Belemnite

The belemnite is a marine cephalopod — an invertebrate related to modern squid and cuttlefish. What survives as a fossil is its hard internal structure called a guard or rostrum: a dense, bullet-shaped piece of calcite that outlasts the soft body by millions of years.

Belemnitella americana is the species designated as Delaware's official state fossil. Its guards turn up in the Cretaceous-age sediments of northern Delaware, where a warm shallow sea once covered the land during the Campanian stage.

The belemnite looked like a small squid with a stiff internal skeleton. The fossilized guard alone reaches about 3 to 5 inches (7 to 13 cm) in length; the full animal, including soft tentacles and mantle, was probably 6 to 12 inches long.

Belemnites were active swimmers and hunters. They used their tentacles to catch small fish and crustaceans. Belemnitella americana lived during the Campanian stage of the Late Cretaceous, roughly 83 to 72 million years ago, when a warm shallow sea covered what is now Delaware.

The entire belemnite group went extinct at the end of the Cretaceous period, about 66 million years ago, in the same mass extinction that killed the non-bird dinosaurs.

Delaware designated Belemnitella americana its official state fossil in 1996. The species was chosen because its guards occur specifically in Delaware's Cretaceous rock layers and are durable, distinctive, and easy to identify in the field.

Belemnite guards had been collected from Delaware creek banks and canal cuts for decades before receiving official recognition. The designation gave the fossil formal status alongside the geological heritage it had represented for well over a century.

Most belemnite fossils in Delaware come from the Late Cretaceous sediments of New Castle County in the northern part of the state. The Chesapeake and Delaware Canal, which cuts through layers of Cretaceous rock, is one of the most productive sites. Its exposed banks yield guards from the Merchantville and Mount Laurel formations, where Belemnitella americana is most abundant.

Nearby creek banks in New Castle County also expose the same formations. Fossil collectors have picked up guards from these outcrops for more than a century, making the belemnite one of the most familiar fossils in Delaware long before it received its official designation.