Diversity dynamics of Ordovician Bryozoa

Abstract

This study presents a compilation of the temporal distribution of 200 bryozoan genera during the Ordovician. Bryozoans appeared in the earliest Ordovician (Tremadoc), diversified rapidly until the late Sandbian, and then suffered three distinct extinctions in the Late Ordovician. In the early Katian, the first significant extinction eliminated 22.7% of bryozoan genera. That was the highest taxonomic loss in the Ordovician; however, due to high origination rates, the magnitude of this extinction was the lowest among the three extinctions. The second extinction wave occurred in the late Katian, resulting in taxonomic loss of 22.4%. This event can be estimated as the most severe for bryozoans during the Ordovician because of extremely low origination rates what resulted in the highest net decrease of diversity. The third extinction of bryozoans occurred during the Hirnantian resulting in the lowest taxonomic loss (16.5%) and intermediate net decrease of diversity. The diversity dynamics of bryozoans in the Ordovician was apparently controlled by climatic changes, provinciality and food availability.