The Great American Biotic Interchange

Abstract

After the end of the Cretaceous, South America became an island continent with no connections to other continents, and developed its own unique groups of land animals. These included marsupials that evolved to resemble dogs, hyenas, and saber-toothed cats; gigantic ground sloths and armadillo-like glyptodonts; and an evolutionary radiation of native hoofed mammals that occupied the ecological niches, of mastodonts, rhinos, hippos, horses, camels, rabbits, and many other forms. The isolation persisted until about 10 million years ago, when the first North American groups appeared: mastodonts, tapirs, peccaries, and the extinct deer-like palaeomerycids. Meanwhile, two groups of giant ground sloths made it to Central America. Between 10 and 3.5 million years ago, a few kinds of ground sloths, glyptodonts, capybaras, porcupines, and large predatory birds managed to migrate north to Central and North America, while coatimundi relatives appeared in South America about 7 million years ago, and camelids like llamas about 4 million years ago. By 3.5–2.8 million years ago, the permanent Panama land bridge was formed, and the rest of the “Great American Interchange” occurred. These northern invaders included cats (jaguars, cougars, and saber-toothed cats), dogs (ancestors of the maned wolf and bush dog), bears, skunks, weasels, horses, deer, and additional species of mastodonts, camels, tapirs, and peccaries. The Great American Interchange was highly asymmetrical, with far more North American mammals invading South America and displacing its native fauna, and only a few South American groups managing to spread into North America.