Besanosaurus leptorhynchus is a species of ichthyosaur extracted from the formation of the Bituminous Schists of Besano (Varese, Italy), and lived in the Middle Triassic (between 247 and 235 million years ago approximately) in the Tethys Sea. The specimen was found in 1993 at the << Sasso Caldo >> site thanks to an excavation opened by the Museum of Natural History in Milan in 1985, and was then described in 1996.
 It is the oldest large swimming diapsid, and represents the oldest and most primitive group of ichthyosaurs ichthyosaurs shastasaurs, which also lived in China and North America.
 At the moment, 6 specimens of B. leptorhynchus are known which have made it possible to reconstruct the different stages of growth of the species, with the largest specimen reaching almost 8 meters in length, while the smallest is just over a meter long.
 The species is characterized by a large rostrum that allowed it to feed on small prey, indicating that it was not a species at the top of the food chain. This particular adaptation may have contributed to the increase in body size allowing the species a low competition with other predators found in the same formation.
 
 
 Bindellini G, Wolniewicz AS, Miedema F, Scheyer TM, 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  https://doi.org/10.7717/peerj.11179