From radiation to provinces: spatial scaling of Cambrian diversity

The Cambrian radiation is commonly described as a rapid increase in biodiversity and morphological disparity, yet the spatial organization underlying this diversification remains less well resolved. Using fossil occurrence data compiled from global databases, this chapter examines how Cambrian diversity was assembled across space and how patterns of regional differentiation varied through time. Our results show that global diversity increased alongside a pronounced rise in spatial differentiation during the Fortunian - Cambrian Stage 3 interval, driven largely by taxonomic turnover among regions rather than hierarchical nesting. Measures of beta-diversity, endemism, and network structure indicate that strong regional contrasts were established early in the Cambrian and persisted throughout this period, despite fluctuations in global diversity. Analyses of latitudinal turnover further suggest that faunal differentiation is not organized as a continuous latitudinal gradient, but instead reflects regionalization that is weakly related to latitudinal separation. Overall, we demonstrate that the Cambrian radiation was characterized not only by increasing diversity, but also by the early establishment of pronounced spatial differentiation among both endemic and non-endemic faunas, which persisted through the Cambrian in spite of high temporal turnover.