The closure of the Central American Seaway had tremendous effects on oceanic circulation and the biogeography of the adjacent seas, isolating many species and triggering speciation and diversification of tropical and sub-tropical marine fauna. The inflow of nutrient-rich water of deep Pacific origin into the Caribbean was blocked and so local species had to adapt to an environment of lower productivity. It had an even larger impact on terrestrial life. The seaway had isolated South America for much of the Cenozoic, which allowed the evolution of a wholly-unique diverse mammalian fauna there. When it closed, a faunal exchange with North America ensued and led to the extinction of many of the native South American forms.
