Bioerosion traces on the Campanian turtle remains: New data from the lagoonal deposits of the Quseir Formation, Kharga Oasis, Egypt

The uppermost part of the Campanian Quseir Formation of Kharga Oasis, Egypt, contains a concentration of turtle skeletal remains in a lagoon setting. They appear as three successive horizons (I‒III), alternated between the variegated shales and the glauconitic mudstones and conglomeratic layers within the Hindaw Member. However, bones recovered in horizon III present a higher preservation potential than the others. Therein, turtle remains are represented by mostly complete shells, partial shells and many scattered and weathered shell fragments. The studied turtles lived in small ponds and marshes and were deposited as autochthonous to parautochthonous relics. Their bones display significant bioerosion signatures on both carapace and plastron. The morphological analysis of the bioerosion structures preserved revealed 11 ichnospecies, belonging to nine ichnogenera. Eight of these ichnotaxa are recorded for the first time in turtle bones of Egypt. The recognised bioerosional structures appear as borings, shallow chambers, grooves, and punctures produced by ticks, beetles, polychaetae worms, fishes/crocodile, and gastropods. They were attributed to the ichnogenera Karethraichnus, Cubiculum, Osteocallis, Radulichnus, Osteichnus, Osedacoides, Sulculites, and Machichnus. In addition, some bite marks assigned to Nihilichnus also occur on a carapace peripheral. This grade of bioerosion was likely caused by relatively long exposure time before the final deposition or burial. In some cases, borings may be produced during the host’s lifetime. The new material considerably expands the stratigraphic and geographic distribution of this trace fossil assemblage and reveals that their producers may have been able to survive in other paleoenvironmental conditions.