Description and phylogenetic relationships of Taniwhasaurus antarcticus (Mosasauridae, Tylosaurinae) from the upper Campanian (Cretaceous) of Antarctica

The Antarctic tylosaurine mosasaur Taniwhasaurus antarcticus (Upper Cretaceous, Campanian) is redescribed and rediagnosed based on the holotype. The reexamination of this specimen reveals that T. antarcticus is clearly distinguishable by a set of skull features from other species of the genus, including an almost straight fronto-parietal suture, the extreme reduction of the infrastapedial process of the quadrate, and the L-shaped coronoid. Phylogenetic analysis indicates that T. antarcticus and T. oweni are sister taxa, confirming their assignment to the same generic entity. The most striking feature of T. antarcticus is the configuration of the posterior terminus of the skull and its articulation with the quadrate. The posteroventral expansion of the supratemporal embraces medially the ventral half of the posterior border of the paroccipital process, preventing the quadrate head from extended posterior displacement. Although in T. oweni this region of the skull has not been preserved in natural position, the same configuration of the quadrate-supratemporal-squamosal and paroccipital process complex can be inferred based on the quadrate morphology.