Article: A new palaeontological technique describing temporal shape variation in Miocene bivalves

Principal components quantitative shape analysis (PC shape analysis) is demonstrated to be a rapid and effective palaeontological morphometric technique for quantifying shape. It allows easy interpretation, as morphology can be reconstructed from PC scores. Results of PC shape analysis have revealed that temporal patterns of shape variation in four Chesapeake Group (Miocene) taxa from Maryland are not congruent. Whilst there was a significant monotonic trend towards more disc-shaped valves in Dosinia acetabulum, then was no significant temporal trend in Lucina (Stewartia) anodonta valve shape. Whilst the evolutionary tempo in an Anadara lineage was more consistent with punctuated equilibrium, with interspecific changes controlling ultimate shape transformation and reversing intraspecific trends, the Astarte lineage had an evolutionary tempo not inconsistent with phyletic gradualism, where intraspecific trends were generally preserved during speciation.