Abstract
Ten graptolite species have been recognized by a general revision of all the material (both historical and new) collected from the Kraluv Dvur Formation of the Prague Basin. One species belongs to the dicranograpid genus Dicellograptus and the remaining are biserial taxa assigned to the diplograptid genera Diplograptus and Anticostia, the lasiograptids Paraplegmatograptus and Phormograptus, the climacograptid Styracograptus, and the neodiplograptid genera Normalograptus and Metabolograptus.
Although graptolite specimens are rare in these strata, there does appear to be a regular succession among the species, which results in a relatively low diversity of graptolites throughout the formation. The maximum species diversity is in the upper part preceding the distinct carbonate Pernik Bed sedimentation.
Three of the four species that occur in the lower part of the formation are endemic to the study region, however, Anticostia teres occurs in P. linearis Zone strata in Baltica (Bornholm and Sweden). Three of the four species that occur in the middle and upper part of the unit are more widely distributed species that occur also in the late Katian of the paleotropics.
The uppermost Kraluv Dvur Formation is marked by impoverishment that reduced the fauna to a single cosmopolitan species that occupies a narrow interval below the first early Hirnantian diamictite. This graptolite distribution pattern appears to reflect changing global environmental conditions, including a late Katian climate amelioration (with expanded geographic ranges of several paleotropical graptolite species) followed by cooling and climate deterioration during latest Katian and early Hirnantian interval.
Based on the new data, a biostratigraphic scheme has been modified and the Kraluv Dvur Formation is inferred to be of mid Katian (P. linearis) to the earliest Hirnantian (early M. extraordinarius) age.