The land contact between North and South America has long been a fountain of research. The Isthmus of Panama—the narrow strip of land between the two continents—fully emerged about 3.5 million years ago. It allowed contact between terrestrial North and South American mammals, and resulted in wide-scale invasions of placental mammals into South America and the ultimate extinction of most southern marsupials.
Click here for original story, When two ecosystems collided, ichthyosaurs re-evolved the ability to consume large prey
Source: Phys.org