PALEOBIOGEOGRAPHY OF HADOPRIONIDS, PALEOZOIC JAWED POLYCHAETES

Scolecodonts are the jaws of marine polychaetes. They are fairly common in shallow Paleozoic sediments. The knowledge of the taxonomy, ecology, stratigraphical and geographical distribution of the polychaetes is still fairly poor. This study is based on the jaws of the polychaete family Hadoprionidae. These jaws are rare, very characteristic and large but show a slow evolution. Despite its rarity, Hadoprion is a genus that has now been identified in several different regions and stratigraphic levels. It was originally described by Hinde (1879), although under a different generic name, and subsequently revised and re-described based on a collection from the type Cincinnatian region by Eriksson & Bergman (1998). It appears as if hadoprionids originated in Laurentia and spread to Baltica and Avalonia during the Silurian. Stratigraphically Hadoprion ranges from the U. Ordovician (Mohawkian) through the Late Silurian (Ludlovian). In Laurentia, Hadoprion cervicornis is abundant in the “deeper water” shale-dominated settings suggesting that Hadoprion mainly preferred muddy bottoms formed distally on the platform. Its highest occurrence was found in the Maysvillian Miamitown Shale (12%) in Indiana. H. cervicornis is normally rare but widely distributed in the Silurian strata of Gotland. Here it is also found in muddy bottom conditions in a tropical shelf Sea. At present, only two species are assigned to the genus Hadoprion. A closely related but distinct species is encountered at one locality in Silurian strata of Scania, the southernmost province of Sweden. That area formed the southern part of the Baltic shield at that time. The environment was shallow warm marine sea. Although the two species are found only some hundred km apart and their stratigraphical distribution coincides, they have not been encountered together. The ocean that existed south of Baltica during the Ordovicium closes during the Silurian. The “Scanian species” could indicate a connection to a southern polychaete faunal province still unknown.