Dinocyst
The first person to recognize fossil dinoflagellates was Christian Gottfried Ehrenberg, who reported his discovery in a paper presented to the Berlin Academy of Sciences in July 1836.
Along with them, and of comparable size, were spheroidal to ovoidal bodies bearing an array of spines or tubes of variable character.
[2] A first relation between dinoflagellate thecae and cysts was made through morphological comparison of both by Bill Evitt and Susan E.
[3] Further evidence came from detailed culture studies of dinoflagellate cysts by David Wall and Barrie Dale at Woods Hole Oceanographic Institution in the sixties.
[6] For example, for this last special case, all cysts described from species of the order Phytodiniales (e.g. Cystodinium, Stylodinium, Hypnodinium, Tetradinium, Dinococcus, Gloeodinium), are coccoid stages.
[21] It has previously been suggested that morphological characters from the cyst stage may be phylogenetically important in marine species[22] and this may to an even greater extent be the case for freshwater dinoflagellates,[23] confirmed by new observations[24][25] and recently reviewed.
[21] Transmission electron microscopy (TEM) studies (e.g.[44]) suggest that endophragm and periphragm are not morphologically separable.
[45] Within the cyst wall, a thick cellulose-like layer called the endospore is present which is birefringent under crossed nichols.
[46] Cysts may be identified using the overall body shape but more often based on the characteristic furrows housing the flagella (cingulum and sulcus) or details of the patterns of plates covering many motiles (thecal tabulation).
The one distinctive feature common to all cysts is the excystment opening (archaeopyle) through which the emerging new motile stage exits.
[55] Resting stages also constitute a reservoir of genetic diversity, which increases the survival potential of the populations.
[56] Thus, dinoflagellate cysts have great ecological importance and act as "seed banks", comparable to those found in terrestrial ecosystems.
[81] Such surface sediment studies show that dinoflagellate cyst distribution is controlled by ranges of temperature, salinity and nutrients.
[84] Recent molecular work has shown the presence of such cold-water indicator, a life-stage of Islandinium sp.
[85] Other species are thermophilic, such as the "living fossil" Dapsilidinium pastielsii currently found in the Indo-Pacific Warm Pool only.
This has been documented for the warm water species Operculodinium israelianum and Polysphaeridium zoharyi which were interpreted to have been transported along the Southern coast of the United States.
Changes in Quaternary dinocyst assemblages reflect the palaeoceanography through variations in productivity,[97][98][99][100][101] temperature,[102][103][104] salinity[105][106][107] and ice cover.
[108][109][110] Palynodinium, a fossil species of dinoflagellate cyst, is used to demarcate the K/Pg boundary, which marks the terminal Cretaceous and the extinction of the dinosaurs.
[140] Organic-walled dinocyst morphology is shown to be controlled by changes in salinity and temperature in some species, more particularly process length variation.
[149] Organic-walled dinoflagellate cysts have a long geological record with lowest occurrences during the mid Triassic,[150] whilst geochemical markers suggest a presence to the Early Cambrian.
[155] The fossil record supports a major adaptive radiation of dinoflagellates during later Triassic and earlier Jurassic times.
