TIMING DEEP DIVERGENCE EVENTS IN CALCAREOUS DINOFLAGELLATES(1)

Area of Science:

• Paleontology
• Molecular Biology
• Marine Biology

Background:

• Calcareous dinoflagellates (Thoracosphaeraceae, Peridiniales) form a monophyletic group with three main clades.
• Understanding their evolutionary history requires integrating morphological and molecular data.

Purpose of the Study:

• To determine the divergence times of calcareous dinoflagellate clades using molecular clock analysis.
• To investigate the impact of the K/T boundary on dinoflagellate diversity.

Main Methods:

• Relaxed Bayesian molecular clocks were applied to nuclear rRNA sequences of 18 dinoflagellate representatives.
• Stratigraphically documented first occurrences of archeopyle types were used as calibration points.
• Divergence estimates were compared with first stratigraphic occurrences of taxa not used as constraints.

Main Results:

• The initial diversification of extant calcareous dinoflagellates likely occurred in the Late Jurassic.
• All three major clades were established by the Cretaceous period.
• The K/T boundary showed a limited effect on the diversity of this group, with lineages predating 65 million years ago.

Conclusions:

• Molecular clock estimates align with stratigraphic occurrences of key taxa like Thoracosphaera and Calciodinellum.
• Independent evolution of mesoepicystal operculum types from apical archeopyles is suggested.
• Discrepancies in some taxa may stem from fossil misassignment due to homoplasy or incomplete knowledge of extant diversity.