THE EARLY MESOZOIC RADIATION OF DINOFLAGELLATES

Dinoflagellates are a major component of the marine microplankton and, from fossil evidence, appear to have been so for the past 200 million years. In contrast, the pre-Triassic record contains only equivocal o ccurrences of dinoflagellates, despite the fact that comparative ultra structural and molecular phylogenetic evidence indicates a Precambrian origin for the lineage. Thus, it has often been assumed that the dear th of Paleozoic fossil dinoflagellates was due to a lack of preservati on or recognition and that the relatively sudden appearance of dinofla gellates in the Mesozoic is an artifact of the record. However, new ev idence from a detailed analysis of the fossil record and from the biog eochemical record indicates that dinoflagellates did indeed undergo a major evolutionary radiation in the early Mesozoic.