Chesapecten jeffersonius is the state fossil of the State of Virginia in the United States. It is the fossilized form of an extinct scallop, which lived in the early Pliocene epoch between four and five million years ago on Virginia's coastal plain. In 1687, Martin Lister published a drawing of C. jeffersonius, making it the first North American fossil to be illustrated in scientific literature. Scientist Thomas Say, at ANSP, described the species and named it Pecten jeffersonius to honor Thomas Jefferson.