<P> In the last million years since the Late Miocene , South America became connected with the continent of North America via the Panama Block that closed the marine Bolivar Trough , leading to the Great American Interchange , the interchange of biota from both continents . The first species discovered to have made the northward migration was Pliometanastes , a fossil ground sloth species , roughly the size of a modern black bear . Several migrations to the Southern Hemisphere were undertaken by tougher , North American mammal carnivores ; fewer species migrated in the opposite direction from south to north . The result of the intrusion of North American fauna was that hundreds of South American species became extinct in a relatively short time and that about 60 % of present - day South American mammals have evolved from North American species . However , some species were able to adapt and spread into North America . Apart from Pliometanastes , during the Irvingtonian stage of the mammal land stages , around 1.9 Ma , species as Pampatherium , a giant armadillo , ground sloth Megatherium , giant anteater Myrmecophaga , a Neogene capybara ( Hydrochoerus ) , Meizonyx , opossum Didelphis , and Mixotoxodon followed the route north . The terror bird Titanis was the only discovered South American carnivore species who made the journey into North America . </P>
when did south america take form that it has today
In the last million years since the Late Miocene