Neotrigonia, the Sole Surviving Genus of the Trigoniidae (Bivalvia, Mollusca)

Abstract

The bivalve mollusk genus Neotrigonia holds a special place in the history of evolutionary biology. When it was discovered in 1802, naturalists had believed for many years that the family to which it belongs, the Trigoniidae, had disappeared at the end of the Mesozoic Era, about 65 million years ago (Gould 1968). Thus, Neotrigonia has been regarded as a “living fossil” in the sense that it is the sole surviving genus of a once flourishing and widely distributed family. In Upper Cretaceous deposits (ranging from about 100 million years old to 65 million years old) approximately 20 genera of trigoniids are recognized (Cox et al. 1969). In early Cenozoic deposits, however, only one trigoniid genus has been found; this is Eotrigonia, the apparent ancestor of the living genus.