![Sample our Geography journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/5937/TOC-Subject-Sample-2021-Geography.jpg"})
Abstract
Fossil dinoflagellate cysts of the Paleogene peridiniacean subfamily Wetzelielloideae have a stable tabulation pattern similar to that of other fossil peridiniaceans, but distinguished by a four-sided (quadra) rather than a six-sided (hexa) 2a plate. Aside from tabulation, wetzelielloideans show great morphological variability, especially in ornamentation and horn development, but also in wall structure. This diversity has 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. Important factors are the shape and relative dimensions of the archeopyle and whether the operculum is attached (adnate) 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 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. We make numerous taxonomic proposals, including the following new genera: Castellodinium, Dolichodinium, Epelidinium, Kledodinium, Michouxdinium, Petalodinium, Piladinium, Rhadinodinium, Sagenodinium, Sophismatia, Stenodinium, Stichodinium and Vallodinium. We emend the diagnoses of Charlesdowniea, Dracodinium and Wilsonidium, and erect the species Kledodinium filosum, Petalodinium sheppeyense and Sagenodinium franciscanum.
Acknowledgements
A paper of this kind relies on support from many colleagues, and to this end, we are grateful for the help provided, especially in the provision of images, by Graham Dolby, Alina Iakovleva, Dan Michoux, Henrik Nøhr-Hansen and Jo Prebble. GLW is also grateful to colleagues who have shared images with him over the years. We thank Bill MacMillan for his expert help with the drafting of some of the figures, and Nelly Koziel for technical assistance. Jen Galloway and Peta Mudie read early versions of the manuscript and provided suggestions for its improvement, for which we are grateful. We greatly appreciate the input of reviewers Chris Clowes and Alina Iakovleva, who provided perceptive insights that resulted in considerable improvements to the manuscript. We are additionally grateful to Alina for providing information on zonations involving wetzeliellioideans published in Russian. We are appreciative of helpful suggestions from Martin Pearce. Last but not least, thanks to editor Jim Riding for his advice and encouragement. GLW and RAF are grateful for the support of the Geological Survey of Canada, part of the Earth Sciences Sector (ESS) of Natural Resources Canada, for support. This is ESS Contribution no. 20140222
Additional information
Notes on contributors
Graham L. Williams
GRAHAM WILLIAMS's main field of interest is Mesozoic-Cenozoic palynostratigraphy of offshore eastern Canada, including arctic areas. His interest in dinoflagellates has led to studies of these palynomorphs in both hemispheres, including the deep ocean basins. After seven years at Pan American Petroleum Corporation (for anyone who remembers that far back), Graham joined the Geological Survey of Canada in 1971. He has spent the last 43 years at Bedford Institute of Oceanography in Nova Scotia, where he has the good fortune to work with some outstanding colleagues.
Sarah P. Damassa
In a previous existence, SARAH PIERCE Damassa was a Palaeogene dinoflagellate specialist, having studied with Bill Evitt, Al Loeblich and Helen Loeblich. She then worked as a consulting palynologist for around fifteen years. A career change then led her to Lexington, Massachusetts, where she has taught Environmental Earth Science to ninth-grade students for twenty years. She has also coached the school's National Ocean Science Bowl team for the last twelve years. Thanks to her co-authors, she has managed to retain a tenuous toehold in the world of fossil dinoflagellates, and has thoroughly enjoyed working with them on the Wetzeliella paper.
Robert A. Fensome
Like Graham, ROB FENSOME works for the Geological Survey of Canada in their Atlantic Division at the Bedford Institute of Oceanography, Dartmouth, Nova Scotia. During his 31-year tenure at GSC, Rob has focussed mainly on the Mesozoic-Cenozoic dinoflagellate cysts from off Canada's east coast, but is now venturing into projects involving assemblages from northwestern and Arctic Canada. While biostratigraphic and paleoenvironmental studies justify his paycheck, he also has a strong interest in dinoflagellate evolution.
G. Raquel Guerstein
G. RAQUEL GUERSTEIN is a professor at the Universidad Nacional del Sur in Bahía Blanca, Argentina, and a scientific researcher of the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). She graduated in geological oceanography from the Universidad Nacional del Sur, Argentina and received her PhD degree in geology in 1987 from the same university. She studies organic-walled dinoflagellate cyst assemblages from various sedimentary basins in Argentina. Her research interests are focused on the climatological and paleoceanographical evolution of the Southern and South Atlantic oceans during the transition from greenhouse to icehouse conditions during the Cenozoic.