Tertiary Pectinidae of Japan
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概要
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From a more than ten years research on the Tertiary Pectinidae fauna of the Japanese Islands, a total of 136 species or subspecies distributed in 20 genera and six subgenera belonging to four subfamilies of which one is distinguished as new to science were distinguished. Among the total discriminated pectinids 16 species or subspecies and two subgenera are described for the first time in this work. These pectinids are distributed in time from the Eocene to Pliocene, whereas those belonging to the Quaternary and Recent fauna are reserved for another opportunity. The Paleogene pectinid fauna, particularly from sediments of Oligocene age is found in northwestern Kyushu, southern Shikoku, Kanto, several localities in Northeast Honshu and Hokkaido. These amount to 13 in number of species and eight genera including subgenera, and are characterized particularly by their small individual number, rather simplicity in surface sculpture and more or less restricted distribution. By their specific characters they show remarkably contrasting features compared with those from the Early Miocene sediments extensively distributed in the Japanese Islands. Consequently, the distinction of the Paleogene from the Neogene pectinids is recognized from stability of the fauna, specific and generic including subgeneric compositions of the assemblages reflected from the characters of the surface sculpture, size and shape of the shells, individual numbers, degree of variation presented by them, and evolutionary changes as would be expected from the differences in both space and time. The Neogene pectinid fauna is a very large one, being represented by a total of 128 species or subspecies distributed within 20 genera and subgenera. The respective assemblages represented in the different paleo-zoological provinces distinguished, furnish sufficient evidence for the establishment of fauni-zones respectively influenced by the paleo-oceanographical conditions (temperature, latitude, salinity, nutrient, etc.), yet reveal intimate relationships between the southern and northern faunal zone types discriminated in both Middle and Late Miocene deposits throughout the Japanese Islands. Although the number of species decreases with the advance of geological time, yet there can be recognized even within the Pliocene, faunal zones analogous with those of the Miocene yet distinguishable from them by the specific constituents of the respective pectinid assemblages inclusive also of the frequency. Demarcation of geological time into periods of Oligocene, Miocene and Pliocene based upon the characteristics of the pectinids treated is rendered not only possible but also quite reasonable, there being represented in the later parts of the subjacent periods and in the early parts of the superjacent periods outstanding taxonomic characteristics correlatable with size, shape, sculpture, frequency, and other features of the pectinids, all of which can be readily understood as the reflection not only of differences in geological age but also in the instability of the prevailing physico-oceanographical conditions as related with the diastrophic history and evolutionary backgrounds of the respective pectinids. The biology of the pectinids, their ecology and paleoecology reflected in the sediments in which they occur as well as the faunal assemblages and the faunal zones they construct, when viewed from the point of distribution in time and space as treated in this work afford concrete evidence for correlation of the stratigraphical units which yielded them regardless of their remoteness within the Japanese Islands, from the Oligocene through the Pliocene. Although it is known that until a full study has been made of the pectinid fauna of Japan from sediments younger than the Pliocene have been completed, conclusive expressions concerning minute accounts on their geographical distribution, evolution, and migration within the Pacific area and dispersion, should be reserved. However, so far as the Paleogene and Neogene rocks are concerned, the faunal relationship of the pectinids within the Pacific area as outlined in the present work seems to offer evidence that the application of the pectinids in biostratigraphy because of their evolutionary trends being rather distinct and since their zoning has become established, will serve to facilitate problems related with the interrelationship of geographically isolated sedimentary basins and may be a new view towards the development of paleo-oceanography. Besides the systematic descriptions given in the later part of the present work it is pointed out from taxonomic fundamentals that the systems in classification previously adopted in molluscan paleontology should be subjected to certain revisions because of the present progress in molluscan systematics and the development of fine-cut methods, new views or methods of which are presented in this work, and which has lead to the proposal of the new classification of the Tertiary pectinid fauna of Japan. This newly proposed system of classification incorporates although not actually indicated, both genera and species unknown from the Pacific area.
- 東北大学の論文
- 1962-03-10
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関連論文
- Tertiary Pectinidae of Japan
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