Oedipina Complex (IMAGE) Smithsonian Tropical Research Institute Caption Scientists think that salamanders from North America arrived in South America before the accepted date for the closure of the Isthmian land bridge 3 million years ago, supporting Bacon et al's assertion that the Isthmus closed at an earlier date. Credit STRI Archives Usage Restrictions Credit: STRI Archives License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.