Fossils
Online ISSN : 2424-2632
Print ISSN : 0022-9202
ISSN-L : 0022-9202
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Volume 110
Displaying 1-7 of 7 articles from this issue
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  • Radiolarians from Jurassic accretionary complex of the Chichibu belt in the western Akaishi Mountains and chert pebbles of the Miocene Wada Formation in Minami-Shinano, central Japan
    Tsuyoshi Ito, Yoshihiro Nakamura
    2021 Volume 110 Pages 3-16
    Published: September 30, 2021
    Released on J-STAGE: October 15, 2021
    DOIhttps://doi.org/10.14825/kaseki.110.0_3
    JOURNAL FREE ACCESS
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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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  • Comparison of predatory behavior and drillhole characteristic between Rapana venosa and Glossaulax didyma
    Kengo Mikura, Shin’ichi Sato
    2021 Volume 110 Pages 17-25
    Published: September 30, 2021
    Released on J-STAGE: October 15, 2021
    DOIhttps://doi.org/10.14825/kaseki.110.0_17
    JOURNAL FREE ACCESS
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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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