First Middle Devonian Bivalves from Argentina, new records from The Punta Negra Formation and insights on Middle Paleozoic Faunas from Precordillera Basin

STERREN. A.F.; RUSTÁN, J.J.; SALAS, M.J.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2015 vol. 52

0002-7014

Middle Devonian bivalves are reported by the first time from Argentina, based on records of the Precordilleran Punta Negra Formation (Emsian?Frasnian?), San Juan province. This finding constitutes the first Middle Devonian bivalve record from Argentina, and the youngest Devonian one from southernmost South America. An impoverished bivalve association, integrated by five shallow infaunal deposit feeders, is documented in this unit including Nuculites argentinum, Anthracoleda (Pseudoleda) minuta, Praenucula sp., Deceptrix sp. and Praectenodonta sp. The distribution of the Siluro?Devonian bivalves from Precordillera shows a decreasing diversity trend during this interval, due to potential biases in sampling and paleoecology suggesting that this trend might be apparent. Early and Middle Devonian bivalves from Precordillera show a strong cosmopolitan paleobiogeographic signature, in contrast with other geographically related basins which exhibit endemic (Malvinokaffric) signals during the Devonian. In addition a contrasting endemic composition is recorded in the Precordillera Basin based in coeval Malvinokaffric groups such as ostracods and trilobites. Although more information is needed, the cosmopolitan character of Devonian bivalve assemblages from the Argentine Precordillera Basin might be interpreted in light of a unique history driving biogeographic processes affecting different taxonomic groups in different ways.