Columnar shell structures in early linguloid brachiopods – new data from the Middle Cambrian of Sweden

Abstract

The records of columnar shell structures of linguloid brachiopods (Class Lingulata, Order Lingulida, Superfamily Linguloidea) are reviewed in the light of the discovery of two new taxa from the Middle Cambrian Forsemölla Limestone Bed of southern Sweden. The linguloid taxa, described here as Eoobolus? sp. aff. E. priscus (Poulsen) and Canalilatus? simplex sp. nov., are both characterised by a columnar shell structure, a structural type that is representative for acrotretoid brachiopods and that has previously only rarely been reported from the linguloids. Though the two taxa are superficially similar to known genera, i.e., Eoobolus and Canalilatus, their shell structure challenges such affiliations, as the shell structure of the type species of these genera is previously unknown. Linguloid families whose morphological characteristics agree the most with those of the new taxa, i.e., the Zhanatellidae and the Eoobolidae, and from which columnar shell structures have been reported, i.e., the Lingulellotretidae and the Kyrshabaktellidae, are reviewed briefly. Many taxa assigned to these families completely lack shell structure data and are in need of restudy in order to elucidate their systematic position. Knowledge of the representative type of shell structure of the various suprageneric taxa within the Linguloidea is considered crucial, in order to unravel their currently poorly resolved phylogenetic relationships.