Abstract

Phylogenetic reconstructions of two tropical American venerid genera, Chione and Chionopsis (subfamily Chioninae) were attempted at the species-level. The purposes of the analyses were to provide historical reconstructions of origination and extinction events in the two clades, as well as patterns of invasion and diversification. The analyses were based entirely on conchological characters to facilitate the inclusion of a substantial number of fossil taxa, but difficulties were encountered due to the quality of preservation and availability of material. Nevertheless the two genera were established as monophyletic clades, and the reconstructions yielded considerable insight into their histories in tropical America. The analyses suggest that both genera originated in the tropical western Atlantic, Chionopsis by at least the early Oligocene, and Chione in the early Miocene. Various branches of both genera subsequently invaded the tropical eastern Pacific several times prior to Seaway closure, with only one possible reciprocal invasion of the western Atlantic. Pliocene extinction affected both genera more significantly in the western Atlantic relative to the eastern Pacific, and diversity is higher today in the latter region. These conclusions are not entirely consistent with the fossil records of the genera, but this incongruency highlights the need for much more extensive sampling of the eastern Pacific Cenozoic record.