leaf location (IMAGE) Penn State Caption Researchers collect fossils cliffside in the Lefipan formation in southern Argentina. The scientists pictured mid-cliff are searching a layer of the late Cretaceous period, while the sandstone ledge above them marks the beginning of the Paleogene period. Credit Peter Wilf, Penn State 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.