Millions of years before humans set foot in the Americas, an influx of aliens began to arrive in South America.
As the isthmus of Panama came up from the waves, the North and South American continents, llamas, raccoons, wolves, bears, and many other species turned south. At the same time, the ancestors of Armadillos, Cosums and Sorcupines moved north.
Paleontologists call this phenomenon the Great American Interchange. But they have long wondered about one aspect of it: why did most of the mammals go south instead of the other way around? What happened to southern mammals?
After a detailed analysis of fossil data from both continents, a group of researchers believe they have the answer: a nasty extinction phenomenon made South American mammals available to move north by replacing each other. His research was published in the Proceedings of the National Academy of Sciences on Monday.
After the extinction of the dinosaurs and the gradual recovery of the Earth’s biosphere, animals have been exchanged between North America and Asia for millions of years. During this period, the ancestors of modern horses, ls nto, and cats crossed the land bridge back and forth. But South America spent most of this period, the Cenozoic, as an island continent, full of its own exotic pastoralities: vast land sloths, exotic native euglets, tank-like armadillo relatives, and saber-toothed marsupial predators.
Then 10 million years ago, a series of tectonic events gave birth to the Panama Isthmus, connecting two very different fauna.
“Initially, this exchange was relatively balanced,” said Juan Carillo, a fellow at the Smithsonian Tropical Research Institute in Panama and author of the study. “There was a mass of both mammals migrating in both directions. But what we found was that plurality had a disproportionate decrease in diversity five million years ago. ”
Dr. Carillo said the source of the disappearance is unclear. The weather in the Pliocene continued to dry up, pushing back the forests of South America and triggering a cycle of global cooling, which eventually led to the Ice Age. As habitats changed, considerable considerable stress began to come on South American ecosystems.
Also participated in a competition from the northern species, in which northern predators such as dogs, bears, and saber-toothed cats could benefit from relatively large brains and more efficient teeth. Some of those migrants to the south may have brought parasites and diseases with them.
“Presumably the cause of this extinction is quite complex, and involves some biological interactions and habitat changes,” said Dr. Said Carillo.
Whatever the reasons for the extinction, it seems that by the Pleistocene ice age, when humans began to show up, North American species made up the bulk of South America’s mammals for the sake of moving north.
Nonetheless, some South American species were remarkably successful: giant ground sloths made it all the way to Alaska, and Florida remained the final breath of terror birds. But only a few, such as Consume and Armadillos, survived the extinction of Pleistocene.
When the American Interchange took millions of years, Dr. The advent of industrial humanity has seen races of exotic species around the world, not needing land bridges, Carillo said. Indian antelope graze in Texan ranches. Eurasian feral pigs run in large numbers in North America. African hippos have also set foot in Colombia with the help of Pablo Escobar’s drug empire.
The team’s research on the Great American Interchange suggests that although such exotic species are adapting to new environments, such representations could lead to unexpected changes in the shape of ecological communities.
“This movement of animals, which humans do today, could have some important long-term consequences,” said Dr. Said Carillo.
