It may have been one of the most cataclysmic geologic events of the last 60 million years, which shaped America as we know it today. The narrow, 400-mile-long Isthmus of Panama, once buried below the sea, rose up and connected North and South America. This new land bridge unleashed an astonishing animal encounter: Prehistoric predators and prey each unique to their worlds came face-to-face for the first time.