Reassessment of Paraleptopecten (Bivalvia: Pectinidae) with description of a new species from the middle Miocene of Patagonia

Paraleptopecten is a pectinid genus characterized by high, elongated auricles, cuspate commarginal lamellae, and heterogeneous ornamentation of major and minor plicae on the left valve. Its modern distribution is restricted to tropical and subtropical regions of the eastern Pacific and western Atlantic oceans. We report the first occurrence of this taxon in Argentina, extending its palaeogeographical and stratigraphical ranges to the Middle Miocene of Patagonia. The studied material comes from the Saladar Member of the Gran Bajo del Gualicho Formation (Río Negro Province), with the fossil-bearing horizons dated as Langhian (∼15.3 Ma) based on 87Sr/86Sr radiometric data from associated Nodipecten salis. The new Paraleptopecten species represents the oldest and southernmost record of the genus, constituting the first Neogene occurrence of Paraleptopecten in the southwestern Atlantic Ocean. During the Late Miocene, Paraleptopecten also occurred in the Caribbean Sea, from where it likely dispersed to the eastern tropical Pacific Ocean during the latest Late Miocene. Its presence in Patagonia reflects a southward expansion of tropical–subtropical pectinid fauna during the Middle Miocene Climatic Optimum, which may have been facilitated by warm water incursions along the South American Atlantic margin.María Belén Santelli* [mbsantelli@gmail.com], División Paleoinvertebrados, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACN-CONICET), Av. Ángel Gallardo 470, C1405DJR, Ciudad Autónoma de Buenos Aires, Argentina;Claudia J. del Río [claudiajdelrio@gmail.com], División Paleoinvertebrados, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACN-CONICET), Av. Ángel Gallardo 470, C1405DJR, Ciudad Autónoma de Buenos Aires, Argentina;Alejandra Rojas [alejandra@fcien.edu.uy], Departamento de Paleontología, Instituto de Ciencias Geológicas, Facultad de Ciencias, Universidad de la República, Iguá, 4225, 11400, Montevideo, Uruguay.