subfamily
In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...
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
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 ...
Praenuculidae
Praenuculidae is an extinct family of prehistoric bivalves in the superfamily Nuculoidea. Praenuculidae species lived from the early Ordovician, Arenig stage through the Early Devonian Emsian stage.
. Concavodontinae species lived from the
middle Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. The Ordovician spans 41.6 million years from the end of the Cambrian Period Ma (milli ...
late Ordovician
The Late Ordovician is the third and final epoch of the Ordovician period, lasting million years and spanning from around 458.2 to 443.1 million years ago. The rocks associated with this epoch are referred to as the Upper Ordovician Series.
At ...
Ashgill epoch.The Paleobiology Database Concavodontinae entry accessed 19 January 2012The Paleobiology Database ''Concavodonta'' entry accessed 19 January 2012 Concavodontinae fossils are found in Europe and South America, and species are thought to have been stationary attached to 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 subfamily Concavodontinae was named by Teresa M. Sánchez in 1999.
Description
Concavodontinae is composed of three described genera and a total of five described species. The type genus '' Concavodonta'' is composed of three species found in Bavaria, France, and Argentina. The second genus, ''
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 ...
monotypic
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...
, and known only from the
Argentine
Argentines, Argentinians or Argentineans are people from Argentina. This connection may be residential, legal, historical, or cultural. For most Argentines, several (or all) of these connections exist and are collectively the source of their ...
precordillera
Precordillera is a Spanish geographical term for hills and mountains lying before a greater range, similar to foothills. The term is derived from ''cordillera'' (mountain range)—literally "pre-mountain range"—and applied usually to the Andes.
...
. ''Concavodonta'' is a small bivalve which was first described in 1972 by Claude Babin and Michel Melou. The structuring of the shell in ''Concavodonta'' has been noted to be anomalous. While several specimens from other taxa, such as '' Praeleda costae'' and '' Ctenodonta'' have been found with occasional concavodont teeth, they are not typical. All genera in Concavodontinae are identified by the hinge displaying chevron shaped teeth where the concavity in the chevron faces the center of the hinge and the umbo. In both ''Concavodonta'' and ''Emiliodonta'' both the anterior and posterior rows of teeth in the shell face outwards away from the umbo. In ''Hemiconcavodonta'' only the posterior teeth are concavodont, while the anterior teeth are convexodont and thus facing away from the hinges center. Concavodontinae differs from the second subfamily in Praenuculidae,
Praenuculinae
Praenuculinae is an extinct subfamily (biology), subfamily of prehistoric bivalves in the family (biology), family Praenuculidae. Praenuculinae species lived from the middle Ordovician through the late Devonian.