The State Fossil of Tennessee
Pterotrigonia thoracica
Phyium Mollusca
Class Pelecypoda
Coon Creek Formation
McNairy County, Tennessee
70 million years ago



Pterotrigonia (Scabrotrigonia) thoracica (nicknamed “Ptero”) was a Cretaceous bivalve found in the Coon Creek Formation of West Tennessee. It was a wedge shaped, shallow-burrowing suspension feeder that inhabited the marine clayey sand ocean floor that was West Tennessee 70 million years ago. Shells of “Ptero” are preserved unaltered in great abundance and are easily recognized by collectors. The associated ocean floor inhabitants were diverse and included other bivalves, snails, squid-like animals, worms, sponges, corals, crustaceans, sharks, fish, turtles, and marine reptiles. “Ptero” now is extinct. In fact, the extinction event that was responsible for the demise of the dinosaurs 65 million years ago may have contributed to the demise of Ptero (Scabrotrigonia) thoracica. Only the genus Neotrigonia, with five species, has survived to the present, and is found only in the Pacific Ocean, most commonly near New Zealand. This fossil is sitting on its matrix, the clay sediment of the sea floor.