生物測定にもとづく珪藻化石 Denticulopsis lauta の形態解析 : 大きさと形による種の認識

概要

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The Genus Denticulopsis Simonsen (planktonic diatom) flourished in the North Pacific through the middle-to-late Miocene Epoch. Most species under this genus are useful as an index because of their rapid progress in evolution and abundant occurrence from both onshore strata and deep sea sediments. Denticulopsis lauta is one of the most important species in establishing biostratigraphy and reconstructing paleoenvironments at the time of about 15 Ma. 1100 specimens, collected from Hitachiota City, northeast Honshu, Japan, are examined under the light microscope for the size and shape of diatom valves. In order to appreciate the details of valve structure, I have defined a new term of "chamber" which signifies the space between pseudosepta, and counted the sum of the "chamber" in each valve. D. lauta keeps an odd number of "chamber" essentially. Valves having either 3 or 5 of "chambers" occupy more than 70% of the total specimens. I have distinguished three types of valves among the samples of D. lauta on the basis of apical pseudosepta's mode within the apices of diatom skeletons. The number of "chambers" and mode of apical pseudosepta are the most important character in analyzing life cycles in which diatom valves gradually decrease in size through the process of cell division.
日本古生物学会の論文
1988-06-03