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. An armor-plated ancestor of the armadillo. A saber-toothed marsupial. A horse-like creature with three-toed feet. Evolutionary history changed forever as animals from the continents clashed. National Geographic joins scientists on a quest to discover what happened and which creatures survived.