New research suggests mammals from North and South America may have mixed earlier than scientists once believed, before the Panamanian isthmus fully linked the two continents around 2.8 million years ago. That idea challenges the simpler view that major animal movement began only after a permanent land connection formed.
For a long stretch of prehistory, the two landmasses developed very different mammal communities. South America was known for animals such as marsupials and sloths, while North America was home to groups including camels, horses and pronghorn. Because the continents were separated, these lineups evolved largely on their own.
The new findings point to some level of interchange before the final connection through Panama. In other words, mammals appear to have found ways to move between the continents earlier than the standard timeline suggests. Even limited crossings would have had important effects on where species lived and how their evolutionary history unfolded.
If that interpretation holds up, it could reshape how researchers understand animal dispersal in the Americas. Instead of one dramatic migration beginning only after the land bridge formed, the history may have involved earlier episodes of contact that started blending the continent’s mammal faunas long before the final geographic link was in place.
