An Isthmus is a narrow land bridge that joins two larger bodies of land. The world’s most famous isthmus, now split by the Panama Canal, connects the continents of North and South America and cuts the once continuous Tropical American seaway into two.
The question ‘When did the Isthmus of Panama form’ has recently been reinvigorated by new geophysical evidence that led researchers to suggest that rather than forming around three million years ago, as was widely accepted, the Isthmus had formed over 10 million years previously.
This finding is important for many reasons. Global paleoclimate models are sensitive to how much water could pass from the Tropical Pacific to the Atlantic ocean and vice versa, myriad theses on the evolutionary and biogeographical history of tropical american biotas are dependent on knowing until when significant marine connections existed and when dry land joined the American continents for the first time, and the widely-applied molecular clock method is calibrated by the timing of seaway severance.