Heterochronic events in the macroevolutionary history of the Carditidae (Bivalvia: Archiheterodonta)

PEREZ, DAMIÁN EDUARDO

San Luis

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2017

Asociación Paleontológica Argentina

The main life habit among Recent and fossil Carditidae bivalves is infaunal burrowing, but the presence of changes in life habits in their macroevolutionary history has been proposed by different authors. First, a shift from a byssate mode of life to an infaunal one had considered. Posteriorly, an opposite pathway has been proposed, with infaunal burrowing type as the basalmost. These events imply changes in the timing of emergence or development of different morphological traits. The changes can be considered as heterochronic changes (paedomorphosis or peramorphosis). A new whole phylogenetic framework of the family (including 77 taxa from Late Triassic to Recent) allows to explore them. Eleven ontogenetic traits were scored and optimized for this framework, including adult size, presence of byssus (inferred from byssal gap), sharpness of radial ribs in different shell regions, persistence of lateral teeth, elongation of outline, and thickening of shells. As results, some lineages show an important amount of juvenile states of traits (subfamilies Thecaliinae, Carditinae, Carditamerinae and alticostate Venericardiinae) while others include mainly adult states (planicostate Venericardiinae and genus Cyclocardia). The most ancient true carditids, the Palaeocarditinae, may be byssally-attached bivalves but posterior lineages would be infaunal burrowers with secondary reversions to a byssate mode of life (in Thecaliinae, Carditinae and some Carditamerinae). These reversions were accompanied with the retention of juvenile traits in adults. The different changes suggest an active role of paedomorphic or peramorphic process among the evolution of the group, but the mechanism that were acting cannot yet be identified.