After the late Mesozoic breakup of Gondwana , South America spent most of the Cenozoic era as an island continent whose `` splendid isolation '' allowed its fauna to evolve into many forms found nowhere else on earth , most of which are now extinct .
After the late Mesozoic breakup of Gondwana , South America spent most of the Cainozoic era as an island continent . Its `` splendid isolation '' allowed the fauna to evolve into many forms found nowhere else on earth , most of which are now extinct .