New Middle Jurassic hybodontiform shark-like chondrichthyans from the Umbria-Marche Basin (Italy)

In this study we describe two newly identified isolated teeth of hybodontiform shark-like chondrichthyans from the Middle Jurassic deposits of the Umbria-Marche-Sabina (UMS) Domain in the Apennines, Italy. The specimens, identified as Strophodus sp. and Acrodus sp., contribute to the sparse fossil record of marine vertebrates from this region, particularly within the unique Jurassic PCP-basin environments. The Strophodus specimen (MUST NS.169.12) exhibits a robust crushing morphology characterised by a reticulated occlusal surface, indicative of the durophagous feeding adaptation of the genus. The Acrodus specimen (MUST NS.169.13) possesses a transverse crest and radial ridges, with a general morphology compatible to an anterior tooth position. Microfacies analysis of the embedding sediments attributes both specimens to the Aalenian–lower Bajocian interval. These finds mark the first documented occurrence of Acrodus in the Apennines and the first Middle Jurassic record of the genus in Italy. The palaeoenvironmental context suggests that these hybodontiform shark-like chondrichthyans inhabited shallow marine settings rich in benthic invertebrates, which aligns well with their durophagous diet. Their presence enhances our understanding of marine vertebrate diversity within the UMS Basin and helps us to improve our knowledge of the ecological dynamics of the peculiar Jurassic Pelagic Carbonate Platform-Basin ecosystems.