Lower Silurian polychaetaspid and ramphoprionid polychaetes from Gotland : aspects on taxonomy and palaeoecology

Sammanfattning: The Silurian strata of Gotland yield a wide variety of polychaete jaws. The investigated polychaetes include the family Polychaetaspidae with the two genera Polychaetaspis and Kozlowskiprion, and the monotypic family Ramphoprionidae with the genus Ramphoprion. The fauna derives from the sections at Lusklint and Lickershamn 2 which comprise the three stratigraphically oldest units on Gotland: the Lower Visby Beds, the Upper Visby Beds, and the Högklint Beds. These Beds are exposed in the northeastern part of the island and range in age from Late Llandovery to Early Wenlock. Identification of the species is based on isolated jaw elements (scolecodonts) and apparatuses, utilizing a biological species concept. Of the elements forming an apparatus only the first maxillary pieces (MI), have been studied. Three new species are introduced: Polychaetaspis olofi n. sp., Ramphoprion anderssoni n. sp., and R. ? bergmani n. sp. The remaining seven taxa are all polychaetaspids and include P. marlenediesae (Eller, 1942), P. "obliquus" (Eichwald, 1854), P. cf tuberculatus Kielan-Jaworowska, 1966, P. cf. latus Kielan-Jaworowska, 1966, P. wyszogrodensis Kozlowski, 1956, P. cf. gadomskae Kielan-Jaworowska, 1966, and Kozluwskiprion cf. longicavernosus Kielan-Jaworowska, 1966. The taxonomic diversity is highest in the Högklint Beds and most of the investigated species indicate a preference for warm and shallow marine environments. Only the two species K. cf. longicavernosus and P. cf. latus are present from the Lower Visby Beds to the Högklint Beds, and these are presumably more tolerant to environmental changes and show a preference for deeper water strata. This study presents an extended range for the ramphoprionids into the Silurian, so now both Ordovician and Silurian strata are included. One transposed, left jaw element probably of P. marlenediesae was found.