Simosaurus

Simosaurus is an extinct genus of marine reptile within the superorder Sauropterygia from the Middle Triassic of central Europe. Fossils have been found in deposits in France and Germany that are roughly 230 million years old. It is usually classified as a nothosaur, but has also been considered a pachypleurosaur or a more primitive form of sauropterygian.

Description
Simosaurus grew from 3 to 4 metres (9.8 to 13.1 ft) in length. It has a blunt, flattened head and large openings behind its eyes called upper temporal fossae. These fossae are larger than the eye sockets but not as big as those of other nothosaurs. Simosaurus also differs from other nothosaurs in that it has blunt teeth that were probably used for crushing hard-shelled organisms. The jaw joint is set far back, projecting beyond the main portion of the skull.

History
The type species of Simosaurus, S. gaillardoti, was named by German paleontologist Christian Erich Hermann von Meyer in 1842. In the same year, von Meyer also named S. mougeoti. He named a third species, S. guilelmi, in 1855. Oscar Fraas named S. pusillus in 1881. A year later, however, it was reassigned to its own genus, Neusticosaurus.[2] S. mougeoti and S. guilelmi have more recently been considered junior synonyms of S. gaillardoti, meaning that they represent the same species.

The first fossils of Simosaurus, those described by von Meyer, were found in Lunéville, France. These were found in the upper Muschelkalk, which dates back to the Ladinian stage of the Middle Triassic. Material found in France includes the holotype skull of S. gaillardoti and a partial mandible referred to S. mougeoti. Both were described by von Meyer. The skull, which served as the basis for the first description of Simosaurus, has since been lost. Although initially attributed to Simosaurus, the mandible was labeled as "Nothosaurus mougeoti" in one of von Meyer's later papers.

Additional remains of Simosaurus were found in Franconia and Württemberg in Germany. Duke William of Württemberg discovered a complete skull and sent it to von Meyer in 1842. Von Meyer named S. guilelmi on the basis of this skull, noting that it was smaller and narrower than those of the type species. A complete skeleton first referred to S. guilelmi has been designated the neotype of Simosaurus. Some German fossils have been found in the stratigrafically younger Keuper deposits, but are very rare. Simosaurus is present in biozones of the Muschelkalk that are distinguished by different ammonite fauna. Simosaurus first appears in the nodosus biozone, where fossils of the ammonite Ceratites nodosus are abundant. Specimens becomescommon in the slightly younger dorsoplanus biozone, characterized by the ammonite Ceratites dorsoplanus.[