Cirripedes (Thoracica, Crustacea) from the Maastrichtian of Kalaat Senan, Tunisia

An assemblage of large and robust pedunculate scalpellomorph cirripede barnacles from the Maastrichtian of Kalaat Senan (Tunisia) is described, and their stratigraphical position within the Abiod and El Haria formations is noted. Four taxa are documented, three of which are confined to the Kalaat Senan area, namely Pachyscalpellum heltzeli, Cretiscalpellum robaszynskii sp. nov. and Diotascalpellum sp.; the fourth, Diotascalpellum curvatum, was previously recorded only from the Maastrichtian of the Farafra Oasis in the Western Desert of Egypt, 2000 km to the southeast. The record of Pollicipes glaber from this locality may well be conspecific with C. robaszynskii sp. nov. The new finds yield clues to the evolution of the composition of the North African cirripede assemblages during the early and late Maastrichtian, up close to the Cretaceous–Paleogene (K/Pg) boundary mass extinction. The fauna is of remarkably large size and strongly armoured for the supposedly offshore open-marine palaeoenvironment of Kalaat Senan, a faunal character that seems to have developed after the Campanian and disappeared by the Danian. The presence of Pachyscalpellum, a genus that was previously restricted to Australasia, indicates faunal connections with the eastern Tethys. Their documented first arrival coincides roughly with the first documented occurrence of northern American scaphitid ammonite genus Discoscaphites. The original description of P. heltzeli is extended; it is characterised particularly by a very elongated scutum. Similar scuta are shown to have evolved independently in the scalpellid genus Regioscalpellum of the European Upper Cretaceous. The family assignment of Pachyscalpellum as a scalpellid is questioned.