MesosaurusFrom Wikipedia, the free encyclopediaMesosaurusTemporal range: Cisuralian,299280 Ma PreOSDCPTJKPgNMesosaurus tenuidensSien!i"i lassi"ia!ionKingdom: AnimaliaPhylum: ChordataClade: ParareptiliaOrder: MesosauriaFamily: Mesosauridaeenus:Mesosauruser!ais, "#$%&$$T#pe speiesMesosaurus tenuidenser!ais, "#$%&$$S#non#ms Mesosaurus brasiliensis Mcregor, "'(# Ditrochosaurus capensis urich, "##' Mesosaurus capensis )urich, "##'*Mesosaurus )meaning +middle li,ard+* is an e-tinct genus of reptile from the .arly Permian of southern Africa and /outh America0 Along 1ith the genera Brazilosaurus and Stereosternum, it is a mem2er of the family Mesosauridae and the order Mesosauria0 Mesosaurus 1as long thoughtto ha!e 2een one of the first marine reptiles, although ne1 data suggests that at least those of 3ruguay inha2ited a hypersaline 1ater 2ody, rather than a typical marine en!ironment04"5 6n any case, it had many adaptations to a fully a7uatic lifestyle0 6t is usually considered to ha!e 2een anapsid, although Friedrich !on 8uene considered that it 1as synapsid,495 and this hypothesis has 2een re!i!ed recently04:54%5Con!en!s " ;escription 9 Palaeo2iology : ;istri2ution % a1s04?5=he 2ones of the postcranial skeleton are thick, ha!ing undergone pachyostosis0 Mesosaurus is unusual among reptiles in that it possesses a cleithrum0 A cleithrum is a type of dermal 2one that o!erlies the scapula, and is usually found in more primiti!e 2ony fish and tetrapods0 =he head of the intercla!icle of Mesosaurus is triangular, unlike those of other early reptiles, 1hich are diamond&shaped04$5Palaeo$iolog#