Cranial anatomy of Besanosaurus leptorhynchus Dal Sasso & Pinna, 1996 (Reptilia: Ichthyosauria) from the Middle Triassic Besano Formation of Monte San Giorgio, Italy/Switzerland: taxonomic and palaeobiological implications

A new analysis of Besanosaurus leptorhynchus, a Middle Triassic ichthyosaur from Monte San Giorgio, reveals it as the earliest large diapsid with extreme longirostry—a specialized skull morphology suggesting a novel ecological niche focused on small, elusive prey. The study re-examines cranial osteology and assigns five additional specimens to this taxon, including four previously undescribed ones, while synonymizing Mikadocephalus gracilirostris. Phylogenetic analysis places it as a basal merriamosaurian, with uncertain relationships within Shastasauridae. This specialization likely contributed to the diversification of ichthyosaurs in the Besano Formation by reducing competition among coexisting species.

Bindellini, G., Wolniewicz, A. S., Miedema, F., Scheyer, T. M., & Dal Sasso, C. (2021). Cranial anatomy of Besanosaurus leptorhynchus Dal Sasso & Pinna, 1996 (Reptilia: Ichthyosauria) from the Middle Triassic Besano Formation of Monte San Giorgio, Italy/Switzerland: taxonomic and palaeobiological implications. PeerJ, 9, e11179. Portico. https://doi.org/10.7717/peerj.11179