Smooth and rugose wall textures in earliest Danian trochospiral planktic foraminifera from Tunisia

Abstract

New scanning electron microscopy (SEM) photographs of planktic foraminiferal specimens from Tunisian sections (El Kef, Aïn Settara, Elles) have revealed the occurrence of two lineages of primitive trochospiral species in the lowermost Danian. The first lineage to appear, which evolves at the P0-Pa transition, exhibits a smooth and/or granular wall texture (with pore-murals), and its species were attributed to the parvularugoglobigerinids (Parvularugoglobigerina and Palaeoglobigerina). The second to appear at the Pa-P1 transition has a rugose wall texture (with rugosities and isolated irregular pore-mounds) and is herein assigned to the new genus Trochoguembelitria. Both lineages co-occur in the upper part of Pa (middle-upper part of Eoglobigerina simplicissima Subzone), containing quasi-homeomorph species - pseudocryptic under stereomicroscopy - only differentiated under SEM by their wall texture (e.g., Palaeoglobigerina alticonusa vs Trochoguembelitria alabamensis). The data at our disposal suggest Trochoguembelitria derived from triserial Guembelitria and its species evolved in parallel with the parvularugoglobigerinids in the earliest Danian.