Fordillidae is an extinct

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. Idea ...

of early bivalves and one of two families in the extinct superfamily

Fordilloidea Fordilloidea is an extinct superfamily of early bivalves containing two described families, Fordillidae and Camyidae and the only superfamily in the order Fordillida. The superfamily is known from fossils of early to middle Cambrian age fo ...

. The family is known from fossils of early to middle Cambrian age found in North America, Greenland, Europe, the Middle East, Asia, and Australia.The Paleobiology Database Fordillidae entry
accessed 4 January 2012The Paleobiology Database ''Fordilla'' entry
accessed 4 January 2012 The family currently contains two genera, ''

Fordilla ''Fordilla'' is an extinct genus of early bivalves, one of two genera in the extinct family Fordillidae. The genus is known solely from Early Cambrian fossils found in North America, Greenland, Europe, the Middle East, and Asia.Pojetaia ''Pojetaia'' is an extinct genus of early bivalves, one of two genera in the extinct family Fordillidae. The genus is known solely from Early to Middle Cambrian fossils found in North America, Greenland, Europe, North Africa, Asia, and Austral ...

'', each with up to three described species. Due to the size and age of the fossil specimens, Fordillidae species are included as part of the Turkish

Small shelly fauna The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambri ...

Description

''Fordilla'' are small bivalves with

valves 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 ...

that are equal in size and suboval in shape. In size ''Fordilla'' specimens reach a total shell length of up to and a height of . The shells are compressed laterally and the back edge is slightly broadened. The rear adductor is less developed and smaller than the front adductor, while the small pedal retractor muscle scar is positioned near the front adductor scar. The valve hinge is usually straight to slightly convexly curved and each valve will have at most one tooth present. The external surface of the shell occasionally show faint ribbing. Similar to ''Fordilla'', species of ''Pojetaia'' are small, with valves to less than in length. ''Pojetaia'' species have an overall shape which is suboval, with the subequal valves slightly elongated. The ligament is straight with an umbo which is central to subcentral. In contrast to ''Fordilla'' the rear adductor muscle was larger and more developed then the front adductor, with pallial muscles arranged along the valve margins. Also in contrast to ''Fordilla'', valves of ''Pojetaia'' possess between one and three teeth, with up to two teeth per valve. The exteriors of the shells show faint ribbing and fine comarginal growth lines. The inner shell layers of ''Fordilla'' and ''Pojetaia'' species both consist of layers of

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

, which is akin to the laminar

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

layer found in extant

monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell inhabiting deep sea environments . Extant representatives were not recognized as such until 1952; previously they were known only from ...

. The structuring is similar to shell layering found in the extinct genera '' Anabarella'' and '' Watsonella'' which is thought to suggest that members of the phylum Mollusca developed nacre independently several times.

References

{{Taxonbar, from=Q5468085 Prehistoric bivalve families Cambrian molluscs Cambrian first appearances Cambrian extinctions