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

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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.