Taxonomic selectivity and continuous variation in mass and background extinctions of marine taxa

Abstract

Analysis of extinction rates^1,2 has gone a long way towards identifying the approximate time and magnitude of major mass-extinction episodes in Earth's history: late Ordovician, late Devonian, late Permian, late Triassic, and late Cretaceous. Here I extend an earlier analysis³ and present patterns of family-level background and mass-extinction rates for ten major marine groups. I show that (1) except for the late Permian event, mass-extinction rates for each taxon were often not higher than many of their 'normal' background rates evincing continuous variation between them; (2) mobile benthic organisms show low mass-extinction rates and low background rates but (3) planktonic and sessile organisms tend to have high mass-extinction and background rates. Thus the mass-extinction events appear qualitatively similar to background extinctions, reflecting more of the same processes, in contrast to a recent proposal⁴.