The extinction of the Pleistocene megafauna in the Pampa of southern Brazil

The Late Pleistocene-early Holocene faunal turnover in South America was characterized by the extinction of all mammals with body mass >300 kg and several smaller taxa, but the driving mechanisms behind it are still poorly understood. Here is presented an analysis of the extinction in the Pampa of southern Brazil (Rio Grande do Sul state), based on fossil assemblages found in the coastal plain (CPRS) and western area of the state (WRS). The comparison between fossil and extant mastofaunas show that 90% of the mammals represented in fossil assemblages went extinct, and allowed distinguishing three groups: 1) taxa that underwent local extinction, i.e., disappeared locally but survived in other regions until becoming extinct later (including all megamammals); 2) pseudoextinct taxa that disappeared locally but survive until today in other areas, and 3) taxa that disappeared locally but returned during the Holocene. The faunal changes recorded along stratigraphic successions and available numerical ages indicate two phases of extinction, the first around 30 ka b2k in the CPRS (apparently also recorded in Argentina and Uruguay) would have been related to the onset of the cold and dry conditions of the stadial MIS 2, predating the arrival of humans to the region by about 25 kyrs. The second phase eliminated taxa that survived until about 12.7 ka BP in WRS in reduced suitable environments ('refugia') associated with perennial rivers; it coincides with the transition from glacial to interglacial conditions, but pollen data suggest that humans may have contributed for environmental modifications through fire. The results show that the Pleistocene xenarthran-dominated mastofauna was replaced by a Holocene fauna dominated by small rodents and carnivores, and indicate that climate-driven environmental changes, also influenced by sea-level oscillations, were a major agent in the Late Pleistocene mammalian extinctions in the Brazilian Pampa.