Co-existence of interarea and palintrope: contribution of a new pentameride brachiopod from the Upper Ordovician of Sweden

Abstract

A new genus of pentameride brachiopod, Costilamnulella, described herein from the middle Ashgill of Sweden, is particularly interesting in that the ventral valve possesses both an interarea and a palintrope. Brachiopods normally have one or the other, but both structures do occur amongst the pentamerides, e.g. in Clorinda, Anastrophia and Brevilamnulella. The presence of these structures in three separate pentameride families indicates the persistence of the more primitive condition of an interarea whilst the more advanced palintrope is becoming established. Costilamnulella is interpreted as a restricted side line of the main development of the more widely occurring Brevilamnulella, which survived the end-Ordovician event and may have shared its ancestry with the ubiquitous Clorinda.