leaves (IMAGE) Penn State Caption The scientists examined more than 3,500 fossils to identify survivor pairs - plants that grew in both the Cretaceous and Paleogene periods. The two fossils on the left are from the Cretaceous, and the two on the right are from the Paleogene. Credit Elena Stiles Usage Restrictions non commercial use only 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.