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

为了弄清底栖生物在大灭绝之后是如何恢复的以及新的分类类群是如何出现的，我们对两个案例进行了古生态学研究，一个是在P-T之后，另一个是在白垩纪末期大灭绝之后。到目前为止，已经获得了以下结果：为了测量P-T大灭绝前底栖动物多样性的变化，对日本北部北上山晚二叠世（长兴期）近海浅滩的微量化石进行了研究。结果表明，在P-T边界之前，底栖动物的多样性已经很低了。为了阐明早三叠世底栖动物的多样性恢复情况，对北上山的硅屑沉积进行了研究。来自这片海域的史密斯动物群显示出大范围的但多样性较低的群落，日本的这一例子早于北美和南亚其他类似动物群的出现。了解长期的捕食者-猎物相互作用是很重要的，特别是当硬食性捕食者出现时，以及它们有多强大。本文对日本浅水沉积的21个地层（9个中生代和12个新生代）进行了调查，以确定这些地层中是否含有双壳类和腹足类的角状碎片。中生代地层很少含有双壳类和腹足类动物的角状碎片，只有一个白垩纪晚期的地层含有这种角状碎片。另一方面，新生代地层中有丰富的角壳碎片。我们还用翻滚桶对贝壳进行了机械磨损实验，以观察这种机械损伤是否会产生我们在浅水沉积物中看到的角状贝壳碎片。翻滚桶的结果表明，这种磨损的壳不会出现角度破碎的形状。野外调查和滚翻实验表明，角状壳碎片是由硬食性捕食者产生的，这种捕食活动自新生代开始，即K-T大灭绝之后，愈演愈烈。少

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