EVOLUTIONARY DYNAMICS OF PRAGIAN DACRYOCONARIDA (LOWER DEVONIAN, TENTACULITOIDEA) - EVIDENCE FROM PALEONTOLOGICAL DATA AND DELTA-C-13 OF MARINE CARBONATES FROM CZECH-REPUBLIC

A detailed palaeontological study was performed on 38 successive assem blages of dacryoconarids (Tentaculitoidea) sampled along the Cerna rok le 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 diversit y. Oxygen and carbon isotope compositions of the dacryoconarid-bearing carbonates were measured to evaluate the possible influence and contr ol of the environmental conditions on the evolutionary dynamics of the dacryoconarid faunas. Large and rapid delta(13)C excursions occur in the marine carbonate sequence of the Cerna rokle section, some of whic h 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 factor s. Environmental variations cannot be regarded as having preponderantl y influenced the dacryoconarid evolution, which more probably resulted from intrinsic biotic factors. (C) 1998 Elsevier Science B.V.