Dinoflagellata systematics

From Palaeos.org

Eukarya
  |--+--Fungi
  |  `--Metazoa
  |--Amoebozoa
  `--+--Rhizaria
     |--Metamonada
     `--o--Plantae
        `--o--Chromista
           `--Alveolata
                |--Ciliophora
                `--Miozoa
                     |--Dinozoa
                     |    `--Dinoflagellata
                     `--Apicomplexa

[edit] Systematics

Relationships within the dinoflagellates are ...

So, what are the apomorphies which we might use to classify fossil cysts?

We cannot say, for sure, though there are some characteristics which we can confidently say are not apomorphies. The nature of the ornamentation – whether chorate or whatever – has long been, for convenience, used to define form taxa at the generic level. Yet we see these characteristics recurring again and again, in lineages which are patently far removed. Intuitively, we realise that gross features like this, which clearly exercise a considerable effect on the life functions (e.g. flotation characteristics) of the organisms, are highly sensitive to evolutionary pressures, and are therefore likely to evolve quickly and repeatedly. Thus it is that the convenient, gross morphological features beloved of stratigraphers, and for so many years the underpinning of dinoflagellate taxonomy, are quite useless indicators of phylogeny.

This may seem obvious today, when words like 'apomorphy' are a standard part of any taxonomists vocabulary, but it was not always so. The writer once ventured the observation that "I consider such features as the clarity with which the cingulum is delimited by sutural or penitabular septa, and indeed the distinction between these two types of ornament, to be relatively unimportant; of infrageneric significance only" (Clowes 1984, p. 29), only to be pilloried by the journal's anonymous referee. Mercifully, the then editor, Doug Nichols, was made of sterner stuff and sought a second opinion. I am grateful to him to this day. Although the paper missed the publication deadline for that volume, and so was delayed by a year, the quoted passage finally appeared without amendment.

... associations of characteristics ...

"Although it is a worthy objective, a widely accepted classification of fossil dinoflagellates at the family level has yet to be devised. Currently, divergent views on principles and criteria are more evident than is any general agreement on results. A comprehensive classification of fossil cysts that originated conceptually with Eisenack (1961) and was elaborated by Sarjeant and Downie (1966) has now been modified by them (Sarjeant and Downie, 1974; Sarjeant, 1974) and by others (Norris, 1978; Tappan, 1980) into several similar arrangements by which fossil cysts are distributed among about 40 families. While based mos.tly on cyst morphology, these families are regarded by Norris, at least, as approaching phylogenetically defensible entities. In contrast, Evitt (1975b) contended that a few modern genera collectively encompass the affinities of a majority of fossil cysts. In line with that view, but with modifications reflecting more recent interpretations, Table 1 .1 lists 13 families, including nine from the hierarchy of modern taxa, that would appear to accommodate the great majority of fossil cysts (admitting that considerable uncertainty must attach to many fossils with highly "generalized" morphology). However, it is not the intent in this volume to pursue the problems of a phylogenetic classification. Instead, with obvious philosophical allegiance to the second approach mentioned above, we will focus attention in Chapter 8 on 17 morphological categories. While they will be defined without strict regard to family boundaries and will include cysts with "generalized" as well as "distinctive" morphology, their approximate correspondence to the families listed at the left in Table 1.1 is shown at the right" (Evitt 1985, p. 27).

[edit] Kingdom? Alveoles [Authority?]

[edit] Phylum* Dinoflagellata Bütschli 1885

1885 Dinoflagellata Bütschli

1914 Pyrrhophyta Pascher

1985 Pyrrhophyta, Evitt, p. 26

1993 Dinoflagellata (Bütschli 1885) Fensome et al., p. ??

• Dinoflagellates are protests - neither plants nor animals. Mercifully, taxonomy has not yet been cursed with an International Code of Protistan Nomenclature (given that the objective is the same, and the issues to be overcome nearly so, it is quite bad enough that there exists separate botanical and zoological codes) so it is necessary to treat dinoflagellates as one or the other, for the purposes of nomenclature. The botanical code has been settled upon, more or less by historical accident. Botanists frequently refer to the phylum-level taxonomic rank as a "division" - another absurd terminological distinction where there is no difference.

Type: [?] [Authority]

Original Diagnosis: xxx

Description: xxx

Habit: xxx

Distribution Occurrence: xxx

Discussion: xxx

Review of sub-ranks, if appropriate...

[edit] Class Dinophyceae [Authority]

Type: [?] [Authority]

Original Diagnosis: xxx

Description: xxx

Habit: xxx

Distribution Occurrence: xxx

Discussion: xxx

Evitt pp. 26-27:

Class DINOPHYCEAE -pyrrhophytes in which one flagellum is whiplike and extends longitudinally, while the second is ribbon-like and follows a circular path in a plane about at right angles to the first. .

Order PROROCENTRALES -dinoflagellates in which the flagella are inserted terminally (desmokont condition), the longitudinal one extending in advance of the cell, and the transverse one encircling the other anterior to the cell body. Some forms have a cellulosic theca of distinctive structure. Preservable resting cysts are unknown and there is no certain fossil record, although the order is conceivably represented by some of the organic-walled fossils currently regarded as acritarchs. Representative genera: Exuviaella (nonthecate), Prorocentrum (thecate).

Note: In all three of the following orders for which the living cell is known, the flagella are inserted laterally (dinokont condition), the longitudinal one extends posteriorly, and both normally lie, at least in part, within channels (the so-called flagellar furrows) defined by various features on the cell surface. Fossil cysts of the extinct fourth order appear to record a similar organization.

• Order Dinophysiales - dinoflagellates having the transverse flagellar furrow near the anterior limit of the cell; cell normally shows moderate to strong lateral compression; two lateral plates of the cellulosic theca are much larger than any others. Preservable resting cysts are unknown and there is no unequivocal fossil record. Representative genera: Dinophysis, Ornithocercus.

• Order Peridiniales - dinoflagellates having the transverse flagellar furrow normally located within the medial third of cell length; theca composed of several tens of cellulosic plates organized in several series paralleling the transverse furrow. Preservable resting cysts are found in some living species and there is an extensive fossil record. Representative living genera: Peridinium, Gonyaulax, Ceratium. Representative fossil genera: Deflandrea, [[Gonyaulacysta]], Odontochitina. Silurian, Triassic-Holocene.

• Order Gymnodiniales - dinoflagellates having the transverse flagellar furrow usually located within the medial third of cell length; cellulosic thecal plates lacking or (rarely) thin, but corresponding vesicles more numerous than typical for Peridiniales, small, and all of about similar size. Preservable resting cysts are known in a few living species. Moderate fossil record of cysts and distinctive sporopollenin coverings of possibly motile cells. Representative living genera: Gymnodinium, Polykrikos. Representative fossil genera: Dinogymnium, ?Distatodinium, ?Suessia. Triassic-Holocene.

• Order Nannoceratopsiales - dinoflagellates having the transverse flagellar furrow near anterior extremity of cell; cell compressed laterally as in Dinophysiales; tabulation of inferred theca similar to Peridiniales in anterior part, similar to Dinophysiales in posterior part. Fossil; sole genus: Nannoceratopsis. Jurassic.

Class Ebriophyceae -nonphotosynthetic, biflagellate, free-Iiving pyrrhophytes, lacking a resistant external covering but having a fossilizable internal siliceous skeleton. Representative genus: Ebria. Geologic range: Cretaceous to Holocene.

Class Ellobiophyceae- attached parasitic pyrrhophytes without known fossil record.

Class Syndiniophyceae -intracellular parasites without known fossil record.

[edit] Further Information

"Significant works on living dinoflagellates include books edited by Spector (1984) and Taylor (1987a) and monographs by Sournia (1986; an overview of marine taxa) and Popovsky & Pfiester (1990; an overview of nonmarine taxa). Dodge (1985) published an atlas of scanning electron photomicrographs of extant dinoflagellates. Fossil dinoflagellates have been discussed in detail by Evitt (1985). Sarjeant (1974) and Edwards (1993) provided overviews of living and fossil dinoflagellates, Williams (1977, 1978) surveyed fossil dinoflagellates, Dale (1983) and Sarjeant et al. (1987) reviewed the morphology and ecology of dinoflagellate cysts with emphasis on the fossil record, and Fensome, Taylor et al. (1993) treated the classification and evolution of both fossil and living dinoflagellates. Several catalogs and indices produced in recent decades include: the catalog series initiated by Eisenack & Klement (1964) , with subsequent issues by Eisenack (1967), Eisenack & Kjellström (1971, 1972, 1975a, b, 1981a, b) and Fensome, Gocht et al. (1991, 1993); the indexes of Lentin & Williams (1973, 1975, 1977, 1981,1985, 1989, 1993); and several compendia of genera, including Stover & Evitt (1978), Artzner et al. (1979), Wilson & Clowes (1980) and Stover & Williams (1987)" (Fensome et al. 1996, p. 107).