The Chesapeake Group is famous for its fossils. Fossils have been found from every animal phylum, where the organisms have hard body parts that are more readily fossilized. Approximately 624 species have been identified, roughly two thirds of which are molluscs. Marine mammals are represented by the fossilized remains of whales, dolphins, and sea cows. Fossil teeth from sharks and fossil dental plates from rays are common finds for collectors.
Mollusc fossils are overwhelmingly either gastropods or bivalves.
In 1685, a gastropod fossil from the St. Marys Formation, Ecphora quadricostata , was the first North American fossil to be described. Since that time, more than 200 species of gastropods have been found in Chesapeake Group sediments. Bivalves are equally abundant, with more than 180 species having been identified. Representative genera include Chesapecten , Astarte , Dallarca , and Isognomon . Cephalopod fossils, however, are rarely found in these sediments.