Molecular Fossils Demonstrate
Precambrian Origin of Dinoflagellates
J. Michael Moldowan, Stephen R. Jacobson, Jeremy Dahl,
Adnan Al-Hajji, Bradley J. Huizinga, and Frederick J. Fago
The natural product chemistry of modern organisms shows that dinosterols are concentrated in, and are nearly exclusive to, dinoflagellates. Saturated dinosteroid (dinosteranes) and triaromatic dinosteroid hydrocarbons found in rock extracts and petroleum are molecular fossils of dinosterols. We observed a virtually continuous dinosterane record in Precambrian to Cenozoic organic-rich marine rocks. Ratios of dinosterane concentrations to those of steranes with affinities to other taxa are uneven, with relatively high ratios in some Vendian to Devonian extracts, low ratios in Carboniferous to Permian extracts, and high ratios in Upper Triassic through Cretaceous extracts. A similar record was found for triaromatic dinosteroids, which were absent (undetected) in the Carboniferous to Permian extracts. These results show a parallel trend between fossil dinosteroids and the combined cyst records of acritarchs and dinoflagellates. This record reflects the high abundance and diversity of Cambrian to Devonian acritarchs, the relatively low abundance and diversity of Carboniferous to Permian acritarchs, and emergence, diversification, and increasing biomass of dinoflagellates in Triassic to Cretaceous rocks. The dinosteroid hydrocarbon record supplements morphologic and ultrastructural arguments that either modern dinoflagellates evolved from ancient (Precambrian) acritarchs or early dinoflagellates did not commonly encyst. In either case the chemical lineage shown by the dinosteroid hydrocarbons indicates a heritage that dates at least from the Riphean.
IN A SURVEY OF marine rocks of various geological ages, Moldowan et al. (1996) reported triaromatic dinosteroids (1—numbers in this style refer to figure 21.1) in Precambrian to Devonian organic-rich sedimentary rocks. Also, in an earlier report Summons et al. (1992) noted dinosterane (2) occurrences in extracted organic matter from Precambrian rocks. These data appear to provide the long sought-for evidence that dinoflagellates (or closely related protists) have an ancient origin, a hypothesis