A new mesenosaurine from the lower Permian of Germany and the postcrania of Mesenosaurus : implications for early amniote comparative osteology

Based on an exceptionally well-preserved articulated postcranial skeleton, the early amniote Cabarzia trostheidei gen. et sp. nov. is described. As the lack of the skull hampers its taxonomic assignment, a large sample of basal amniotes is included as part of an exhaustive comparison. Considering the slender, long-limbed proportions of the skeleton, several potential determinations are suggested in order to test for bolosaur, millerettid, araeoscelid, basal neodiapsid, or synapsid affinities. Numerous character conditions are re-evaluated regarding their distributions among early amniote subclades. The closest match to Cabarzia is found to be the middle Permian Mesenosaurus from Russia. The documentation for both genera provides the most complete postcranial descriptions of non-varanodontine varanopids. One of the main differences from Mesenosaurus is the curved ungual phalanx, indicating a use related to predatory behavior. An investigation of limb proportions, such as slender trunks, elongated hindlimbs, and relatively short forelimbs, may suggest the occurrence of facultative bipedalism in Mesenosaurus and Cabarzia . The oldest known mesenosaurine, C. trostheidei from the Asselian/Sakmarian, also pushes back the oldest evidence of bipedal locomotion by more than 15 Ma.