Relationships between Ordovician Baltic and North American Midcontinent conodont faunas

During most of the Early and Middle Ordovician, epicontinental seas of Laurentia, Baltica, and islands in the Iapetus Ocean between them were centers of diversification of different groups of conodonts. The most important were Phragmodontidae in Laurentia, Periodontidae in the Iapetus area, and Balognathidae in Baltica. Spectra of fossil assemblages (analyzed in terms of conodont lineages) were very stable through time in each of these biogeographic provinces. Relatively few lineages passed the biogeographic boundaries and successful immigrations were rare. An especially stable composition characterizes the Baltic faunas. A profound change in the composition of faunas in Baltica took place in the Oanduan (late Caradocian) through influx of several lineages previously confined to islands in the Iapetus. Conodont faunas of Laurentia, at times enriched by Iapetus-born lineages, evolved rather gradually until the end of the Ordovician. Diversity of Ordovician conodont assemblages seems to depend more on local ecologic factors and bathymetry than on climate.