Adaptive divergence and taxonomic radiation in post-Palaeozoic bivalves

Abstract

Abstract Post-Palaeozoic marine bivalve families diversified with significant persistence. None of seven distinct clades dominated the expansion; most were involved. Only the pteriomorphs showed a decline, connected with the prolonged demise of exposed byssate taxa. Nine other autecological categories recognized by us recruited families more or less proportionately, although siphonate burrowers proliferated disproportionately at the expense of non-siphonate burrowers. Increasing predation pressure on bivalves from early in the Mesozoic, associated with the ‘Mesozoic marine revolution’, is identified as the main cause of these changes. The various adaptive pathways followed by different clades were highly conditioned by the constructional attributes of their body plans, a major role being played by the form of the ligament. Siphons evolved in several burrowing clades as a secondary adaptation.