Palaeobiogeography and diversification of Tournaisian-Viséan bryozoans (lower-middle Mississippian, Carboniferous) from Eurasia

The Mississippian represented the last diversification event of bryozoans in the Palaeozoic which affected all taxonomic levels. Within the borders of modern Eurasia Tournaisian-Viséan bryozoans are known from 24 areas, with a total of 878 species in 180 genera. Palaeobiogeographical analysis is here made according to the stages and substages of the Tournaisian and Viséan. Six characteristic species were identified for the lower Tournaisian which are distributed in more than one region of the continent, and for the upper Tournaisian there are two such species. Eleven species occur in the narrow stratigraphic interval of the lower Viséan that display a wide geographic distribution within Eurasia, in the upper Viséan there are 14 such species. Analysis of the generic composition showed the closest similarity between Tournaisian bryozoans of Kazakhstan, the Kuznetsk Basin and Eastern Transbaikalia. Significant similarity in the generic composition of Germany, Britain, Ireland and France is observed during the Viséan. Two centres of radiation bryozoans were identified: «Eastern» and «Western».