Palaeopleurosaurus

{{Short description|Extinct genus of reptiles}} {{Italic title}} {{speciesbox |name = ''Palaeopleurosaurus'' | image = Palaeopleurosaurus posidoniae.JPG | image_caption = Fossil specimen | fossil_range = Early Toarcian, {{fossilrange|181}} | genus = Palaeopleurosaurus | parent_authority = Carroll, 1985 | species = posidoniae | authority = Carroll, 1985 }} left|thumb|Restoration of the skull in lateral and dorsal view '''''Palaeopleurosaurus''''' (meaning "old side lizard") is an extinct genus of diapsid reptiles belonging to the group Sphenodontia.<ref name=anatomy>Dupret, V. (2004). The pleurosaurs: anatomy and phylogeny. ''Revue de Paléobiologie'', '''9''': 61-80.[https://scholar.google.com/scholar?hl=en&q=The+pleurosaurs+%3A+anatomy+and+phylogeny&btnG=&as_sdt=1%2C31&as_sdtp=]</ref> ''Palaeopleurosaurus '' fossils were discovered in Germany (Holzmaden and Kerkhofen) from the Lower Toarcian (Early Jurassic), Posidonia Shale, dated to about 182-180 million years ago.<ref name=description>R. L. Carroll, R. L. (1985). ''A pleurosaur from the Lower Jurassic and the taxonomic position of the Sphenodontida''. Palaeontographica Abteilung A, 1985. Volume 189. Pages 1-28.</ref><ref name=pleuro2/> The holotype come from the Middle Section, just under the Seagrasschiefer section (=Bifrons subzone) on both localities, probably linked with the coeval measured sea regression.<ref name=description/> Initially, ''Paleopleurosaurus'' was described to represent an intermediate morphology between Late Triassic-Lower Jurassic terrestrial sphenodontia and the late Jurassic fully aquatic ''Pleurosaurus''.<ref name=description/> The study of a new specimen provided additional information, corroborating the existence of an early lineage of elongated sphenodontians, although with retained characters of terrestrial genera such as ''Kallimodon''.<ref name=pleuro2/>

==Paleobiology== thumb|left|Model ''Palaeopleurosaurus'' evidences that there was a slightly skeletal specialization for an aquatic lifestyle, achieved through the Jurassic gradually on pleurosaurs, a lifestyle supported by increased bone density in its gastralia.<ref name="density">{{cite journal | first1 = N. | last1 = Klein | first2 = T.M. | last2 = Scheyer | date = 2017 | title = Microanatomy and life history in ''Palaeopleurosaurus'' (Rhynchocephalia: Pleurosauridae) from the Early Jurassic of Germany | journal = The Science of Nature | volume = 104 | issue = 4 | pages = 4 | doi = 10.1007/s00114-016-1427-3 | pmid = 28005148 | bibcode = 2017SciNa.104....4K | s2cid = 27133670 }}</ref> It has similarities 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.<ref name=pleuro2/> 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''.<ref name=pleuro2>Carroll RL, Wild R (1994) Marine members of the Sphenodontia. In: Fraser N, Sues H-D (eds) In the shadow of the dinosaurs—early Mesozoic tetrapods. Cambridge University Press, Cambridge, pp. 70–83</ref> ''Palaeopleurosaurus'' probably was still able to walk on land, for example for Oviposition.<ref name=pleuro2/> Recent studies suggest a shorter lifespan than modern Tuatara, based on irregular spacing of growth marks.<ref name=anatomy/> Histology shows that the number of growth rings in ''Palaeopleurosaurus'' was smaller than the living tuatara, possibly indicating a shorter lifespan.<ref name="density"/>

==References== {{Reflist}}

Category:Rhynchocephalia Category:Prehistoric reptile genera Category:Toarcian life Category:Jurassic lepidosaurs Category:Jurassic Germany Category:Fossils of Germany Category:Posidonia Shale Category:Fossil taxa described in 1985