First record of the noncalcareous macroalga Perissothallus from shallow-water deposits (Pennsylvanian) in the Kladno-Rakovník Basin, Czech Republic

The fossil genus Perissothallus is used for adpression fossils of late Palaeozoic noncalcareous freshwater algae consisting of erect, cylindrical branches that radiate from a central holdfast and dichotomize repeatedly. The taxon currently includes P. versiformis from the Upper Pennsylvanian of North America and P. densus from the Lower Permian of Germany. In this paper we describe a third species, Perissothallus dekovensis nov. sp., from the Gzhelian (Stephanian B;Upper Pennsylvanian) of the Kladno-Rakovnik Basin, Czech Republic. The new species differs from the previously described forms with regard to thallus size and branching pattern of the erect parts. Sedimentological data and the fossils that co-occur with the algal thalli suggest that P. dekovensis lived in shallow-water areas of a lake or abandoned channel that was surrounded by tree ferns, cordaites (especially Poacordaites-type), and lycopsids.