Paleoecological study on the recovery and adaptive radiation of benthic invertebrate faunas after the mass extinctions

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In order to clarify how the benthic organisms recovered and how the new taxonomic groups appeared after the mass extinctions, paleoecological work has been done on the two case studies, one after the P-T, and the other after the end-Cretaceous mass extinctions. Up to now, following results have been obtained.1.In order to measure the diversity change of benthic faunas before the P-T mass extinction, trace fossils in the Late Permian (Changsingian) offshore fades of Kitakami Mountains in northern Japan were examined. As a result, it was suggested that the diversity of benthic faunas had already been low prior to the P-T boundary.2.In order to clarify the diversity recovery of benthic faunas in the Early Triassic, siliciclastic fades of Kitakami Mountains were examined. The Smithian fauna from this fades showed pandemic but low-diversity community, and this Japanese example has predated other occurrences of similar fauna from north America and south Asia.It is important to know the long- … More tern predator-prey interaction, especially when and how strong durophagous predators appeared.We surveyed 21 formations (9 Mesozoic and 12 Cenozoic formations) consisting of shallow-water deposits in Japan to detect whether these formations contain angular-shaped fragments of bivalves and gastropods. Mesozoic formations rarely contained such angular fragments of bivalves and gastropods, and only one example containing such angular fragments was observed from the late Cretaceous. On the other hand, there were abundant angular shell fragments from the Cenozoic formations. We also conducted experiments of mechanical abrasion of shells by using a tumbling barrel, in order to see if such mechanical damage would produce angular shell fragments, the kind we see in the shallow-water deposits. The results of tumbling barrel showed that such abraded shells never show angularly broken shapes. As a result of the field survey and the tumbling experiments, it has been clarified that the angular shell fragments were produced by durophagous predators, and such predatory activity has become intensified since the beginning of the Cenozoic, after the K-T mass extinction. Less