Durania cornupastoris rudist from the Turonian of El-Hassana Dome (Abu Roash area), Egypt: Systematic palaeontology and palaeoecology

Abstract

Abstract Based on newly-collected exhaustive rudist materials from the Turonian Abu Roash Formation at El-Hassana dome, Durania cornupastoris (Des Moulins) was clearly-identified. In many literatures, the Durania arnaudi (Choffat) is considered a synonym of Durania cornupastoris (Des Moulins). Our investigation is based on several characteristics that include dimensions, ornamentation, radial bands, interbands and shell microstructures of the right valves. These characters and comparison with specimens described in the literature were used to identify the collected specimens as Durania cornupastoris and differentiate it from Durania arnaudi. The external shape of the shell, widths of the radial bands and number of the longitudinal ribs in the interband were the main characteristics of Durania cornupastoris. In the described right valves, the interband (Ib) is bulge and has four to six ribs that excluded an attribution to Durania arnaudi. Moreover, the ventral radial band (Vb) of Durania cornupastoris is wider than the posterior one (Pb). The ecological and taphonomic characteristics of D. cornupastoris were highlighted. The elevator D. cornupastoris rudists of El-Hassana Dome form significant biostrome in shallow marine environments. The D. cornupastoris individuals are in growth position and they are densely packed. The borings are distributed on the D. cornupastoris shells. Moreover, these shells exhibit compaction features that appeared as fractures, deformation and/or destruction of the cellular structures in the right valves. The borings and the fractures in the shells are filled with silica materials during the silicification process. The carbon isotopic data (δ13C) of the Durania cornupastoris from Abu Roash area are similar to those from Sinai. However, the oxygen isotopic values (δ18O) measured from this species are high when compared with those from the Turonian rudist shells of Sinai.