Palaeopleurosaurus

Palaeopleurosaurus is an extinct genus of diapsid reptiles belonging to the group Sphenodontia.
 
"Palaeopleurosaurus" fossils were discovered in Bavaria, Germany from the Toarcian (Early Jurassic) Posidonia Shale, dated to about 183 million years ago. "Palaeopleurosaurus" evidences that there was an slightly skeletal specialization for an aquatic lifestyle, achieved trougth the Jurassic gradually on pleurosaurs, a lifestyle supported by increased bone density in its gastralia. It has similities with other marine reptiles, such with members of Sauropterygia the presence of a defined suture between the centrum and the neural arch, along with reducted sternum. However, the lack of increase in rib and femur bone density suggests that the lineage of "Palaeopleurosaurus" became gradually adapted to aquatic lifestyles, not as adapted as "Pleurosaurus", as show limited morphological evidence of adaptation to a complete aquatic lifestyle, defined by no Osteosclerosis and the lack of Pachyostosis, except for a thicker shaft region in the humerus, that is as narrow as in terrestrial rhynchocephalians, such as the terrestrial "Clevosaurus". "Palaeopleurosaurus" probably was still able to walk on land, for example for Oviposition. Recent studies suggest a shorter lifespan than modern Tuatara, based on irregular spacing of growth marks. Histology shows that the number of growth rings in "Palaeopleurosaurus" was smaller than the living tuatara, possibly indicating a shorter lifespan. 