Spent a lot of time on the short bus did ya? Here ya go - you're never to old to learn, right? >
In the Paleozoic and Early Mesozoic eras, South America and Africa were connected in a landmass called Gondwana, as part of the supercontinent Pangaea. In the Albian, around 110 Ma, South America and Africa began to diverge along the southern Mid-Atlantic Ridge, giving rise to a landmass of Antarctica and South America. During the late Eocene, around 35 Ma, Antarctica and South America separated and South America became a massive, biologically rich island-continent. During approximately 30 million years, the biodiversity of South America was isolated from the rest of the world, leading to evolution of species within the continent.
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. :laugh::laugh:>