Praenuculidae is an extinct

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of prehistoric

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

s in the superfamily

Nuculoidea Nuculoidea is a superfamily of bivalves. It belongs to the order Nuculida. It comprises one living family, Nuculidae Nuculidae is a family (biology), family of small seawater, saltwater clams in the order (biology), order Nuculida. Species in ...

. Praenuculidae species lived from the

early Ordovician The Early Ordovician is the first epoch (geology), epoch of the Ordovician period, corresponding to the Lower Ordovician series (stratigraphy), series of the Ordovician system. It began after the Cambrian Stage 10, Age 10 of the Furongian epoch o ...

, Arenig stage through the

Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the Pr ...

Emsian stage.The Paleobiology Database Praenuculidae entry
accessed 11 January 2012 Praenuculidae fossils are found worldwide, present on every continent except

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

. Species in this family are thought to have been sessile, attached to the substrate in shallow infaunal marine water environments, where they formed shells of an

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

composition. The family Praenuculidae was named by A. Lee McAlester in 1969.

Description

Praenuculidae first emerged in the early Ordovician and diversified from around 6 genera in the early Orodvician to a maximum of thirteen genera by the Late Ordovician. As a result of the Ordovician–Silurian extinction event the family was reduced to three genera during the

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

and by the end of the Devonian the family was entirely extinct. The family is composed of up to seventeen genera, most divided between the two described subfamilies erected by Teresa M. Sánchez in 1999. The structure of the chevroned hinge teeth is the dominant feature by which members of Praenuculidae are divided between the two subfamilies. The majority of Praenuculidae genera possess teeth with a chevron concavity that faces towards the outer sides of the shell and a chevron point facing the umbo. These genera are grouped into the larger subfamily, Praenuculinae. Three of the genera are placed into the second subfamily, Concavodontinae, based on the teeth having chevron concavities which face in the reverse, towards the center of the hinge and points facing the outside edges of the shell. In the original 1999 description of the subfamilies, '' Cardiolaria'' was not placed into a specific subfamily due to the uncertain family affinities of the genus. ''Cardiolaria'' was placed in Praenuculidae by McAlester in 1969 with the original description of the family. It was suggested by John C. Cope in 1997 that the genus may belong elsewhere in the subclass

Protobranchia Protobranchia is a subclass of bivalve molluscs. It contains the extant orders Nuculanida, Nuculida, and Solemyida. These are deep water clams of a small and primitive order with a taxodont hinge (composed of many similar, small teeth), g ...

, formerly called Palaeotaxodonta. Both ''Deceptrix'' and ''Cardiolaria'' are currently accepted as members of the family Cardiolariidae erected by Cope in 1997.The Paleobiology Database Cardiolariidae entry
accessed 5 February 2012 The genus '' Eritropis'' was formerly included in the family, however it was moved to a new family, Eritropidae by John C. Cope in 2000.

Genera

* Concavodontinae **'' Concavodonta'' **''

Emiliodonta ''Emiliodonta'' is an extinct genus of bivalve in the extinct family Praenuculidae. The genus is one of three genera in the subfamily Concavodontinae. ''Emiliodonta'' is known solely from late Ordovician, Caradocian epoch, fossils found in So ...

'' (syn. ''Emiliania'') **'' Hemiconcavodonta'' * Praenuculinae **'' Cuyopsis'' **'' Fidera'' **'' Ledopsis'' **'' Palaeoconcha'' **'' Paulinea'' **'' Pensarnia'' **'' Praeleda'' **'' Praenucula'' (type genus) **'' Trigonoconcha'' **'' Similodonta'' **'' Villicumia'' *''

incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'' **'' Pseudonucula'' A number of genera which were placed in the family have been moved to other families. They include: * Cardiolariidae **'' Cardiolaria'' (syn. ''Honeymania'') **'' Deceptrix'' **'' Inaequidens''

References

{{Taxonbar, from=Q3401210 Early Ordovician first appearances Ordovician bivalves Silurian bivalves Devonian bivalves Early Devonian extinctions Prehistoric bivalve families