学研究，推测第四纪日本列岛及其周边地区曾有3次陆桥形成，分别为1.2Ma、0.6Ma和0.4Ma，冰桥仅在津轻海峡形成，形成时间为20ka。陆桥形成的频率和持续时间比以前认为的要少得多。第四纪以来，特别是中更新世以来，哺乳动物的迁入受到限制，因此该时期的哺乳动物区系与大陆哺乳动物区系有很大不同。在考古学方面，晚更新世之前的旧石器时代工具在日本群岛是未知的，而早更新世到晚更新世的工具在大陆大量出现。此外，最近的人类学修订显示，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，它们被确定为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都很有限。人类可能是在晚更新世的寒冷时期，通过摆渡和漂流技术穿越由海平面下降形成的狭窄海峡移民的。

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.