Tennessee State Fossil

Bivalve Mollusc

(Pterotrigonia thoracica)

Adopted in 1998.

In 1998, Tennessee designated an official State Fossil, the bivalve mollusc, Pterotrigonia thoracica,  from the Late Cretaceous (Maastrichtian) age Coon Creek Formation. "Ptero," as it is affectionately known, inhabited the floor of an ocean that covered West Tennessee about 70 million years ago.

The campaign to have Ptero named as the State Fossil began in 1996 at The University of Tennessee at Martin. Spearheading the effort was UT Martin's GeoClub, a student organization dedicated to geological and geographic studies. Between 1996 and 1998, GeoClub members and geology professor Michael A. Gibson worked on determining a suitable nominee for state fossilhood and laying the groundwork for legislative action. With the supportive sponsorship of State Senator Roy Herron (D-Dresden), Ptero was named State Fossil in 1998 by the Tennessee legislature.

 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.

Animals of the Class Bivalvia are known as bivalves because they typically have two-part (The hard largely calcareous covering of a mollusc) shells, with both parts being more or less  symmetrical. The Class has 30,000 ((biology) taxonomic group whose members can interbreed) species, including (Edible marine bivalve having a fluted fan-shaped shell that swim by expelling water from the shell in a series of snapping motions) scallops, (Burrowing marine mollusk living on sand or mud) clams, (Marine mollusks having a rough irregular shell; found on the sea bed mostly in coastal waters) oysters and (Marine or freshwater bivalve mollusk that lives attached to rocks etc.) mussels. The name is also spelled Bivalva. An old name for the Class is Pelecypoda.

Bivalves are exclusively aquatic; they include both marine and freshwater forms.

Bivalves lack a  radula and feed by siphoning and filtering small particles from water. Some bivalves are epifaunal: that is, they attach themselves to surfaces in the water, by means of a (Tuft of strong filaments by which e.g. a mussel makes itself fast to a fixed surface) byssus. Others are infaunal: they bury themselves in sand or other sediments. These forms typically have a strong digging foot. Some bivalves can swim.