Tennessee: Pterotrigonia thoracica (state fossil)

The official state fossil of Tennessee is a small bivalve, known to science as Pterotrigonia thoracica. Bivalves are the class of molluscs that includes clams, oysters, mussels, and scallops. This bivalve lived during the Cretaceous Period, around 70 million years ago, when Tennessee was encroached upon by a shallow sea.

At that time, the Appalachians were towering mountains, having formed during the collision of North America with Europe and Africa millions of years previously. These mountains caused abundant rainfall which constantly replenished the land and sea. The continental shelf environment was home to a teeming ecosystem of snails, cephalopods, worms, sponges, corals, crustaceans, and bivalves. Of these bivalves, Pterotrigonia is one of the most common, and is distinguished by its wedge-shaped shell and prominent ribs.

Many of the best Pterotrigonia specimens are found in the Cretaceous sediments of western Tennessee, especially the Coon Creek Formation. They are frequently found in vast beds, possibly indicating mass die-offs. Pterotrigonia went extinct at the end of the Cretaceous Period, but its close relative, Neotrigonia, lives off the coast of New Zealand today.

The University of Tennessee at Martin's GeoClub, led by paleontology professor Michael Gibson, sponsored the drive to crown Pterotrigonia the state fossil. Their efforts were rewarded in 1998 when the governor signed House Joint Resolution 552.

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Tennessee State Fossil