Chapter 2 – Evolution

The bivalve molluscs have a fossil record that extends from the Cambrian, approximately 550 million years. The record is long enough and eventually (as a result of adaptive radiation) rich enough in species and morphotypes to serve in estimating rates and modes of evolution, and the phylogenetic relationships necessary to evaluate different evolutionary scenarios. It has been described as “rich” and “exceptional” and, together with an abundant and diverse living fauna, the bivalves now “…provide an exceptional model system for evolutionary and macroecological studies”. Many symposia have been called to document and review the evolutionary narrative for bivalves. More recently, multiauthor efforts to assemble the appropriate phylogenies have multiplied, and there is a growing list of websites designed to communicate the results. For example, Bivalves in Time and Space ( www.bivatol.org ) states as part of its rationale the value of the bivalve fossil record for calibrating and testing phylogenetic and evolutionary hypotheses. The evolutionary narrative of the oysters is discussed in this chapter.