The skull of the pistosaurAugustasaurusfrom the Middle Triassic of northwestern Nevada

The skull of Augustasaurus hagdorni from the Middle Triassic of northwestern Nevada is described in detail, and compared to those of Pistosaurus and Plesiosaurus. New information amends the earlier description of the postcranial skeleton of Augustasaurus. Phylogenetic analysis corroborates the sister-group relationship of Augustasaurus and Pistosaurus. These two taxa form a clade that is the sister-group of Plesiosaurus. The paleobiogeographical implication of the sister-group relationship of Augustasaurus and Pistosaurus is discussed and linked to the exotic terrane model.