Cyclocardia Conrad, one of the most diverse genera of carditids (Bivalvia: Carditidae): A monophyletic group or a wasebasket taxon?

PEREZ, DAMIÁN EDUARDO

Puerto Madryn

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2018

Asociación Paleontológica Argentina

More than a hundred species were assigned to the genus Cyclocardia in the bibliography, including living and fossil taxa covering a long time-lapse (Eocene?Recent) and wide geographical range (South and North America, East Russia, Antarctica, and Europe). Previous phylogenetic and systematic analyses suggested the non-monophyly of this taxon. In this work, phylogenetic and morphospace analyses of several species of Cyclocardia and other related taxa are performed using morphological shell-characters, and including fossil and living species (94 taxa and 147 characters). In all the searches (using equal and implied weighting) Cyclocardia results a polyphyletic group. A monophyletic Cyclocardia is composed only by C. borealis (type species of Cyclocardia), C. novangliae and C. compressa (all living Atlantic species). The previously proposed genera Ainicardita, Lunulicardita and Crassicardia are all monophyletic groups in most of the searches (with Ainicardita as part of the planicostate lineage). European species of Cyclocardia fall in the genus Scalaricardita. The proposed group ?awamoensis? for New Zealand and South American fossil Cyclocardia is paraphyletic in most of the searches. A clade composed by C. hamiltonensis, C. yakatagensis, and C. barbarensis (all taxa from the North Pacific) is obtained in all the searches. When a monophyletic Cyclocardia is constrained the resulting topology comprises 49 more steps in equal weighted searches. Morphospace analysis shows a Cyclocardia group with a wide occupation of the morphospace, at least as large as the remaining carditids, but restricted to a defined portion of this. Therefore, ?Cyclocardia? group is a morphological grade rather than a monophyletic clade.