First mention of the venericardid genus Scalaricardita Sacco, 1899 (Bivalvia, Carditidae) in the Neogene of Patagonia, Argentina

PEREZ, DAMIÁN EDUARDO; CLAUDIA DEL RÍO

Mar del Plata

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2015

Asociación Paleontológica Argentina

The short-ranged fossil genus Scalaricardita is an uncommon and low diversified taxon distributed in the Miocene-Pliocene of Australia, New Zealand and Europe, being the present one, the first record in the American continent, including two species. Its oldest representative in Patagonia is S. camaronesia (Ihering), from the Camarones Formation (Chubut Province) of Middle Miocene age, and supposed by Ihering to be the ancestor of the Recent Southwestern Atlantic taxon, Cyclocardia compressa (Reeve). According to the present phylogenetic analysis, the fossil species did not give rise to the extant one, since Scalaricardita and Cyclocardia are not closely related genera, being Scalaricardita better related to Vimentum Iredale and Pleuromeris Conrad. The Scalaricardita-Vimentum-Pleuromeris clade differs from Cyclocardia because of its triangular outline and subcentral umbos, instead of the rounded shells with umbos anteriorly placed of Cyclocardia, and because of the development of a large right anterior tooth and radial ribs that do not vanish out ventrally. Scalaricardita is also represented by S. laciarina, recorded in the marine sedimentites exposed in the surroundings of Cerro Laciar (Santa Cruz Province), and recently placed in the Early Pliocene. Both species has been previously considered to belong in Venericardia but, they must be placed in Scalaricardita by the development of subtriangular-shaped shells with small umbos subcentrally placed, large and flat lunule, and 23-27 radial ribs with subrectangular-shaped nodes that are separated by narrow interspaces. Like most other carditid genera of the Cenozoic of Patagonia, Scalaricardita also became extinct. Supported by ANPCyT-PICT 57 and CONICET-PIP 320 to CJD.