The Cenozoic Gonyaulacacean Dinoflagellate Genera Operculodinium Wall, 1967 and Protoceratium Bergh, 1881 and Their Phylogenetic Relationships
Abstract
The palynology of Ocean Drilling Program Site 1007, leeward of the present Bahamas
Bank, provides insights into upper Oligocene–lower Pleistocene dinoflagellate cyst
associations in the tropical Americas. These associations are reviewed along with the
sedimentary paleoenvironment to provide context for a morphological study of the cystdefined
dinoflagellate Operculodinium bahamense and its comparison with the thecadefined
dinoflagellate Protoceratium reticulatum which produces a cyst assignable to the
cyst-defined genus Operculodinium. Detailed reconstructions of the tabulation in both
species reveal strong similarities, having a sexiform hyposomal tabulation and L-type or
modified L-type ventral organization. Protoceratium reticulatum has dextral torsion of
the hypotheca, requiring assignation of the genus to the subfamily Cribroperidinioideae,
whereas Operculodinium bahamense has neutral torsion requiring assignation to the
subfamily Leptodinioideae. Results either imply polyphyletic origins for the genus
Operculodinium or that combinations of ventral organization and torsion cannot always
be applied rigidly to subdivide the family Gonyaulacaceae.