Understanding linguloid brachiopods: Obolus and Ungula as examples

Emig (2002) re-examined the taxonomy of the genus Obolus Eichwald from the Middle Cambrian - earliest Ordovician of the East Baltic region as part of a proposal for a wholesale revision of the principles of linguloid systematics. He contended that previous taxonomic studies on Obolus and related forms were carried out erroneously using characters that have no taxonomic value. Emig's proposed revision is based mainly on the limited morphological diversity between fossil and Recent taxa within a single linguloid Family, the Lingulidae. However, the present study demonstrates the taxonomic validity of the diagnostic characters used for classification within the mostly extinct families of the Superfamily Linguloidea, for they exhibit far more variation in morphology. This study also shows that Emig has provided no satisfactory basis for his radical changes and revisions to the existing widely accepted taxonomy of the Cambrian to earliest Ordovician Obolidae of the East Baltic. Obolus Eichwald and Ungula Pander are shown to constitute distinctive and discrete genera comprising the species Obolus apollinis Eichwald, O. ruchini Khazanovitch et Popov, O. transversus (Pander), Ungula ingrica (Eichwald), U. inornata (Mickwitz), and U. convexa Pander.