''Chesapecten'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of

scallop Scallop () is a common name that encompasses various species of marine bivalve mollusks in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related families ...

known from marine strata from the early Miocene to the early Pleistocene of the Eastern United States. It flourished in the shallow seas along the Mid-Atlantic during this period. Other scallops lived at the same time, but Chesapectens were the most abundant.

Physical Description

Like some other large scallops, the shells of ''Chesapecten'' are characterized by a pattern of wide ribs which radiate outward from the apex of the shell. A distinctive feature of ''Chesapecten'' is that the radial ribs on its shell are crossed by much smaller, rough, concentric ribs, which follow the contours of the edges of the shell (are "conmarginal"). The left valve of ''Chesapecten'' is more convex than the right valve. The

adductor muscle A adductor muscle is any muscle that causes adduction. It may refer to: Humans * Adductor muscles of the hip, the most common reference in humans, but may also refer to ** Adductor brevis muscle, a muscle in the thigh situated immediately behind ...

scar is large and rounded.

Distribution

The geographical distribution of ''Chesapecten'' is limited to the

Atlantic coastal plain The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, where it can be found as far south as Florida, and as far north as Delaware. One species of ''Chesapecten'', ''

Chesapecten jeffersonius '' Chesapecten jeffersonius '' 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. Chesapecten jeffersonius are commonly found in strata ex ...

'', is the state fossil of Virginia.

History of the taxonomy

''Chesapecten'' was the first genus of North American fossil to be described and illustrated; a drawing of ''C. jeffersonius'' appeared in English naturalist Martin Lister's ''Historiae Conchyliorum, Liber III'' in 1687. However, Lister did not give ''Chesapecten'' its name. ''Chesapecten'' was formally named in 1975 by the paleontologists Ward and Blackwater. In 1980, it was assigned to the family '' Pectinidae'' by Harold E. Vokes. The name ''Chesapecten'' comes from the Chesapeake Bay, where eroding cliffs and outcrops along the beaches regularly expose specimens. Chesapecten barnacles Pliocene VA

Habitat and behavior

''Chesapecten'' lived on the seabed in coastal waters ranging in depth from a few feet to 130 feet. When not moving, it is assumed to have rested its flatter right valve on the seafloor. It is very likely that ''Chesapecten'' could move suddenly to escape a predator by flapping its valves and using the resulting jet propulsion, in a manner similar to that of almost all living

Species

Chesapecten jeffersonius fossil, Tellus Science Museum

Different species dominated during different intervals of time: middlesexensis during the Miocene (Eastover Formation); ''

'' during Early Pliocene (Lower Yorktown Formation, about 4.5 to 4.3 million years ago); and madisonius during Late Pliocene time (Upper Yorktown Formation, about 4 to 3 million years ago). Species in the genus ''Chesapecten'' include: *†''C. crassus'' *†''C. coccymelus'' *†'' C. jeffersonius'' *†''C. madisonius'' **†''C. m. sarasotensis'' *†''C. marylandicus'' *†''C. middlesexensis'' **†''C. m. bayshorensis'' **†''C. m. hunterae'' *†''C. monicae'' *†''C. nefrens'' *†''C. patagonensis'' *†''C. quinarius'' *†''C. santamaria'' *†''C. sayanus'' *†''C. septenarius'' *†''C. skiptonensis''

Physical Description

Distribution

History of the taxonomy

Habitat and behavior

Species

References

Further reading