A comparison of morphological adaptations in the cardiid bivalves Cardium and Budmania

Abstract

A comparison of the Neogene lymnocardiine Budmania with Neogene to Recent Cardiinae, and especially Cardium costatum Linnaeus, shows homoplasy in the relatively low shell thickness, presence of conspicuous, internally hollow keels and overall shell geometry. However, Budmania lacks the secondary shell resorption and associated features found in Cardiinae, and an inferential analysis of the adaptive significance of shell morphology reveals further differences between the two taxa. In particular, the keels in C. costatum are optimised for a dual function as mechanical strengthening and as anchors within the sediment, but only for the latter function in Budmania.