Scallop

Chesapecten jeffersonius is Virginia's official state fossil, designated by the General Assembly in 1993. It is an extinct scallop — a bivalve mollusk closely related to the scallops sold in fish markets today — that lived in the shallow warm sea covering Virginia's coastal plain during the Pliocene epoch, roughly 4 to 3 million years ago. It is one of the most commonly found fossils in the state.

The species carries a notable name: jeffersonius honors Thomas Jefferson, who described fossil shells collected near the York River in his 1787 book Notes on the State of Virginia. That description is one of the earliest scientific accounts of an American fossil, making Chesapecten jeffersonius a piece of both natural and intellectual history.

Chesapecten jeffersonius had a broad, fan-shaped shell up to 6 inches across, marked by 17 to 19 raised ribs running from the hinge to the outer edge. A pair of flat, wing-like extensions flanked the hinge on either side. The overall shape is immediately recognizable as a scallop — the same basic design used by the living Atlantic bay scallop found in Chesapeake Bay today.

The animal lived in shallow, warm coastal waters and fed by pulling plankton and organic particles through its gills. The Pliocene sea that covered Virginia's coastal plain was slightly warmer than today's Atlantic, supporting dense shellfish beds. Chesapecten jeffersonius went extinct about 3 million years ago as ocean temperatures cooled at the close of the Pliocene.

Virginia designated Chesapecten jeffersonius as its state fossil in 1993. The species had been well known to Virginia geologists for more than a century: the Yorktown Formation, the Pliocene rock unit where C. jeffersonius is most abundant, was named and mapped in the 1800s and remains one of the most-studied geological formations on the East Coast.

The Jefferson connection added weight to the choice. In Notes on the State of Virginia, Jefferson described large fossil shells found near the York River — almost certainly Chesapecten jeffersonius — as evidence of a former sea covering the coastal plain. Later scientists formally named the species in his honor. Designating it as the state fossil connected Virginia's geological heritage to one of the state's most famous figures.

The Yorktown Formation runs in a broad band across Virginia's coastal plain, from the Potomac River south through the Hampton Roads area and out to the Eastern Shore. Wherever the formation is exposed — in river bluffs, road cuts, and eroding shorelines — Chesapecten jeffersonius shells wash out. The York River near Yorktown, where Jefferson collected his specimens in the 1780s, remains one of the most productive stretches.

York River State Park near Williamsburg and Chippokes Plantation State Park on the south bank of the James River both offer access to Yorktown Formation outcrops where scallop fossils can be found at the surface after storms and high water. The Eastern Shore counties of Northampton and Accomack also expose the Yorktown Formation in creek banks and low coastal bluffs.