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The configuration of the continents has changed during the earth history because of different geologic processes that in turn shaped the natural world. At the scale of millions of years, we are able to recognize that the evolution of the earth’s geographic features and plate tectonics have a strong impact on animals, plants and climate. During the Cenozoic, the time period after the extinction of the dinosaurs, South America was isolated from other continents.

Here you can explore some paleogeographic global reconstructions at different times of earth history. At that time South America was the home of an endemic fauna. Do the words notoungulate and isotemnids make you wonder what these animals looked like? Go here to find out what characteristics these organisms had! Marsupial dogs, bears, sabertooth tigers, and weasels sound fascinating? Take a look at this Scientific American blog post.

The northern continent had its own, different, fauna, with animals more familiar to us such as horses, bears, and saber-toothed cats.

North and South America were separated by a marine connection between the Pacific and Atlantic oceans. Around 15 million years ago (Ma) Central America was a peninsula connected to North America, and a narrow seaway of approximately 200 km separated it from South America. Plate tectonics caused South America to collide with the Central American arc, and gradually the Panamá Isthmus started to emerge. It continued until it closed the communication between Caribbean and Pacific waters at 3-4 Ma, around the time when the first hominids appeared in Africa.

The division of the Atlantic and Pacific Oceans had several consequences. First, the transport of deep water currents stopped. The emerging land increased the salinity in the Caribbean, and produced a collapse of a strong upwelling, the process by which the deeper, colder, nutrient rich waters rise to the ocean’s surface. The collapse of the upwelling reduced planktonic productivity in the Caribbean. Today, the Pacific Ocean and Caribbean Sea are very different, the Caribbean has higher salinity and warmer temperature year-round; in contrast, the Pacific shows seasonal temperature and salinity differences because it retained upwelling events. The uplift of the Panama arc also forced the reorganization of the global oceanic circulation. It allowed the establishment of the Thermohaline circulation, that transports warm water across the Atlantic and influences the climate of the east coast of North America from Florida to Newfoundland, and the west coast of Europe. The land bridge was a barrier for many marine organisms, like mollusks, crustaceans, foraminifera, bryozoans and fish. This barrier separated the populations of many marine organisms on each side of the isthmus, the Pacific and Caribbean, facilitating the allopatric speciation.

The narrow strip of land also served as a connection between the Americas and allowed the exchange of terrestrial plants and animals between the two continents. This event is called the Great American Biotic Interchange, and is one the major episodes of biological migration in the earth history. Terrestrial organisms could now cross, and different waves of dispersals took place. The Great American Biotic Interchange is a great example that shows how a geologic process can substantially modify the composition and distribution of life on earth at continental scales. The formation of the Isthmus of Panama is directly related with the great biodiversity that we observe today in the region and modified the oceanic conditions, water currents and the global climate.