Prehistoric Biodiversity (IMAGE) University of Chicago Caption An outcrop of 20-million-year-old fossil shells on the western shore of Chesapeake Bay in Maryland. Paleontologists have published a detailed, global study of clam preservation intended to determine what's missing from the fossil record and why. Credit Photo courtesy of Susan Kidwell 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.