Radiolarian extinction event in the Middle Paleozoic

通过对日本和蒙古上志留统-中泥盆统硅质岩中放射虫动物群的变迁和地球化学研究，探讨了早泥盆世可能的生物大灭绝事件。研究结果表明：（1）Inaniguttidae在早泥盆世中期开始衰落并最终灭绝;（2）Palaeoscenidididae作为一个典型的机会类群占据了早泥盆世晚期的放射虫动物群;（3）Entactiniidae在中泥盆世开始明显多样化。根据硅质岩的地球化学分析结果，有一种可能性，这一灭绝事件与早泥盆世的环境变化归因于一个大的火成岩活动的因果关系。

Radiolarian faunal transition and geochemistry of Upper Silurian to Middle Devonian siliceous rocks in Japan and Mongolia were investigated to understand a possible mass extinction event in Early Devonian time. The result of the present study indicates the following faunal transition process: (1) the decline and subsequent extinction of Inaniguttidae occurred in the middle Early Devonian, (2) Palaeoscenidiidae that is a typical opportunistic group occupied a late Early Devonian radiolarian fauna, and (3) subsequent diversification of Entactiniidae became pronounced in the Middle Devonian. Based on the results of geochemical analysis of chert, there is a possibility that this extinction event has a causal relationship with Early Devonian environmental change attributed to a large igneous activity.