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TitleA review of the areoligeracean dinoflagellate cyst Cyclonephelium and morphologically similar genera
AuthorRiding, J B; Fensome, R A; Wood, S E L; Williams, G L
Source52nd Annual Meeting, AASP-The Palynological Society, program book; 2019 p. 73 Open Access logo Open Access
LinksOnline - En ligne (complete volume - volume complet, PDF, 4.35 MB)
Alt SeriesNatural Resources Canada, Contribution Series 20190139
PublisherAASP - The Palynological Society
Meeting52nd Annual Meeting of AASP-The Palynological Society; Ghent; BE; June 30-July 5, 2019
Mediaon-line; digital
File formatpdf
Subjectspaleontology; Science and Technology; Nature and Environment; Paleogene; Neogene; micropaleontology; microfossils; systematic paleontology; taxonomy; fossil morphology; paleoenvironment; paleoecology; Dinoflagellates; Cyclonephelium; Phanerozoic; Cenozoic; Tertiary; Mesozoic; Cretaceous; Jurassic
ProgramGEM2: Geo-mapping for Energy and Minerals Mackenzie Corridor, Shield-to-Selwyn geo-transect, Mackenzie-Selwyn sub-activity
Released2019 06 01
AbstractA group of mainly Cretaceous areoligeracean dinoflagellate cyst genera, which we call the 'Cyclonephelium group', has proved difficult to classify. The group comprises Aptea, Canningia, Canninginopsis, Cassidium, Cauveridinium, Cerbia, Circulodinium, Cyclonephelium, Doidyx, Senoniasphaera and Tenua. As a group, they also converge morphologically with ceratiaceans. Cyclonephelium group taxa show considerable morphological diversity and gradation. However, the most important criteria for discriminating dinoflagellate cyst-based genera - tabulation and archaeopyle type - are uniform among areoligeraceans and ceratiaceans and so are not useful in this case. Any subdivision of the Cyclonephelium group will break apparently natural continuities; nevertheless, any resolution must involve on a hierarchy of morphological criteria. In developing a 'best-fit' hierarchy of morphological criteria for the Cyclonephelium group, and its separation from ceratiaceans, we consider historical concepts, morphological variation, illustrations in the literature (especially of types) and taxonomic stability. We conclude that the most pragmatic distinguishing feature of ceratiaceans in contrast to the Cyclonephelium group (and areoligeraceans in general) is that the former possesses a lateral horn or distinct prominence on the inner body or wall. The hierarchy we favour within the Cyclonephelium group (in decreasing importance) is: 1) wall structure; 2) whether the ornament is linear or free standing; and 3) the distribution of the ornament. As a consequence, we propose one new genus (Trimuridinium), one new species (Aptea cassis), two new names (Canningia glomerata for Senoniasphaera rotundata and Circulodinium vectensis for Pseudoceratium distinctum), 49 new combinations and one new status. We emend the descriptions/diagnoses of Aptea, Circulodinium, Cyclonephelium, Pseudoceratium, Senoniasphaera, Tenua and Tenua hystrix. Cyclonephelium group taxa predominate in neritic marine palaeoenvironments, and their use in palaeocological analyses should be improved by a more cohesive and consistent taxonomy. The group may have been the root stock for ceratiaceans in the Late Jurassic, the two families becoming more clearly separate from the Late Cretaceous onwards. Cyclonephelium group areoligeraceans are sparse in the Palaeogene and confirmed species are absent in the Neogene.
Summary(Plain Language Summary, not published)
Dinoflagellate cysts are one of the primary biostratigraphic tools for dating Mesozoic¿Cenozoic sedimentary rocks. Hence their taxonomy, leading to accurate identification and communication of species concepts, is critical for accurate application. A group of mainly Cretaceous genera, the ¿Cyclonephelium group¿, has proven difficult to classify. The modern classification of dinoflagellates is based on the arrangement of cellulosic plates that armour the cell, and their reflection on the cyst; plus the nature of the excystment opening oin the cyst. In the Cyclonephelium group, these features are uniform, so that the group has been inconsistently and sporadically treated taxonomically, reducing its usefulness in applied studies. We propose a revised classification of the group as a whole based on a consistent hierarchy of morphologically features that should promote its biostratigraphic and paleonvironmental utility.

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