Dinoflagellate Evolution and Diversity Through Time

Introduction Unlike most other groups of protists, dinoflagellates have left an extensive fossil record. This record is restricted essentially to the last 245 million years (Mesozoic and Cenozoic), though comparative anatomical and molecular phylogenetic studies of modern dinoflagellates indicate a probable Precambrian (greater than 570 million years) origin for the group. This Paleozoic (245-570 million years) gap in the dinoflagellate fossil record has been used to suggest that this record is seriously flawed and therefore cannot be used to deduce the evolutionary history of the group (Evitt 1981). However, recent studies using large datasets (Fensome et al. in press; MacRae et al. in press) and informal cladistic analyses (Fensome et al. 1993) demonstrate that the fossil record can indeed be used to meaningfully examine the past diversity and evolution of this major planktonic group of organisms. This work also has broader implications in helping understand the development of modern plankton biodiversity and its vital role in modern ecosystems. Aspects of this ongoing research are reviewed in the present paper.