Ammonite Fossil (image) University of Washington Caption A 2009 image shows the excavation of a large ammonite on James Ross Island in Antarctica. The hole in the center was left when a core sample was extracted so the fossil could be dated using a process called magnetostratigraphy. Credit Thomas Tobin/U. of Washington Usage Restrictions News use only. 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.