The Bering land bridge is well-known in Alaska. In the ice age, this broad corridor connected Alaska with Siberia, allowing the migration of animals such as bison, mastadons, wolves, bears and people.
But another land bridge existed in North America before the ice age, that had a profound impact on wildlife and ecosystems - and that land bridge still exists. It's the Isthmus of Panama.
After the time of the dinosaurs ended, about 65 million years ago, mammals evolved separately on the landmasses that were to become North and South America. Just three million years ago, very recent in geologic time, plate techtonics brought the continents together. The connection of the two great land masses profoundly altered ocean currents in both the Atlantic and the Pacific, changing the climate of the western hemisphere. It also allowed animals to move north and south. Cats were unknown in South America, and the big saber-toothed cats of the Pliocene period found good hunting in the virgin territory of South America. Bears also moved from North America to the southern continent, as did the North American camel species that evolved into llamas and alpacas. Other animals came north. From South America came armadillos, opossums and porcupines. The ancestors of Alaska's porcupines migrated north to Alaska from South America three million years ago, crossing the narrow land bridge at the Isthmus of Panama.