A new record of Gunnellichnus moghraensis from the Middle Miocene of Belgium, with some remarks on the origin of this seemingly uncommon ichnospecies

In spite of the common and widespread occurrence of turtle shell remains in many fossil vertebrate assemblages worldwide, only a few palaeontological studies exist detailing the occurrence and significance of turtle bone modification features. Among the few ichnotaxa that have recently been described from fossil plastral and carapacial elements of both terrestrial and aquatic turtles, Gunnellichnus moghraensis is currently only known from the holotype and five associated specimens occurring on a single plastron of the freshwater turtle Erymnochelys from the Lower Miocene of Egypt. Here, we report on new examples of G. moghraensis occurring on a marine turtle costal plate from the lower Middle Miocene (ca. 15.97 to 14.8 Ma) strata of the Antwerpen Member of the Berchem Formation at Berchem, near Antwerp, in northern Belgium. A scrutiny of palaeontological literature reveals that similar traces also occur on carapacial elements of the Upper Cretaceous cheloniid Allopleuron hofmanni from the Maastrichtian type area. The hypothesis that G. moghraensis and the allied ichnospecies Gunnellichnus akolouthiste represent the product of bacterial and/or fungal degradation of the turtle shell is here preferred to alternative explanations that involve the joint action of sessile epibiotic macro-invertebrates