化石
Online ISSN : 2424-2632
Print ISSN : 0022-9202
ISSN-L : 0022-9202
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110 巻
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  • 赤石山脈西部に分布する秩父帯ジュラ紀付加体及び南信濃の中新統和田層のチャート礫から産出した放散虫
    伊藤 剛, 中村 佳博
    2021 年 110 巻 p. 3-16
    発行日: 2021/09/30
    公開日: 2021/10/15
    DOIhttps://doi.org/10.14825/kaseki.110.0_3
    ジャーナル フリー
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    Jurassic accretionary complex of the Chichibu belt is distributed in the western Akaishi Mountains, central Japan. The Miocene Wada Formation, composed mainly of mudstone with basal conglomerate, is exposed in Minami-Shinano, Iida City, Nagano Prefecture, central Japan. This article reports the occurrences of Permian, Triassic, and Jurassic radiolarians from the Jurassic accretionary complex and Triassic radiolarians from the chert pebbles within the basal conglomerate of the Wada Formation. The chert pebbles are most probably derived from accretionary complex of the Chichibu belt exposed near the distributional area of the Wada Formation. Meanwhile, clasts of Cretaceous-Paleogene chert derived from the Shimanto belt nor metamorphic rock from the Sambagawa belt have never been discovered from the Wada Formation so far. This implies that the Shimanto and Sambagawa belts have not largely exposed in the Miocene in the hinterland of the Wada Formation.
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  • 肉食性巻貝類アカニシとツメタガイの捕食行動と捕食痕の比較
    三倉 健吾, 佐藤 慎一
    2021 年 110 巻 p. 17-25
    発行日: 2021/09/30
    公開日: 2021/10/15
    DOIhttps://doi.org/10.14825/kaseki.110.0_17
    ジャーナル フリー
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    In order to extract information about predators from the drillhole characteristics, predatory behavior, drillhole-site selectivity, and preference of prey size and species were examined in Rapana venosa and Glossaulax didyma. Laboratory experiments used predators and the prey bivalves collected from Lake Hamanako in Shizuoka Prefecture, central Japan. Glossaulax didyma always drilled around umbo of bivalve shell, and it preferred similar prey size to its shell size. In contrast, observation of predatory behavior of R. venosa revealed that this species usually killed prey bivalve without drillhole but left slit-shaped scratches or nomarks using probably poisoning or suffocation. Rapana venosa preferred the largest individuals among the different sizes of Ruditapes philippinarum, and it consumed first Cyclina sinensis rather than R. philippinarum and Scapharca kagoshimensis. Our results made clear the differences of the drillhole characteristics and preference of prey size between R. venosa and G. didyma, and enabled to suggest the predator species from the dead and fossil shell.
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