The bivalve fauna from the Letná Formation (Upper Ordovician) of Bohemia: Significance for palaeobiogeography, palaeoecology and diversification of bivalves

The bivalve fauna from the Sandbian Letná Formation of the Prague Basin includes ten species: Praenucula bohemica, Myoplusia cf. incisa, Synek sp., Pseudarca? incola, Cuneamya catilloides, Modiolopsis draboviensis, Macrodesma flexa, Ectenocardiomorpha veterana, Whiteavesia antiquior, and Myodakryotus patricia. Modiolopsis, often used as a “cumulative” name for pteriomorphids from the Late Ordovician, is recorded from the Letná Formation, including only one species. Species palaeoecology is analysed and briefly discussed. Although the infaunal and semi-infaunal elements still prevail, the epifaunal bivalves are also significantly represented. The Sandbian bivalve fauna of the Barrandian area comes from high latitudes of the Southern hemisphere. Pteriomorphids are dominant, but heteroconchs and protobranchs belong also to important elements in the bivalve association from the Letná Formation. From coarse quartzose sandstones of the Letná Formation the Modiolopsis draboviensis Association of the Modiolopsis Community is established. The composition of the Late Ordovician bivalve fauna from the different areas and sedimentological environments are compared and discussed. There is a clear trend toward rapid diversification of pteriomorphids and epifaunal bivalves in all palaeocontinents. Bivalves from the Letná Formation of the Barrandian area show affinities to the Sandbian bivalve faunas from Avalonia, Laurentia and Morocco.