1996 Fiscal Year Final Research Report Summary
Shell structure of the Mesozoic bivalve Gryphaea and its adaptative significance
| Project/Area Number |
06640597
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Stratigraphy/Paleontology
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
CHINZEI Kiyotaka Kyoto Univ., Dept.Geol.Mineral., Professor, 大学院・理学研究科, 教授 (70011517)
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| Project Period (FY) |
1994 – 1996
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| Keywords | Mesozoic fossils / oysters / shell structure / ligament / adaptation |
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| Research Abstract |
Mesozoic oyster Gryphaea was one of mud-dwelling oysters, and is thought to stabilize its posture on soft mud by means of its peculiar morphology and heavyweight shell. This research aims to clarify shell sturucture of Gryphaea and ascertain if they have a lightweight shell to float on mud. It also describe strucure of ligament of oysters and other sessile bivalves in comparison with swimming bivalves.
Some shells of Gryphaea retain original structure. The shells are comopsed of thin layrs of lath-like calcite crystals, and the layrs alternate showing slightly different directions to each other. The structure is called the cross-foliated which is known among Hytissa and some of other oysters. Notable fact is that there is no lightweight structure such as chalky layr or honeycomb structure that are seen among other mud-dwelling oysters. Egyptial Mid-Cretaceous oysters Ilymatogyra and Rhyncostreon were obserbed in order to check their shell structure and compare with Gryphaea. There are thick chalky deposits in Ilymatogyra shell that indicate the emproyment of floating strategy by this coiled oyster. However, none of these strucutres are observed in Rhyncostreon shells. The two oysters show different adaptive shell structure.
Ligaments of swimming acallops are composed of central plastic part and marginal calcified parts. the organic fibers seen in the central part run parpendicular to the direction of compression and parallel to the axis of the shell, while in the marginal parts the fibers are arranged perpendicular to shell axis. The significance of the differnt arrangement of the fibers may be related to the quick release of stress when valves were open.
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