Did radiolarians become extinct at the Paleozoic/Mesozoic boundary? - The paleontological study of the Earliest Triassic radiolarians

地球历史上最大规模的物种灭绝事件发生在二叠系/三叠系交界处。放射虫是古生代至中生代具有硅质骨架的海洋浮游生物的代表，从二叠纪到三叠纪发生了巨大的变化。然而，这种变化的细节仍然不清楚，因为全球缺乏最早三叠纪时代的含放射虫的远洋沉积物。包括首席调查员在内的研究小组发现了一个特殊的远洋二叠纪-三叠纪界线序列，暴露在新西兰北岛北岛的一个小岛--Arrow Rock(奥鲁特马努岛)。本研究对三叠纪早期(主要是印度河早期)放射虫进行了古生物学研究，明确了P/T界线上放射虫的详细动物群变化，在格里斯巴克期(印度河早期)和戴奥里亚早期(印度河晚期)硅质岩层序中发现了保存相对完好的放射虫。在这些放射虫中辨别出40多种，报告和/或描述了约20种(Takemura和Aono，2007年；Takemura等人，2007年)。首席调查员已经对其他物种进行了描述，并准备提交分类论文。最早的三叠纪放射虫动物群包括Entaktinens、Latentifiulsians和Albaillens，所有这些都是二叠纪放射虫动物群的组成部分。许多物种与二叠纪物种完全相同，因此它们在P/T界线上幸存下来。原始的Nassellaria是中、新生代动物群的代表，产于印度河晚期(Kamata等人，2007年)。放射虫动物群在P/T界线附近和三叠纪早期逐渐发生变化。这种动物群的变化可能受到从Oruateanu组检测到的双重海洋缺氧事件的影响(Hori等人，2007年)。《箭岩》研究专著(Sporli等人)(编辑)，2007年)作为这一研究项目的成果之一出版。

The largest mass extinction event in earth history occurred at the Permian/Triassic boundary. Radiolarians, representative of Paleozoic to Mesozoic oceanic plankton with siliceous skeletons, drastically changed from Permian to Triassic time. The details of this change, however, remain unclear, because of the global lack of radiolarian-bearing pelagic sediments of Earliest Triassic age. The research group including the head investigator discovered an exceptional pelagic Permian-Triassic boundary sequence exposed at Arrow Rocks (Oruatemanu Island), a small islet at Northland, North Island of New Zealand. In this research project, the paleontological study of Earliest Triassic (mainly Early Induan) radiolarians was made to clarify the detailed faunal change of radiolarians across the P/T boundary.Relatively well-preserved radiolarians occurred in about 10 horizons within Griesbachian (early Induan) and early Dienerian (late Induan) chert sequence from Arrow Rocks. More than 40 species were discriminated among these radiolarians and about 20 species were reported and/or described (Takemura and Aono, 2007 ; Takemura et al., 2007). The head investigator had described the other species and prepares to submit the taxonomic paper.The Earliest Triassic radiolarian faunas include Entactinarians, Latentifistularians and Albaillellarians, all of which are components of Permian radiolarian faunas. Many species are the quite same one as Permian, and therefore they survived across the P/T boundary. Primitive Nassellaria, which are representative of Mesozoic and Cenozoic faunas, occurs in late Induan (Kamata et al., 2007). The radiolarian fauna had changed gradually around P/T boundary and within Earliest Triassic. This faunal change may be influenced by the double oceanic anoxic events detected from the Oruatemanu Formation (Hori et al., 2007). The Arrow Rocks research monograph (Sporli et al. (eds.), 2007) was published as one of the result of this research project.