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Mammals moving between the Americas stopped over in Mexico

Time to adapt to warm environments may have given North American mammals an advantage

An topographical map shows the green-and-brown Isthmus of Panama against a blue backdrop.

Before the Isthmus of Panama — now the modern nations of Panama and Costa Rica — emerged from the sea 2.8 million years ago, South America floated in what scientists call “splendid isolation.” Afterward, mammals surged across the land bridge — and those who had time to adapt to warmth and dry environments in Mexico beforehand had a huge advantage on the southern continent.

Image Courtesy SRTM Team NASA/JPL/NIMA

By Bethany Brookshire

In the Miocene, 10 million years ago, the Central American Seaway separated North and South America, leaving the southern continent in what scientists call “splendid isolation.”