A review of the Early Palaeozoic biogeography of bryozoans

The palaeogeographical distributions of Early Palaeozoic bryozoan faunas are reviewed. Previous studies are examined and new databases have been assembled of the stratigraphical and geographical distribution of Ordovician and Silurian taxa. Analysis was carried out using cluster analysis based on Jaccard’s coefficient and paired group method, as well as principal coordinate analysis based on Jaccard’s coefficient, to examine the relationships between different localities. Bryozoan faunas increased in diversity throughout the Ordovician peaking with 133 genera during the Katian. In the earliest Ordovician provincialism is difficult to determine, but by the Darriwilian five distinct provinces developed, decreasing to four in the Sandbian. There was a decrease in provinciality throughout the Katian as faunas became less endemic, caused by the reduction of geographical barriers. Following the extinction of many genera at the end of the Ordovician, early Silurian faunas contain remnant taxa. Subsequently fenestrates began to dominate faunas. During the Llandovery bryozoans began to show distinct provincialism, but this declined during the Wenlock, only to re-emerge during the Ludlow. Late Silurian (Pridoli) faunas are sparse but nevertheless show possible division into two provinces.