Editing Mesosaur (section)

{{Short description|Extinct family of reptiles}}
{{distinguish|text=[[mosasaur]]s, marine reptiles of the Late Cretaceous}}

{{Automatic taxobox
| taxon = Mesosauridae
| name = moasasaurus
| image= Mesosaurus BW.jpg
| image_caption = ''[[Mesosaurus]]''
| fossil_range = [[Cisuralian]], {{Fossil range|299|270.6}}
| display_parents = 3
| parent_authority = [[Harry Govier Seeley|Seeley]], [[1892 in paleontology|1892]]
| authority = Baur, [[1889 in paleontology|1889]]
| subdivision_ranks = Genera
| subdivision =
* †''[[Brazilosaurus]]''
* †''[[Mesosaurus]]''
* †''[[Stereosternum]]''
}}
'''Mesosaurs''' ("middle lizards") were a group of small aquatic reptiles that lived during the early [[Permian]] period ([[Cisuralian]]), roughly [[Geologic time scale|299 to 270 million years ago]]. Mesosaurs were the first known aquatic [[reptile]]s, having apparently returned to an aquatic lifestyle from more terrestrial ancestors. It is uncertain which and how 
many terrestrial traits these ancestors displayed; recent research cannot establish with confidence if the first [[amniotes]] were fully terrestrial, or only amphibious.<ref name=AC&ML10/> Most authors consider mesosaurs to have been aquatic,<ref name=AC&ML10/><ref name=SM06/> although adult animals may have been amphibious, rather than completely aquatic, as indicated by their moderate skeletal adaptations to a semiaquatic lifestyle.<ref name=GP08/><ref name="Pablo Nuñez Demarco 2018">Pablo Nuñez Demarco et al. Was Mesosaurus a Fully Aquatic Reptile? Front. Ecol. Evol, published online July 27, 2018; doi: 10.3389/fevo.2018.00109</ref> Similarly, their affinities are uncertain; they may have been among the most basal [[sauropsids]]<ref name=ML&RR95/><ref>{{Cite journal | doi=10.3389/feart.2017.00088|title = A Reassessment of the Taxonomic Position of Mesosaurs, and a Surprising Phylogeny of Early Amniotes| journal=Frontiers in Earth Science| volume=5|year = 2017|last1 = Laurin|first1 = Michel| last2=Piñeiro| first2=Graciela H.|page = 88|bibcode = 2017FrEaS...5...88L| doi-access=free|hdl=20.500.12008/33548|hdl-access=free}}</ref> or among the most basal [[parareptile]]s (in the case of which parareptiles were basal sauropsids).<ref name=MSP99/><ref>MacDougall, M.J.; Modesto, S.P.; Brocklehurst,N.; Verriere, A.; Reisz, R.R.; Fröbisch, J. (2018). "Response: A Reassessment of the Taxonomic Position of Mesosaurs, and a Surprising Phylogeny of Early Amniotes". ''Front. Earth Sci.'' 6:99 doi: 10.3389/feart.2018.00099</ref>