The pectoral girdle and forelimb of Carsosaurus marchesetti (Aigialosauridae), with a preliminary phylogenetic analysis of mosasauroids and varanoids

The aigialosaur Carsosaurus marchesetti is represented by a nearly complete skeleton from the Upper Cretaceous (Cenomanian-Turonian) of Slovenia. Dermal girdle elements include portions of the clavicles and a small interclavicle with a short anterior process. Endochondral girdle elements include a small scapula and large unfenestrated coracoid. A mineralized sternum is also present. The carpus is anguid-like and consists of ten ossified elements. Reduction of the procoelous nature of centrum articular surfaces is restricted to the caudal series. The type of C. marchesetti is the largest aigialosaur specimen known (>1.5 m) and has proportionally larger propodials than any other aigialosaur. Phylogenetic reconstruction places Carsosaurus within a polytomous clade composed of all known aigialosaurs. Aigialosaurs are the sister-group to Mosasauridae, forming the Mosasauroidea, and are within Anguimorpha but distinct from Varanoidea. Supposed synapomorphies of varanids and mosasauroids are identified as either plesiomorphies of Anguimorpha, or as misidentified homologs. Results of a principal component analysis of limb measurements suggest that aigialosaurs occupy a position on a functional continuum reflective of terrestrial not aquatic animals. Morphometric criteria cannot validate the exclusion of Carsosaurus from the Aigialosauridae.