Middle Katian/lowermost Hirnantian ostracods from the Prague Basin (Czech Republic): Diversity responses to climatic changes

Ostracods are an abundant but long undervalued component of the fossil associations occurring in the Kraluv Dvur Formation (Prague Basin; Czech Republic) of the mid Katian to the earliest Hirnantian (Late Ordovician) age. It has been known that they are abundant but it is first evincibly shown that they were also extraordinary diversified. Twenty-eight (plus two dubious) species are described, with only seven (plus the two dubious) having been recorded in the formation before. Ten species are newly established, one established in another area, and ten are kept in open nomenclature. The stratigraphic distribution of the taxa throughout the formation was observed below, inside and above the Pernik Bed, the layer of the carbonaceous mudstone interpreted as a response to climatic changes. The taxa from the Pernik Bed are described for the first time and those from the interval above this unit have not been studied in detail yet. The pattern of stratigraphic ranges of the species in the Kraluv Dvur Formation shows a decreasing diversity toward the top, and a strong but temporary influence by the taxa which appeared in the Prague Basin during the sedimentation of the Pernik Bed in the upper part of the formation. It is significant that only several taxa ranging throughout the formation survived above the Pernik Bed. They are interpreted as opportunistic, based on such a distribution pattern. All taxa first appeared in the Pernik Bed interval (supposed immigrants), and a part of the basin dwellers prior to the sedimentation of the Pernik Bed sedimentation disappeared. Such a distribution pattern is interpreted by cooling accompanied by fluctuations in the latest Katian, which is in agreement with the generally accepted model of strong climatic changes in this stratigraphic interval. Analysis of the genera distribution clearly demonstrates the very close relationship of ostracod associations recorded in the Kraluv Dvur Formation to Baltica and noticeably weaker migration among the Prague Basin, Avalonia and Laurentia.