Silvestrosaurus is an extinct aquatic genus of lariosaurinenothosaurid sauropterygian known from the Middle Triassic of Monte San Giorgio, southern Switzerland. It contains a single species, Silvestrosaurus buzzii, originally considered to be a species of the closely related Lariosaurus. The species was named by Tschanz in 1989, based solely on the holotype PIMUZ T/2804 comprising the skull, the lower jaw, and a dis-articulated partialpostcranial skeleton. Cyamodus hildegardistooth bearing elements were found in the stomach region of the specimen. The holotype was collected at Punkt 902 of MonteSan Giorgio, from layer 97 of the Grenzbitumen zone, dating to the Anisian-Ladinian boundary of the Middle Triassic. Kuhn-Schnyner reassigned the species to its own genus, creating the combination S. buzzii. The generic namehonors a church near the collection locality of the holotype, dedicated to Saint Sylvester, a Pope during the reign of Constantine the Great, and from Greeksaurus, meaning "lizard", a common suffix for genus names of extinct reptile. Rieppel reassigned S. buzzii back to its original combinationLariosaurus buzzii, together with another lariosaurine genus Ceresiosaurus. Rieppel found the two species to form a clade with Lariosaurus valceresii, while the other species of Lariosaurus formed a second clade, a sister taxon to the first. In 2004, however, this synonymy was objected by Hänni who described and named a second species for Ceresiosaurus, and by several other authors since.
Features
Silvestrosaurus is very similar to its close relative Lariosaurus but there are enough differences for most people to assign them to different genera. The nasal has no contact with the prefrontal, separated by processes of the frontal and maxilla, and many parts of the skull, such as the parietal and postfrontal bones, are much broader and flatter than in Lariosaurus. The clavicles do not meet in an anteromedial suture, unlike in Lariosaurus. In Silvestrosaurus the radius is slightly longer than the ulna, but in Lariosaurus they are the same length or the radius is shorter. As the back half of the skeleton is missing, we cannot compare the number of vertebrae. Nor can we compare the hindfeet to see if Silvestrosaurus had paddles like Ceresiosaurus rather than individual toes like Lariosaurus. However, the front limbs definitely had paddles. Silvestrosaurus was only around 60–70 cm long as an adult, making it relatively small for a nothosaur.
