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TitleWetzeliella and its allies - the "hole" story: a new look at the Paleogene dinoflagellate subfamily Wetzelielloideae
AuthorWilliams, G L; Damassa, S P; Fensome, R A
SourceThe Atlantic Geoscience Society (AGS) 41st colloquium and annual meeting, program with abstracts; 2015 p. 43
Alt SeriesEarth Sciences Sector, Contribution Series 20150033
MeetingThe Atlantic Geoscience Society (AGS) 41st colloquium and annual meeting; Sackville; CA; January 30-31, 2015
Mediapaper; on-line; digital
File formatpdf
Subjectspaleontology; stratigraphy; fossils; biostratigraphy; fossil descriptions; fossil morphology; Dinoflagellates; Wetzelielloideae; Cenozoic; Mesozoic
ProgramBaffin Petroleum Systems, GEM2: Geo-mapping for Energy and Minerals
LinksOnline - En ligne
AbstractDinoflagellate cysts are found as organic-walled microfossils in Mesozoic-Cenozoic strata. They have distinctive and variable morphology and evolved rapidly; hence they have become invaluable for providing biostratigraphic control in shelfal marine sediments. Many living dinoflagellates have a distinctive cellulosic "armour" of plates, the pattern of which tends to be reflected in various ways on the resistant organic walls of fossilizable cysts. For example, the excystment aperture (archeopyle) of cysts tends to consistently occur within a genus or species at the site of one or more specific reflected plates. The Paleogene (now extinct) subfamily Wetzelielloideae have a stable reflected tabulation pattern distinguished by a four-sided (quadra) rather than a six-sided (hexa) mid-dorsal 2a plate. Aside from tabulation, wetzelielloideans show great morphological variability, especially in ornamentation and horn development, but also in wall structure. This variation shows no clear trends through time, but has dominated criteria for the definitions of genera and species, leading to frustrations in attempts to use wetzelielloideans as stratigraphic index fossils. Diversity in shape, wall structure and ornamentation has also distracted attention from the morphological variation of the archeopyle, which, although always formed through loss of the 2a plate only, shows variations that we consider critical in unravelling the group's phylogeny, and hence stratigraphic utility. Important factors are the shape and relative dimensions of the archeopyle and whether the operculum is attached or detached. These parameters allow us to define five archeopyle types: equiepeliform, hyperepeliform, hypersoleiform, latiepeliform and soleiform. Based primarily on archeopyle type and secondarily on wall and morphology and ornamentation, we recognise six genera with an equiepeliform archeopyle, four with a hyperepeliform archeopyle, five with a latiepeliform archeopyle, five with a soleiform archeopyle, and one with a hypersoleiform archeopyle. The earliest-known wetzelielloideans, which occur around the Paleocene?Eocene boundary, have an equiepeliform archeopyle. Other archeopyle types evolved rapidly: taxa with hyperepeliform, latiepeliform and hypersoleiform types are known from the Ypresian. Latiepeliform and hyperepeliform types are restricted to the Ypresian and Lutetian. Forms with the soleiform archeopyle appeared in the late Lutetian, but were rare until the Bartonian, when they became the dominant type, and they were the only type in Priabonian and younger strata. Wetzelielloideans became extinct in the middle Oligocene. Applying our criteria increases the usefulness of wetzelielloideans in determining the ages of Paleogene strata, as well as providing a better understanding of evolutionary trends within the group.
Summary(Plain Language Summary, not published)
The origination and extinction of species constitute the principal information that we use to date sedimentary rocks younger than 550 million years (biostratigraphy). Thus it is critical that we define species clearly and communicate species concepts accurately among specialists. The genus Wetzeliella and its allies are an important group of fossil dinocysts in the Paleogene, but their biostratigraphic usefulness over the years has been disappointing because of the various characters used to define taxa. By giving priority to one particular feature, the archeopyle, which evolves in a series of morphologies through time, we can restrict the stratigraphic ranges of species and thus improve the stratigraphic utility of this group of dinocysts, in particular in ongoing work on the Labrador-Baffin Seaway. A more refined taxonomy is fundamental to a detailed biostratigraphic framework, which can then be applied to an understanding of the history of a sedimentary basin and its petroleum systems.