Late Neogene megariver captures and the Great Amazonian Biotic Interchange

Recently published time-calibrated molecular phylogenies have brought to light a large-scale biotic interchange between the Western and Eastern Amazon basins, associated with the late Neogene (c. 10–4.5 Ma) uplift of the Northern Andes and formation of the modern transcontinental Amazon river. This important macroevolutionary event was previously overlooked due to poor understanding of alpha taxonomy and geographic distributions, lack of species-dense phylogenetic analyses, and insufficient methods for estimating biogeographic range evolution and lineage divergence times. Rapid improvements in all these areas have now provided the community with a corpus of historical biogeographic studies using species-dense and time-calibrated molecular phylogenies of plant and animal taxa distributed across Greater Amazonia. In this study we present historical biogeographic analyses of two clades of freshwater fishes (potamotrygonid stingrays and apteronotid electric fishes), and synthesize these results with those of 18 other published studies of Amazonian taxa, including riverine and upland (terra firme) clades of plants (n = 5), insects (n = 2), and representatives of all five vertebrate classes; i.e. fishes (n = 4) amphibians (n = 3), non-avian reptiles (n = 2), birds (n = 2), and mammals (n = 2). Our results support the hypothesis that tectonically-driven megariver capture events facilitated a massive biotic interchange between the Western and Eastern Amazon basins, which we name the Great Amazonian Biotic Interchange. These same megacapture events also separated the modern Amazon and Orinoco basins, contributing to the biotic distinctiveness of these megadiverse regions, and thereby elevating the total biodiversity of Greater Amazonia. The results highlight the role of large and rare (Black Swan) landscape evolution events in preserving and promoting biodiversity that had accumulated over tens of millions of years and across the whole of the South American continental platform.