Pterotrigonia (Scabrotrigonia) thoracica, or "Ptero" for short is the official state fossil of Tennessee. The Ptero is a distinctive looking bivalve mollusk that lived during the Cretaceous Period when West Tennessee was covered by a shallow semi-tropical sea.  This sea, known as the Mississippi Embayment, was home to an abundance of life.  Ptero was one of the more common bivalves and is distinguished by it wedge-shape shell and prominent ribs.  It was a burrowing, suspension feeding clam that is now extinct.  Many of the best specimens are found at Coon Creek.

Only one of its relatives, Neotrigonia, has survived to the present and is found off the coasts of Australia and New Zealand.  It is considered to be a living fossil.

Check out Tennessee State Fossil Home Page -UT Martin Department of Geology Geography and Physics for more info.