''Concavodonta'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of early

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 ...

in the

family

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.

. The genus is one of three genera in the subfamily Concavodontinae. ''Concavodonta'' is known solely from

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 ...

, Caradoc epoch, fossils found in Europe and South America. The genus currently contains three accepted species, ''Concavodonta imbricata'', ''Concavodonta ovalis'' and the type species ''Concavodonta ponderata''.

Description

''Concavodonta'' is a small bivalve which was first described in 1972 by Claude Babin and Michel Melou. Generally the shells of ''Concavodonta'' are fairly rounded to ovoid in shape. As the type genus for the subfamily Concavodontinae, the hinge displays the typical chevroning of teeth where the concavity in the chevron faces away from the center of the hinge and the umbo. The adductor muscles for the shell are unequal in shape. The external surface of the shells show regular concentric ornamentation. The type species for the genus, ''Concavodonta ponderata'', has been found in Middle to late Ordovician, Caradoc epoch sediments of Europe. The species was first described in 1881 by

Joachim Barrande Joachim Barrande (11 August 1799 – 5 October 1883) was a French geologist and palaeontologist. He was particularly known for his work on trilobites, published in the ''Systéme Silurien de la Bohéme'' which he published in 22 parts. Trained und ...

as ''Nucula ponderata''. The species has been found in three

Bohemia Bohemia ( ; ; ) is the westernmost and largest historical region of the Czech Republic. In a narrow, geographic sense, it roughly encompasses the territories of present-day Czechia that fall within the Elbe River's drainage basin, but historic ...

n formations, the Bohdalec, Vinice, and Zahorany. It has since been found in the Late Ordovician sediments of

Normandy Normandy (; or ) is a geographical and cultural region in northwestern Europe, roughly coextensive with the historical Duchy of Normandy. Normandy comprises Normandy (administrative region), mainland Normandy (a part of France) and insular N ...

, France. ''C. ponderata'' can be distinguished from the other two species in the genus by the structuring of the structure of the hinge plate, which is curved in ''C. imbricata'', and by the overall shell outline, which is ovoid in ''C. ovalis''. ''Concavodonta imbricata'' was described by Joseph Ellison Portlock as ''Nucula acuta?'' var ''imbricata'' based on a

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen which has since been lost. With the reexamination of the species in 1982 by Steve Tunnicliff a

lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...

specimen, NMI G.1. 1979 for the species which is deposited in the

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Dublin Dublin is the capital and largest city of Republic of Ireland, Ireland. Situated on Dublin Bay at the mouth of the River Liffey, it is in the Provinces of Ireland, province of Leinster, and is bordered on the south by the Dublin Mountains, pa ...

. The fossils are found in sediments of the late Ordivician,

Cautleyan 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 (millio ...

aged Killey Bridge Formation which outcrops near Pomeroy,

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. The species ranges in shell length from and has a height between . The third species of ''Concavodonta'' to be described, ''Concavodonta ovalis'', is from sediments of the late Middle Ordivician, Caradocian aged Don Braulio Formation. The formation outcrops on the flank of Sierra de Villicum in the

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

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. ...

.The Paleobiology database "Sierra de Villicum" entry
accessed 17 January 2012 The overall shape of ''C. ovalis'' shells, oval, is the base for the etymology of the specific name. The shells have an umbo positioned subcentrally on the posterior edge of the shell and nine to ten teeth in the hinge structure. ''Concavodonta ovalis'' ranges in shell length from and has a height between .

References

{{Taxonbar, from=Q5158272 Praenuculidae Ordovician bivalves Prehistoric bivalve genera Ordovician animals of Europe Fossils of the Czech Republic Letná Formation Fossil taxa described in 1972