白亜紀二枚貝 Sphenoceramus schmidti (Michael) の産状と古生態

概要

論文の詳細を見る
Offshore conditional mudstone beds of the Upper Himenoura Subgroup (Upper Cretaceous) distributed in the Koshikijima area of Kyushu yield many well-preserved specimens of Sphenoceramus schmidti (Michael). In particular, swarms of many individuals occurring from laminated mudstone of the upper part of U-IV Formation undoubtedly represent autochthonous colonies. In this mudstone interbedded with thin fine-to medium-grained sandstones, we have not found any other organic remains than S. schmidti. The maximum shell convexity of S. schmidti lies in the anterior part of the vertical cross-section of shell. This species is certainly a byssally attached and equivalve bivalve, probably being an edgewise recliner (Seilacher, 1984). All of the specimens are horizontally lying down in the mudstone with the right or left valves uppermost. Although the umbones usually pointed to the north or south, the posterior wings to the east. If the life position of S. schmidti is reconstructed as an edgewise recliner, most of the individuals have preferred orientaion, which is statistically tested, with their umbones pointed to the east. This shell arrangement after reconstruction may be probably related to the life habit of this species, for example feeding. However, the implication of shell arrangement should be researched in the future.
日本古生物学会の論文
1992-06-30