About two and a half million years ago, it was joined with North America. Land mammals were then able to pass back and forth over the Panamanian land bridge. Actually, North American animals seemed to do most of the continent jumping. Many South American animals became extinct as they encountered new predators and competitors form the north. South American animals that did make it into North America include the giant ground sloth, which became extinct at the end of the Ice Age.
Few people know that several species of opossums and porcupines live in South America.
Just one of each now lives in the United States. It's properly known as the nine-banded armadillo. There have been others, including an armadillo about the size of a black bear. But all U.S. armadillos disappeared between 5,000 and 10,000 years ago. Fortunately, the nine-banded armadillo survived in Mexico.