Reassessment of Neovenericor Rossi de García, Levy & Franchi, 1980 (Bivalvia: Carditidae) using a geometric morphometric approach, and revision of planicostate carditids from Argentina

Abstract

Various systematic approaches have been applied to the Neogene planicostate carditids of Patagonia. Some authors have included these species within Venericor (known from the Eocene of North America and Europe) or in Megacardita (recorded from the Miocene of Europe). By contrast, Rossi de García et al. erected the endemic Neovenericor in 1980 for Patagonian species. The three proposed genera have variable outlines and similar hinge teeth configuration. Two geometric morphometric analyses were performed, which included the type species of the following taxa: M. jouanneti (middle Miocene, Mediterranean Basin), V. planicosta (middle Eocene, Paris Basin) and N. austroplata (early Miocene, Chenque Formation, Chubut Province). In the first approach, an Elliptic Fourier Analysis was used to test the general variability of outlines. In the second, a landmark-based method was employed to analyse the hinge configuration, followed by a Discriminant Function Analysis. The outline analysis discriminated Megacardita from the other two taxa based on its more elongate and rectangular shells. The Landmark Analysis distinguished the three taxa based on both, left and right hinges. The Discriminant Function Analysis showed significant values for this differentiation. Neovenericor has a higher hinge plate, broader and less posteriorly inclined teeth, and a less sinuous ventral edge than Megacardita; and it has larger and more posteriorly inclined teeth than Venericor. Other morphological characters of the genus include an intermediate number of radial ribs that do not dissipate ventrally, and wide and deep intercostal spaces. Thus, Neovenericor is clearly a distinct taxon. All Argentinian planicostate carditids were revised and included in this genus because they embrace its diagnostic features.