日本における Taxodiaceae の絶滅期

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It has already been clarified from the point of view of the plant fossils that in the Tertiary age in Japanese islands, the extinct genera such as Cunninghamia, Sequoia, Metasequoia, Taxodium, Glyptostrobus belonging to Taxodiaceae and the other Liquidambar, Nyssa etc. which are extinguished in Japanese islands at present, but had once presented the age of predominance. The writer can clarify the period of extinction of Taxodiaceae above mentioned which is unsolved at present, based on pollen analysis which he has studied for years. The results of investigations are summarized as follows : The Shimizu lignite bed consists of the lignite of Pliocene, and the result of pollen analysis is given in the Fig. 2 : the pollen grains of six genera of Cryptomeria, Sequoia, Metasequoia, Taxodium, Glyptostrobus belonging to Taxodiaceae and the other Liquidambar, Nyssa etc. are detected in each depth of the lignite bed, and indicate the especially dominant age of Taxodiaceae. The result of pollen analysis of the lignite bed in the Izumikawa of Pliocene, however, as is given in Fig. 3,shows that Taxodiaceae were almost not to be found, and in place of them, Abies, Tsuga, Picea and Pinus were dominant, which indicated the Pinaceae period. Especially it is noteworthy that in about the middle of the age of the lignite formation, 5 genera of Taxodiaceae except Cryptomeria are not to be found at all and does not appear even once until the end of the age of the lignite formation. Namely, it may be the clear fact that of the Taxdiaceae that flourished in the age of the first half of Pliocene, five genera such as Cunning-hamia, Sequoia, Metasequoia, Taxodinm and Glyptostrobus except Cryptomeria came to be extinguished in about the middle of the age of the Izumikawa lignite formation Liquidambar, Nyssa, and Liriodendron that appeared in the Shimizu lignite bed are not to be found at all in each depth in the Izumikawa lignite bed. Consequently, it is thought that above mentioned 3 genera was extinguished before the Izumikawa lignite formation. From the result of pollen analysis, the writer reestablished the constituental state of the forests in those days, and deduced the climatic condition which was then dominant. Namely, in the age of the Shimizu lignite formation warm and moist climate was dominant, and in the age of the Izumikawa lignite formation dry and cold climate was dominant. Consequently, the writer can conclude that the extinction of Taxodiaceae was due to the dried and cold climate.
京都府立大学の論文
1956-09-01

日本における Taxodiaceae の絶滅期

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