Radiolarian Kalimnasphaera from the Cambrian Shuijingtuo Formation in South China

• The genus Kalimnasphaera is described from the Early Cambrian for the first time.
• The known oldest radiolarian fauna does not belong to Order Archaeospicularia.
• Early Cambrian radiolarians were complex in structure and diverse in morphology.
• Our study supports the result of Braun et al. (2007).

The origin of radiolarians and their early evolution are of great interest for paleontologists and biologists. The needle-like or spicular construction of radiolarians represented by Order Archaeospicularia has been considered as an ancestor of radiolarians until Braun et al. (2007) discovered some radiolarians with latticed shells from the Early Cambrian in South China. The two radiolarian tests reported here were collected from the Shuijingtuo Formation corresponding to the basal part of Cambrian Series II, in South China. One of them is spherical, latticed, and similar to the radiolarians described by Braun et al. (2007). The other is grouped within the genus Kalimnasphaera formerly reported only from the Ordovician. The result indicates that the oldest known radiolarian fauna does not belong to Order Archaeospicularia. The hypothesis that Archaeospicularia is the representative of the oldest radiolarian group needs to be reexamined. Further investigation of early forms of radiolarians in the Early Cambrian or older strata is warranted.