Benthic daily oxygen variability and stress as drivers for animal diversification in the Cambrian

Abstract

The delay between the origin of animals in the Neoproterozoic and their Cambrian diversification remains perplexing. Animal diversification mirrors an expansion in marine shelf area, but the mechanisms linking this environmental change to early organismal ecology are unclear. In this study, we used a biogeochemical model to consider oxygen dynamics at the sunlit sediment–water interface over night-day (diel) cycles in the early Cambrian under a greenhouse climate. We found that temperatures dictated the diurnal benthic oxic-anoxic shifts that were physiologically stressful to early animals and this dynamic expanded over nutrient-rich shelf areas as continents were flooded in the Cambrian. We suggest that the combination of a greenhouse climate and continental flooding combined to amplify diurnal benthic redox variability, which promoted the adaptive radiation of animals tolerant to oxygen fluctuations and stress, the Metazoa.