''Concavodonta'' is an extinct

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 nom ...

of early bivalve in the extinct 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 Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

, 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. Career Barrande was born at Saugues, Haute Loire, and educated in the École Polytechnique and École Nationale des Ponts et Chaussées at Paris. A ...

as ''Nucula ponderata''. The species has been found in three Bohemian formations, the Bohdalec, Vinice, and Zahorany. It has since been found in the Late Ordovician sediments of

Normandy Normandy (; french: link=no, Normandie ; nrf, Normaundie, Nouormandie ; from Old French , plural of ''Normant'', originally from the word for "northman" in several Scandinavian languages) is a geographical and cultural region in Northwestern ...

, 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 Major-General Joseph Ellison Portlock (30 September 1794 – 14 February 1864) was born at Gosport and was a British geologist and soldier, the only son of Nathaniel Portlock, and a captain in the Royal Navy. Educated at Blundell's School and t ...

as ''Nucula acuta?'' var ''imbricata'' based on a

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

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 attached. In other words, a type is an example that serves to anchor or centralizes the ...

specimen, NMI G.1. 1979 for the species which is deposited in the National Museum of Ireland,

Dublin Dublin (; , or ) is the capital and largest city of Ireland. On a bay at the mouth of the River Liffey, it is in the province of Leinster, bordered on the south by the Dublin Mountains, a part of the Wicklow Mountains range. At the 2016 c ...

. The fossils are found in sediments of the late Ordivician, Cautleyan aged Killey Bridge Formation which outcrops near Pomeroy,

County Tyrone County Tyrone (; ) is one of the six counties of Northern Ireland, one of the nine counties of Ulster and one of the thirty-two traditional counties of Ireland. It is no longer used as an administrative division for local government but retai ...

Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...

. 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 ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

precordillera.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 molluscs Prehistoric bivalve genera Ordovician animals of Europe Fossils of the Czech Republic Letná Formation Fossil taxa described in 1843 Fossil taxa described in 1999 Fossil taxa described in 1881