Leaf comparison (IMAGE) University of Bonn Caption The fossil leaf of an oak (Quercus neriifolia, top) shows brown roundish deposits. They resemble calcium oxalate crystals on present-day oak leaves (Quercus variabilis, bottom). Credit © Mahdieh Malekhosseini / University of Bonn Usage Restrictions Please use this image only in connection with the press release. License Original 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.