CONICET | Buscador de Institutos y Recursos Humanos

The Middle Miocene has been identified as a time of great diversification inmodern lineages now distributed in tropical South America, and when basic archetypical traits defining Amazonia appear, including climatic humid conditions, basic floral physionogmy, and phylogenetic composition of modern rainforests. Nonetheless, Middle Miocene localities in South America are poorly known, especially at low latitudes where only one locality, La Venta in Colombia, has been extensively studied. The present contribution describes the mammal fauna of Fitzcarrald, a new Middle Miocene local fauna from western Amazonia in Peru. Fitzcarrald is correlated with the Laventan South American Land Mammal Age based on the presence of taxa defining the ?Miocochilius assemblage zone? in La Venta. The taxonomic composition of Fitzcarrald comprises 24 mammalian taxa among cingulates, folivores, astrapotheres, notoungulates, litopterns, rodents, odontocetes, and a possible marsupial. At this epoch, tropical South America was characterized by the presence of the Pebas megawetland, a huge lacustrine complex that provided unique ecological and environmental conditions most likely isolating northern South America from southern South America. These isolating conditions might have come to an end with its dissapearance at the Late Miocene and the establishment of the subsequent Acre system, the predecessor fluvial system of modern Amazonia. Results of faunistic similarity between Fitzcarrald and other Miocene faunas throughout South America support these scenarios. The Fitzcarrald mammal fauna exhibits FADs and LADs of various taxa, showing that tropical South America has played a crucial role in the evolutionary history and biogeography of major clades, and revealing a more complex biological history than previously proposed, based on the record of the southern cone of the continent.