Resumen
A long necked chelid turtle species from the Anacleto Formation (late Santonian-early Campanian) cropping out at Valle de La Luna Rojo, Rio Negro Province, Argentina, is assigned to Yaminuechelys cf. gasparinii De la Fuente, De Lapparent de Broin and Manera de Bianco, 2001 and it represents the oldest record of a long-necked chelid. We suggest that the common ancestor of Yaminuechelys and Hydromedusa lived in Southern Gondwana before the separation of Australia from the remaining Southern Gondwanan landmasses. The presence of this chelid taxon in the Late Cretaceous of Patagonia and some previous phylogenetic analyses support the hypothesis of an early differentiation and diversification of chelids on Southern Gondwana.