Isorthoceras wahlenbergi, a new Late Ordovician cephalopod from the Boda Limestone of Dalarna, Sweden

Abstract

A new species of Isorthoceras (Proteoceratidae: Cephalopoda), I. wahlenbergi, is described from the Upper Ordovician Boda Limestone in Dalarna, central Sweden. The Boda Limestone consists of up to 20 isolated carbonate mounds ranging in size from a few meters to over 400 m in diameter and attaining 70 m in thickness (Jaanusson, 1982; Cocks, 2005). Each mound is divided into a micritic core facies, a pelmatozoan flank facies, and a bioclastic terminal facies (Suzuki and Bergstrom, 1999). The diverse faunas of the Boda Limestone include well documented taxonomic groups such as trilobites (e.g., Warburg, 1925; Suzuki, 2002), brachiopods (e.g., Wright, 1974, 1993; Cocks, 2005) and gastropods (e.g., Koken and Perner, 1925; Ebbestad and Peel, 1997). These faunas are suggestive of a middle Ashgillian age for these limestones. In contrast to these, taxonomic studies of cephalopods from the Boda Limestone are limited to Frye (1982, 1987), who described 18 species belonging to the orders Ascocerida, Oncocerida, Tarphycerida and Barrandeocerida.