The Central American Seaway (also known as the Panamanic Seaway, Inter-American Seaway and Proto-Caribbean Seaway) was a prehistoric body of water that once connected the Pacific Ocean to the Atlantic Ocean, separating North America from South America. It formed during the Jurassic (200–154 Ma) during the initial breakup of the supercontinent Pangaea into Laurasia and Gondwana, forming a mediterranean sea between the Panthalassia and Tethys Ocean, and finally closed when the Isthmus of Panama was formed by volcanic activity in the late Pliocene (2.76–2.54 Ma). The modern-day remnants of the seaway are the Gulf of Mexico, Caribbean Sea and the Central Atlantic region around the Sargasso Sea.
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.
