Radiolarian fauna from the Chiungchussuan Shuijingtuo Formation(Cambrian Series 2) in Western Hubei Province, South China

Little is known regarding characteristics and evolution of radiolarian fossils in the early Cambrian due to its rarity and poor preservation. Here we report a new radiolarian fauna from the Cambrian Shuijingtuo Formation corresponding to the Chiungchussuan Stage(Cambrian Series 2) in western Hubei, China. It contains over 300 radiolarian tests and these fossils belong to 4 morphotypes, including Paraantygopora porosa gen.et sp. nov., Braunosphaera sinensis gen.et sp. nov., Tetrasphaera? sp. and incertae spherical radiolarians. In taxonomy, Spumellaria predominates in the fauna and comprises 92% of the total. In shell structure, about 73% of all specimens are similar to the early Ordovician radiolarian fossils, with the shell walls characterized by perforated plate structures. The spherical radiolarians with latticed shells constitute another feature of the early Cambrian radiolarian fauna. The radiolarian fauna reported here contains many fossil specimens and covers different taxonomical taxa. These specimens usually consist of distinctive concentric multi-layers with complex structure. These characteristics indicate that Radiolaria had already thrived during the Cambrian Chiungchussuan Stage(Series 2, Stage 3), which may have occurred synchronously with the explosion and prosperity of macrobiota recorded in the strata deposited in shallower water condition.

Extinction pattern and process of siliceous sponge spicules in deep-water during the latest Permian in South China

Diverse and abundant siliceous sponge spicules were found in the latest Permian beds, Dongpan and Ma'anying sections, South China, including 52 types and 85 forms. Further investigation on these spicules allows us to understand extinction patterns and processes of deep-water sponges. These sponge spicules rapidly decreased below the Permian/Triassic boundary (PTB), and the extinction rates reach up to 88%-90% for types and 88%-92% for forms. Their extinction pattern is a gradual one that consists of two stages: the first is characterized by a gentle and slow extinction speed and low extinction rate, and the second by sharp and fast extinction speed and high extinction rate. The morphological extinction process is involved in the disappearance first of the triaxons and tetraxons, then of the polyaxons and demas, and last of monaxons. In exterior structure extinction, the complex spicules with branches and spines became extinct more easily than did smooth spicules. After the end-Permian mass extinction, only five common and smooth forms survived: Oxeas A, Oxeas B, Strongles B, Oxy-orthpentactines and Oxy-orthohexactines A.