connection terminated at the lastest by 2.45 million years ago. The earliest recent literature date for first closure is 15 million years ago Great American Interchange The first exchanges (land) and separation of species (sea) took place by 20 million years ago but genetic drift data seems to indicate that surface ocean connections may have existed of the order of 1 million years ago. Development of differences in marine assemblages and their isotopic signatures in the Caribbean from those in the Pacific The saline and carbon data are fairly suggestive for a range of surface water interface loss between 4.6 million years ago to 4.2 million years ago Consequences The closing of the seaway allowed a major migration of land mammals between North and South America, known as the Great American Interchange. That allowed species of mammals such as cats, canids, horses, elephants, and camels to migrate from North America to South America, and porcupines, ground sloths, glyptodonts and terror birds made the reverse migration. There is much controversy about glacial and interglacial climates in South America. Research shows that vegetation in most of the Amazon basin has changed very little since glacial times, but it is believed there was more savanna present during that period. A closed seaway would have led to a very different North Atlantic Ocean circulation, but it impacted the surrounding atmospheric temperatures, which in turn affected the glacial cycle. The emergence of the isthmus caused a reflection of the westward-flowing North Equatorial Current northward and enhanced the northward-flowing Gulf Stream. The Pacific coast of South America would have cooled as the input of warm water from the Caribbean was cut off. That trend is thought to have caused the extinction of the marine sloths of the area. The closure of the seaway led to an increased poleward salt and heat transport, which strengthened the North Atlantic thermohaline circulation 2.95–2.82 million years ago. That in turn increased the moisture supply to Arctic latitudes, which contributed to both Arctic continental glaciation and sea ice formation. Eventually, with the orbitally-paced extension of Gelasian ice sheets, that led to the Quaternary ice age. See also References Historical oceans Natural history of North America Natural history of South America Natural history of Central America