Evolutionary dynamics of Pragian Dacryoconarida (Lower Devonian, Tentaculitoidea): evidence from palaeontological data and °13C of marine carbonates from Czech Republic

A detailed palaeontological study was performed on 38 successive assemblages of dacryoconarids (Tentaculitoidea) sampled along the Černá rokle section (Praha basin, Czech Republic). This section represents the whole Pragian stage (Lower Devonian) and roughly corresponds to a 6 Ma time span. Dacryoconarid assemblages change in abundance and diversity. Oxygen and carbon isotope compositions of the dacryoconarid-bearing carbonates were measured to evaluate the possible influence and control of the environmental conditions on the evolutionary dynamics of the dacryoconarid faunas. Large and rapid δ13C excursions occur in the marine carbonate sequence of the Černá rokle section, some of which apparently correspond with faunal variations. However, no clear and simple relationship appears between carbon isotope ratio fluctuations and dacryoconarid evolutionary dynamics. Occurrence and extinction of the dacryoconarid species appear to be mainly related to biotic factors. Environmental variations cannot be regarded as having preponderantly influenced the dacryoconarid evolution, which more probably resulted from intrinsic biotic factors.