Around three million years ago, South America became connected to North America via the Isthmus of Panama, and an event called the Great American Biotic Interchange took place, where wildlife from South America moved north and vice versa. Prior to this, South America had been isolated from most of the rest of the world since the Cretaceous Period, and connected only to Antarctica until they separated about 30 million years ago, allowing little exchange of wildlife from other places in world. As such, South America was a 'lost continent,' a strange land cut off almost completely from the rest of the world, with its own array of unique organisms, the characters in their own isolated evolutionary story. It was into this strange world that the North American emigrants came some three million years ago, and it was into the fossil echoes of this world that a very different group of North Americans came in the early 20th century.
 |
Some Patagonian fossils from the Cenozoic Era. They include notoungulates (top row
and left middle row) such as the sheep-sized digger Mesotherium (top centre), superficially
elephantine astrapotheres (lower jaw of Parastrapotherium, middle right), and the extant
xenarthrans (bottom row), including the flattened armour of an armadillo.
[photograph by the author] |
