Cheloniellid Arthropod (IMAGE) Yale University Caption Researchers found more than 1500 fossils of marine creatures, such as this cheloniellid arthropod, that lived nearly 500 million years ago. Credit Peter Van Roy/Yale University Usage Restrictions With appropriate credit 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.