LATE ORDOVICIAN SCOLECODONTS FROM THE LA POLA AND DON BRAULIO FORMATIONS, VILLICUM RANGE, ARGENTINE PRECORDILLERA

Abstract

Scolecodonts were particularly abundant during the Ordovician, with low extinction rates that experienced a slight increase in the
Late Ordovician. In this work, we describe for the first time a Late Ordovician scolecodont fauna from La Pola creek, in the Villicum Range of the Eastern Precordillera. This fauna was collected from the upper part of the La Pola Formation and the lower members of the Don Braulio Formation. The recovery methodology included modifications to standard techniques to obtain complete forms without mechanical and/or chemical damage. Two distinctive scolecodont assemblages have been identified. The oldest assemblage, named Assemblage A, located in the La Pola Formation, is characterized by Xanioprion sp. 1, Xanioprion sp. 2, Oenonites aff. O. eichwaldi, and Oenonites sp. The youngest assemblage, Assemblage B, located in the Fossiliferous Mudstones and Sandstones Member, includes Andiprion paxtonae, Xanioprion cf. X. borealis, Kettnerites sp., and forms of the Ramphoprionidae family. Both assemblages span the Sandbian, Katian, and Hirnantian sequences. A significant difference in polychaete diversity has been observed between the two assemblages. This difference relates to geological events during the Katian–Hirnantian interval, including tectonic activity, sea level changes, glaciation, and the potential for massive extinction.