''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 Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomencla ...

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 The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

to the early

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

of the Eastern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territo ...

. 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 A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...

of ''Chesapecten'' is more convex than the right valve. The adductor muscle 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's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe an ...

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 C ...

, where it can be found as far south as

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to th ...

, and as far north as

Delaware Delaware ( ) is a state in the Mid-Atlantic region of the United States, bordering Maryland to its south and west; Pennsylvania to its north; and New Jersey and the Atlantic Ocean to its east. The state takes its name from the adjacent Del ...

. 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 expo ...

'', is the state fossil of

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth are ...

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 English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ide ...

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 Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

Ward and Blackwater. In 1980, it was assigned to the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...

Pectinidae 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 ...

'' by Harold E. Vokes. The name ''Chesapecten'' comes from the

Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the Eastern Shore of Maryland / E ...

, where eroding

cliff In geography and geology, a cliff is an area of rock which has a general angle defined by the vertical, or nearly vertical. Cliffs are formed by the processes of weathering and erosion, with the effect of gravity. Cliffs are common on coa ...

s and outcrops along the

beach A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc shells ...

es 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