How did the Pliocene land connection between North and South America affect animal migration?

The formation of the Isthmus of Panama during the mid-Pliocene, approximately 3.5 million years ago, created a land bridge that ended the long-standing isolation of South American fauna and triggered a massive faunal exchange known as the Great American Interchange.123

This connection facilitated two-way migration:

• South to North: Various South American mammals, including ground sloths, glyptodonts, armadillos, opossums, and porcupines, migrated northward, reaching as far as the southern United States.13
• North to South: A significantly larger wave of Northern Hemispheric animals moved south, including dogs, wolves, cats, raccoons, horses, tapirs, llamas, peccaries, and mastodons.12

This migration had profound ecological consequences; the influx of northern invaders is believed to have contributed to the extinction of many mammals endemic to South America, which had previously evolved in isolation.1