Many authors have noted the apparent “decoupling” of the taxonomic and ecological severity of mass extinction events, with no widely accepted mechanistic explanation for this pattern having been offered. Here we test between two key factors that potentially influence ecological severity: biosphere entropy (a measure of functional redundancy), and the degree of functional selectivity (in terms of deviation from a pattern of random extinction with respect to functional entities). While theoretical simulations suggest that the Shannon entropy of a given community prior to an extinction event determines the expected outcome following a perturbation of a given magnitude, actual variation in Shannon entropy between major extinction intervals is insufficient to explain the observed variation in ecological severity. Within this information-theoretic framework, we show that it is the degree of functional selectivity which is expected to primarily determine the ecological impact of a given perturbation when levels of functional redundancy are not substantially different.

Raw data was downloaded from the Paleobiology Database and filtered according to the method described in the core manuscript. All remaining material (e.g., R code) was written by Daniel G. Dick.

See included document "LIST OF SUPPLEMENTARY MATERIAL.docx" for a complete list of files and what is included in each.