DIVERSITY PARTITIONING DURING THE CAMBRIAN RADIATION

The fossil record offers unique insights into the environmental and geographic partitioning of biodiversity during global diversifications. Using a global, stratigraphically vetted compilation of 40,000 fossil occurrences from the Paleobiology Database we explored biodiversity patterns during the Cambrian radiation. We assessed how the global increase of diversity in the Early Cambrian is manifested in changes of within-community (alpha) diversity and between community (beta) diversity and what this tells us about the underlying processes. The global diversification was governed more by an increase of beta than of alpha diversity and their combined trajectories suggest a low-competition (but possibly high-predation) process. Total beta is equally governed by increasing dissimilarity between environments and regions. Turnover between adjacent paleo-continents was especially profound as demonstrated by the steep increase of geographic beta with geographic distance in the 2000-4000 km distance interval throughout the first three Cambrian stages. Our study elucidates that global biodiversity during the Cambrian radiation was driven by niche contraction at the local scale and allopatric speciation at the regional scale. The latter supports previous arguments for the importance of plate-tectonics in the Cambrian radiation, namely the breakup of Pannotia.