When did geology open a road for species to move between the Americas?

We recently covered a study indicating that the Isthmus of Panama docked with South America earlier than we once thought, connecting North and South America and separating the Pacific from Caribbean waters. Instead of linking up just 3 million to 4 million years ago, those researchers found evidence that a connection was present by 14 million years ago.

One of the loose ends created by the new result was that the exchange of North and South American species had also been pinned at about 3.5 million years ago. That raised the question of why species waited to migrate. One possible explanation is that migrations were triggered by a climatic cooling around 3 million years ago.

Well, a new study led by Smithsonian Tropical Research Institute and University of Gothenburg researcher Christine Bacon re-examines the evidence for the exchange of species, dubbed the Great American Biotic Interchange, and suggests that there might not be much of a delay to explain.