Response of organophosphatic brachiopods to the mid-Ludfordian (Late silurian) carbon isotope excursion and associated extinction events in the Prague Basin (Czech Republic)

Abstract

The present paper represents the first results of an on-going multidisciplinary study focused on the response of marine faunas to the mid-Ludfordian (late Silurian) carbon isotope excursion and associated extinction events (Ludfordian, late Silurian). The paper describes the stratigraphical distribution of organophosphatic brachiopods from the uppermost part of the Neocucullograptus inexpectatus to lower part of Monograptus parultimus graptolite biozones (i.e. early Ludfordian to earliest Přídolí). Numerical analysis of the stratigraphical distribution, based on more than 1300 determinable valves of 15 organophosphatic brachiopod species, revealed three groups being significantly supported. They are here formalized as new organophosphatic brachiopod communities: the oldest Opsiconidion ephemerus Community, the Kosoidea fissurella Community, and the youngest Opsiconidion parephemerus-Kosagittella clara Community. The Opsiconidion ephemerus Community and the Opsiconidion parephemerus-Kosagittella clara Community have distinct similarities in their taxonomic composition, moderate species diversity and low dominance indices. The communities are separated by the monospecific Kosoidea fissurella Community present just after the Lau and Kozlowskii bioevents during the period of high δ13C values which is interpreted as an opportunistic community. Re-occurrence of some brachiopod taxa after the bioevents and the mid-Ludfordian carbon isotope excursion raises the question, at least for organophosphatic brachiopods, as to the extent to which the Lau and Kozlowskii bioevents represent true global extinction events and whether their significance has not been overestimated. Two new speciesare erected: Opsiconidion bouceki and Opsiconidion parephemerus.