Demarcation problem in fusuline classifcation: A case for Verella/Eofusulina discrimination

Abstract

The eofusulinin genera Verella and Eofusulina formed an important lineage among fusulines to de? ne the Bashkirian/Moscovian transitional interval in the Pennsylvanian (Upper Carboniferous) subsystem. We studied morphologies of Verella transiens, a highly evolved form in the genus, and the ?rst Eofusulina species from the Los Tornos section in the Cantabrian Zone of northern Spain, to understand the discriminating diagnosis of these two genera. We conclude that Eofusulina is distinguishable from Verella in having stronger septal fluting, lesser development of secondary deposits, generally larger proloculus, absence of early tightly coiled volutions, and with some lesser extent slightly larger diameter of shell and absence of polar torsion. No single morphological character provides a reliable criterion to distinguish the two genera, but rather only a combination of all these morphological criteria enables reliable generic discrimination. In order to better understand the morphology, we emphasise the usefulness of non-oriented specimens in this study.