A Miocene Fossil of the Amazonian Fish Arapaima (Teleostei, Arapaimidae) from the Magdalena River Region of Colombia--Biogeographic and Evolutionary Implications

Abstract

A fragmentary fossil fish skull from the Miocene La Venta fauna, Villavieja Formation, in the upper Magdalena River Valley of Huila Department, Colombia, is determined to be similar and closely related to Arapaima gigas (Arapaimidae), a living species distributed east of the Andes in the large lowland rivers of the Amazon basin and the Guianas. This fossil offers an additional example of a long and conservative history for South American riverine fishes. This discovery corroborates biogeographic and geological evidence for a direct connection of the Magdalena region with the middle Tertiary Amazon watershed and its fauna. The fossil Arapaima and several other fishes from the same area suggest former aquatic communities in the Magdalena region that were once more diverse than the modern fauna. The Magdalena fish fauna was isolated as its watershed formed with Late Miocene uplift of the eastern Cordillera, and this fauna suffered local extinctions presumably as a result of tectonic activity and later Cenozoic climatic change. Older fossils belonging to the Arapaimidae indicate that the Arapaima lineage originated before the Cretaceous Afro-South American drift/vicariance event.