New and more complete specimens of pleurodiran turtles from the Salamanca Formation (lower Paleocene) of Patagonia are described. The shell sculpturing, size, and morphology of these specimens match with the characteristics of the largest of Staesche's species (?Najadochelys maior Staesche, 1929 and Osteopygis sculptus Staesche, 1929). Osteopygis sculptus is considered a junior synonym of ?Najadochelys maior. This taxon is the only valid one of Staesche's large species, and is assigned to the chelid genus Yaminuechelys de la Fuente et al. 2001 as Y. maior (Staesche, 1929) new comb. The phylogenetic hypothesis proposed supports a sister-group relationship between Yaminuechelys and Hydromedusa. This clade plus the Australasian genus Chelodina form a monophyletic group supported by cranial and postcranial derived characters, and differentiated in Patagonia at least as early as the upper Cretaceous.