Descriptive Classification of Closed Nassellarians: Proposal of Non-taxonomic Names of Jurassic–Cretaceous Radiolarian Fossils for Practical Age Index

抄録

Radiolaria is a valuable age index fossil through the Phanerozoic. This article describes the characteristics of the non-taxonomic names of closed nassellarian radiolarians, that is, di-segmented closed nassellarian (DiCN), tri-segmented closed nassellarian (TrCN), tetra-segmented closed nassellarian (TeCN), and multi-segmented closed nassellarian (MuCN), based on the number of segments. This article points out a potential as a practical age index for DiCN and TrCN. The TrCN occurrence indicates a Jurassic–Cretaceous age. In particular, the waterdrop-shaped TrCN-dominant occurrence suggests a Middle–Late Jurassic age; the spherical TrCN-dominant occurrence suggests a Cretaceous age. DiCN occurrence indicates a Jurassic–Cretaceous age, and abundant in the Middle Jurassic–Cretaceous.