Taxonomy and distribution of the Ordovician conodont Drepanodus arcuatus Pander, 1856, and related species

Drepanodus arcuatus Pander, 1856, is one of the geographically most widely distributed conodont species in the Ordovician, and has been reported to range practically throughout the entire Ordovician System. Topotype material from the Prioniodus elegans Zone in the St. Petersburg area of Russia has been studied in order to better define the species, and large D. arcuatus collections from Sweden, ranging in age from the Tremadocian Paltodus deltifer Zone and into the basal Pygodus serra Zone in the Darriwilian, have been examined to estimate the limits of variation. Most of the investigated material is of Arenigian age. In this process, two additional speciesof Drepanodus were identified in the Swedish collections, and at least one of these, Drepanodus reclinatus (Lindström, 1955), also has a rather wide distribution in North America and southern China. This species and the new species, Drepanodus parformis n. sp., are much less common than D. arcuatus in the great majority of the investigated samples, but they seem to have largely the same stratigraphical range as D. arcuatus. Biofacies patterns as well as palaeogeo-graphic distribution of the taxa discussed are documented.