The oldest bivalved arthropods from the early Cambrian of East Gondwana: Systematics, biostratigraphy and biogeography

The oldest bradoriid fauna from Australia, occurring in the lower Cambrian Ajax and Wirrapowie limestones of the Flinders Ranges, South Australia consists of eleven taxa, including one new genus and species, 'Quadricona madonnae' gen. et sp. nov. and two new species, 'Liangshanella circumbolina' sp. nov. and 'Zepaera jagoi' sp. nov. In the Ajax Limestone, 'Liangshanella circumbolina' sp. nov. occurs c. 20 m below the FAD of the zonal trilobite 'Abadiella huoi'. This pre-trilobitic occurrence represents the oldest bivalved arthropod hitherto known from East Gondwana and suggests a lower Cambrian (Series 2, Stage 3) age for the assemblage. The recognition of distinct bradoriid assemblages associated with the 'Abadiella huoi' (Atdabanian), 'Pararaia tatei', 'P. bunyerooensis' and 'P. janeae' (all Botoman) trilobite biozones in South Australia indicates great potential for future regional biostratigraphic correlation. Quantitative biogeographic analysis including new taxonomic data from the lower Cambrian of South Australia, highlights the strong endemism displayed by early Cambrian bradoriid communities and strengthens the close faunal affinities with South China and Antarctica.