Prehistoric Mammal Migration Between Americas Predates Land Bridge Formation
UC Berkeley paleontologists have discovered that mammals from North America migrated into Mexico and beyond as early as 10 million years ago, well before the formation of the Panamanian land bridge 2.8 million years ago. This finding challenges the traditional view of the Great American Biotic Interchange (GABI), which was thought to have occurred only after the land bridge connected North and South America. The study, based on a new database of fossil mammals from Mexico, suggests that these animals waited in a 'holding pen' in Mexico before some continued southward around 7 million years ago. 
