# Trigonoconcha

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{{Short description|Extinct genus of bivalves}}
{{Speciesbox
| fossil_range = [Caradoc](/source/Caradoc_(age)) {{Fossil range|460.9|449.7}}
| genus = Trigonoconcha
| species = acuta
| authority = Sánchez, 1999
}}

'''''Trigonoconcha''''' is an [extinct](/source/extinct) [genus](/source/genus) of [bivalve](/source/Bivalvia) in the [extinct](/source/extinct) family [Praenuculidae](/source/Praenuculidae).  The genus is one of eleven genera in the subfamily [Praenuculinae](/source/Praenuculinae).  It is one of three Praenuculinae genera known solely from [Late Ordivician](/source/Ordivician), [Caradoc](/source/Caradoc_Series) epoch, fossils found in South America.  ''Trigonoconcha'' currently contains a [single](/source/monotypic) accepted species, '''''Trigonoconcha acuta'''''.<ref name="Sánchez1999">{{cite journal |last1=Sánchez |first1=T.M. |year=1999 |title=New Late Ordovician (Early Caradoc) Bivalves from the Sierra de Villicum (Argentine Precordillera) |journal=Journal of Paleontology |volume=73 |issue=1 |pages=66–76 |doi=10.1017/S0022336000027554 |jstor=1306745|bibcode=1999JPal...73...66S |s2cid=133414164 }}</ref>

==Description==
''Trigonoconcha acuta'' was first described in 1999 by Teresa M. Sánchez from fossils 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](/source/Argentina) [precordillera](/source/precordillera).<ref name="Sánchez1999"/><ref name="TPBDB">[https://paleobiodb.org/classic/displayCollResults?collection_no=13513 The Paleobiology database "Sierra de Villicum" entry] accessed 11 February 2012</ref>

The shells of ''Trigonoconcha'' have anterior and posterior sides which meet at an angle of no more than sixty-five degrees.  While this is similar to the related genera ''[Palaeoconcha](/source/Palaeoconcha)'' and ''[Similodonta](/source/Similodonta)'', they are both noted for anterior-posterior angles of no less than ninety degrees. The presence of an auricle, a finger-like projection on the underside of the umbo, in ''Palaeoconcha'' also distinguishes specimens from ''Trigonoconcha''. ''Similodonta'' is distinguished from both other genera by an edentulous space, a region on the hinge that lacks teeth. The umbo of ''Trigonoconcha'' is located at the [vertex](/source/Vertex_(geometry)) formed by the anterior and posterior sides and the ventral margin forms a broad curving edge. On smaller shells, possibly from immature specimens, the ventral margin curves abruptly to meet the anterior and posterior margins creating a triangular shell outline.<ref name="Sánchez1999"/>

The anterior edge is host to up to fifteen teeth while the posterior edge has a maximum of ten.  The ''Trigonoconcha'' ranges in shell length from {{convert|2.2|to|6.0|mm|in}} and has a height between {{convert|2.5|and|7.0|mm|in}}.  When described, the genus name ''Trigonoconcha'' was chosen by Sánchez in reference to the triangle created by the anterior and posterior margins of the shell.<ref name="Sánchez1999"/>  Similarly, the species epithet ''acuta'' was coined as a reference to the acute angle formed by the anterior and posterior margins.<ref name="Sánchez1999"/>

''Trigonoconcha'' was described from one [holotype](/source/holotype) specimen, number CEGH-UNC 16158, which is an internal mold of a left valve.  A series of twelve other right and left valve molds were also examined and used in the description.  The specimens are currently deposited in the Department of Geology [paleontology](/source/paleontology) collections in the [National University of Córdoba](/source/National_University_of_C%C3%B3rdoba).<ref name="Sánchez1999"/>

==References==
{{Reflist}}

{{Taxonbar|from=Q7841816}}

Category:Praenuculidae
Category:Ordovician bivalves
Category:Ordovician animals of South America
Category:Ordovician Argentina
Category:Fossil taxa described in 1999
Category:Monotypic prehistoric bivalve genera

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Adapted from the Wikipedia article [Trigonoconcha](https://en.wikipedia.org/wiki/Trigonoconcha) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Trigonoconcha?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.