We describe new fossil vertebrates from the Loncoche Formation in the Calmu-Co area of Mendoza Province, Argentina. At this site the lower section of the formation corresponds to lacustrine and mean-dering fluvial environments (facies associations A and B, respectively), whereas the middle levels of the formation are assigned to marginal marine deposits (facies association C). The vertebrates were found in facies association C and include fishes (i.e., Chondrichthyes, Teleostei, Lepisosteidae and Dipnoi), Chelidae turtles (cf. Yaminuechelys, cf. Prochelidella), dinosaurs (Titanosauria) and plesiosaurs (Elasmosauridae). The remains, found in clastic and calcareous facies (mudstones and grainstones), are interpreted to reflect channel and deltaic plain environments. The diverse ecology (terrestrial, fresh water, marine) and the fragmentary character of these skeletal concentrations suggest mixing of fossil remains from littoral environments and fluvial systems. Our findings indicate that the Atlantic marine ingression that covered northern Patagonia reached Calmu-Co, in the western part of the Neuquén basin, Vertebrates from Calmu-Co area are assigned to the late Campanian-early Maastrichtian on the basis of similarities with vertebrates assemblages found in other sites within Mendoza (Ranquil-Có) and northern Patagonia (Río Negro and Chubut provinces, Allen, La Colonia and Los Alamiros formations).