In the Miocene epoch, approximately 10 million years ago, the Central American Seaway isolated North and South America, leading to what scientists refer to as 'splendid isolation' for South America. By around 2.8 million years ago, the Isthmus of Panama formed, connecting the two continents. However, the exchange of species was not equal; over half of the 217 mammal genera in South America originated from North America, while only four genera in South America can be traced back to the north. Researchers suggest that the success of North American mammals can be attributed to their adaptation in a warm ecosystem in what is now Mexico and parts of Central America before the continents were connected. Fossil evidence indicates that ancient mammals, such as sloths, arrived in Mexico from South America around 9 million years ago and adapted to the climate before moving further north into the colder regions of the U.S. and Canada. This adaptation hotspot hypothesis has been established in literature for both plants and animals moving from South America to North America, indicating that northern mammals were not biologically superior but had acquired preadaptations that became advantageous during significant tectonic changes. The research highlights the importance of Mexico as a critical area for mammal diversification and adaptation during a time of profound geological transformation.
