The Permian-Triassic extinction event and invertebrate developmental modes

Permian-Triassic extinction removed perhaps 90% or more of marine invertebrate shelf species and permanently altered the higher taxonomic composition of shelf faunas. It is a plausible hypothesis that planktotrophic lineages were disproportionately victimized; so far as can be told, the survivors of some formerly dominant tropical clades were all nonplanktotrophic, and most of the new clades appearing in the Lower Triassic are nonplanktotrophic also. An analysis of the changing patterns of diversity and endemism across the Permian-Triassic boundary suggests that even if planktotrophs had dominated the Permian tropics, a differential extinction of 1.3–1.5 planktotrophs for each nonplanktotroph could account for the inferred pattern. The extinctions may have been associated with change in the pattern of oceanic productivity.