Dinoflagellates are a major component of the marine microplankton and, from fossil evidence, appear to have been so for the past 200 million years. In contrast, the pre-Triassic record contains only equivocal occurrences of dinoflagellates, despite the fact that comparative ultrastructural and molecular phylogenetic evidence indicates a Precambrian origin for the lineage. Thus, it has often been assumed that the dearth of Paleozoic fossil dinoflagellates was due to a lack of preservation or recognition and that the relatively sudden appearance of dinoflagellates in the Mesozoic is an artifact of the record. However, new evidence from a detailed analysis of the fossil record and from the biogeochemical record indicates that dinoflagellates did indeed undergo a major evolutionary radiation in the early Mesozoic.

Dinoflagellates, single-celled protists at or near the base of the food chain, showed remarkable patterns in species diversity in the Mesozoic–Cenozoic. First appearing in the mid Triassic, they rapidly increased to a Jurassic maximum of 420 species in the Kimmeridgian. After a minor decline, diversity rose to an all-time peak of 584 in the Albian, followed by a significant drop to 315 in the Coniacian: this may in part reflect the short duration of that stage. Diversity then recovered to a second Cretaceous peak of 568 in the Maastrichtian, followed by a major decline in the Early Paleocene (361 species), although relatively few of these species appear to have become extinct at the Cretaceous–Tertiary boundary. Other than a major peak of 518 in the Early Eocene, there is a continuing decrease through the Tertiary. Our plots are based on over 30 000 records of age ranges from a major database. Although previous studies show similar plots, these were based on manually compiled records of substantially fewer species. Nevertheless, the resemblance between our plots and earlier ones is striking, supporting the premise that the patterns reflect natural events and processes rather than artifacts of literature or methodology. The present species diversity plot shows some similarity to the long-term sea-level curve, which may reflect the preference of dinoflagellates for shelf environments. Keywords: dinoflagellates, diversity, plankton, extinctions, fossils, paleoecology.

SYNOPSIS Palynomorphs, especially dinoflagellate cysts (dinocysts), have been at the forefront of research carried out on Mesozoic-Cenozoic sediments on the Scotian Margin over the last 30-40 years: this research has been driven by the need to develop a stratigraphical framework to better understand the region's petroleum systems. To support the compilation of a detailed event stratigraphical scheme for the Late Cretaceous to Cenozoic of the margin, emphasising dinocysts but with information from other fossil groups and non-biostratigraphical data, there is a need to formalise the dinocyst taxonomy. In this paper, we fulfill this need by illustratingand, where appropriate, describing and discussing taxa used in our event biostratigraphical scheme. The following taxa (dinocysts except where indicated) are new:Areoligeracircumsenonensis,Axiodinium,Axiodiniumprearticulatum, Cordosphaeridium delimurum, Glaphyrocysta extensa, Hafniasphaera delicata, Impletosphaeridium capitatum, Mendicodinium robustum (validation of previously proposed name), Minisphaeridium,Oligokolpoma, Oligokolpoma tubulus, Palaeocystodinium obesum, Palaeocystodinium teespinosum, Palaeohystrichophora palaeoinfusa, Pentadinium sabulum, Pervosphaeridium granaciculare, Talladinium, Wetzeliella caviarticulata and Cingutriletes tyriskos (a trilete spore). The following are newly proposed combinations (with a former name in parentheses): Cerebrocysta waipawaensis (Pyxidinopsis waipawaensis), Cerodinium glabrum (Cerodinium speciosum subsp. glabrum), Dinopterygium alatum (Xiphophoridium alatum), Kleithriasphaeridium cooksoniae (Florentinia cooksoniae), Kleithriasphaeridium perforatum (Florentinia perforata), Minisphaeridium latirictum (Hystrichosphaeridium latirictum), Nyktericysta tripenta (Balmula tripenta), Pentadinium granulatum (Pentadinium laticinctum subsp. granulatum) Talladinium? clathratum (Charlesdowniea clathrata) and Talladinium wulagenense (Charlesdowniea wulagenensis). Emendations of the following taxa are proposed: Apectodinium, Dinopterygium, Distatodinium, Glaphyrocysta, Hafniasphaera, Isabelidinium, Kleithriasphaeridium, Manumiella, Nyktericysta, Palaeocystodinium, Rhombodinium, Wetzeliella and Wetzeliella articulata. Material from the Kiowa Formation of Kansas supports our concept of Dinopterygium. We review several morphological terms already in the literature and introduce the following new ones: mesotabular, obtabular, contabular, penicontabular, epeliform, equi-epeliform and lati-epeliform.

Umbicysta octopedifomis and Limbicysta quadriformis are new acritarch species from the upper Aibian Bastion Ridge and Strand Fiord formations of the Sverdrup Basin, Canadian Arctic Islands. They are similar to the type species, Limbicysta pediformis Marshall, but have eight asymmetric or four symmetric process tips versus the four asymmetric and one symmetric process tips of L, pediformis. They are distinguished from other species of Limbicysta by their single wall layer, lack of longitudinal folds, and degree of compression. Like other species of Limbicysta, both new species are found associated with indicators of brackish-water paleoenvironments-in this example, assemblages dominated by terrestrial palynomorphs and with a low diversity of dinoflagellate cysts dominated by Nyktericysta spp, and acritarchs.

The late Palaeozoic Cumberland Basin of Nova Scotia and New Brunswick (eastern Canada) developed as a strike-slip basin in the aftermath of the Middle Devonian Acadian Orogeny. Following deposition of thick salt during the middle Vis ean (middle Mississippian), this basin mainly accommodated fault-controlled continental deposits during the late Vis ean, which generated halokinesis from clastic loading. The Mississippian halokinetic history of this basin is cryptic, as it was severely distorted by subsequent tectonic and halokinetic overprints. After minor structural restoration, the study of upper Vis ean minibasin units in wide coastal sections and deep wells allowed a fairly detailed reconstruction of the Mississippian halokinetic setting to be made. Paleoenvironments and depositional settings in the western part of the basin include sectors that were proximal to three fault-bounded source areas and characterized by alluvial fan systems transitioning laterally into gravelly to sandy braidplain environments. More central areas of the basin were characterized by tidal flats transitioning laterally into shallow marine environments. Because of halokinesis, the marine body was eventually forced to subdivide into three separate salt expulsion minibasins. Although late Vis ean marine incursions were short-lived in the rest of eastern Canada due to ongoing glacioeustatic variations, there are sedimentologic and stratigraphic lines of evidence for the long-lasting entrapment of restricted marine bodies in salt expulsion minibasins of the western Cumberland Basin. In one minibasin that was characterized by especially high accommodation rates, NE of Hopewell Cape (New Brunswick), the proximal conglomerates and marine carbonates of a fan-delta setting transition laterally into thick sulphate over a short distance, away from freshwater inputs from the source area. The vertical continuity of the latter sulphate succession suggests that this entrapped evaporitic basin was cut-off from significant marine influxes, even at times of glacioeustatic highstands. This is in contrast with salt expulsion minibasins in open marine shelf settings, which always remain open to global marine transgressions and regressions.