The region around Cincinnati, Ohio, is known throughout the world for the abundant and beautiful fossils found in limestones and shales that were deposited as sediments on the sea floor during the Ordovician Period, about 450 million years ago--some 250 million years before the dinosaurs lived. In Ordovician time, the shallow sea that covered much of what is now the North American continent teemed with marine life. The Cincinnati area has yielded some of the world's most abundant and best-preserved fossils of invertebrate animals such as trilobites, bryozoans, brachiopods, molluscs,...