Abstract
Plant macrofossil assemblages from the upper Pliocene to the lower half of the lower Pleistocene of the Osaka Group in the southern part of the Osaka basin are described. 221 taxa including 48 extinct plants are identified. Seven assemblage zones, OS-I to OS-VII in ascending order, are established. Zones OS-I, OS-III, OS-V, and OS-VII are characterized by the occurrence of subtropical elements, suggesting warmer climatic conditions than those of zones OS-II, OS-IV, and OS-VI. During the deposition of zone OS-I, about 3 million yrs BP, the climate was the warmest in the Plio-Pleistocene, and many extinct plants flourished. During zone OS-II, the climate became colder. From zone OS-II to OS-III, in combination with climatic deterioration, a change in topography resulted in the extinction of plants including Keteleeria sp., Liquidambar sp., Melliodendron sp., and Sequoia sp., and a increased occurrence of conifers including Abies, Tsuga, and Cryptomeria. Most of the plant species had become extinct by the end of zone OS-III, about 2.5 million yrs BP.
