Ammonite stratigraphy and the belemnite genus Hibolithes in the higher Serdj Formation (Aptian-Albian boundary interval) in north central Tunisia

The identifications of some ammonite findings from the Aptian-Albian boundary interval of the type locality of the Serdj Formation at Djebel Serdj in north central Tunisia are revised and their biostratigraphic value is discussed. From this stratigraphic section, a single belemnite finding is described that has been previously identified as Neohibolites. A newly prepared thin section of the guard shows the internal structure of rostrum and phramoconus, including some septa, and allows an assignment as Hibolithes cf. obtusirostris (Pavlow in Pavlow & Lamplugh 1891). It represents the youngest record of this genus from the Tethys where the youngest record of Hibolithes was hitherto early Barremian. The new evidence is also of palaeobiogeographic interest, since Hibolithes is originally a genus of the Tethys, which migrated early into the Boreal and from there later on again into the Tethys.