The Great American Interchange

The Great American Interchange, also known as the Great American Biotic Interchange (GABI), was a significant paleozoogeographic event in the late Cenozoic era, which reshaped the biodiversity of the Americas. It occurred when the volcanic Isthmus of Panama rose from the sea, forming a land bridge that connected North America and South America. This geological event facilitated the migration of various land and freshwater fauna between the two continents, resulting in one of the most profound biotic exchanges in Earth's history.

Geological Context

The formation of the Isthmus of Panama during the Pliocene epoch was a pivotal event that marked the beginning of the interchange. Before this land bridge existed, the Central American Seaway separated the two continents. The closure of this seaway not only enabled the terrestrial interchange but also resulted in significant oceanic changes, leading to what is known as the Great American Schism. This schism led to diversification and extinction events among marine biota by isolating the Caribbean Sea from the Pacific Ocean.

Faunal Exchange

The interchange had a dramatic impact on the zoogeography of mammals, as well as reptiles, amphibians, arthropods, flightless and weak-flying birds, and freshwater fish. Notable North American animals that migrated south include camels and horses, while iconic South American species such as the giant sloth and armadillos moved north.

North to South Migrations

North American species that moved south included:

Camelids: Ancestors of modern llamas spread to South America, where they continued to evolve.
Proboscids: These Afrotherian mammals, including mastodons, expanded their range.
Carnivorans: Such as bears and cats, found new territories in South America.

South to North Migrations

South American species that ventured north included:

Opossums: Small marsupials that adapted well to the diverse environments of North America.
Porcupines: Rodents that crossed over and thrived in new regions.
Phorusrhacids: Also known as terror birds, these large predatory birds are one of the few successful South American predators that migrated north.

Impact on Biodiversity

The interchange had lasting effects on the biodiversity of both continents. North America's fauna, characterized as Boreoeutherian and supplemented with Afrotherian proboscids, saw the introduction of numerous new species from South America. Conversely, South America, which had been an isolated evolutionary laboratory, experienced an influx of diverse North American species.