Battle for the Americas

摘要

The formation of the Isthmus of Panama allowed the fauna of two continents to mingle, transforming biogeography. A radical new hypothesis holds that the land bridge formed millions of years earlier than scientists thought. Panama, 3 million years ago. A narrow strip of land bridging the Americas turns into a migratory highway. Heading north is an assemblage of creatures isolated for tens of millions of years: porcupines and armadillos; the elephant-sized ground sloth Megatherium; opossums and other marsupials; and bizarre life forms like the terror bird, a flightless carnivore that reached 3 meters in height and sprinted like a cheetah. Beating a southward path are more familiar animals, including horses, cougars, and saber-toothed cats.