Review of ascocerid cephalopods from the upper Silurian of the Prague Basin (Central Bohemia) – history of research and palaeobiogeographic relationships

Abstract

Abstract The order Ascocerida Kuhn, 1949 includes rare and morphologically unique early Palaeozoic cephalopods, in which periodic shell truncation occurred during ontogeny; mature shells subsequently became inflated, with thin sigmoidal septa and phragmocone chambers situated above the living chamber. The ascocerids are at present known mainly from North America and Baltoscandic Europe. The group was first described by J. Barrande in the mid 1800’s from the upper Silurian of Bohemia. Finds of ascocerid fossils in Bohemia are generally scarce but Barrande’s collection includes tens of well-preserved specimens. These are briefly reviewed in the present paper and additional, more recently collected material is also discussed. In Bohemia (Prague Basin), ascocerids occur in limestones of Ludlow to late Přídolí age. Their maximum diversity and abundance was reached close to the Ludlow/Přídolí boundary interval. Five out of the fourteen currently recognized Bohemian species are also known from late Silurian strata in Sweden (the island of Gotland). The ascocerids thus illustrate palaeobiogeographic relationships between the Prague Basin and Baltica during the late Silurian.