ARE SEPKOSKI'S EVOLUTIONARY FAUNAS EVOLUTIONARY LITHOFACIES?

Sepkoski's identification of three great evolutionary faunas (EFs), each with characteristic rates of turnover and richness patterns, is one of his most important contributions to paleobiology. Sepkoski and others have suggested that temporal patterns within and between the EFs might reflect biotic interactions among groups taxa that have, on average, different ecologies and life history strategies. Analysis of >250,000 genus occurrences in the Paleobiology Database demonstrates that the Paleozoic EF has a positive affinity for carbonate environments and that the Modern EF has a positive affinity for siliciclastic environments, raising the possibility that physical environmental forcing may have been important as well.

To test this possibility, hiatus-bound packages of carbonate and siliciclastic sediments were compiled from the AAPG COSUNA charts. Area-weighted measures of rock quantity and rates of expansion and contraction of preserved sediments were then calculated for each lithofacies group. Carbonates decline in abundance over the Phanerozoic and there is a sharp decline, driven by a large increase in truncation rate, at the P/T boundary. Siliciclastics, by contrast, increase in abundance over the Phanerozoic and show no sharp decline at the P/T. In general, carbonates have higher mean rates of turnover and greater volatility than siliciclastics. These features reproduce quantitatively many of the same dynamics observed in the Paleozoic and Modern EFs, including selectivity at many of the major mass extinctions, suggesting that Sepkoski's EFs may reflect, at least in part, changes in the physical environment.