VERTEBRATE TAPHONOMY OF UPPER CRETACEOUS VERTEBRATES FROM THE LONCOCHE FORMATION IN CALMU-CO (MENDOZA, ARGENTINA): PALEOENVIRONMENTAL AND PALEOGEOGRAPHICAL IMPLICATIONS. This paper presents a taphonomic study of vertebrate fossils from the Loncoche Formation (late Campanian—early Maastrichtian) found in the Calmu-Co area in Mendoza, Argentina. Four environmental stages were recognized in this site, (1) saline lacustrine systems; (2) fluvial systems; (3) deltaic systems; (4) shallow fluvial and lacustrine systems. The vertebrates found in the deltaic environment comprise disarticulated parautochthonous—allochthonous concentrations (taphofacies 1) of fishes (Chondrichthyes, Teleostei, Lepisosteidae and Ceratodontidae), turtles (Chelidae), dinosaurs (Titanosauria) and plesiosaurs (Plesiosauria). The disarticulated and fragmentary feature of these mixed concentrations (terrestrial, freshwater, marine) suggest a mixture of remains from littoral environments and fluvial systems. The above interpretation is based on the taphonomic attributes of these concentrations, which showed a high degree of weathering, abrasion and time-averaging. On the other hand, disarticulated parautochthonous concentrations (taphofacies 2) of dinosaurs were registered in the fluvial environment. These remains showed processes of fragmentation and abrasion due to hydraulic transport. Fossil-diagenetic processes include events of permineralization and cementation of vascular canals and fractures, phenomena of deformation and lithostatic compression. These evidences indicate that the Atlantic marine ingression (Maastrichtian—Paleocene) which covered northern Patagonia, spread until Calmu-Co, in the western Neuquén Basin.