ArticlePDF Available

Dinoflagellate macroevolution: some considerations based on an integration of molecular, morphological and fossil evidence

Authors:
Dinoflagellate macroevolution: some considerations based
on an integration of molecular, morphological and
fossil evidence
L. K. MEDLIN1* & R. A. FENSOME2*
1
Marine Biological Association of the UK, The Citadel, Plymouth PL1 2PB, UK
2
Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography,
PO Box 1006, Dartmouth, Nova Scotia, Canada B2Y 4A2
*Corresponding authors (e-mail: lkm@mba.ac.uk and rfensome@nrcan.gc.ca)
Abstract: Dinoflagellates have been regarded as bizarre products of evolution. They belong to
one of the most strongly supported macrolineages among the protists, the superphylum/
kingdom Alveolata, which contains three main phyla: the Dinoflagellata, the Apicomplexa and
the Ciliata. These organisms all have cortical alveoli and micropores. Until the early 1990s,
living and fossil dinoflagellates were classified separately and both relied almost exclusively on
morphological characters. During the early 1990s, fossil and living taxa were brought together
in a detailed morphological classification that emphasized tabulation. Since that time, molecular
studies have supported many morphological groups, but have shown others to be paraphyletic.
Our understanding of phylogenetic relationships within the dinoflagellates has changed as
more taxa have been described and more genes have been analysed. Relationships among the
lineages also vary widely with the algorithm used to analyse the data. A highly unusual and
notable feature of dinoflagellates is the variety of plastid types that they have acquired by second-
ary and even tertiary symbiosis; indeed, they possess the most diverse array of plastids of any
eukaryotic lineageand they are truly the kings of symbioses. Genome rearrangements have
taken place as the plastids evolved. The genes that have moved to the nucleus in dinoflagellates
with peridinin plastids are different from those moved in all other eukaryotes; moreover the few
genes left behind in the peridinin plastid have become uniquely arranged into mini-circles.
Where tertiary endosymbiosis has taken place, the plastid genome was rearranged again. Mito-
chondrial modifications in the dinoflagellates are also unique among the eukaryotes. While
study of these factors remains critical in understanding dinoflagellate phylogeny, the fossil
record continues to contribute by presenting morphologies that are unrepresented (or under-
represented) among extant taxa; such observations can suggest relationships to be tested by
molecular analyses.
Dinoflagellates are protists that typically possess
a unique type of nucleus in which the chromoso-
mes are permanently condensed and in which the
motile cell typically possesses two distinctive, dis-
similar flagella. Other aspects of dinoflagellates
are also very unusual; for example, their metabolic
processes rarely follow the norm and the origin of
their plastids is enigmatic. Unlike many related
protistan groups, dinoflagellates have left a signifi-
cant (albeit incomplete) fossil record, mainly in
the form of resistant organic-walled or calcareous
resting cysts. In this review, we will discuss dino-
flagellate origin and evolution as evidenced by
both molecular methods and morphology, the lat-
ter including extensive observations from fossils.
We will also review the relationship between dino-
flagellates and other protists, and the evolution of
dinoflagellate plastids and mitochondria.
Origin and relationships with other
protists
Fensome et al. (1993) developed a phylogenetic tree
for dinoflagellates and their closest allies based
on ultrastructure (Fig. 1). It shows that dinofla-
gellates (dinokaryotes and syndinians) share the
possession of cortical vesicles (alveolae) with api-
complexans and ciliates, a grouping of protists
classified together as the alveolates (see also Adl
et al. 2005). According to this tree, alveolates in
turn share the possession of tubular mitochondrial
cristae, an intranuclear spindle (which in dinofla-
gellates purportedly became secondarily extranuc-
lear) and rod trichocysts with chromophytes. At
the base of the lineage to dinokaryotes (dinoflagel-
lates ‘proper’) and their sister group, the syndinians,
From:Lewis, J. M., Marret,F.&Bradley, L. (eds) 2013. Biological and Geological Perspectives of Dinoflagellates.
The Micropalaeontological Society, Special Publications. Geological Society, London, 263– 274.
#The Micropalaeontological Society 2013. Publishing disclaimer: http://www.geolsoc.org.uk/pub_ethics
Fensome et al. (1993) noted the development
of the characteristic dinoflagellate flagella and
redevelopment of an extranuclear mitotic spindle.
In the dinokaryote clade, Fensome et al. (1993)
interpreted the development of the temporary
dinokaryon (as in Noctilucales, which only have
condensed chromosomes in the gamete stage, and
Blastodiniales) as a basal trait, followed by the deve-
lopment of a permanent dinokaryon in all other
dinoflagellates. Saunders et al. (1997, fig. 4) built
upon this model by interpreting the peduncle mode
of feeding (myzotosis) as a basal trait leading to
free-living autotrophic dinoflagellates.
Subsequent molecular data confirm that the
dinoflagellates are a monophyletic group, with the
so-called pre-dinoflagellate Oxyrrhis lying outside
core dinoflagellates. In the Fensome et al. (1993)
tree, Oxyrrhis would diverge between ciliates and
syndinians prior to development of dinokont fla-
gella and an extranuclear spindle. Molecular stud-
ies have confirmed dinoflagellates as the sister
group to the apicomplexans (perkinsid flagellates)
with high bootstrap support, which are in turn sis-
ter to the ciliates, again with high bootstrap support
(Leander & Keeling 2004). A less robust sister
relationship (,50%) has been commonly recovered
between alveolates (apicomplexans) and the stra-
menopiles (¼heterokont organisms) (Leander &
Keeling 2004), leading to a grouping of the alveo-
lates with the cryptomonads and haptophytes to
form the chromalveolates. The chromalveolates
have the least bootstrap support and lack firm mol-
ecular evidence, but are nevertheless still thought
to be monophyletic. Recent re-analysis of 108
genes from nuclear, plastid and mitochondrial
genomes have failed to recover a well-supported
host-cell lineage for the chromalveolates (Baurain
et al. 2010).
A date for the divergence of stramenopiles
(heterokonts) and alveolates at 950 Ma has been
determined by molecular clocks using fossils other
than dinoflagellates for calibration (Douzery et al.
2004). Using fossil dinoflagellates to calibrate
the clock, Medlin (2008, 2011) dated the divergence
of the dinoflagellates from the apicomplexans at
650 Ma. The presence of triaromatic dinosteroids,
assumed to be derived from dinoflagellates, has
been recorded in some acritarchs (organic-walled
microfossils of uncertain origin on morphologi-
cal grounds) of pre-Carboniferous age (Moldowan
et al. 1996; Moldowan & Talyzina 1998). These bio-
geochemical markers could therefore reflect the
existence of ancestral members of the dinoflagellate
lineage. An alternative suggestion could be that at
least some acritarchs represent one or more extinct
lineages with no surviving descendants.
Although biogeochemical evidence of the exist-
ence of pre-Mesozoic dinoflagellates is compel-
ling, it is not backed up by fossil morphological
evidence either because pre-Mesozoic members of
the dinoflagellates did not leave a preservable
record, or because pre-Mesozoic dinoflagellate
remains are not clearly recognizable as such. The
few claims based on morphology for dinoflagel-
late affinity among pre-Mesozoic fossils have not
been convincing (see Fensome et al. 2000). The
most famous of these is the Silurian fossil Arpy-
lorus, which Le Herisse et al. (2012) have con-
vincingly shown not to be a dinoflagellate but part
of a more complex biological structure possibly
associated with eurypterids. One recent intriguing
observation by Servais et al. (2009) was that some
Ordovician calcareous microfossils display wall
structures that are surprisingly similar to those of
calcareous dinoflagellate cysts. All confirmed
calcareous cysts are peridinioids, a group that on
compelling evidence aside from crystal structure
originated in the Jurassic. Speculation by Servais
et al. (2009) that these fossils could represent the
ancestors of dinoflagellates, if borne out, would
therefore be a fundamental challenge to current
ideas on the pattern and timing of dinoflagellate
evolution.
APICOCOMPLEXANS
SYNDINIANS
DINOKARYOTES
CILIATES
CHROMOPHYTES
6
9
7
11
10
8
13
4
5
123
12
Fig. 1. A phylogenetic tree for dinoflagellates
and their allies based on ultrastructure as proposed by
Fensome et al. (1993). The length of the lines is not
significant. Derived character states (indicated by
numbers): 1, tubular mitochondrial cristae; 2,
intranuclear spindle; 3, rod trichocysts; 4, compound
flagellar hairs; 5, cortical (amphiesmal) vesicles
(alveolae); 6, apical complex; 7, polykineties; 8, nuclear
dimorphism; 9, donokont flagella; 10, extranuclear
spindle; 11, dinokaryon (temporary); 12, dinokaryon
(permanent); 13, dinokaryon (temporary); loss
of trichocysts.
L. K. MEDLIN & R. A. FENSOME264
Plastid evolution
A series of endosymbiotic events has given rise
to all photosynthetic organisms. Initially a hetero-
trophic ancestor engulfed a cyanobacterium and
transformed it into a plastid to form the first photo-
synthetic cell. This single primary endosymbiosis
resulted in the red, green and glaucophyte algae
(see reviews in Archibald & Keeling 2002 and
Sanchez-Puerta & Delwiche 2008). Molecular ana-
lyses have shown that the host and the plastid
lineages in this event are both monophyletic, so this
event happened only once. Another heterotrophic
organism then engulfed either a red or green alga
from the first endosymbiosis to form the secondary
event. If plastids in a particular alga are surrounded
by two membranes, then the alga was derived from
the primary endosymbiosis; if three to four mem-
branes surround the plastid, then the alga is derived
from a secondary endosymbiosis (Keeling 2004).
The hypothesis that this secondary endosymbiosis
also happened only once has been controversial
(Yoon et al. 2002); the recent re-analysis of multiple
genes from multiple genomes that failed to recover a
monophyletic origin for all plastids from the sec-
ondary endosymbiosis (Baurain et al. 2010) has res-
urrected the hypothesis of multiple secondary
endosymbiosis events for each plastid in the second-
ary endosymbiosis.
Recently, Moustafa et al. (2009) have uncovered
unusual evidence from whole genome and expres-
sed sequence tag (EST) analyses, which suggests
that a sequence of unusual endosymbiotic events
led to the chromalveolate lineage. Traces of green
genes can be found in this lineage, which today is
a red algal plastid lineage. This has been inter-
preted to mean that algae in the lineage first had
green plastids, but this green plastid type was sub-
sequently replaced by a red plastid. Falkowsky
et al. (2004) hypothesized that red plastids had
an adaptive advantage only after the end-Permian
mass-extinction event at 251 Ma. At that time,
oceans became anoxic and their trace-metal chem-
istry changed such that iron became abundant. The
red plastid-bearing microalgae have iron-containing
cytochrome c6 in their photosynthetic electron
carrier complex instead of the copper-containing
plastocyanin of the photosystem of green plastid-
bearing algae.
If chromalveolates underwent multiple second-
ary endosymbioses (Baurain et al. 2010), then each
lineage should have acquired a red algal plastid
and dumped the green one at different times.
Medlin (2011) constructed a molecular clock to
determine if the radiations in the different chromal-
veolates lineages relate to the end-Permian event.
She found that it corresponded to different taxo-
nomic levels of radiation in the various lineages,
and that this supported the idea that the green plas-
tid was replaced by the red plastid multiple times.
Dinoflagellates have many different types of
plastid. The predominant peridinin plastid is
believed to have originated from a red algal second-
ary endosymbiosis. Supposedly, a tertiary endosym-
biosis occurred in the dinoflagellates when the
original plastid from the secondary endosymbiosis
(this should be the peridinin plastid) was replaced
by another plastid from the secondary endosym-
biotic algae. Cryptophyte, prasinophyte and hapto-
phyte plastids, which are each originally derived
from a red algal secondary endosymbiosis, were
therefore incorporated into the dinoflagellate line-
ages by various species (see Saldarriaga et al. 2001).
However, the peridinin lineage does not appear
independent in any of the plastid gene trees in dino-
flagellates as it does in the heterokont, cryptophyte
and haptophyte plastid lineages (Yoon et al. 2005;
Verbruggen 2011; A. Moustafa, pers. comm., 2012).
In contrast, the peridinin lineage is either (1)
embedded in the heterokont lineage as sister to the
diatoms (Yoon et al. 2005) or, with better taxon
sampling, as sister to the chrysophytes/synurophyte
lineage, which is sister to the diatoms (Verbrug-
gen 2011); or (2) embedded in the green lineage.
Evidence therefore suggests that all dinoflagellate
plastids are the result of at least four tertiary endo-
symbioses (heterokont ¼diatom, cryptophyte, hap-
tophyte and peridinin ¼heterokont chrysophytes).
This means that in the dinoflagellates, there was
no transformation of either a red or a green plastid
into the peridinin plastids and all modern plastids
in the dinoflagellates are the result of tertiary endo-
symbioses. Furthermore, it also suggests that it was
the green plastid that was eliminated at the time of
the four tertiary endosymbiosis. If the timing of
the end-Permian event is placed over the dinoflagel-
late tree using a molecular clock, this extinction
event corresponds to radiation at the generic level
in the dinoflagellates, at the order and family level
radiation in the haptophytes and at the phylum
level radiation in the heterokonts (Medlin 2011).
Generic level radiation of the extant dinoflagellates
also is also supported by their early Mesozoic fossil
record (Fensome et al. 1996). After the end-Permian
mass extinction, the dinoflagellates likely evolved
from a heterotrophic lineage to an autotrophic or
mixotrophic lineage by only tertiary endosymbioses
of several different algal groups replacing the orig-
inal green plastid. However, it makes no evolution-
ary sense to have re-engulfed a green algal cell if
the green algal plastid was a disadvantage at this
time; it is more likely that the dinoflagellate/green
lineage represents a relict green plastid that was
originally present in the entire alveolate lineage.
There is evidence that the last common ancestor of
dinoflagellates, apicomplexans and ciliates likely
CONSIDERATIONS OF DINOFLAGELLATE MACROEVOLUTION 265
had a green plastid, because there are traces of green
plastid genes in all of the host lineages (Takishita
et al. 2003; Hackett et al. 2004; Patron et al. 2006;
Moustafa et al. 2009). The common mode of feed-
ing by a peduncle in the ancestral dinoflagellates
would mean that the host cell membrane was left
behind after the dinoflagellate finished sucking out
its contents, which would result in typically only
three membranes around the dinoflagellate plastid
instead of the four membranes found around the
plastid in the other algal groups involved in the
secondary endosymbiosis.
The transformation of the heterokont plastid
into the peridinin plastid after it was engulfed
provides some of the most intriguing genomic rear-
rangement known in the eukaryotic world. Only
about 12 genes coding for plastid function are left
behind following the massive transfer of genes
from the plastid into the nucleus. These 12 genes
form mini-circles of genes of different sizes in
different species of the same genus but the mini-
circles from different species within a genus share
nearly identical spacer regions between the genes
(Zhang et al. 2002). This same massive gene trans-
fer and gene rearrangement did not happen in the
haptophyte and cryptophyte plastid-bearing dino-
flagellates, which adds more evidence that the ter-
tiary endosymbioses are independent events and
that the red algal plastid in each of these lineages
came from a different, independent secondary endo-
symbiosis. The genes encoded by the plastid pos-
sess another different feature. The normal poly A
tail of the messenger ribosomal nucleic acids
(mRNA) in the plastid is replaced by a poly T tail
(Wang & Morse 2006), so when converting mRNA
to complementary Deoxyribonucleic acid (cDNA)
all plastid-encoding ESTs from dinoflagellates can
be differentially separated from other plastids.
Evolution within the dinoflagellates:
morphological background
Prior to the late 20th century, little effort was made
to develop a view of dinoflagellate evolution that
accommodated evidence from both fossils and
modern forms. The first concerted attempt to relate
the two realms was that of Evitt (1985), who made
detailed and extensive comparisons of tabulation
patterns reflected on fossil cysts with the tabulation
patterns of living taxa. However, Evitt (1985) made
little attempt to couch his comparisons in phyloge-
netic terms; that was left to Fensome et al. (1993)
who, building on Evitt’s work, produced the first
modern phylogenetically based classification that
incorporated both fossil and living dinoflagellates.
A key feature of dinoflagellate anatomy is
tabulation. As alveolates all dinoflagellates have
vesicles in the cortex, beneath the cell’s outer cell
membrane. In dinoflagellates, this cortical region
is referred to as the amphiesma, and the vesicles
are known as amphiesmal vesicles. Amphiesmal
vesicles may remain empty or they may contain cel-
lulosic plates, termed thecal plates. Collectively,
thecal plates form a cell wall known as a theca.
The arrangement of amphiesmal vesicles (with or
without thecal plates) is called tabulation. (The
term paratabulation is sometimes used to refer to
‘reflected’ tabulation on cysts.) Arrangement of
the thecal plates varies to form tabulation patterns,
many elements of which tend to be consistent and
stable within related taxa or lineages. Tabulation
and tabulation patterns are therefore important in
unravelling phylogenetic relationships among many
groups of dinoflagellates. Fensome et al. (1993)
recognized six basic tabulation pattern types
(Fig. 2):
(1) gymnodinioid, in which amphiesmal vesicles
(usually without thecal plates) are numerous
and arranged randomly or in more than ten
latitudinal series
(2) suessioid, in which amphiesmal vesicles
(usually with thecal plates) are arranged into
seven to ten latitudinal series and a cingulum
that tends not to be distinctly differentiated
(3) gonyaulacoid-peridinioid, in which amphies-
mal vesicles (with thecal plates) are arranged
in five or six latitudinal series, with a clearly
differentiated cingulum
(4) dinophysioid, in which amphiesmal vesicles
can be attributed to four latitudinal series
with a distinctive cingulum, and in which a
sagittal (longitudinal) suture, perpendicular
to the plane of the cingulum, divides the
theca into left and right halves
(5) nannoceratopsioid, in which the hyposome
(that part of the cyst posterior to the cingulum)
is ‘dinophysioid’ and the episome (anterior to
the cingulum) is ‘gonyaulacoid-peridinioid’
(6) prorocentroid, in which the vesicles are
arranged into two very large plates separated
by a sagittal suture and an area of small
plates surround the flagellar apertures.
The earliest confirmed fossil dinoflagellates are
from the (possibly) MiddleLate Triassic, 240
200 Ma. Distinctive among these were forms with
a suessioid tabulation pattern, although a variety
of tabulation patterns were represented by Late Tri-
assic and Early Jurassic forms. From the Middle
Jurassic, most fossil dinoflagellates have a clearly
gonyaulacoid-peridinioid tabulation pattern. In an
early attempt to make sense of the dinoflagellate
fossil record, Bujak & Williams (1981) proposed
three possible evolutionary models: the plate
increase model, in which early tabulation involved
L. K. MEDLIN & R. A. FENSOME266
relatively few plates, the number of plates tending
to increase with time; the plate reduction model
with the reverse trend (a model which would make
sense if forms such as Suessia were indeed early-
derived); and the plate fragmentation model, which
would involve early, perhaps prorocentroid-like,
forms with few plates leading to later multi-plated
forms. As has become apparent with hindsight and
armed with molecular data, these models are too
simplistic. They did provide a timely stimulus for
tying fossils and living forms together from an evol-
utionary perspective, however.
A question among fossil dinoflagellate research-
ers in the latter decades of the 20th century was
whether the appearance of dinoflagellates during
the later Triassic Early Jurassic reflected a real
evolutionary event, or perhaps the ‘switching on’,
of preservable cyst-forming capability in one or
more lineages with a long pre-Mesozoic ancestry.
Researchers at the time were concerned about the
incompleteness of the fossil record and worried
that this might hamper anything meaningful being
determined from fossils about the evolution of the
group (Evitt 1981). However, Fensome et al.
(1996) reasoned that the early Mesozoic record of
dinoflagellates bore clear hallmarks of a true
evolutionary radiation, with highly variable ‘exper-
imental’ morphologies (at least as reflected by
tabulation) over a few tens of millions of years
during the later Triassic and Early Jurassic, before
stabilization into a few ‘standard’ tabulation types
from about 175 Ma to the present day (again in
terms of mostly gonyaulacoid and peridinioid tabu-
lation patterns). Although multi-plated Suessia,
as well as forms such as Rhaetogonyaulax with
a plate-rich gonyaulacoid-peridinioid tabulation,
were prominent during the Late Triassic, Valvaeo-
dinium, a gonyaulacoid-peridinioid with below-
average plate numbers for the group, was also a
member of the Late Triassic assemblage. Also pre-
sent among Jurassic assemblages was Nannocera-
topis, a strange combination of dinophysioid and
gonyaulacoid-peridinoid tabulation features (Piel
& Evitt 1980).
In their intra-dinoflagellate tree, Fensome
et al. (1993, p. 206; slightly modified as Fig. 1 here)
placed the Noctilucales and Blastodiniales as
basal groups because of their ‘part-time’ dinokar-
yon, with the Gymnodiniales basal to the remainder
of the dinoflagellates, followed in order of deriva-
tion by the Suessiales, Gonyaulacales, Peridin-
iales, Dinophysiales and Prorocentrales. No major
advances based on dinoflagellate morphology have
been proposed since this scheme was introduced.
Below we will explore how this scheme holds up
against subsequently established molecular trees.
(a)
(d)(e)(f)
(b)(c)
Fig. 2. Dinoflagellate tabulation types: (a) gymnodinioid, (b) suessioid, (c) gonyaulacoid-peridinioid, (d) dinophysioid,
(e) nannoceratopsioid, (f) prorocentroid.
CONSIDERATIONS OF DINOFLAGELLATE MACROEVOLUTION 267
Evolution of the dinoflagellates: molecular
results
Unfortunately, most molecular trees for dinoflagel-
lates have concentrated on closely related genera
or groups of species rather than the entire range
of the group. An exception was the tree produced
by Saldarriaga et al. (2004). Using ciliates as the
outgroup, parasitic and atypical taxa such as Amoe-
bophrya and Cryptosporidium diverge early, as pre-
dicted by their morphological features, before the
core dinoflagellates radiate. In this radiation, gym-
nodinioid clades (in which all taxa are athecate or
naked) alternate in divergence with clades that con-
tain peridinioid taxa. Although most thecate genera
were well supported and monophyletic in the var-
ious peridinioid clades, Gymnodinium was paraphy-
letic and relationships between the gymnodinioid
clades were not supported. The Gonyaulacales were
in the final divergence and the Prorocentrales were
paraphyletic.
A maximum likelihood analysis of 1246 dinofla-
gellate 18S rRNA gene sequences has not improved
the resolution but has added a few new surprises
(Fig. 3). The core dinoflagellates diverge simul-
taneously into four major clades. The first major
clade contains a mixture of gymnodinioid and peri-
dinioid taxa; Amphidinium commonly occurs as a
basal divergence in a peridinioid clade; prorocen-
troids are split into benthic and planktonic clades
not too distantly related; and dinophysioids are a
basal not derived divergence. The second major
but smaller clade is a gymnodinioid clade. The
third major clade also contains a mixture of peri-
dinioid and gymnodinioid taxa; surprisingly, the
Noctilucales are embedded in this clade, as also
seen by Hoppenrath & Leander (2010) in their
heat shock protein tree, as are the Blastodiniales.
Gonyaulacoids are a final divergence in this clade.
The fourth major clade is primarily composed of
naked forms, with the extant suessioids as a final
divergence. Most clades consist of either thecate
or non-thecate forms, the exception being in the
first major clade, in which Amphidinium spp. are
at the base of some peridinioid lineages. Basically,
this tree shows that the taxa conventionally attri-
buted to the Gymnodiniales and Peridiniales
have evolved multiple times and only a few con-
ventional orders, such as the Gonyaulacales, are
monophyletic.
More recent trees with more genes show a
similar pattern of divergences from the ciliates to
the core dinoflagellates along with other significant
relationships. Using three genes and a reduced
taxon sampling, Zhang et al. (2007) found that
Amphidinium was at the base of the entire dinofla-
gellate lineage. In the tree of Zhang et al. (2007),
the core dinoflagellates diverge into two major
well-supported clades: an endosymbiotic clade
and a free-living clade in which the gonyaulacoids
are monophyletic with one exception. Zhang et al.
(2007) contended that the prorocentroids are a
monophyletic group, as also recovered by Hop-
penrath & Leander (2010) using the heat-shock
protein gene.
Toward a reconciliation of morphological
and molecular approaches
We can now test the tree proposed by Fensome
et al. (1993) (slightly modified as in Fig. 4) against
molecular results. Fensome et al. (1993) consid-
ered a temporary dinokaryon (a dinoflagellate-
style nucleus that occurs only in part of the life
cycle) to be a primitive feature and so placed the
Noctilucales and Blastodiniales at the base of the
tree, derived early from the core dinoflagellates.
This prediction is supported by the Saldarriaga et al.
(2004) tree but it is not supported in the tree in
Figure 3 or in the heat-shock protein tree by Hop-
penrath & Leander (2010). This suggests that the
temporary dinokaryon is not (consistently) a sym-
plesiomorphic feature but can be re-instated from
time to time among different lineages.
The most recent molecular trees suggests that
the athecate (naked, unarmoured) condition tradi-
tionally grouped as the Gymnodiniales is para-
phyletic, indicating that loss and (re)gain of thecal
plates has happened repeatedly throughout dinofla-
gellate evolution. This makes sense when consider-
ing that the athecate state is not the equivalent of
gymnodinioid tabulation pattern, and presumably
gymnodinioids in the sense of athecate forms may
arise in lineages with non-gymnodinioid tabulation
patterns.
Molecular trees (Saldarriaga et al. 2004; Zhang
et al. 2007, fig. 3) show that modern dinoflagel-
lates attributed to the Suessiales (primarily Sym-
biodinium) appear to be derived, suggesting that
the modern forms are not closely related to the
Triassic fossil taxon Suessia. This is perhaps no sur-
prise as Fensome et al. (1993) based the grouping
of Symbiodinium with fossils, such as Suessia, gen-
erally on a particular range in the number of plate
series and not on tabulation details. However, the
indication that Symbiodinium and Suessia are not
closely related does make the suggestion that
Suessia was in some way related to the rise of
scleractinian corals through symbiosis less compel-
ling, even though the first appearance of Suessia
broadly coincides with the time of origin of the
modern corals in the Triassic.
The separation of gonyaulacoids and peridi-
nioids as a fundamental split has long been recog-
nized among palaeontologists. The molecular
L. K. MEDLIN & R. A. FENSOME268
results (Saldarriaga et al. 2004; Zhang et al. 2007,
Fig. 3) support a strong gonyaulacoid clade but
indicate that modern peridinioids are paraphyletic.
In the tree published by Saldarriaga et al. (2004,
fig. 1), within the gonyaulacoids, goniodomoids
and ceratioids fall out very clearly as separate
clades. The goniodomoids are represented by the
clade at the top of the diagram that connects
species of Pyrocystis,Fragilidinium,Alexandrium
and Pyrodinium. Below these in the same tree,
species of Ceratium, the modern representative of
an important and coherent fossil-rich family, fall
neatly into a single lineage. Below these, with
common derivation, are clades containing other
forms that would generally be considered gonyau-
lacacean on the basis of morphology occur on the
remaining major gonyaulacoid clade. The molecu-
lar evidence thus accords well with a gonyaulacoid
lineage that, based on fossils, has been separate for
the past 175 180 Ma. Interestingly, Saldarriaga
et al. (2004) indicated that part of the grouping that
Fensome et al. (1993) had assembled as the Phy-
todiniales is molecularly associated with Gonyaulax
spinifera, the type of Gonyaulax. Other forms
considered by Fensome et al. (1993) to be phyto-
dinialeans fell out in very different lineages. Like
the presence of an athecate amphiesmal and a part-
time nucleus, the inclusion of a prominent coccoid
life-cycle stage is therefore a feature developed or
retained by several separate lineages, not a synapo-
morphy that can be used to define high-level taxa.
In all trees so far published (e.g. Saldarriaga
et al. 2004; Zhang et al. 2007, Fig. 3) peridinioids
resolve into several clades and thus the morpho-
logically based Peridiniales is shown to be poly-
phyletic. This is surprising from a palaeontological
perspective because the tabulation among fossil
peridinioids is so consistent and apparently stable,
especially from the Late Jurassic to the Miocene,
far more so than the gonyaulacoid fossil record.
To understand this discordance between the fos-
sil and molecular evidence, it may help to delve
a little deeper into the nature of the former for
peridinioids. Fensome et al. (1993) designated a
‘standard’ peridinioid tabulation involving 4 api-
cal plates, 3 anterior intercalaries symmetrically
arranged on the dorsal surface, 7 precingulars, 5
postcingulars and 2 symmetrically disposed ant-
apicals. Especially characteristic and commonly
recognizable through archeopyle formation, even
if the rest of the tabulation is not reflected, is the
mid-dorsal second anterior intercalary plate (2a),
which is most often 6-sided. These tabulation char-
acteristics are present in the vast majority of peridi-
nioid genera including calcareous forms from the
Middle Jurassic to the Palaeogene, and the stability
of this tabulation pattern despite other types of
morphological variation (overall shape, cyst-wall
composition, archeopyle details) strongly suggests
a single clade, even though this can never be con-
firmed by molecular evidence.
From primarily fossil evidence, Fensome et al.
(1993) (and palaeontologists in general over recent
decades) recognized a protoperidinioid lineage
separate from the peridinioid mainstream from the
Late Cretaceous. Partly recognized by cyst-wall
characteristics and by a distinctive cingular tabula-
tion evidenced by modern forms (cingular details
are almost always not discernible on fossils), fossil
and modern protoperidinioids are characterized by
a variation in episomal tabulation, especially dor-
sally; this is in contrast to the stability of this
feature among fossil peridinioids. As illustrated by
the molecular tree published by Saldarriaga et al.
(2004; as also represented by unlabelled clade 5 in
Fig. 3), it is not surprising that protoperidinioids
resolve into a clade separate from other peridinioids.
What is unexpected from a palaeontological
perspective is that peridiniaceans (sensu stricto,
thus excluding protoperidiniaceans) resolve onto a
number of clades, some quite distant from others.
The youngest-known fossil organic-walled peridi-
niacean, Palaeocystodinium, made its last appear-
ance in the Miocene. Perhaps, non-calcareous
fossils with a standard peridinioid tabulation can
be considered part of a clade, the last representative
of which became extinct in the Miocene. The stable
tabulation of fossil peridiniaceans is most like
modern Peridinium bipes; indeed the symmetrical
dorsal episomal tabulation of fossil peridinioids is
sometimes referred to as ‘bipesioid’. Perhaps, the
fossil peridiniacean clade is related to Peridinium
bipes. However, fossil ‘bipesioids’ (peridiniaceans)
are all marine, like modern protoperidiniaceans,
whereas the modern peridiniaceans in the clade
containing Peridinium bipes are all non-marine.
Because the Early Jurassic peridinioids and a
few later ones such as Cretaceous Angustidinium
had five apical plates (in contrast to four in the vast
majority of later fossil peridinioids; see Below
1987), Fensome et al. (1993) placed these forms
with modern Heterocapsa in the suborder Hetero-
capsineae. From the molecular trees of Saldarriaga
et al. (2004) and Figure 3, Heterocapsa appears
to be a relatively derived peridinioid. The pre-
sence of five apical plates in early peridinioids
and Heterocapsa is a very broad similarity, but in
detail the apical thecal plates of the two entities
are not closely similar in arrangement, and the simi-
larity in apical plate number most probably rep-
resents convergence. Early fossil forms with five
apical plates are therefore probably not related to
Heterocapsa, but may well represent a group ances-
tral to other Jurassic Miocene peridinioids.
Among dinoflagellates with calcareous life-
cycle stages (primarily if not always cysts),
CONSIDERATIONS OF DINOFLAGELLATE MACROEVOLUTION 269
L. K. MEDLIN & R. A. FENSOME270
Fig. 3. (a) Maximum likelihood analysis of 1296 SSU rRNA sequences currently held in the ARB database and
alignment by secondary structure. Black dots indicate the simultaneous divergence of four clades. (b) The opening of the
gonyaulacoid clade from A.
RHAETOGONYAULACINEAE
COMPARODINIACEAE
STEPHANELYTRACEAE
NANNOCERATOPSIALES
SYNDINIALES
NOCTILUCALES
DESMOCAPSALES
GYMNODINIINEAE
ACTINISCINEAE
PTYCHODISCALES
SUESSIALES
PHYTODINIALES
THORACOSPHAERALES
GONIODOMINEAE
GONYAULACINEAE
CERATIINEAE
CLADOPYXIINEAE
GLENODINIINEAE
HETEROCAPSINEAE
PERIDINIACEAE
PROTOPERIDINIACEAE
OXYTOXACEAE
DINOPHYSIALES
PROROCENTRALES
BLASTODINIALES
Fig. 4. Slightly modified phylogenetric tree with principle dinoflagellate taxa, originally developed by
Fensome et al. (1993).
CONSIDERATIONS OF DINOFLAGELLATE MACROEVOLUTION 271
Fensome et al. classified the Calciodinelloideae as a
subfamily of the Peridiniaceae and treated Thora-
cosphaera (which lacks indications of tabulation
and had been interpreted not to be a cyst) in its
own order, the Thoracosphaerales. The tree pub-
lished by Saldarriaga et al. (2004) clearly associ-
ated Thoracosphaera with Scrippsiella, which is a
modern representative of the calciodinelloids; the
separation of Thoracosphaera from other dinofla-
gellates with calcareous life-cycle stage is therefore
not upheld. However, neither is a close relationship
between calciodinelloids and Peridinium bipes.
The tabulation of the calciodinelloids, where it can
clearly be seen on fossil cysts, is consistently the
‘standard peridiniacean pattern’ and thus conforms
with that of most Jurassic Miocene organic-walled
cysts. Other than cyst-wall composition, the most
significant difference between fossil peridiniaceans
with organic-walled cysts and those with calcareous
cysts (calciodinellods) is the archeopyle type. In
organic-walled forms, the archeopyle in almost all
genera is focused on the second anterior intercalary
plate; in calcareous forms it is generally apical
however, a fundamental difference going back into
the Mesozoic.
One aspect of the fossil record is that it provides
unique evidence for whole groups of taxa not rep-
resented today and of which we have no other
record. Nannoceratopsis, cited above, is an excel-
lent example; the basal position of the dinophysioids
in Figure 3 seems in accordance with the early pres-
ence of Nannoceratopsis in the fossil record.
Another exclusive fossil lineage is represented by
the wetzelielloids, a group of peridinioids with an
episomal tabulation that is basically bipesioid, but
with a four-sided rather than a five-sided 2a plate.
This may seem a subtle difference, but wetzeliel-
loids were a highly distinctive and prominent
group of Palaeogene dinoflagellates. They appear
to have left no descendants, despite early and now-
disproven claims that they were protoperidinioids.
Wetzelielloids appear to have had a peridiniacean
cingular tabulation and a tabulation overall that
was symmetrical and stable, like that of other
fossil peridiniaceans but in contrast to the variable
and commonly asymmetrical protoperidiniacean
tabulation.
The fossil record also reveals what can be
thought of as ‘iceberg’ taxa, ones with far greater
representation in the past that at the present time.
An example is the cladopyxioid lineage, repres-
ented by just two or three modern genera (including
Cladopyxis) but which has a significant, mainly
JurassicCretaceous, fossil record. Indeed, from
tabulation details, the cladopyxoids appear to be
transitional between gonyaulacoids and peridi-
nioids, so a molecular analysis of a modern mem-
ber of the lineage would be very interesting.
Mitochondrial evolution
The mitochondria of dinoflagellates are another
example in which the group has taken a bizarre
evolutionary pathway. Lukes et al. (2009) docu-
mented that within the alveolate lineage, ciliates
have a normal-sized circular mitochondrial ge-
nome; apicomplexans and dinoflagellates how-
ever have a reduced genome with only three genes
and, after transcription, the mRNAs can be modified
to change the codons or the amino acid sequence
into other proteins. It therefore does not matter
that they have reduced their mitochondrial genome
to only three genes because they have post-
transcriptional modification of the mRNAs.
An unusual case of convergent evolution?
Although the dinoflagellates have evolved many
unusual features, similar features also occur in
the Euglenozoa (Lukes et al. 2009). Are such simi-
larities the result of convergent evolution? Shared
similarities include flagella with a paraflagellar rod;
a large nucleolus and permanently condensed
chromosomes, mucocysts or trichocysts ejected
through pores; cell walls composed of ‘protein-
aceous/cellulosic’ strips or plates; thylakoids with
three lamellae; and chloroplast endoplasmic reticu-
lum (CER) composed of three membranes. Another
comparison is that the dinoflagellate mitochond-
rion has only three genes and euglenoid mitochon-
dria have mini-circles with three genes. It is
tempting to suggest that the reduction of the mito-
chondrial genome to only three genes is the next
evolutionary step before the formation of the mini-
circles. Both dinoflagellates and euglenoids have
post-transcriptional editing of their mitochondrial
mRNA. The unique splice leaders to the mRNA
are conserved at the class level in dinoflagellates
and at the species level in euglenids. Both groups
have mRNAs transcribed with multiple genes. In
the dinoflagellates they are tandem repeats of the
same gene, but these are different genes in the eugle-
nophytes. Each of these strange features likely
conveys some evolutionary advantage in these two
very different lineages of eukaryotic microalgae.
It would therefore seem that, although the dino-
flagellates exhibit some rare and unusual cellular
features, they are not alone in having these features
and their bizarre evolutionary pathways are not as
unique as once believed.
Conclusions
As with the two ‘solitudes’ of fossil and extant
dinoflagellate studies until the 1980s and 1990s,
the morphological (primarily fossil) and molecular
L. K. MEDLIN & R. A. FENSOME272
approaches to dinoflagellate evolution have, until
now, largely developed separately in recent years.
Our attempt here to bring the two approaches
together will, we hope, pave the way for greater col-
laboration in the quest to understand dinoflagellate
macroevolution.
Current combined evidence suggests that dino-
flagellates separated from their apicomplexans
cousins some 650 Ma. Although they did not leave
a convincing morphological record until the Meso-
zoic, biogeochemical evidence provides some
evidence for the group during the Palaeozoic. Evi-
dence from molecular analyses and plastids sup-
ports the fossil evidence for an early Mesozoic
radiation of dinoflagellates, during which it seems
that the morphology of the group as we know it
today, with cingulum, sulcus and characteristic fla-
gella and tabulation patterns, first appeared. Some
lineages reflected by the fossil record, such as cera-
tioid gonyaualacaleans and protoperidiniod peridi-
nialeans, are strongly supported by molecular
evidence. Other relationships, such as that of the
Triassic fossil Suessia with modern Symbiodinium,
appear to be unfounded by molecular data. Molecu-
lar evidence is clearly our strongest indication for
phylogenetic relationships, but any overall evol-
utionary tree must accommodate morphologies rep-
resented only by fossils.
We thank Jane Lewis and the DINO 9 team for the invita-
tion to collaborate on this paper and Jane especially for
unwavering encouragement and help in completing the
task. We are grateful to Jim Riding and an anonymous
reviewer for helpful reviews. The second author would
like to thank Jennifer Galloway and James White for pro-
viding feedback on an early draft, and to many colleagues
over the years for discussions on dinoflagellate evolution,
most notably Jim Riding, Max Taylor and Graham Wil-
liams. This publication constitutes ESS Contribution no.
20130070. This work was supported in part by FP7 EU
MIDTAL, contract number 701924.
References
Adl, S. M., Simpson,A.G.B.
et al
. 2005. The new higher
level classification of eukaryotes with emphasis on the
taxonomy of the protists. Journal of Eukaryotic Micro-
biology,52, 399– 451.
Archibald,J.M.&Keeling, P. J. 2002. Recycled plas-
tids: a ‘green movement’ in eukaryotic evolution.
Trends in Genetics,18, 577– 584.
Baurain, D., Brinkmann,H.
et al
. 2010. Phylogenomic
evidence for separate acquisition of plastids in crypto-
phytes, haptophytes, and stramenopiles. Molecular
Biology and Evolution,27, 1698– 1709.
Below, R. 1987. Evolution und Systematik von
Dinoflagellaten-Zysten aus der Ordnung Peridiniales.
I. Allgemeine Grundlagen und Subfamilie Rhaetogo-
nyaulacoideae (Familie Peridiniaceae). Palaeontogra-
phica, Abteilung B,205, 1– 164.
Bujak,J.P.&Williams, G. L. 1981. The evolution of
dinoflagellates. Canadian Journal of Botany,59,
2077– 2087.
Douzery, E. J. P., Snell, E. A., Bapteste, E., Delsuc,F.
&Philippe, H. 2004. The timing of eukaryotic evol-
ution: Does a relaxed molecular clock reconcile pro-
teins and fossils. Proceedings of the National
Academy of Sciences,101, 15386– 15391.
Evitt, W. R. 1981. The difference it makes that dinoflagel-
lates did it differently. International Commission for
Palynology Newsletter,4,67.
Evitt, W. R. 1985. Sporopollenin Dinoflagellate
Cysts: Their Morphology and Interpretation. Ameri-
can Association of Stratigraphic Palynologists,
Dallas, USA.
Falkowsky, P. G., Katz, M. E., Knoll, A. H., Quigg,
A., Raven, J. A., Schofield,O.&Taylor,F.J.R.
2004. The evolution of the modern phytoplankton.
Science,305, 354– 359.
Fensome, R. A., Taylor, F. J. R., Norris, G., Sarjeant,
W. A. S., Wharton,D.I.&Williams, G. L. 1993. A
classification of fossil and living dinoflagellates.
Micropaleontology Press Special Paper,7, 351.
Fensome, R. A., MacRae, R. A., Moldowan, J. M.,
Taylor,F.J.R.&Williams, G. L. 1996. The early
Mesozoic radiation of dinoflagellates. Paleobiology,
22, 329338.
Fensome, R. A., Saldarriaga,J.F.&Taylor,F.J.R.
2000. Dinoflagellate phylogeny revisited: reconciling
morphological and molecular based phylogenies.
Grana,38, 66– 80 (cover date 1999).
Hackett, J. D., Andersen, D. M., Erdner,D.L.&
Bhattacharya, D. 2004. Dinoflagellates: a remark-
able evolutionary experiment. American Journal of
Botany,91, 1523– 1524.
Hoppenrath,M.&Leander, B. S. 2010. Dinoflagellate
phylogeny as inferred from heat shock protein 90 and
ribosomal gene sequences. PLOS One,5, e13220.
Keeling, P. 2004. A brief history of plastids and their
hosts. Protist,155,37.
Leander,B.S.&Keeling, P. 2004. Early evolutionary
history of dinoflagellates and apicomplexans (Alveo-
lata) as inferred from hsp90 and actin phylogenies.
Journal of Phycology,40, 341– 350.
Le Herisse, A., Masure, E., Javaux,E.J.&Mar-
shall, C. P. 2012. The end of a myth: Arpylorus
antiquus Paleozoic dinoflagellate cyst. Palaios,27,
414423.
Lukes, J., Leander,B.S.&Keeling, P. J. 2009. Cas-
cades of convergent evolution: the corresponding evol-
utionary histories of euglenozoan and dinoflagellates.
Proceedings of the National Academy of Sciences,
106, 9963– 9970.
Medlin, L. K. 2008. Molecular clocks and inferring evol-
utionary milestones and biogeography in the microal-
gae. In:Okada, H., Mawatari, S. F., Suzuki,N.&
Gautam, P. (eds) Origin and Evolution of Natural
Diversity, Proceedings of International Symposium,
15 October 2007, Sapporo.21
st
Century COE for
Neoscience of Natural History, Hokkaido University,
Japan, 31– 42.
Medlin, L. K. 2011. The Permian Triassic Extinction
forces the radiation of the modern phytoplankton. Phy-
cologia,50, 684– 693.
CONSIDERATIONS OF DINOFLAGELLATE MACROEVOLUTION 273
Moldowan,J.M.&Talyzina, N. M. 1998. Biogeochem-
ical evidence for dinoflagellate ancestors in the Early
Cambrian. Science,281, 1168– 1170.
Moldowan, J. M., Dahl,J.
et al
. 1996. Chemostrato-
graphic reconstruction of biofacies: molecular evi-
dence linking cyst-forming dinoflagellates with
pre-Triassic ancestors. Geology,24, 159– 162.
Moustafa, A., Beszteri, B., Maier, U. G., Bowler, C.,
Valentin,K.&Bhattacharya, D. 2009. Genomic
footprints of a cryptic endosymbiosis in diatoms.
Science,324, 1724– 1726.
Patron, N. J., Waller,R.F.&Keeling, P. J. 2006. A
tertiary plastid uses genes from two endosymbionts.
Journal of Molecular Biology,357, 1373–1382.
Piel,K.M.&Evitt, W. R. 1980. Paratabulation in the
Jurassic dinoflagellate genus Nannoceratopsis and a
comparison with modern taxa. Palynology,4, 79–104.
Saldarriaga, J. F., Taylor, F. J. R., Keeling,P.J.&
Cavalier-Smith, T. 2001. Dinoflagellate nuclear
SSU rRNA phylogeny suggests multiple plastid
losses and replacements. Journal of Molecular Evol-
ution,53, 204–213.
Saldarriaga, J. F., Taylor, F. J. R., Cavalier-Smith, T.,
Medden-Duer,S.&Keeling, P. J. 2004. Molecular
data and the evolutionary history of dinoflagellates.
European Journal of Protistology,40, 85– 111.
Sanchez-Puerta,M.V.&Delwiche, C. F. 2008. A
hypothesis for plastid evolution in chromalveolates.
Journal of Phycology,44, 1097– 1107.
Saunders, G. W., Hill, D. R. A., Sexton,J.P.&Ander-
son, R. A. 1997. Small-subunit ribosomal RNA
sequences from selected dinoflagellates: testing clas-
sical evolutionary hypotheses with molecular sys-
tematic methods. Plant Systematics Evolution,11,
237259.
Servais, T., Munnecke,A.&Versteegh,G.J.M.
2009. Silurian calcispheres (Calcitarcha) of Gotland
(Sweden): comparisons with calcareous dinoflagel-
lates. Comptes Rendus Palevol,8, 527– 534.
Takishita, K., Ishida,K.&Maruyama, T. 2003. An
enigmatic GAPDH gene in the symbiotic dinoflagellate
genus Symbiodinium and its related species (the order
Suessiales): possible lateral gene transfer between two
eukaryotic algae, dinoflagellate and euglenophyte.
Protist,154, 443– 454.
Verbruggen, H. 2011. Evolution of the algal ionome: pro-
gress and perspectives. Phycologist,80, 10.
Wang,Y.&Morse, D. 2006. Rampant polyuri-
dylylation of plastid gene transcripts in the dinoflagel-
late Lingulodinium.Nucleic Acid Research,34,
613–619.
Yoon, H. S., Hackett, J. D., Pinto,G.&Bhatta-
charya, D. 2002. The single, ancient origin of chro-
mist plastids. Proceedings of the National Academy
of Sciences,99, 15507– 15512.
Yoon, H. S., Hackett, J. D., van Dolah, F. M., Nosenk,
T., Lidie,K.L.&Bhattacharya, D. 2005. Tertiary
endosymbiosis driven genome evolution in dinoflagel-
late algae. Molecular Biology and Evolution,22,
1299– 1308.
Zhang, Z., Cavalier-Smith,T.&Green, B. R. 2002.
Evolution of dinoflagellate unigenic minicircles and
the partially concerted divergence of their putative
replicon origins. Molecular Biology and Evolution,
19, 489– 500.
Zhang, H., Bhattacharya,D.&Lin, S. 2007. A three-
gene dinoflagellate phylogeny suggests monophyly of
Prorocentrales and a basal position for Amphidinium
and Heterocapsa.Journal of Molecular Evolution,
65, 463– 474.
L. K. MEDLIN & R. A. FENSOME274
... However, taxa with available DNA sequence information and a partiform hypotheca (i.e., Amphidomataceae) do not show clear phylogenetic proximity to either of these two major dinophyte lineages. Thus, extant Cladopyxidaceae may provide a missing link of thecate dinophytes that would enable a better understanding of the first evolutionary transformations from ancestral configurations towards the more abundant and derived patterns in Gonyaulacales and Peridiniales 15,26,[30][31][32] . To investigate this potential link, as well as the taxonomy of the constituent elements of the Cladopyxidaceae, the morphology of the thecal plate pattern and phylogenetic placement must be determined. ...
... The two major branches of dinophytes, Gonyaulacales and Peridiniales, present a mosaic combination of ancestral and derived character states. Despite the small number of extant species, cladopyxidoid protists are important for evolutionary interpretations because their seemingly rare plate pattern allows character polarity to be identified 15,26,31,32 . The precise systematic position of Cladopyxidaceae within the Dinophyceae, their internal taxonomic delimitations, and the phylogenetic relationships between their constituent elements have not sufficiently worked out. ...
Article
Full-text available
Dinophyte evolution is essentially inferred from the pattern of thecal plates, and two different labelling systems are used for the important subgroups Gonyaulacales and Peridiniales. The partiform hypotheca of cladopyxidoid dinophytes fits into the morphological concepts of neither group, although they are assigned to the Gonyaulacales. Here, we describe the thecate dinophyte Fensomea setacea , gen. & sp. nov . , which has a cladopyxidoid tabulation. The cells displayed a Kofoidean plate formula APC, 3′, 4a, 7″, 7C, 6S, 6′′′, 2′′′′, and slender processes were randomly distributed over the echinate or baculate surface. In addition, we obtained rRNA sequences of F. setacea , gen. & sp. nov . , but dinophytes that exhibit a partiform hypotheca did not show a close relationship to Gonyaulacales. Character evolution of thecate dinophytes may have progressed from the ancestral state of six postcingular plates, and two more or less symmetrically arranged antapical plates, towards patterns of only five postcingular plates (Peridiniales) or more asymmetrical configurations (Gonyaulacales). Based on our phylogenetic reconsiderations the contact between the posterior sulcal plate and the first postcingular plate, as well as the contact between an antapical plate and the distalmost postcingular plate, do not represent a rare, specialized gonyaulacoid plate configuration (i.e., the partiform hypotheca of cladopyxidoid dinophytes). Instead, these contacts correspond to the common and regular configuration of peridinioid (and other) dinophytes.
... The Cladopyxidaceae is a family of dinoflagellates within the order Gonyaulacales Taylor, which combines extant, photosynthetic, warm marine (specifically oceanic) genera with fossil genera occurring in marine strata of Early Jurassic to Neogene age; no undisputable fossils are known from the Quaternary (Fensome et al. 1993(Fensome et al. , 1996Medlin and Fensome 2013;Goodman 2017). Extant cladopyxidaceans may provide a missing link to better understand the first evolutionary transformations from ancestral configurations toward the more abundant and more derived patterns in Gonyaulacales and Peridiniales (Below 1987;Edwards 1990;Fensome et al. 1996Fensome et al. , 1999Medlin and Fensome 2013 Micracanthodinium is an extant cladopyxidacean genus created by Deflandre (1937) for a Cladopyxis species described by Lohmann (1903). ...
... The Cladopyxidaceae is a family of dinoflagellates within the order Gonyaulacales Taylor, which combines extant, photosynthetic, warm marine (specifically oceanic) genera with fossil genera occurring in marine strata of Early Jurassic to Neogene age; no undisputable fossils are known from the Quaternary (Fensome et al. 1993(Fensome et al. , 1996Medlin and Fensome 2013;Goodman 2017). Extant cladopyxidaceans may provide a missing link to better understand the first evolutionary transformations from ancestral configurations toward the more abundant and more derived patterns in Gonyaulacales and Peridiniales (Below 1987;Edwards 1990;Fensome et al. 1996Fensome et al. , 1999Medlin and Fensome 2013 Micracanthodinium is an extant cladopyxidacean genus created by Deflandre (1937) for a Cladopyxis species described by Lohmann (1903). Its type species, M. setiferum (Lohmann) Deflandre, is a small cell with thin, unbranched extensions, particularly present along the cingulum. ...
Article
Among dinoflagellates, extant cladopyxidaceans may provide a missing link to better understand the first evolutionary transformations from ancestral configurations towards the more abundant and more derived patterns in Gonyaulacales and Peridiniales. A restudy of the extant, motile-defined Micracanthodinium setiferum from plankton samples from the Indian and Atlantic Oceans and Mediterranean Sea demonstrates that the correct plate formula is Po Pt X 3′+*4′ 4a 7′′ 7C 4S? 6′′′ 0p 2′′′′. A ventral pore is found between 1′, 3′ and *4′. A restudy of the extinct, fossil-defined Cladopyxidium saeptum from the upper Paleocene of Delaware (U.S.A), demonstrated the presence of an identical tabulation. A ventral pore (=porichnion) was positioned between *1′ and 7′′. Cladopyxidium is morphologically closer to Micracanthodinium than to Cladopyxis. However, since Cladopyxidium has been extinct since the middle Eocene it is unlikely that Micracanthodinium and Cladopyxidium will have a direct biological link; the close morphological link between both does suggest an important phylogenetic relationship between both in the evolution of cladopyxidaceans.
... The evolutionary trajectory of the dinoflagellates has been the subject of considerable debate (e.g. Bujak and Williams 1981;Fensome et al. 1996aFensome et al. , b, 1999van de Schootbrugge et al. 2005;Medlin and Fensome 2013). Only around 15% of living dinoflagellate species, mostly marine forms, produce 'fossilizable' cysts and it is generally assumed that a similar percentage formed resistant organic-walled cysts in the geological past (Head 1996;Riding and Lucas-Clark 2016). ...
... There is substantial cytological, geochemical and molecular clock evidence that the dinoflagellates are a relatively ancient lineage, with origins in the Neoproterozoic (Moldowan et al. 1996;Moldowan and Talyzina 1998;Medlin and Fensome 2013). However Janouškovec et al. (2017, fig. ...
Article
This contribution is an overview of the Early Jurassic dinoflagellate cysts of the Lusitanian Basin in Portugal, with particular emphasis on the effects of the Jenkyns Event (Toarcian Oceanic Anoxic Event – T-OAE) on the evolution of this planktonic group. We review and discuss data from 214 samples from six Lower Jurassic successions (upper Sinemurian— upper Toarcian) in the Lusitanian Basin. The late Pliensbachian radiation of dinoflagellate cysts was well recognised in this basin. The pre-Jenkyns Event interval is highly productive, with maximum abundance and species richness values. However, this palaeoenvironmental perturbation severely affected the evolution of this group for the remainder of the Early Jurassic. The prolonged recovery of the dinoflagellates in the Toarcian following the Jenkyns Event is not typical of the northern regions (Arctic and Boreal realms), where new species began to evolve earlier compared with southern European basins.
... Biogeochemical evidence, including the isolation of dinosteranes and 4α-methyl-24-ethylcholestane (steroidal alkanes abundant in extant dinoflagellates), along with molecular clock data both suggest dinoflagellates originated in the earliest Cambrian or more likely the Neoproterozoic Moldowan and Talyzina, 1998;Fensome et al., 1999;Medlin and Fensome, 2013). Furthermore, the strong correlation between the greater abundance of these dinosteranes and the higher acritarch diversities between the Proterozoic and Devonian, suggests that many acritarchs may have been cryptic dinoflagellates . ...
... Although this model is broadly sustained by the fossil record, it is not supported by the neontological evidence and cannot accommodate for the anterior insertion of the flagellae as a primitive feature (Loeblich III, 1976;Bujak and Williams, 1981). Indeed, the plate reduction, plate increase and plate fragmentation models of Bujak and Williams (1981) are all considered overly simplistic by Fensome et al. (1999) and Medlin and Fensome (2013), who both noted that molecular evidence strongly suggests a substantially more complex evolutionary scenario. However, the overall stabilisation of dinoflagellate cyst tabulation by the Middle Jurassic is broadly accepted, as is the considerable experimentation in tabulation during the Late Triassic. ...
Article
The Late Triassic radiation of cyst-forming dinoflagellates in the Southern Hemisphere is investigated in the Northern Carnarvon Basin, Western Australia. This major depocenter, situated on the southern margin of the Tethys Ocean, accumulated extensive deltaic and shallow marine successions at this time, that frequently host early dinoflagellate cyst assemblages. Numerous petroleum exploration wells in the basin have penetrated the fluvially dominated Mungaroo Formation and shallow marine Brigadier Formation, of Anisian–Norian and Rhaetian ages, respectively. Consequently, huge numbers of cuttings and sidewall core samples from these northwest prograding deltaic systems are available for study. Many of the dinoflagellate cysts from the Mungaroo and Brigadier formations have not been taxonomically formalized, including many forms that are used in open nomenclature within the oil and gas industry. This study formally documents these occasionally abundant and diverse dinoflagellate cyst assemblages with the aim of providing a consistent taxonomic framework for future work on the Upper Triassic successions of the Northern Carnarvon Basin. This will aid the recognition of individual flooding events via their characteristic palynomorph signatures and help to build on significant recent advances in regional sequence stratigraphy. One new genus, 14 new dinoflagellate cyst species and 1 new subspecies are described from the most diverse Late Triassic dinoflagellate assemblage yet published. A further 9 genera and 15 dinoflagellate species are also recorded from the Carnian–Rhaetian R. wigginsii, W. listeri, H. balmei, R. rhaetica and D. priscum dinoflagellate zones. The documented assemblages are not only significant biostratigraphically, but it is also postulated that high diversity Triassic dinoflagellate cyst associations were paleoclimatically controlled, and were likely confined to the temperate and cool temperate paleolatitudes.
... The dinoflagellates are an important group of unicellular flagellate protists (Fensome et al. 1996a;Medlin and Fensome 2013). Most representatives are marine, planktonic cells called thecae, but dinoflagellates are also present in freshwater ecosystems. ...
Article
A comprehensive, illustrated guide to to the preparation (i.e. extraction, concentration and microscope slide production) of palynomorphs from samples of sediments, sedimentary rocks and other materials is presented. The traditional technique, based upon mineral acid digestion of the sample matrix, is subdivided into four phases. These are: sampling and pre-preparation; acid digestion; palynomorph concentration; and presentation of palynomorphs for study and archiving of materials. Modifications for preparing Quaternary and modern materials such as acetolysis are outlined, as are methods of preparation which do not use hazardous acids. One of the most effective non-acid preparation techniques uses sodium hexametaphosphate as a clay deflocculant and works well on clay-rich samples which are not intensely lithified. Hydrogen peroxide is another reagent which can be used. The contamination of samples by material from other samples or modern pollen can lead to spurious data and interpretations. Strenuous efforts to avoid contamination should be made. Modifications of the traditional preparation technique are described for 14 specific sample materials. For example, many pure limestones only require digestion with hydrochloric acid. Moreover, coal is typically simply oxidised using nitric acid or Schulze’s solution then reacted with dilute potassium hydroxide solution to produce organic substances which are then rinsed away using water. Traditional preparation techniques are used for all palynomorph groups irrespective of their biological affinity, however certain of these require some specific modifications. For example chitinozoa and megaspores are substantially larger than acritarchs, dinoflagellate cysts, miospores and pollen, therefore modifications to the technique must be used, principally in the sieve sizes used. Some attempts have been made to automate palynomorph processing. The equipment for this is discussed, together with other technological solutions such as microwave digestion. Eight techniques closely associated with palynological processing and the microscopical observation of palynomorphs such as scanning electron microscopy are also reviewed.
... As one of the important groups of unicellular eukaryotic life forms, Dinophyceae (or Dinoflagellata under zoological nomenclature) are nothing less but diverse from every single point of view (Morden and Sherwood 2002;Pochon et al. 2012;Gottschling and McLean 2013;Burki 2014). Together with Ciliata and Apicomplexa (= Sporozoa), Dinophyceae belong to Alveolata and are a well-supported monophyletic group based on molecular data and numerous unique anatomical characteristics (Harper et al. 2005;Medlin and Fensome 2013;Keeling et al. 2014;Janouškovec et al. 2017). Compared to all other eukaryotes, the genome of dinophytes is highly unusual with respect to structure and regulation (Moreno Díaz de la Espina et al. 2005;Wisecaver and Hackett 2011). ...
Article
Tertiary endosymbiosis is proven through dinophytes, some of which (i.e. Kryptoperidiniaceae) have engulfed diatom algae containing a secondary plastid. Chloroplasts are usually inherited together permanently with the host cell, leading to co-phylogeny. We compiled a diatom sequence data matrix of two nuclear and two chloroplast loci. Almost all endosymbionts of Kryptoperidiniaceae found their closest relatives in free-living diatoms and not in other harboured algae, rejecting co-phylogeny and indicating that resident diatoms were taken up by dinophytes multiple times independently. Almost intact ultrastructure and insignificant genome reduction are supportive for young, if not recent events of diatom capture. With their selective specificity on the one hand and extraordinary degree of endosymbiotic flexibility on the other hand, dinophytes hosting diatoms share more traits with lichens or facultatively phototrophic ciliates than with green algae and land plants. Time estimates indicate the dinophyte lineages as consistently older than the hosted diatom lineages, thus also favouring a repeated uptake of endosymbionts. The complex ecological role of dinophytes employing a variety of organismic interactions may explain their high potential and plasticity in acquiring a great diversity of plastids.
... Microfossil diversity replotted from Falkowski et al. [48], based on original tabulations from Spencer-Cervato [49], phytoplankton evolution that largely corroborates the one reconstructed from microfossils [53][54][55], suggesting that marine sediments faithfully record a Mesozoic revolution in phytoplankton composition. Neither do molecular clocks suggest long prehistories for these clades [56][57][58][59] . Unambiguous dinoflagellate microfossils first appear in upper Triassic rocks and the group radiated through the Jurassic, reaching a diversity maximum in Cretaceous oceans, and much the same is true of coccolithophorids [60]. ...
Article
Full-text available
Mesozoic and Early Cenozoic marine animals across multiple phyla record secular trends in morphology, environmental distribution, and inferred behaviour that are parsimoniously explained in terms of increased selection pressure from durophagous predators. Another systemic change in Mesozoic marine ecosystems, less widely appreciated than the first, may help to explain the observed animal record. Fossils, biomarker molecules, and molecular clocks indicate a major shift in phytoplankton composition, as mixotrophic dinoflagellates, coccolithophorids and, later, diatoms radiated across shelves. Models originally developed to probe the ecology and biogeography of modern phytoplankton enable us to evaluate the ecosystem consequences of these phytoplankton radiations. In particular, our models suggest that the radiation of mixotrophic dinoflagellates and the subsequent diversification of marine diatoms would have accelerated the transfer of primary production upward into larger size classes and higher trophic levels. Thus, phytoplankton evolution provides a mechanism capable of facilitating the observed evolutionary shift in Mesozoic marine animals. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
Article
Full-text available
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 early-branching 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.
Article
Occasionally (and fortunately), circumstances and timing combine to allow an individual, almost singlehandedly, to generate a paradigm shift in his or her chosen field of inquiry. William R. (Bill) Evitt (1923-2009) was such a person. During his career as a palaeontologist, Bill Evitt made lasting and profound contributions to the study of both dinoflagellates and trilobites. He had a distinguished, long and varied career, researching first trilobites and techniques in palaeontology before moving on to marine palynomorphs. Bill is undoubtedly best known for his work on dinoflagellates, especially their resting cysts. He worked at three major US universities and spent a highly significant period in the oil industry. Bill's early profound interest in the natural sciences was actively encouraged both by his parents and at school. His alma mater was Johns Hopkins University where, commencing in 1940, he studied chemistry and geology as an undergraduate. He quickly developed a strong vocation in the earth sciences, and became fascinated by the fossiliferous Lower Palaeozoic strata of the northwestern United States. Bill commenced a PhD project on silicified Middle Ordovician trilobites from Virginia in 1943. His doctoral research was interrupted by military service during World War II; Bill served as an aerial photograph interpreter in China in 1944 and 1945, and received the Bronze Star for his excellent work. Upon demobilisation from the US Army Air Force, he resumed work on his PhD and was given significant teaching duties at Johns Hopkins, which he thoroughly enjoyed. He accepted his first professional position, as an instructor in sedimentary geology, at the University of Rochester in late 1948. Here Bill supervised his first two graduate students, and shared a great cameraderie with a highly motivated student body which largely comprised World War II veterans. At Rochester, Bill continued his trilobite research, and was the editor of the Journal of Paleontology between 1953 and 1956. Seeking a new challenge, he joined the Carter Oil Company in Tulsa, Oklahoma, during 1956. This brought about an irrevocable realignment of his research interests from trilobites to marine palynology. He undertook basic research on aquatic palynomorphs in a very well-resourced laboratory under the direction of one of his most influential mentors, William S. Bill Hoffmeister. Bill Evitt visited the influential European palynologists Georges Deflandre and Alfred Eisenack during late 1959 and, while in Tulsa, first developed several groundbreaking hypotheses. He soon realised that the distinctive morphology of certain fossil dinoflagellates, notably the archaeopyle, meant that they represent the resting cyst stage of the life cycle. The archaeopyle clearly allows the excystment of the cell contents, and comprises one or more plate areas. Bill also concluded that spine-bearing palynomorphs, then called hystrichospheres, could be divided into two groups. The largely Palaeozoic spine-bearing palynomorphs are of uncertain biological affinity, and these were termed acritarchs. Moreover, he determined that unequivocal dinoflagellate cysts are all Mesozoic or younger, and that the fossil record of dinoflagellates is highly selective. Bill was always an academic at heart and he joined Stanford University in 1962, where he remained until retiring in 1988. Bill enjoyed getting back into teaching after his six years in industry. During his 26-year tenure at Stanford, Bill continued to revolutionise our understanding of dinoflagellate cysts. He produced many highly influential papers and two major textbooks. The highlights include defining the acritarchs and comprehensively documenting the archaeopyle, together with highly detailed work on the morphology of Nannoceratopsis and Palaeoperidinium pyrophorum using the scanning electron microscope. Bill supervised 11 graduate students while at Stanford University. He organised the Penrose Conference on Modern and Fossil Dinoflagellates in 1978, which was so successful that similar meetings have been held about every four years since that inaugural symposium. Bill also taught many short courses on dinoflagellate cysts aimed at the professional community. Unlike many eminent geologists, Bill actually retired from actively working in the earth sciences. His full retirement was in 1988; after this he worked on only a small number of dinoflagellate cyst projects, including an extensive paper on the genus Palaeoperidinium. © 2016 National Environment Research Council (NERC)-British Geological Survey (BGS).
Article
Full-text available
Among modern eukaryotic marine phytoplanktonic lineages possessing red algal plastids are the diatoms, dinoflagellates and haptophytes including coccolithophorids. Although origins of these host lineages and the timing of the endosymbioses leading to their ability to photosynthesize are ancient, their modern radiations are not. Molecular clocks suggest the timing of the origins and the radiations of these host lineages are different among the three groups. Dinoflagellates and haptophytes had class and order level radiations from 500 to 600 megaannum (Ma) and genus-level radiations, especially among the thecate dinoflagellates, about 250 Ma. Pigmented heterokonts, the last divergence in the heterokont tree, originated between 770 and 1000 Ma, but most planktonic unicellular groups diverged at the Permian-Triassic (P/T) boundary (250 Ma) and radiated thereafter based on a clock constrained by both fossil first appearances and biochemical evidence. Recent molecular evidence suggests that heterokont and haptophyte protistan host cells originally possessed both green and red algal plastids with endosymbiosis of the green plastid older than the red one. If one assumes that once the green algal plastid was eliminated, the red algal plastid lineages could then proliferate, then my clocks suggest that this event likely occurred at the P/T extinction. The possession of the red plastid only became advantageous at the P/T extinction when oceanic chemistry changes provided a habitat in which red algal plastids were better adapted and could out-compete green algal plastids. Prior to the P/T, red algal lineages were not dominant as judged by the fossil record, and there is an absence of a dominant green plastid lineage in the modern plankton. Therefore, expulsion of the green algal plastid in favour of a red algal plastid and divergence and subsequent radiation of the planktonic heterokont algae and major orders/families/genera in the haptophytes and the dinoflagellates were likely forced by the Permian-Triassic extinction event.
Article
Full-text available
Arpylorus antiquus, erected by Calandra in 1964, was isolated from upper Silurian sedimentary rocks from the Mechiguig 1 borehole in southern Tunisia, with other palynomorphs. The folded vesicle and the quadrangular form of the aperture break down into platelike fragments, resembling the tabulation of dinoflagellates. The presence of these elements has been used to interpret A. antiquus as a dinoflagellate cyst. The morphology and affinity of A. antiquus is reinterpreted herein based on investigation of larger sets of samples, including material from the type locality, together with material of Algeria, Saudi Arabia, and Brazil. More complete specimens than those previously described have been observed using gentle laboratory techniques, showing a large development of a fine membrane at the periphery of vesicles. This element was destroyed using classical palynological treatments, implying that the holotype is an incomplete specimen. The membrane at the periphery of vesicles and dorsoventral differentiation of these vesicles suggest that A. antiquus is a part of a more complex biological structure. We suggest a possible relationship with eurypterids, arthropods related to phyllocarids, represented by abundant fragments in the assemblages. Arpylorus antiquus is possibly a structure of storage. The chemical composition of A. antiquus using a Fourier transform infrared FTIR microspectroscopy analysis, reveals a wall composed of biopolymer that is not consistent with dinosporin. We conclude that Arpylorus antiquus is definitively not a dinoflagellate cyst. Although dinoflagellates may have older Paleozoic or even Proterozoic ancestors as the biomarker record may suggest, the dinoflagellate tabulation evolved only in the early Mesozoic.
Article
The dinoflagellates are a large, richly diverse group of protists with marine and freshwater representatives, photosynthetic and heterotrophic nutritional modes, toxic and non-toxic isolates and some species that form resting cysts that can be found in the fossil record dating back to the Triassic or perhaps earlier. Traditional classification and phylogeny of the dinoflagellates has been based largely on the structure of their cell wall or amphiesma. More recently, however, a number of molecular phylogenies have emerged that challenge the more traditional perspectives. A review of these molecular results is presented with comparative reference to the long-standing traditional views.
Article
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.
Article
We have sequenced small-subunit (SSU) ribosomal RNA (rRNA) genes from 16 dinoflagellates, produced phylogenetic trees of the group containing 105 taxa, and combined small- and partial large-subunit (LSU) rRNA data to produce new phylogenetic trees. We compare phylogenetic trees based on dinoflagellate rRNA and protein genes with established hypotheses of dinoflagellate evolution based on morphological data. Protein-gene trees have too few species for meaningful in-group phylogenetic analyses, but provide important insights on the phylogenetic position of dinoflagellates as a whole, on the identity of their close relatives, and on specific questions of evolutionary history. Phylogenetic trees obtained from dinoflagellate SSU rRNA genes are generally poorly resolved, but include by far the most species and some well-supported clades. Combined analyses of SSU and LSU somewhat improve support for several nodes, but are still weakly resolved. All analyses agree on the placement of dinoflagellates with ciliates and apicomplexans (=Sporozoa) in a well-supported clade, the alveolates. The closest relatives to dinokaryotic dinoflagellates appear to be apicomplexans, Perkinsus, Parvilucifera, syndinians and Oxyrrhis. The position of Noctiluca scintillans is unstable, while Blastodiniales as currently circumscribed seems polyphyletic. The same is true for Gymnodiniales: all phylogenetic trees examined (SSU and LSU-based) suggest that thecal plates have been lost repeatedly during dinoflagellate evolution. It is unclear whether any gymnodinialean clades originated before the theca. Peridiniales appear to be a paraphyletic group from which other dinoflagellate orders like Prorocentrales, Dinophysiales, most Gymnodiniales, and possibly also Gonyaulacales originated. Dinophysiales and Suessiales are strongly supported holophyletic groups, as is Gonyaulacales, although with more modest support. Prorocentrales is a monophyletic group only in some LSU-based trees. Within Gonyaulacales, molecular data broadly agree with classificatory schemes based on morphology. Implications of this taxonomic scheme for the evolution of selected dinoflagellate features (the nucleus, mitosis, flagella and photosynthesis) are discussed.
Article
Scanning electron microscope studies of specimens of Nannoceratopsis senex and N. gracilis from the Tmetoceras scissum zone (Lower Bajocian) of England permit us to establish for the first time an unmistakable paratabulation and the presence of a unique archeopyle type. The paratabulation formula for both species is ?pr, 5 ‘, 5 “, 4c, 4s, 4H; and the archeopyle is formed by the loss of the third cingular paraplate. Nannoceratopsis is shown to be remarkable in combining features heretofore considered diagnostic of two distinct groups of dinoflagellates, the Peridiniales and Dinophysiales, and suggests that the evolutionary linkage between them is not so remote as generally had been thought.
Article
New data from numerous detailed mass-spectrometric studies have detected triaromatic dinosteroids in Precambrian to Cenozoic rock samples. Triaromatic dinosteroids are organic geochemicals derived from dinosterols, compounds known in modern organisms to be the nearly exclusive widely occurring products of dinoflagellates. We observed the ubiquitous occurrence of these dinosteroids in 49 Late Triassic through Cretaceous marine source rocks and the absence of them in 13 Permian-Carboniferous source rocks synergistic with the dinoflagellate cyst record. However, finding dinosteroids in lower Paleozoic and Precambrian strata presents challenging results for molecular paleontologists, evolutionary biologists, palynologists, and especially for those concerned with the food web at various times of biological crisis. Other than the few species known as parasites and symbionts, many other dinoflagellate species are important as primary producers. The presence of Precambrian to Devonian triaromatic dinosteroids gives chemostratigraphic evidence of dinoflagellates (or other organisms with similar chemosynthetic capabilities) in rocks significantly older than the oldest undisputed dinoflagellate fossils (dinoflagellate cysts from the Middle Triassic, ˜ 240 Ma), and older than the putative Silurian ˜ 420 Ma) dinocyst,Arpylorus antiquus (Calandra) Sargent, from Tunisia. This systematic chemostratigraphic approach can shed light not only on lineages of dinoflagellates and their precursors, but potentially on many other lineages, especially bacteria, algae, plants, and possibly some metazoans.