A MIOCENE FOSSIL OF THE AMAZONIAN FISH ARAPAIMA (TELEOSTEI, ARAPAIMIDAE) FROM THE MAGDALENA RIVER REGION OF COLOMBIA - BIOGEOGRAPHIC AND EVOLUTIONARY IMPLICATIONS

A fragmentary fossil fish skull from the Miocene La Venta fauna, Villa vieja Formation, in the upper Magdalena River Valley of Huila Departme nt, Colombia, is determined to be similar and closely related to Arapa ima gigas (Arapaimidae), a living species distributed east of the Ande s in the large lowland rivers of the Amazon basin and the Guianas. Thi s fossil offers an additional example of a long and conservative histo ry for South American riverine fishes. This discovery corroborates bio geographic and geological evidence for a direct connection of the Magd alena region with the middle Tertiary Amazon watershed and its fauna. The fossil Arapaima and several other fishes from the same area sugges t former aquatic communities in the Magdalena region that were once mo re diverse than the modern fauna. The Magdalena fish fauna was isolate d as its watershed formed with Late Miocene uplift of the eastern Cord illera, and this fauna suffered local extinctions presumably as a resu lt of tectonic activity and later Cenozoic climatic change. Older foss ils belonging to the Arapaimidae indicate that the Arapaima lineage or iginated before the Cretaceous Afro-South American drift/vicariance ev ent.