NEW DATA ON UPPER DEVONIAN PELAGIC BIVALVES

Cephalopod limestones, nodular limestones, fine siliclastics as well as black shales from the Devonian pelagic facies realm are rich in peculiar bivalves. Despite their great quantity in several different horizons, neither their life habits nor their correct stratigraphic rang are well understood. Furthermore, due to the current knowledge which dates back to the beginning of the 19th century, no systematic concept is available for classification and phylogenetic development. A detailed revision is based on old museum collections and on new material from North America, Germany, France, and Morocco. Other records are from Russia, Poland, and Australia. The study on pelagic bivalves provides new data on their systematics, paleoecology, morphology, and biostratigraphy. Commonly known species, which formerly have been assigned to Praecardium, in fact belong to a new and smaller genus. This taxon was restricted to the Uppermost Frasnian / Lower Famennian of the western Prototethys and of the Appalachians. It appeared during the global Upper Kellwasser Event and its extinction coincided with a regressive phase of the Condroz Event. Other groups, such as the loxopteriids, occurred earlier in the Frasnian and disappeared within the Upper Devonian IV, at the end of the hypoxic global Annulata Event. New data concerning shell and soft body morphology of these distinctively inequivalved bivalves could be derived from exceptionally well preserved pyritic specimens, and allows a first interpretation of their possible life habits. This ongoing research sheds light on these bivalve taxa that have been neglected for almost a century.