Dinoflagellates are key species in marine environments, but they remain poorly understood in part because of their large, complex genomes, unique molecular biology, and unresolved in-group ...relationships. We created a taxonomically representative dataset of dinoflagellate transcriptomes and used this to infer a strongly supported phylogeny to map major morphological and molecular transitions in dinoflagellate evolution. Our results show an earlybranching position of Noctiluca, monophyly of thecate (plate-bearing) dinoflagellates, and paraphyly of athecate ones. This represents unambiguous phylogenetic evidence for a single origin of the group’s cellulosic theca, which we show coincided with a radiation of cellulases implicated in cell division. By integrating dinoflagellate molecular, fossil, and biogeochemical evidence, we propose a revised model for the evolution of thecal tabulations and suggest that the late acquisition of dinosterol in the group is inconsistent with dinoflagellates being the source of this biomarker in pre-Mesozoic strata. Three distantly related, fundamentally nonphotosynthetic dinoflagellates, Noctiluca, Oxyrrhis, and Dinophysis, contain cryptic plastidial metabolisms and lack alternative cytosolic pathways, suggesting that all free-living dinoflagellates are metabolically dependent on plastids. This finding led us to propose general mechanisms of dependency on plastid organelles in eukaryotes that have lost photosynthesis; it also suggests that the evolutionary origin of bioluminescence in nonphotosynthetic dinoflagellates may be linked to plastidic tetrapyrrole biosynthesis. Finally, we use our phylogenetic framework to show that dinoflagellate nuclei have recruited DNA-binding proteins in three distinct evolutionary waves, which included two independent acquisitions of bacterial histone-like proteins.
Molecular clock and biogeochemical evidence indicate that the dinoflagellate lineage diverged at around 650 Ma. Unequivocal dinoflagellate cysts/zygotes appeared during the Triassic. These biotas ...were badly affected by the end-Triassic extinction and recovery from this was relatively slow. During the early Middle Jurassic, the family Gonyaulacaceae underwent an explosive diversification event and taxonomic richness steadily increased throughout the rest of the Jurassic. The entire Cretaceous also recorded increases in diversity. This trend reversed during the Oligocene, probably caused by global cooling. Marine cyst-forming peridiniaceans declined substantially through the Oligocene and Neogene, but protoperidiniaceans continued to diversify. Modern taxa, as evidenced by the molecular tree, comprise three major clades: the first two are composed largely of parasitic forms, marine alveolates of unknown identity and the Syndiniales; free-living dinoflagellates form the third clade, which diverges rapidly and bears short branch lengths with no real support for branching order. This suggests that morphological divergence preceded molecular divergence because, as the fossil record indicates, major groups appeared at different ages. Unique features of the dinoflagellates helped the group take on a predominant role in the marine phytoplankton. Living in marine or fresh water, dinoflagellates have demonstrated innovative capacities that have enabled them to live among the phytoplankton or benthos as autotrophic, heterotrophic, mixotrophic free-living organisms or symbiotic and/or as parasitic forms.
Dual nomenclature in dinoflagellates is supported under the current nomenclatural code for algae, fungi and plants and allows a fossil-defined (usually cyst) species to bear a name other than that of ...its equivalent non-fossil species, as established for example by incubation experiments. Two names can then apply to the same cyst morphotype, reflecting the separate but overlapping concepts and criteria used for fossil- and non-fossil taxa. Fossil-species are normally and logically assigned to fossil-genera and non-fossil species to non-fossil genera, a practice that facilitates dual nomenclature. Inconsistencies and ambiguities arise when binomials combine the names of fossil- with non-fossil taxa. Examples of this hybridised nomenclature and its consequences are examined, with problems identified and potential solutions discussed. Accordingly, a new non-fossil genus Lingulaulax is proposed with Lingulaulax polyedra (von Stein 1883) comb. nov. as its type and equivalent to the fossil-species Lingulodinium machaerophorum (Deflandre & Cookson 1955) Wall 1967, along with the new combination Lingulaulax milneri (Murray & Whitting 1899); the genus Lingulodinium Wall 1967 is retained in its exclusively fossil status. The non-fossil name Gonyaulax ellegaardiae Mertens et al. 2015 is validly published herein.
The cyst-defined extant Spiniferites elongatus Reid
1974
and Spiniferites membranaceus (Rossignol
1964
) Sarjeant
1970
are environmentally significant fossil-species of the Quaternary, the former ...often dominating polar and subpolar assemblages. Following cyst incubation experiments and the establishment of cultures, these species were emended to incorporate information on their motile stages, and transferred to the non-fossil genus Gonyaulax Diesing
1866
, as Gonyaulax elongata (Reid
1974
) Ellegaard et al.
2003
and Gonyaulax membranacea (Rossignol
1964
) Ellegaard et al.
2003
. This unified approach to dinoflagellate nomenclature severs an important link with the fossil-genus Spiniferites Mantell
1850
. We have applied dual nomenclature, as sanctioned by the International Code of Nomenclature for algae, fungi and plants, in returning these species to their previous assignments as Spiniferites elongatus and Spiniferites membranaceus, and we propose Gonyaulax ovum (Gaarder
1954
) comb. nov., emend. and Gonyaulax lewisiae sp. nov., respectively, as their equivalent non-fossil species. A distinctive morphotype initially described as Rottnestia amphicavata var. amphicavata Dobell & Norris in Harland et al.
1980
is proposed as Spiniferites elongatus forma amphicavata stat. nov.
The extinct organic-walled dinoflagellate cyst Duosphaeridium rugosum was first described from the Paleocene (Danian) of the southern USA. It has since been documented at several other localities ...around the world. Well-preserved specimens from the Danian of the Dakhla Formation in the Dababiya Corehole in southern Egypt, illustrated by light and scanning electron microscope images, reveal new morphological details, most notably parasutural features revealing the paratabulation. Detailed observations indicate that Duosphaeridium rugosum has an L-type ventral arrangement, an essentially straight sulcus, and apparently dextral torsion indicating a tentative affinity with the gonyaulacacean subfamily Cribroperidinioideae. Duosphaeridium rugosum occurs in an assemblage with many Danian markers; such as Danea californica, Carpatella cornuta and Lanternosphaeridium reinhardtii. Its earliest or first occurrence is contemporaneous with the upper part of nannoplankton zone NP2 and the uppermost part of the planktonic foraminiferal Parasubbotina pseudobulloides (P1a) zone. Its first occurrence is thus a useful stratigraphical marker for the Danian (earliest Paleocene). Duosphaeridium rugosum is associated with relatively abundant dinoflagellate cyst taxa such as Spiniferites, Achomosphaera, Fibrocysta, Pterodinium, Cordosphaeridium and Exochosphaeridium, which characterize neritic marine settings.
An overview of the history of a taxon name and its current status are critical in taxonomy; and selecting the correct name from among synonyms is commonly important in applied studies. This often ...onerous task can be facilitated by working with databases that can be used to develop an overview of the number of species within a genus as well as their spatial and temporal distributions and their frequency of use. For example, a quantitative analysis of the use of competing names can inform formal proposals to conserve, protect, or reject names. Currently, palynologists can consult two extensive databases, Palynodata and the John Williams Index of Palaeopalynology, both of which were discontinued, in 2006 and 2015, respectively. As new data accumulates, analyses require augmentation from uncurated online resources such as Google Scholar. Here, we conducted a case study for four Mesozoic genera relevant for example in studying the Triassic–Jurassic transition in the Germanic Basin. The genera contain a total of 65 species. The study compared the output from the two databases of references and an online source for the species inventory over time by analysing more than 2000 citations and their cross-occurrences. We found that the John Williams Index is the most accurate and extensive, but it can only be consulted in person in London. Palynodata, available as a dataset or online, is the more accessible source of information. Our study also shows that no significant difference results from whether one combines the John Williams Index or Palynodata with Google Scholar since using any two of these sources provide a recovery of at least 75% of all citations compared to using all three. In conclusion, each database has its own advantages and disadvantages, and when working under time pressure, the choice of database depends on the research question asked.
New analyses of the palynological assemblages in 13 offshore wells on the Canadian margin and six on the West Greenland Margin, in conjunction with onshore data, have led to a new biostratigraphic ...framework for the Cretaceous–Cenozoic strata of the Labrador Sea – Davis Strait – Baffin Bay (Labrador–Baffin Seaway) region and the first broad biostratigraphic correlation of the Canadian and Greenland margins. This framework is based on 167 last occurrences and 18 local/regional peak/common-occurrence events for dinocysts, miospores, fungal spores and Azolla. Detailed biostratigraphic evidence has confirmed the following hiatuses: pre-Aptian in the Hopedale Basin; pre-Albian in the Saglek Basin; Albian–Turonian in some wells of the Hopedale Basin; Turonian–Santonian/Campanian in some areas; pre-Campanian and late Campanian – Thanetian on the Greenland Margin; late Maastrichtian and Danian in some wells of the Hopedale Basin and in the Saglek Basin; Selandian in part of the Hopedale Basin, in all the Saglek Basin wells and in two wells on the West Greenland Margin; late Ypresian and/or Lutetian on both sides; Oligocene to middle Miocene of considerable variability on both margins, with all of the Oligocene and the lower Miocene missing in all the West Greenland Margin wells; and middle to late Miocene on the western side. On the Canadian margin, the hiatuses can be partially matched with the five previously recognised regional unconformities; on the Greenland margin, however, the relationship to the five unconformities is more tenuous. Palynomorph assemblages show that most Aptian to Albian sediments were deposited in generally non-marine to marginal marine settings, interrupted by a short-lived shallow marine episode in the Aptian. A marine transgression started in the Cenomanian–Turonian and led to the most open-marine, oceanic conditions in the Campanian–Lutetian; shallowing probably started in the late Lutetian and continued into the Rupelian, when inner neritic and marginal marine palaeoenvironments predominated. Throughout the rest of the Cenozoic, inner neritic palaeoenvironments alternated with marginal marine conditions on the margins of the Labrador–Baffin Seaway. These observations broadly reflect the tectonic evolution of the seaway, with rift conditions prevailing from Aptian to Danian times, followed by drift through much of the Paleocene and Eocene, and post-drift from Oligocene to the present. Dinocysts indicate that climatic conditions in the Labrador–Baffin Seaway region were relatively temperate in the Cretaceous, but varied dramatically through the Cenozoic. The Danian was a time of increasingly warmer climate, a thermal maximum being reached around the Paleocene–Eocene boundary reflecting the global thermal event at this time. Warm to hot conditions prevailed throughout the Ypresian, but the climate began to cool in the Lutetian, a trend that accelerated through the Priabonian and Rupelian. Throughout the Neogene, temperatures generally declined, culminating in the Quaternary.
The cosmopolitan dinoflagellate genus Alexandrium, and especially the A. tamarense species complex, contain both toxic and nontoxic strains. An understanding of their evolution and paleogeography is ...a necessary precursor to unraveling the development and spread of toxic forms. The inclusion of more strains into the existing phylogenetic trees of the Alexandrium tamarense species complex from large subunit rDNA sequences has confirmed that geographic distribution is consistent with the molecular clades but not with the three morphologically defined species that constitute the complex. In addition, a new clade has been discovered, representing Mediterranean nontoxic strains. The dinoflagellates fossil record was used to calibrate a molecular clock: key dates used in this calibration are the origins of the Peridiniales (estimated at 190 MYA), Gonyaulacaceae (180 MYA), and Ceratiaceae (145 MYA). Based on the data set analyzed, the origin of the genus Alexandrium was estimated to be around late Cretaceous (77 MYA), with its earliest possible origination in the mid Cretaceous (119 MYA). The A. tamarense species complex potentially diverged around the early Neogene (23 MYA), with a possible first appearance in the late Paleogene (45 MYA). A paleobiogeographic scenario for Alexandrium is based on (1) the calculated possible ages of origination for the genus and its constituent groups; (2) paleogeographic events determined by plate movements, changing ocean configurations and currents, as well as climatic fluctuations; and (3) the present geographic distribution of the various clades of the Alexandrium tamarense species complex.
New palynological analysis of samples from 13 offshore wells on the Canadian Margin and six wells on the West Greenland Margin has led to a new event biostratigraphic framework for ...Cretaceous–Cenozoic strata of the Labrador Sea – Davis Strait – Baffin Bay (Labrador–Baffin Seaway) region. This framework is based on about 150 dinoflagellate cyst taxa and 30 acritarch, algal, fungal and plant microfossil (mostly miospore) taxa. In the systematics we include three new genera of dinocysts (Scalenodinium, Simplicidinium and Taurodinium), 16 new species of dinocysts (Chiropteridium gilbertii, Chytroeisphaeridia hadra, Cleistosphaeridium elegantulum, Cleistosphaeridium palmatum, Dapsilidinium pseudoinsertum, Deflandrea borealis, Evittosphaerula? foraminosa, Ginginodinium? flexidentatum, Hystrichosphaeridium quadratum, Hystrichostrogylon digitus, Impletosphaeridium apodastum, Scalenodinium scalenum, Surculosphaeridium convocatum, Talladinium pellis, Taurodinium granulatum and Trithyrodinium? conservatum), four emendations of dinocyst genera (Alterbidinium, Chatangiella, Chiropteridium and Surculosphaeridium), six new combinations for dinocyst species (Alterbidinium biaperturum, Deflandrea majae, Kleithriasphaeridium mantellii, Simplicidinium insolitum, Spongodinium grossum, Spongodinium obscurum), one new acritarch species (Fromea quadrangularis), one new miospore species (Baculatisporites crenulatus) and one new combination for miospores (Tiliaepollenites crassipites). Most of the taxa included provide age information, almost exclusively last occurrences (range ‘tops’), but some are useful mainly for environmental interpretations. Collectively, they provide a powerful tool for helping to establish the geological history of the Labrador–Baffin Seaway.
PDF
