Why South America’s ancient mammals may have lost out to northern counterparts
Extinctions left fewer animals available to migrate north, a study suggests
By Jake Buehler
Millions of years ago, North American mammals flooded South America after the two continents joined. But South American mammals failed to return the favor, and now scientists have an idea why.
A new analysis of fossils suggests that many native South American mammal groups were declining early in the continental coupling, leaving fewer species available to head north, researchers report October 5 in the Proceedings of the National Academy of Sciences.
More than 10 million years ago, as the Pacific tectonic plate slid under the South American and Caribbean plates, the Isthmus of Panama began to rise out of the ocean, bridging North and South America. Animals began to move between the continents, in a trickle at first and then in a massive wave after the isthmus had fully formed around 3 million years ago. This exchange, known as the Great American Biotic Interchange, had a major influence on the distribution of mammals in the Americas today.
South American mammals at the time of the event — having evolved for tens of millions of years on an island continent — were stupendously strange. Club-tailed armadillo relatives the size of small cars shuffled about (SN: 2/22/16). Vaguely camel-like and rhinolike herbivores grazed the landscape. Immense ground sloths shambled on land and even swam offshore.