A Bounty of bradoriids -- biodiversity, biogeography and biostratigraphy of richly diverse lower Cambrian assemblages from South Australia

Systematic acid digestion of samples derived from 24 separate stratigraphic sections measured through thick carbonate dominated lower Cambrian successions in the Flinders Ranges (Arrowie Basin) reveals an unexpectedly rich diversity (c. 25 taxa) of well-preserved bradoriid arthropods. The new assemblages occur across a broad spectrum of biofacies including shallow water stromatolitic facies, archaeocyath-cryptalgal bioherms and carbonate slope facies. The oldest known bradoriid taxon (Liangshanella circumbolina) from East Gondwana occurs 20 m below the FAD of the zonal trilobite Abadiella huoi in the lower Cambrian Ajax and Wirrapowie limestones of the Flinders Ranges, South Australia. This occurrence suggests a lower Cambrian (Series 2, Stage 3) age for the earliest bradoriids in Australia. 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. An updated quantitative biogeographic analysis utilising new unpublished taxonomic data from the lower Cambrian of South Australia highlights the strong endemism displayed by early Cambrian bradoriid communities in East Gondwana -- but the presence of a few previously unreported cosmopolitan taxa strengthens the close faunal affinities with South China, Antarctica and Siberia.