Silurian scolecodonts

Abstract

Scolecodonts, polychaete jaws, generally occur abundantly in Silurian shallow marine successions and are known from all continents except Antarctica. The assemblages are typically characterized by taxa with labidognath, placognath and prionognath type jaw apparatuses. They commonly include species of Kettnerites Z̆ebera, 1935, Oenonites Hinde, 1879, Mochtyella Kielan-Jaworowska, 1961, Protarabellites Stauffer, 1933, Atraktoprion Kielan-Jaworowska, 1962, Pistoprion Kielan-Jaworowska, 1966, Vistulella Kielan-Jaworowska, 1961, Xanioprion Kielan-Jaworowska, 1962, Kalloprion Kielan-Jaworowska, 1962, and Leptoprion Kielan-Jaworowska, 1966 . Less common genera, such as Hadoprion Eriksson and Bergman, 1998, Symmetroprion Kielan-Jaworowska, 1966 and Rhytiprion Kielan-Jaworowska, 1966, generally are recorded only from very large collections and/or suitable facies. Many of the common genera, as well as a few species, have been identified in several regions, particularly in Baltica and Laurentia, and evidently had a broad, intercontinental distribution. However, the scolecodont record from regions at higher paleolatitudes, i.e. Gondwana and peripheral paleoplates, is meager. In the famous latest Llandovery to latest Ludlow succession of Gotland, Sweden, scolecodonts are one of the most common microfossil groups, with abundances reaching thousands of specimens/kg rock. Based on an extensive collection, approximately one hundred jawed polychaete species belonging to at least 28 genera and a dozen families have been identified. Polychaetaspids, paulinitids and mochtyellids dominate. The exceptionally rare genus Synclinophora Eisenack, 1975, may belong to the family Oenonidae. If so, this is the only extant family represented in Silurian strata. The diversity patterns and temporal and stratigraphic distribution related to facies reveal that the assemblages house eurytopic as well as stenotopic taxa. Both long-ranging taxa, embracing the entire succession and beyond, and short-ranging taxa occur. Like other metazoan groups, jawed polychaetes were affected by the documented Silurian extinction events. During the globally recognized late Ludlow Lau Event, approximately one third of the identified polychaete taxa went extinct, and some lineages show Lazarus gaps on Gotland.