The Middle and Late Pleistocene mammalian faunas of Japan are described with new opinions on their succession and relation to the continental faunas. Although fossil materials assignable to early Middle Pleistocene are seemingly scarce in Japan, the fauna of that time is considered to have been transitional between the Early and Middle Pleistocene ones. On the other hand, fossil records which are younger than early Middle Pleistocene are abundant from the mainlands of Japan; viz. the Honshu-Shikoku-Kyushu area.
In the middle Middle Pleistocene, the fauna of this area contained a considerable number of taxa which are extant today in the area (about 50%). It was also characterized by a high proportion of endemic species and the predominance of temperate forest elements. From this time to the late Middle Pleistocene, several species disappeared from the fauna; at the same time, immigrants from the continent were scarce. The faunal characters of the late Middle Pleistocene were basically identical with those of the preceding time.
In the early Late Pleistocene, no mammal seems to have immigrated from the neighboring continent, and faunal composition was almost consistent with that of the late Middle Pleistocene. The elements of that fauna still persisted in the late Late Pleistocene, apart from the extinction of a few forms. In addition to the fact mentioned above, immigration from the northern part of the continent was recognized in the late Late Pleistocene, although it was restricted to a few large herbivore forms and to a short time duration.
The introduction of the continental faunas to the mainlands of Japan during Middle and Late Pleistocene times was not so remarkable as previously inferred. Therefore it becomes doubtful that the faunas of the area were drastically replaced by the immigration of the Choukoutien, Wanhsien and Loess faunas of China during those times.