Generic assignment of Pecten actinodes Sowerby (Patagonia, Late Miocene)

SANTELLI, MARÍA BELÉN; ALVAREZ, MAXIMILIANO; DEL RÍO, CLAUDIA JULIA

Mar del Plata

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

Asociación Paleontológica Argentina

Since the beginning of the XX century, Pecten actinodes Sowerby (Puerto Madryn Formation, Late Miocene) has been placed in the Patagonian genus Zygochlamys. Most authors have accepted this generic assignment without any discussion, and even stated unproved phylogenetic relationships with Recent species of the Southwestern Atlantic Ocean and the New Zealand region, today recognized within Psychrochlamys (P. patagonica King y Broderip and P. delicatula Hutton, respectively). The systematic revision of Zygochlamys presently carried out, and the use of a 2D geometric morphometricmethod, allowed to recognize the differences among Early-Middle Miocene co-generic species of Zygochlamys (i.e. Z. jorgensis Ihering, Z. geminata Sowerby), representatives of Psychrochlamys and Pecten actinodes. The latter species differs from Zygochlamys in having adult orbicular shells with higher umbonal angles (up to 109º), lower auricles, a larger number of plicae on both valves (up to 50), left interspaces narrower than plicae, and shagreen microscuplture extended down close to the ventral margin. These characteristics place it in a new genus, which shows substantial differences with Psychrochlamys patagonica and P. delicatula, since these extant species have smaller and thinnershells, smaller and more symmetrical auricles with a shallower byssal notch, the anterior free margin of right auricle slopes forward, posterior free margin of both auricles more inclined backwards, coarse commarginal microsculpture extended overall disc and absence of shagreen microsculpture. It is also proposed the synonymy of Zygochlamys rizzoloi Reichler (Gran Bajo del Gualicho Formation, Late Miocene) with Pecten actinodes.Supported by ANPCyT PICT-RAICES 57 and CONICET-PIP320 to CJD.