FOSSIL DINOFLAGELLATE DIVERSITY, ORIGINATIONS, AND EXTINCTIONS AND THEIR SIGNIFICANCE

Dinoflagellates, single-celled protists at or near the base of the foo d chain, showed remarkable patterns in species diversity in the Mesozo ic-Cenozoic. First appearing in the mid Triassic, they rapidly increas ed to a Jurassic maximum of 420 species in the Kimmeridgian. After a m inor decline, diversity ruse to an all-time peak of 584 in the Albian, followed by a significant drop to 315 in the Coniacian: this may in p art reflect the short duration of that stage. Diversity then recovered to a second Cretaceous peak of 568 in the Maastrichtian, followed by a major decline in the Early Paleocene (361 species), although relativ ely few of these species appear to have become extinct at the Cretaceo us-Tertiary boundary. Other than a major peak of 518 in the Early Eoce ne, there is a continuing decrease through the Tertiary. Our plots are based on over 30 000 records of age ranges from a major database. Alt hough previous studies show similar plots, these were based on manuall y compiled records of substantially fewer species. Nevertheless, the r esemblance between our plots and earlier ones is striking, supporting the premise that the patterns reflect natural events and processes rat her than artifacts of literature or methodology. The present species d iversity plot shows some similarity to the long-term sea-level curve, which may reflect the preference of dinoflagellates for shelf environm ents.