Changes in metazoan functional diversity across the Cambrian Radiation and the first Phanerozoic mass extinction: the Cambrian Sinsk Event.

The Sinsk Event (approx. 513.5 million years ago, Ma) is the first Phanerozoic mass extinction, marking the end of the canonical Cambrian Radiation. We reconstruct taxonomic and functional diversity patterns of skeletal metazoans from the Siberian Platform during the Cambrian Radiation and across the Sinsk Event from approximately 529 Ma to 508 Ma, to investigate the changing occupation of functional space and the evolution of functional traits during the radiation, and the role of these in extinction selectivity at the Sinsk extinction and subsequent recovery. During the radiation, functional richness increased before taxonomic richness as new groups with novel traits emerged and diversified. Taxonomic richness declined sharply at the Sinsk, but thereafter increased rapidly while functional richness continued to decline until approx. 508 Ma, indicating a post-extinction decoupling. While there is limited evidence of extinction selectivity at the Sinsk, certain functional traits are associated with post-extinction recovery from approximately 511 Ma to 508 Ma. Groups with novel functional traits associated with motility, diversified feeding modes and broad water depth tolerances diversified rapidly, while sessile, inshore filtrators and heavily calcified taxa which had been dominant prior to the extinction either failed to recover or became extinct. The Sinsk Event therefore marks a significant transition in marine ecosystem function.