The problem with Mesozoic Carditidae and the phylogenetic affinities of the Cretaceous genus Xenocardita (Bivalvia: Carditidae)

PEREZ, DAMIÁN EDUARDO

La Plata

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina 2019; 2019

Asociación Paleontológica Argentina

The fossil record of the Family Carditidae begins in the Late Triassic with the Palaeocarditinae. The next record of the family is from the Early Cretaceous, and its is poor until Cenozoic times when the group shows an increase in specific diversity. The Palaeocarditinae are not considered true carditids by several authors, and also other Mesozoic carditids are not very well known. Phylogenetic affinities for Mesozoic taxa are not documented and they are only suggested. New molecular and morphological-based phylogenies of the Carditidae proposed the origin of the main lineages back into the Mesozoic, and because of this, along with their diversity expansion in Palaeocene?Eocene times, relationships of Cretaceous taxa are relevant. Based on morphological shell-characters, a new phylogenetic hypothesis including 67 taxa and 152 characters was proposed. The poorly known Aptian carditid Xenocardita Vokes was included based on new observations of its morphological features. This species was recovered as the most basal member of the Venericardiini group (also known as ?alticostates?). Previously, the oldest Venericardiini was recorded near to Campanian?Maastrichtian boundary but this result suggests an older origin for the group. Synapomorphies of this lineage include among others the presence of tripartite radial ribs, a character already present in Xenocardita. Also, this genus has the typical hinge configuration without lateral teeth of the Venericardiinae but with some differences in the orientation and shape of teeth. More information about Mesozoic carditids is needed to clarify the relationships and evolution of the group and its morphological characters.