Mammalian biostratigraphy of Pleistocene fluvial deposits in northern Uruguay, South America

The fossiliferous beds of the Sopas Formation, which outcrop in northern Uruguay, have yielded freshwater molluscs, plants and vertebrates, especially terrestrial and freshwater mammals and trace fossils. Fluvial depositional environments predominate. The mammalian assemblage is correlated biostratigraphically with the Lujanian Stage (Late Pleistocene-Early Holocene) of the Pampean region of Argentina. Minimum radiocarbon ages (43 000 years BP and 45 000 years BP) along with luminescence ages (43·5±3·6 and 58·3±7·4 ka) indicate a Late Pleistocene age for this assemblage. Differences in comparison with the typical Lujanian mammal fauna of the fluvial Guerrero Member of the Luján Formation in Buenos Aires province (Pampean region) could be a consequence not only of temporal differences but also of distinct biogeographical and climatic phases. The Sopas Formation has mammals indicative of various habitats. Some of the extant species inhabit fluvial and lacustrine environments with riparian forest, whereas others indicate open woodland, savanna and grassland. There is discussion of the occurrence of tropical to temperate (‘brasilic’) mammals together with others related to arid conditions.