A Review of the Dinoflagellates and Their Evolution from Fossils to Modern

Molecular clock and biogeochemical evidence indicate that the dinoflagellate lineage diverged at around 650 Ma. Unequivocal dinoflagellate cysts/zygotes appeared during the Triassic. These biotas were badly affected by the end-Triassic extinction and recovery from this was relatively slow. During the early Middle Jurassic, the family Gonyaulacaceae underwent an explosive diversification event and taxonomic richness steadily increased throughout the rest of the Jurassic. The entire Cretaceous also recorded increases in diversity. This trend reversed during the Oligocene, probably caused by global cooling. Marine cyst-forming peridiniaceans declined substantially through the Oligocene and Neogene, but protoperidiniaceans continued to diversify. Modern taxa, as evidenced by the molecular tree, comprise three major clades: the first two are composed largely of parasitic forms, marine alveolates of unknown identity and the Syndiniales; free-living dinoflagellates form the third clade, which diverges rapidly and bears short branch lengths with no real support for branching order. This suggests that morphological divergence preceded molecular divergence because, as the fossil record indicates, major groups appeared at different ages. Unique features of the dinoflagellates helped the group take on a predominant role in the marine phytoplankton. Living in marine or fresh water, dinoflagellates have demonstrated innovative capacities that have enabled them to live among the phytoplankton or benthos as autotrophic, heterotrophic, mixotrophic free-living organisms or symbiotic and/or as parasitic forms.