First Middle Devonian Bivalves from Argentina, New Records from the Punta Negra Formation and Insights on Middle Paleozoic Faunas from the Precordillera Basin

Abstract. Middle Devonian bivalves from Argentina are reported for the first time, based on records of the Precordilleran Punta Negra Formation (Emsian—Frasnian?), San Juan Province. This finding is the youngest Devonian record of bivalves from southernmost South America. The impoverished bivalve association in the Punta Negra Formation includes five shallow infaunal deposit feeders, i.e. Nuculites argentinum Sanchez, Anthracoleda (Pseudoleda) minuta Sanchez, Praenucula sp., Deceptrix sp. and Praectenodonta sp. The distribution of the Silurian—Devonian bivalves from Precordillera shows a decreasing diversity trend during this interval, due to potential biases in sampling and paleoecology and thus 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 showing endemic (Malvinokaffric Realm) signals during the Devonian. Contrarily, an endemic composition i...