As these plates continued to surf the Earth's magma layer far beneath the Pacific Ocean floor, the Caribbean Plate migrated eastward,and about 15 million years ago, South America finally collided with this Central American Arc.
This gradually closed the water connection between the Pacific and the Caribbean, creating a land bridge, which connected North America to South America.
Terrestrial organisms could now cross between the two continents, and from the fossil records, it's evident that different waves of their dispersals took place.
Even though plants don't physically move,they are easily dispersed by wind and waves, so they migrated first, along with a few species of birds.
They were followed by some freshwater fishes and amphibians, and finally, various mammals began to traverse the bridge.