Suppressed speciation rates and compositional changes in Paleozoic faunas.

Abstract

Shifts in the taxonomic composition of Paleozoic communities are commomly ascribed to selective extinctions. Suppression of realized speciation rates owing to shrinkage of available adaptive space (lowering of potential niche number), even though unselective, results in differential diversity losses, the greatest losses being sustained by clades with the highest speciation and extinction rates (the high-turnover caldes). The resulting compositional shifts apear to be selective. Foreclosures of speciation opportunities probably play an important and perhaps in sorne cases a dominant role in taxonomic shifts during the Paleozoic.