RADIATION PATTERNS OF EARLY CAMBRIAN METAZOAN FOSSILS IN SOUTH CHINA

South China with rich fossil records is an important region for studying the radiation scenario of Early Cambrian metazoans. Compilation of a database of metazoan genera from the conventional Lower Cambrian (Cambrian Series 1-2) of South China allows a quantitative analysis of biodiversity changes. Plotting generic diversity shows a two-part, first-order trend: 1, diversity increase through the most of the Meishucunian and Qiongzhusian stages, but punctuated by a modest decline during the upper Meishucunian; followed by 2, diversity decline in the Canglangpuan and Longwangmiaoan stages. The Meishucunian (pre-trilobitic) fauna is dominated by helcionellids, orthothecimorph hyoliths and other enigmatic fossils and is very consistent with the ‘Tommotian Fauna’. Diversity increases in the Qiongzhusian stage, reaching the peak value known for the Cambrian. The Qiongzhusian fauna is characterized mainly by the occurrence of dominant pan-arthropods and crown-group brachiopods, representing an initial phase of the Cambrian Evolutionary Fauna. A substantial decline in generic diversity through the Canglangpuan and Longwangmiaoan stages is due partly to a eustatic regression, and it approximates the global pattern, reflecting an extinction event at the end of the Lower Cambrian.

The fossil record also exhibits that, along with the rapid diversification of metazoans in the Early Cambrian, the metazoans progressively exploited more ecological space. Most of the Meishucunian skeletal faunas are from the shallow sedimentary environments, but during the Qiongzhusian, there already existed a distinct differentiation of shallow water and deep habitats: a strong linkage between the occurrences of the skeletal fossils and sedimentary environments.