The early siphonodellids (Conodonta, Late Devonian-Early Carboniferous): overview and taxonomic state

Previous conodont studies on the Devonian/Carboniferous (D/C) boundary revealed that the current definition of the D/C boundary cannot be maintained due to several problems relating to the index taxon. The base of the Carboniferous System is defined by the first occurrence of the conodont species Siphonodella sulcata, within the S. praesulcata -S. sulcata lineage. However, problems in discriminating S. praesulcata from S. sulcata have been evidenced by the conodont studies of a variety of authors. To provide an overview about the early siphonodellids and the taxonomic state, conodonts from the current GSSP La Serre (Montagne Noire, France), as well as all data from the literature were taken into account. Based on these data, several morphotypes could be distinguished, although the great majority of specimens show intermediate features between the two taxa. Therefore, precise identification of such specimens is very much dependent on personal interpretation, thus strongly influencing the precise position of the D/C boundary which, as a result, is not synchronous. Alternative scenarios for the definition of the D/C boundary need to be considered in the future.