Ecosystem Markers (IMAGE) Brown University Caption A 50-million-year fossil record of ammonoids includes two kind of the nautilus-like creatures, swimmers and floaters. At two points of mass extinction, the swimming ammonoids disappear completely from the fossil record, according to researchers at Brown University and the University of Washington. Credit Zittel, Textbook of Paleontology Usage Restrictions None 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.