Comley Limestone (IMAGE) University of Leicester Caption A thin section slice through the trilobite-rich Comley Limestones (Shropshire, UK) -- the rocks that the fossils used in this studies come from. The elongated curvy features in this image are cross sections through trilobites, which are a group of extinct marine arthropods. The arrow shows the "way-up" of the rock. Credit University of Leicester Usage Restrictions Use only with caption 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.