SILURIAN JAWED POLYCHAETES FROM GOTLAND, SWEDEN

Although Eichwald (1854) was unaware that the ‘remain of a Silurian fish’ from Saaremaa (Estonia) he assigned to Sphagodus obliquus was in fact a scolecodont, he was responsible for the dawn of the research on this intriguing microfossil group. Nearly 150 years later we know that scolecodonts (polychaete jaws) generally are common in Silurian marine sedimentary rocks and they have been recorded from all present-day continents except Antarctica. In the latest Llandovery to latest Ludlow shallow marine succession of Gotland, Sweden, the abundance can reach thousands of scolecodonts/kg rock in productive lithologies. Approximately 100 polychaete species belonging to at least 28 genera and a dozen families (based on multi-element taxonomy) occur in the succession. Although the scolecodont research on Gotland was initiated already by Hinde (1882), only approximately 50% of the taxa have yet been formally described. The labidognath families Polychaetaspidae and Paulinitidae are most abundant and species-rich whereas Ramphoprionidae, Symmetroprionidae, Hadoprionidae, are considerably less common but show frequency peaks in suitable facies. The placognath family Rhytiprionidae is very rare whereas Xanioprionidae and particularly Mochtyellidae are quite abundant but not very taxon rich. Among the generally rare prionognath and prionognath-like families Skalenoprionidae, Kalloprionidae, and Atraktoprionidae, the latter is most abundant and species rich. In addition, some very rare and enigmatic taxa, e.g., Lunoprionella Eisenack, 1975, and Synclinophora Eisenack, 1975, have been identified. The position of the latter genus is reevaluated and it is considered to belong to Oenonidae, the only extant family represented in the Silurian. Diversity and temporal distribution patterns related to facies reveal eurytopic as well as stenotopic taxa. Both long-ranging taxa, ranging through the entire Gotland succession and beyond, and short-ranging taxa occur. Many families and genera were widespread during the Silurian and have been identified also in other regions, particularly in Baltica outside Gotland and Laurentia. Albeit data from higher paleolatitudes are meager some congeneric taxa have been recognized.