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This report contains three principal results of the palaeontological study of the Miyazaki group. They concern with palaeoecology, biostratigraphical correlation, and evolution problem. The Miyazaki g...roup, occupying the south-east part of the Miyazaki Prefecture, Japan, includes two major cycles of sedimentation and is composed of laterally segregated a few sedimentary facies. The faunal and the lineal successions of the mollusks of the Miyazaki group are surprisingly concordant each other and a few distinct faunal zonules and topozones are recognized. The results of the correlation depends much upon the materials based on and they are not always quite harmonious one another according to the different groups of the organisms. My conclusion on age, which is harmonized to the data on the mollusks, higher foraminifers, and plankton foraminifers with least inconsistence, indicates that the Miyazaki group ranges from upper Helvetian to Plaisancian. Salinity and water temperature are respectively one of the most important limiting factors for the neritic benthos. Temperature of the sea water is considered to have lowered down gradually from tropic to subtropic condition in the laspe of time from late Helvetian to Tortonian. Thereafter no essential change took place. While the area was differentiated into several physiological environments including open oceanic one and bay water one and the biofacies apparently correspond to these environments at the beginning of the first transgression. Then the oceanographic conditions became gradually more open oceanic uniformly over the whole area and the minor segregations of the molluscan communities seems to be due to the mutual reaction among organisms. Concerning the evolution of the ancient animals recognition of the speciation process is very important, but it seems to have been neglected by palaeontologists for long period. The approach to this problem, however, may be possible by means of the analysis of the intraspecies polytypy, especially the sympatric subspecies and of the examination of the relation between these subspecies and of the examination of the relation between these subspecies and the environmental factors of their habitats. Paphia (Paphia) exilis SHUTO and a few other examples are offered here.続きを見る
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1.Introduction 2.Acknowledgements 3.A brief note on the lithostraigraphy of Miyazaki group 4.Complete list of the Molluscan Species from the Miyazaki group 5.Palaeoecoligy of the molluscan faunas 6.Afe of the faunas 7.Speciation of some molluscan spcies 8.Works cied
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Mendeley出力
10_02_p073