The exchange of species between North and South America created one of the most biologically diverse regions on Earth. A new study shows that this interchange began millions of years earlier than previously assumed.

The Isthmus of Panama, which links North and South America, plays a crucial role in the planet's atmospheric and oceanic circulation, climate, and biodiversity. Despite its importance across multiple disciplines, the timing of formation and emergence of the Isthmus and the effect it had on those continents' biodiversity have long remained controversial.

A new study led by researchers from the University of Gothenburg, Sweden, rejects the long-held assumption that biological interchange mostly took place in the last 3 million years. In their study, published this week in the Proceedings of the National Academy of Sciences, Christine Bacon and co-authors examined a large number of molecular studies and fossils, including both land and aquatic organisms. They show that species migrations across the Isthmus of Panama began some six times earlier than commonly assumed - about 20 million years ago.

"Even organisms that need very specific conditions to survive like salamanders and freshwater fishes crossed the Isthmus of Panama over six million years ago, which impacts on our understanding of how and when the biodiversity in South America formed," says leading author Christine Bacon.

These results based on biological data corroborate recent advances in geology and definitively reject the long-held assumption that the Isthmus is only ~3 million years old.

An earlier evolution of the Isthmus of Panama has broad implications for the mechanisms driving global climate, such as Pleistocene glaciations and ocean circulation, as well as the rich biodiversity of the American continent, including the Amazonian rain forests.

Bacon, C.D., D. Silvestro, C.A. Jaramillo, B. Tilston Smith, P. Chakrabarty, A. Antonelli. Biological evidence shows earlier emergence of the Isthmus of Panama. Accepted, Proceedings of the National Academy of Sciences USA.