Eocene drill holes in cold-seep bivalves of Hokkaido, northern Japan |
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| Authors: | Kazutaka Amano & Robert G Jenkins |
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| Institution: | Department of Geoscience, Joetsu University of Education, Niigata, Japan; Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan |
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| Abstract: | Four specimens of the thyasirid Conchocele bisecta (Conrad) and one small specimen of the vesicomyid Hubertschenckia ezoensis (Yokoyama), each with a drill hole made by a naticid gastropod, were found at a cold‐seep site in the upper Eocene Poronai Formation of Hokkaido. This is apparently the oldest record not only of drill holes, but also of predation scars, in a cold‐seep fauna. In addition, drilled vesicomyids are known from several Miocene cold‐seep sites in Japan. We suggest that the Eocene and Miocene chemoautotrophic bivalves were drilled only in the shallow‐water settings preferred by most naticids. The lack of drill holes in Oligocene chemoautotrophic bivalves in the northwestern USA suggests that this innovation, which allowed naticids to prey upon highly toxic bivalves, first appeared in the western Pacific during the Eocene. |
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| Keywords: | Cold-seep fauna drilling Eocene fossil seep methane seep predation |
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