Hemiconcavodonta

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Hemiconcavodonta
Temporal range: Caradoc 460.9–449.7  Ma
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Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Nuculida
Family:† Praenuculidae
Subfamily:† Concavodontinae
Genus:† Hemiconcavodonta
Sánchez, 1999
Species:
†H. minuta
Binomial name
†Hemiconcavodonta minuta
Sánchez, 1999

Hemiconcavodonta is an extinct genus of bivalve in the extinct family Praenuculidae. The genus is one of three genera in the subfamily Concavodontinae. Hemiconcavodonta is known solely from late Ordovician, Caradoc epoch, fossils found in South America. The genus currently contains a single accepted species, Hemiconcavodonta minuta. [1]

A genus is a taxonomic rank used in the biological classification of living and fossil organisms, as well as viruses, in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.

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. Praenuculidae fossils are found worldwide, present on every continent except Antarctica. 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 composition. The family Praenuculidae was named by A. Lee McAlester in 1969.

Concavodontinae is an extinct subfamily of prehistoric bivalves in the family Praenuculidae. Concavodontinae species lived from the middle Ordovician, Caradoc epoch through the late Ordovician Ashgill epoch. Concavodontinae fossils are found in Europe and South America, and species are though to have been stationary attached to substrate in shallow infaunal marine water envoronments where they formed shells of an aragonite composition. The subfamily Concavodontinae was named by Teresa M. Sánchez in 1999.

Description

Hemiconcavodonta minuta is a bivalve which was first described in 1999 by Teresa M. Sánchez from fossils from sediments of the late Middle Ordovician, Caradocian-aged Don Braulio Formation. The formation outcrops on the flank of Sierra de Villicum in the Argentina precordillera. [1] [2] Generally the shells of Hemiconcavodonta minuta are ovate to rounded and moderately inflated. The small shells have an umbo positioned subcentrally on the posterior edge of the shell and nine to ten teeth in the hinge structure. H. minuta ranges in shell length from 3.0 to 6.3 millimetres (0.12 to 0.25 in) and has a height between 2.0 and 3.0 millimetres (0.079 and 0.118 in). [1] As a member of Concavodontinae, the hinge displays the chevroning of teeth typical of the subfamily. The teeth have a concavity in the chevron which faces away from the center of the hinge and the umbo. However the teeth of Hemiconcavodonta are unique in the subfamily with only the posterior teeth being concavodont, while the anterior teeth are convexodont thus facing towards the hinges center. The genus name is in reference to the tooth structure being both concavodont and convexodont. The overall small size of H. minuta shells is the basis for the etymology of the specific name. [1]

Argentina federal republic in South America

Argentina, officially the Argentine Republic, is a country located mostly in the southern half of South America. Sharing the bulk of the Southern Cone with Chile to the west, the country is also bordered by Bolivia and Paraguay to the north, Brazil to the northeast, Uruguay and the South Atlantic Ocean to the east, and the Drake Passage to the south. With a mainland area of 2,780,400 km2 (1,073,500 sq mi), Argentina is the eighth-largest country in the world, the fourth largest in the Americas, and the largest Spanish-speaking nation. The sovereign state is subdivided into twenty-three provinces and one autonomous city, Buenos Aires, which is the federal capital of the nation as decided by Congress. The provinces and the capital have their own constitutions, but exist under a federal system. Argentina claims sovereignty over part of Antarctica, the Falkland Islands, and South Georgia and the South Sandwich Islands.

Precordillera is a Spanish geographical term for hills and mountains lying before a greater range, foothills. The term is derived from cordillera —literally "pre-mountain range"—and applied usually to the Andes,.

A solitary fossil from the same location as H. minuta has the same convexodont/concavodont tooth structure as H. minuta. However the placement of the umbo and anterior adductor muscle plus tooth size in the solitary fossil do not match H. minuta and thus Sánchez did not place the specimen into H. minuta. [1]

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References

  1. 1 2 3 4 5 Sánchez, T.M. (1999). "New Late Ordovician (Early Caradoc) Bivalves from the Sierra de Villicum (Argentine Precordillera)". Journal of Paleontology. 73 (1): 66–76. JSTOR   1306745.
  2. ↑ The Paleobiology database "Sierra de Villicum" entry accessed 17 January 2012
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