Taxonomic review, palaeoecological, and palaeobiogeographical significances of Campanian Tethyan oysters from the North Eastern Desert, Egypt.

The Late Cretaceous was a time of high eustatic sea level that enabled extensive epicontinental seaways and carbonate platforms across the Tethyan Realm, providing favorable habitats for oyster communities to flourish. This study focuses on the Campanian Tethyan oysters from the North Eastern Desert of Egypt regarding taxonomy, palaeoecology, and palaeobiogeography. Three oyster species, Nicaisolopha nicaisei (Coquand, 1862), Pycnodonte (Phygraea) vesicularis (Lamarck, 1806), and Ambigostrea bretoni (Thomas and Peron, 1891), were identified from the Campanian succession in two studied sections. The sampled specimens of the genus Nicaisolopha have undergone a systematic palaeontological revision. As a result, N. tissoti (Thomas and Peron, 1891) is considered herein a junior synonym of N. nicaisei (Coquand, 1862). Palaeobiogeographically, the likely primary migration pattern of the studied oysters suggests an east-west trend along the Southern Tethys margin. All identified oysters in this study exhibit a Tethyan affinity and are primarily abundant in two main provinces: the Southern Tethys and the Western Tethys. The macrofaunal contents are categorized into two fossil associations: the Nicaisolopha nicaisei association of the middle-late Campanian age and the Pycnodonte vesicularis association of the late Campanian age. These macrofaunal associations indicate a deepening trend during the middle-late Campanian age, suggesting a transition from shallow inner neritic to middle neritic environments. Additionally, it is observed that Pycnodonteinae tend to grow larger under eutrophic conditions, low-energy environments, and nutrient-rich waters with high carbonate contents.