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TitleA review of the Sentusidinium complex of dinoflagellate cysts
AuthorWood, S E L; Riding, J B; Fensome, R A; Williams, G L
SourceReview of Palaeobotany and Palynology vol. 234, 2016 p. 61-93, (Open Access)
Alt SeriesEarth Sciences Sector, Contribution Series 20160061
Mediapaper; on-line; digital
File formatpdf
Subjectsmorphology; taxonomy; Batiacasphaera; Kallosphaeridium; Pentafidia; Cyclonephelium; dinoflagellate cysts; Sentusidinium complex; taxonomic review; genus; genera; species; Mesozoic; Cenozoic
Illustrationsphotomicrographs; stratigraphic charts; tables
ProgramBaffin Petroleum Systems, GEM2: Geo-mapping for Energy and Minerals
AbstractThe Jurassic to Neogene (Miocene) dinoflagellate cyst genus Sentusidinium has a relatively simple overall morphology. This genus, together with Batiacasphaera, Kallosphaeridium and Pentafidia, comprises the Sentusidinium complex. This is distinct from the superficially similar laterally asymmetrical and subspheroidal/lenticular Cyclonephelium complex. The genus Sentusidinium is an acavate, subcircular, proximate to proximochorate sexiform gonyaulacacean genus, typically with low relief ornamentation and an apical archaeopyle. Since the erection of Sentusidinium in 1978, three other similar genera have been established, which are considered to be taxonomic junior synonyms of that genus: these are Barbatacysta, Escharisphaeridia and Pilosidinium. However, the Early Cretaceous to Miocene genera Batiacasphaera, Kallosphaeridium and Pentafidia are deemed to be valid, and differ significantly from Sentusidinium. The Early Cretaceous to Miocene genus Batiacasphaera has a reticulate to rugulate autophragm and an apical archaeopyle with a free operculum and no or shallow accessory archaeopyle sutures between the precingular plates. By contrast, Kallosphaeridium has a ventrally attached apical archaeopyle with five plates that can be interpreted as type (4A1I)@ or type (5A)@; it also has a small operculum relative to the overall cyst diameter. The six accepted Kallosphaeridium species are confined to the Palaeogene. The Australian genus Pentafidia is unusual in appearing to only have five precingular plates; this comprises two species from the Jurassic¿Cretaeous transition of Western Australia. Therefore, we emend Sentusidinium to restrict it to acavate, proximate or proximochorate dinoflagellate cysts. The autophragm is either devoid of, or covered with, highly varable ornamentation which can be evenly distributed or concentrated locally. Occasionally the elements of ornamentation may be connected, but rarely is a cingulum indicated, and the tabulation is never clearly evident. A kalyptra may be occasionally present. The archaeopyle is apical, type (tA), with a free operculum. Following a comprehensive literature review, we consider that there are 17 valid species of Batiacasphaera. In the genus Kallosphaeridium, we recognise six accepted and six problematical species. There are 38 (34 accepted and four problematical) species assignable to the most diverse genus, Sentusidinium. Kallosphaeridium? helbyi is here transferred to Cyclonephelium without question. The species Batiacasphaera angularis is occasionally tabulate hence we transfer, with question, this species to Meiourgonyaulax. The Sentusidinium complex is clearly polyphyletic, and all three genera are in the order Gonyaulacales. However, Batiacasphaera and Pentafidia can not be confidently assigned to a family, whereas Kallosphaeridium and Sentusidinium are both in the family Gonyaulacaceae. The number of species within the complex has been reduced from 133 to 67; furthermore, all infraspecific taxa have been eliminated.
Summary(Plain Language Summary, not published)
Researchers need to have a clearly defined and readily communicable classification for fossil dinoflagellates in order to use them in biostratigraphic and paleoenvironmental interpretations. The species are our tools, and use of names and concepts can drift over time. The present paper aims to clear up the nomenclature and classification of a group of relatively simple bowl-shaped forms with apical openings. We have reduced the number of names in use and clarified concepts, and thereby sharpened their biostratigraphic utility.