| 概要 |
A paleontological work was carried out for a part of the type Ashiya Group at Iwaya, Kitakyushu City, to approach the community-paleoecology. The relation of the samples with the original communities ...was considered theoretically in regard to the change, especially the decrease of the elements during successive stages from the biocoenoses to the fossil assemblages via thanatocoenoses and buried thanatocoenoses. In the case that the change of the elements at respective stages was minimum, the fossil assemblage can be regarded as a fossil community to represent the original one. After the preliminary survey the locations were selected to obtain appropriate samples verifying good correspondence to the fossil assemblages, which, in turn, represent the original communities respectively. The sample-size is not necessarily sufficient to satisfy the statistic demand for minimum error of estimation of the biological meaning of the fossil communities. The samples are, however, believed to place the firm basis for the discussion of the dominant species and, furthermore, to give useful informations about the biological relation of the lesser species. The result of the study is summarized in figures 1-4 and tables 1-5. The samples consist of less than 11 species respectively and the individual-numbers of the samples show good logarithmic correlation to the species-numbers. The ratio of the individual-number to the species-number is markedly larger than the recent samples of about the same size from off-shore living communities. Life-habit and food requirement of each species of the samples were inferred on the basis of knowledge about the living representatives and applied to analyse the biological relation in the assemblages. If this is acceptable, the first and the second dominant species in a single sample are different from each other in respect to their life-habit and/or food requirement. The analysis of co-occurrence of the species shows that the species comprising pair of close association are different from each other functionally in their life-habit or food. The present fossil communities can be numerically classified into 9 typological communities on the basis of the composition and frequency of the species. While the correspondence of the communities to the physico-chemical environments is not clear from the above communities. Hence certain physico-chemical factors, such as depth, watermass, and water movement, were, on one hand, applied to formulate the ideal environment. On the other hand the hypothetical communities were abstracted from the typological ones on the basis of the selected pairs of species showing close association and verifying the adaptation for certain physico ehemical environmental factors. They are Phaxas izumoensis-Angulus maximus, Dosinia chikuzenensis-Solen connectens, Glycymeris cisshuensis, and Venericardia subnipponica-Acila ashiyaensis communities. Comparison of the functional characters of the elements of the typological communities verified the hypothetical communities should be a more idealized and simpler forms of the former. In other words, modification of the ideal communities corresponding to the deviation of the physico-chemical factors leads to the typological ones. Comparison of the fossil communities with the living ones or fossil ones of different age can be executed more practically on the basis of the ideal communities than the typological ones, because the environmental condition is more apparent in the former than in the latter.続きを見る
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