Benton M.J. Introduction to paleobiology and the fossil record

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198 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

scopic acritarchs, marine plant-like organisms

(see p. 216) that are known from rocks dated

1.45 Ga.

Eukaryotes may be identiﬁ ed by their

nuclei, and paleontologists have hoped to ﬁ nd

such clinching evidence in the fossils. For a

time, many believed that nuclei had been

identiﬁ ed in the diverse eukaryotes from the

much younger Bitter Springs Cherts of central

Australia, dated at about 800 Ma. Some cells

show apparent nuclei (Fig. 8.11b), but the

dark areas probably only represent condensa-

tions of the cell contents. The Bitter Springs

fossils also show evidence of cell division, but

what kind of cell division?

Normal cell divisions in growth are called

mitosis, where all the cell contents, including

the DNA, are shared. Mitosis is seen in asexual

and sexual organisms. The globular Gleno-

botrydion from the Bitter Springs Chert shows

cells in different stages of mitotic division

(Fig. 8.11b), where one cell divides into two,

and then the two divide into four. Eotetrahe-

drion (Fig. 8.11c), once described as a repro-

ducing eukaryote, is now interpreted as a

cluster of cyanobacteria. Other fossils include

Era Ma Major events/radiations

secondary

endosymbiosis

primary endosymbiosis

3500 Earliest Archaean eubacterial fossil

Neo

Proterozoic

Meso

Paleo

Cenozoic

Mesozoic

Paleozoic

1200

900

542

251

1600

Opisthokonta (animals, fungi)

Glaucophytes

Chlorophytes

Charophytes

Bryophytes

Forns

Gymnosperms

Angiosperms

Haptophytes

Stramenopiles

Cryptophytes

Floridophycidae

Red algae

Red algae (Cyanidiales)

Figure 8.10 Diagram showing the evolutionary relationships and divergence times for the red,

green, glaucophyte and chromist algae. These photosynthetic groups are compared with the

Opisthokonta, the clade containing animals and fungi. The tree also shows two endosymbiotic

events. Some time before 1.5 Ga, the ﬁ rst such event took place, when a photosynthesizing

cyanobacterium (CB) was engulfed by a eukyarote. The second endosymbiotic event involved the

acquisition of a plastid about 1.3 Ga. Plastids in plants store food and may give plants color

(chloroplasts are green). (Courtesy of Hwan Su Yoon.)

THE ORIGIN OF LIFE 199

branched ﬁ laments that look like modern

siphonalean green algae (Fig. 8.11d).

Older fossils too look like algae. For

example, in the Lakhanda Group of eastern

Siberia, 1000–950 Ma, ﬁ ve or six metaphyte

species have been found (Fig. 8.12), as well as

a colonial form that forms networks rather

like a slime mold. But the key fossil in under-

standing early eukaryote evolution is Bangio-

morpha (Box 8.3).

Multicellularity and sex

As eukaryotes ourselves, multicellularity and

sex seem obvious. Prokaryotes are single-

celled organisms, although some form ﬁ la-

ments and loose “colonial” aggregations.

True multicellular organisms arose only

among the eukaryotes. These are plants and

animals that are composed of more than one

cell, typically a long string of connected cells

in early forms. Multicellularity had several

important consequences, one of which was

that it allowed plants and animals to become

large (some giant seaweeds or kelp, forms of

algae, reach lengths of tens of meters). Another

consequence of multicellularity was that cells

(a)

(b)

(c)

(d)

Nucleus

(n)

New cell wall

Spore tetrads

Branched tubular

filament

Septum

Figure 8.11 Early fossil “eukaryotes”. (a) The thread-like Grypania meeki, preserved as a

carbonaceous ﬁ lm, from the Greyson Shale, Montana (c. 1.3 Ga). (b, c) Single-celled eukaryotes from

the Bitter Springs Chert, Australia (c. 800 Ma): (b) Glenobotrydion showing possible mitosis (cell

division in growth), and (c) Eotetrahedrion, probably a cluster of individual Chroococcus-like

cyanobacteria. (d) Branching siphonalean-like ﬁ lament. Scale bars: 2 mm (a), 10 μm (b–d). (Courtesy of

Martin Brasier, based on various sources.)

Figure 8.12 A ﬁ lamentous alga from the

Lakhanda Group, Siberia (c. 1000 Ma), 400 μm

wide. (Courtesy of Andy Knoll.)

200 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

could specialize within an organism, some

being adapted for feeding, others for repro-

duction, defense or communication.

But it seems that multicellularity required

sex as well. The ﬁ rst organisms almost cer-

tainly reproduced asexually, that is, their cells

divided and split. Asexual reproduction, or

budding as it is sometimes called, is really just

a form of growth: cells feed and grow in size,

and when they are big enough they split by

mitosis to form two organisms. The DNA

splits at the same time and is shared by the

two new cells. Sexual reproduction, on the

other hand, involves the exchange of gametes

(sperms and eggs) between organisms. Typi-

cally, the male provides sperm that fertilize

the egg from the female. Gametes have half

the normal DNA complement, and the two

half DNA sets zip together to produce a dif-

ferent genome in the offspring, but clearly

sharing features of father and mother. In

eukaryotes, the DNA exists as two copies,

each strand forming one half of the double-

helix structure. Cell divisions in sexual repro-

duction are called meiosis, where the DNA

unzips to form two single copies, one going

into each gamete, prior to fusion after

fertilization.

Box 8.3 Bangiomorpha: origin of multicellularity and sex

Red algae (rhodophytes) today range from single cells to large ornate plants, and they may be toler-

ant of a wide variety of conditions. The modern red alga Bangia, for example, can survive in a full

range of salinities, from the sea to freshwater lakes. The oldest fossil red alga was announced in

1990, and described in detail by Nick Butterﬁ eld from the University of Cambridge in 2000. The

specimens are preserved in siliciﬁ ed shallow marine carbonates of the Hunting Formation, eastern

Canada, dated at 1.2 Ga, together with a variety of other fossils, both prokaryote and eukaryote.

In his 2000 paper, Butterﬁ eld quippishly named the new form Bangiomorpha pubescens, the

species name pubescens chosen “with reference to its pubescent or hairlike form, as well as the con-

notations of having achieved sexual maturity”. The name Bangiomorpha pubescens has even made

it into the dictionaries of bizarre and cheeky names; one web site notes “The fossil shows the ﬁ rst

recorded sex act, 1.2 billion years ago. The ‘bang’ in the name was intended as a euphemism for

sex.” The fossils do not show sex acts, and the commentators surely exaggerate: Nick Butterﬁ eld

may be based at the University of Cambridge in England, home of smutty humor since medieval

times (if not before), but he is Canadian by birth!

Bangiomorpha grew in tufts of whiskery strands attached to shoreline rocks by holdfast structures

made from several cells (Fig. 8.13a). The individual ﬁ laments are up to 2 mm long, and the cells are

less than 50 μm wide. The cell walls are dark and enclose circular to disk-like cells, and the whole

plant is enclosed in a further thick external layer. The individual ﬁ laments may be composed of a

single series of cells, or of several series running side by side, or a combination of the two (Fig.

8.13b). Multiple-series ﬁ laments are composed of sets of wedge-shaped cells that radiate from the

midline of the strand, a diagnostic feature of the modern Bangia and of all so-called bangiacean red

algae.

Many dozens of specimens of Bangiomorpha have been found, and these show how the ﬁ laments

developed. Starting with a single cell, the ﬁ lament grew by division of cells (mitosis) along the ﬁ la-

ment axis. One cell divided into two, then two into four, and so on. Along the ﬁ laments (Fig. 8.13b),

disk-shaped cells occur in clusters of two, four or eight, and these reﬂ ect further cell divisions within

the ﬁ lament. Some broader ﬁ laments show clusters of spherical, spore-like structures at the top end;

if correctly identiﬁ ed, these prove that sexual reproduction and meiosis were taking place. Close

study of the ﬁ laments, and of series of developmental stages, shows that Bangiomorpha was not

only multicellular but that it showed differentiation of cells (holdfast cells versus ﬁ lament cells),

multiple cycles of cell division, differentiated spores and sexually differentiated whole plants.

Read more about Bangiomorpha in Butterﬁ eld’s (2000) paper and at http://www.

blackwellpublishing.com/paleobiology/.

THE ORIGIN OF LIFE 201

Whereas some of the Bitter Springs Chert

fossils were once supposed to show meiotic

cell division, and so sex, this is now doubted.

Must paleontologists ﬁ nd fossils of early

eukaryotes actually engaged in sexual repro-

duction in order to prove the origin of sex?

The answer is no, and a phylogenetic argu-

ment is enough. If we know that all species in

a modern clade show sexual reproduction,

then their ancestors probably did too. Many

modern algae show sexual reproduction, and

the oldest member of a sexually reproducing

group is a 1.2 Ga red alga (see p. 200), so that

provides a minimum date for the origin of

sex.

One of the oldest multicellular organisms is

Bangiomorpha (Box 8.3), obviously multicel-

lular and a member of a modern group that

engages in sex. Multicellularity allowed many

new forms to appear. The term “algae” refers

to a paraphyletic assortment of single-celled

and multicelled organisms, all of them eukary-

otes, and most of them photosynthetic. The

major groups are distinguished by their color,

morphology and biochemical properties.

Molecular phylogenies (see Fig. 8.4) show

that many lines of eukaryotes have tradition-

ally been termed “algae”. Several algal groups

now seem to be closely related to true plants

(see p. 483). The fossil record of algae is patchy,

but exceptions are the biostratigraphically

useful dinoﬂ agellates, coccoliths and diatoms,

and calcareous algae such as dasycladaceans,

charophytes and corallines (see p. 221).

Why have sex? Budding seems to be efﬁ -

cient enough, and it is what Bacteria, Archaea

and many simple eukaryotes have always

done, and continue to do today. The beneﬁ ts

are that the process is quick and efﬁ cient:

what could be better for a successful organism

than to replicate identical clones of itself? Sex,

on the other hand, is a messy and complex

business. Many simple organisms, and even

ﬁ shes and amphibians, produce vast numbers

of eggs, sometimes millions that are shed into

the water, where most are wasted. Sperm of

course is also produced in vast quantities, and

most goes to waste. Nonetheless, the inven-

tion of sex is usually seen as one of the great

milestones in biological evolution (see p. 546).

(a)

(b)

25 μm

250 μm

Figure 8.13 The oldest multicellular eukaryote, Bangiomorpha, from the 1.2 Ga Hunting

Formation of Canada. (a) A colony of whiskery ﬁ laments growing from holdfasts attached to a

limestone base. (b) A single ﬁ lament showing a single-series ﬁ lament making a transition to

multiple series, with sets of four wedge-shaped cells; note the sets of four disk-shaped cells in the

single-series part of the strand. (Courtesy of Nick Butterﬁ eld.)

202 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

The reason for its origin may be obscure, but

its consequences are manifest. Sex allows

rapid evolution and diversiﬁ cation of species

because genetic material is swapped and

changes during each reproductive cycle.

Sexual organisms vary more than asexual

organisms, and they can adapt and specialize

more readily. Finally, sexual organisms can be

multicellular.

The Late Neoproterozoic

The last 100 myr of the Proterozoic, the

Late Neoproterozoic, is marked by a dra-

matic increase in fossil diversity. Sexual repro-

duction and multicellularity opened the door

for more complex, and larger, organisms.

Algal groups, including relatives of plants,

appeared. In addition, multicellular animals

or metazoans, also appeared later in the

Proterozoic, and these included the complex

Ediacaran animals.

Review questions

1 Find out how many distinct creation myths

you can track down on the internet.

Arrange them in a classiﬁ cation that links

major features of the myths, and match

them to their appropriate religions and

time span of general acceptability.

2 Many claims have been made over the

years about the oldest fossils of life. Look

back through the literature to ﬁ nd what

was the oldest acceptable record in 1960,

1970, 1980, 1990 and 2000. Read about

why many of these claimed oldest ﬁ nds

were eventually doubted or rejected, and

list the reasons why.

3 Read around the debate about the univer-

sal tree of life, and consider whether it will

ever be possible to determine which

branched ﬁ rst – Archaea, Bacteria or

Eucarya – and give reasons why some ana-

lysts believe that this will never be

resolved.

4 What are the advantages and disadvan-

tages of sex and of multicellularity?

Catalog as many arguments as you can

ﬁ nd for and against each of these biologi-

cal attributes, and describe the possible

world today if sex and multicellularity

had never arisen.

5 Why are fossils so rare in the

Precambrian?

Further reading

Butterﬁ eld, N.J. 2000. Bangiomorpha pubescens n.

gen., n. sp.: implications for the evolution of sex,

multicellularity, and the Mesoproterozoic/

Neoproterozoic radiation of eukaryotes. Paleobiol-

ogy 26, 386–404.

Cavalier-Smith, T., Brasier, M. & Embley, T.M. (eds)

2006. How and when did microbes change the

world? Philosophical Transactions of the Royal

Society B 361, 845–1083.

Cracraft, J. & Donoghue, M.J. (eds) 2004. Assembling

the Tree of Life. Oxford University Press, Oxford,

UK.

Hazen, R. 2005. Genesis: The Scientiﬁ c Quest for Life’s

Origin. Joseph Henry Press, Washington. http://

darwin.nap.edu/books/0309094321/html/.

Knoll, A.H. 1992. The early evolution of eukaryotes: a

geological perspective. Science 256, 622–7.

Knoll, A.H. 2003. Life on a Young Planet: The First

Three Billion Years of Evolution on Earth. Princeton

University Press, Princeton, NJ.

Tudge, C.T. 2000. The Variety of Life. Oxford Univer

sity Press, Oxford, UK.

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Chapter 9

Protists

Key points

• Micropaleontology is a multidisciplinary science, focused on the study of microorgan-

isms or the microscopic parts of larger organisms.

• Prokaryotes, unicellular microbes lacking nuclei and organelles, include the carbonate-

producing cyanobacteria, the oldest known organisms; their radiation during the mid-

Precambrian promoted an oxygen-rich atmosphere.

• Protists, unicellular organisms with nuclei, include a large variety of organisms with

external protective coverings (tests and cysts) assigned to the kingdoms Protozoa and

Chromista.

• Fossilized protists can also be split into organisms with organic (acritarchs, dinoﬂ agel-

lates, chitinozoans), calcareous (coccolithophores, foraminiferans) or siliceous (diatoms,

radiolarians) skeletons.

• Foraminifera, single-celled animal-like protozoans, contain both benthic and planktonic

forms with chitinous, agglutinated, but most commonly calcareous (hyaline and porcel-

laneous), tests occurring throughout the Phanerozoic.

• Radiolarians, animal-like protozoans with siliceous tests, and diatoms, plant-like pro-

tozoans with silicic skeletons, are both important rock formers.

• Acritarchs, dinoﬂ agellates and chitinozoans are palynomorphs, most commonly pre-

served as cysts, with important biostratigraphic applications. The ﬁ rst two are assigned

to the protozoans, the third is currently difﬁ cult to classify.

• Coccolithophores and diatoms are assigned to the chromistans.

It has long been an axiom of mine that the little things are inﬁ nitely the more

important.

Arthur Conan Doyle (1891) A Case of Identity

PROTISTS 205

The world of microbes is more bizarre than

the most contrived science ﬁ ction novel. The

Earth is host to creatures that ingest iron and

uranium, thrive in environments akin to

boiling sulfuric acid or even live within solid

rock itself (Box 9.1). These amazing organ-

isms have a huge variety of shapes, belong to

a multitude of groups living in many different

environments while pursuing a wide range of

lifestyles with often apparently alien metabo-

lisms. Microbes such as bacteria and viruses

are by far the most abundant life forms on the

planet, a situation undoubtedly true of the

geological past. Microfossils are the micro-

scopic remains, commonly less than a milli-

meter in size, of either microorganisms or

the disarticulated or reproductive parts of

larger organisms. They thus include not only

microbes themselves but also the microscopic

parts of animals and plants.

In his famous book Small is Beautiful,

Schumacher argued for small-scale economics

in the world. Among paleontologists, micro-

paleontologists are obsessed with microscopic

fossils. Until you have screwed up your eyes

and peered down a binocular microscope, you

can have no idea of the exquisite beauty of

microfossils, their tiny shapes showing inﬁ nite

detail in their sculpture, spines and plate

patterns. And they are not only beautiful,

but useful too! Micropaleontology has thus

attracted the attentions of botanists, zoolo-

gists, biochemists and microbiologists together

with, of course, paleontologists and geolo-

gists. The disparate taxonomic groups included

as microfossils are, nonetheless, united by

their method of study – all require the use of

an optical microscope, although more recently

both scanning and transmission electron

microscopes have taken microfossil studies to

new, amazing levels. The majority of micro-

fossils are indeed small and perfectly formed;

but they display often the most complex and

intricate of organic morphologies.

Microfossils thus include material derived

from most of the major groups of life, Bacte-

ria, Protozoa, Chromista, Fungi, Plants and

Animals, although Fungi are rarely found as

fossils. The broad classiﬁ cation adopted by

most textbooks is both conventional and

operational: microfossils are usually divided

into the prokaryotes (mainly bacteria), pro-

Box 9.1 Microbes in extreme environments: the extremophiles

We are aware that microbes are everywhere, but are they as widespread as we believe? Yes, and

probably more so. Scientists have been investigating a range of microbes, the extremophiles (“lovers

of extremes”), that appear to be adapted, with speciﬁ c enzymes, to some of the most extreme envi-

ronments on Earth. Thus acidophiles (acid environments), alkaliphiles (alkaline environments),

barophiles (high pressure), halophiles (saline environments), mesophiles (moderate temperatures),

thermophiles (high temperatures), psychroﬁ les (cool temperatures) and xerophiles (arid environ-

ments) have now been identiﬁ ed. Extremophiles are spread across both the prokaryotes and eukary-

otes, although most belong to the Archaea and Bacteria and some scientists have argued they should

be included in a separate domain on the basis of their unique metabolic processes. Thus if modern

microbes can function in both frozen and geothermal habitats, both acid and alkaline ponds and

even deep within the crust, the extreme environments of the Early Precambrian and perhaps even

space were probably not a great challenge to evolving life of this type. Moreover such groups of

organisms could clearly survive the extreme environments of great extinction events. But it remains

a challenge to identify such groups in the fossil record. One group of ingenious algae, the acritarchs

(see p. 216), made it through one of the most extreme series of ice ages our planet has experienced.

The “snowball Earth” hypothesis (see p. 112) suggests that the planet’s oceans froze over during the

Late Proterozoic, with life coming to a virtual standstill. Acritarch diversity was maintained through

the crises (Corsetti et al. 2006). Have we identiﬁ ed a group of extremophiles, or was the climate not

so harsh as suggested by the snowball Earth hypothesis?

206 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

tists (unicellular eukaryote organisms with a

variety of tests (external shells) and cysts

(enclosed resting stages)), microinvertebrates

(mainly the ostracodes, see p. 383), microver-

tebrates (mainly the conodonts and various

other microscopic parts of ﬁ shes, see p. 441)

and spores and pollen (microscopic reproduc-

tive organs of plants, see p. 493). We devote

this chapter, however, to the more advanced

microbes themselves, represented by the

second group. The protists are most probably

derived from within the Archaea, splitting

from them between 4.2 to 3.5 Ga, but the

group is almost certainly polyphyletic. The

prokaryotic Archaea and Bacteria are inti-

mately tied to the origin of life and the limited

Precambrian fossil record (see pp. 191–4);

this is all the evidence of life in rocks over 1

billion years old!

The abundance and durability of many

microfossil groups makes them invaluable

for biostratigraphic correlation (see p. 25).

Sequences of samples can be collected from

rock outcrops and even from the very small

samples available from drill cores and drilling

muds. Consequently they are very widely used

in geological exploration by petroleum and

mining companies. In addition, many micro-

fossils are produced by planktonic organisms

with very wide biogeographic distributions,

making them invaluable for reliable long-dis-

tance correlation. Microfossils in oceanic

sediments also provide a continuous record of

environmental change and paleoclimate, and

study of changing assemblages and the geo-

chemistry of microfossil shells provide the

fundamental data for paleoceanographic

research. Moreover, consistent color changes

through thermal gradients have made micro-

fossils, particularly conodonts and palyno-

morphs, invaluable for assessments of thermal

maturation and the prediction of hydrocar-

bon windows.

Microorganisms have made a phenomenal

contribution to the evolution of the planet as

a whole. Many, such as the coccolithophores,

diatoms, foraminiferans and radiolarians, are

rock-forming organisms. The prokaryotic

cyanobacteria fundamentally changed the

planet’s atmosphere from anoxic to aerobic

during the Precambrian, and probably contin-

ued to mediate atmospheric and hydrosphere

systems. For example, recent research sug-

gests that carbonate mudmounds – such as

the Late Ordovician mudbanks in central

Ireland, the north of England and Sweden, the

Early Carboniferous Waulsortian mounds in

Ireland and elsewhere, together with the Early

Cretaceous mudmounds in the Urgonian lime-

stones of the Alpine belt – were precipitated

by microbes. The inﬂ uence of microorganisms

may also be more subtle. Coccolith-producing

organisms, for example Emiliania, can, during

blooms, manufacture massive amounts of

calcium carbonate; this material is much more

readily subducted than shelf carbonates and

it is then recycled through volcanoes as carbon

dioxide (CO

). The buildup of this greenhouse

gas probably maintained warmer climates

during the last 200 million years.

The extraction and retrieval of microfossils

from rocks and sediments requires a range of

preparation techniques, some of which can

only be attempted in purpose-built laborato-

ries. For many groups, preparation consists

essentially of disaggregation of the rock in

water or more potent solvents followed by

sieving to remove the clay fraction. The silt-

and sand-sized residue is then hand picked

under a microscope to collect microfossils

such as foraminiferans and ostracods. For

other groups such as radiolarians, diatoms

and conodonts, acetic or hydrochloric acid is

used to remove the carbonate fraction and

concentrate the fossils. For palynomorphs,

the silicate minerals are removed with hydro-

ﬂ uoric acid, an extremely dangerous chemical

that requires special facilities. Finally, micro-

fossils may be concentrated by settling in

heavy liquids or by electromagnetic separa-

tion. Many groups, such as algae and forami-

niferans, may also be studied in thin section.

PROTISTA: INTRODUCTION

The protists are predominantly single-celled

organisms with nuclei and organelles, includ-

ing both autotrophs, organisms that convert

inorganic matter such as CO

and water into

food, and heterotrophs, organisms that eat

organic debris or other organisms. The Pro-

tista is a convenient grouping but it is not well

deﬁ ned. Essentially it consists of all eukary-

otes once the multicellular animals, fungi and

vascular plants are removed. Consequently it

is a paraphyletic collection of rather disparate

organisms. Most are microscopic and unicel-

lular but multicellularity has evolved numer-

ous times and the multicellular algae (seaweeds)

are conventionally included in the Protista too

PROTISTS 207

(Fig. 9.1). Subdividing the diversity of protists

is equally problematic. The division into auto-

trophic protozoans and heterotrophic algae

(chromistans) is important ecologically, but

phylogenetically almost meaningless as both

groups are polyphyletic. The ﬁ rst protists

were almost certainly heterotrophs, but chlo-

roplasts were acquired separately in at least

six lineages, producing heterotrophs, and lost

secondarily even more often: for example, the

classic protozoan ciliates almost certainly

evolved from algae. Protists are also often

subdivided according to their means of loco-

motion, most simply into ﬂ agellates and

amoebans. Again, however, these are poly-

phyletic groups. So simplisitic attempts at

classifying protists do not really work and

they are perhaps better regarded as a loose

grouping of 30 or 40 disparate phyla with

diverse combinations of trophic modes, mech-

anisms of motility, cell coverings and life

cycles. Modern molecular genetic and cyto-

logic research is slowly making sense of this

diversity but this is not the place to go into

the rapidly changing details of this research.

Instead, we should simply note that groups

with microfossil records are widely scattered

across the diversity of protists. Here, follow-

ing Cavalier-Smith (2002) and others, the

protists are grouped into protozoans (forami-

niferans, radiolarians, acritarchs, dinoﬂ agel-

lates and ciliophorans) and chromistans

(coccolithophores and diatoms); chitinozoans

are difﬁ cult to classify in this scheme and are

thus treated separately.

EUKARYOTES ARRIVE CENTER STAGE

So when did the eukaryotes ﬁ rst appear? Uni-

cellular eukaryotes, with nuclei and organelles,

represented by acritarch cysts are known from

rocks dated at about 1.45 Ga. Spiral ribbons

of Grypania, however, have been reported

from rocks as old as 1.85 Ga. One of the oldest

multicellular organisms is a bangiophyte red

alga (rhodophyte) preserved in siliciﬁ ed car-

Chromalveolates

Alveolates

Plantae

Cercozoa +

Opisthokonts

Excavates

Cercozoa

Filosa

Foraminifera

Radiolaria

Haplosporidia

Phytomyxids

Hellozoa

Apusozoa

Chlorophytes

Charophytes

Red Algae

Glaucophytes

Piants

Oxyrrhis

Perkinsus

Brown Algas

Diatoms

Oomycetes

Bicosoecide

Opalinida

Haptophytos

Cryptomonads

Chromists

Dinoflageflates

Aplcomplexa

Colpoderllds

Cillates

Heteroloboses

Euglonids

Discicristates

Dipionemids

Kinetoplastlds

Core Jakobids

Carpediemonas

Diplomonads

Retortamonads

Trichomonads

Hypermastigotes

Tr imastix

Oxymonads

Choanoroa

Amoebozoa

Fungi

Microsporidia

Animals

Nuclcarids

Choanoflagelates

Ichthyospores

Archamoebae

Slime Moulds

Lobosee

Figure 9.1 Protist positions on the tree of life. In this tree, developed by Patrick Keeling, University of

British Columbia, the protozoans (foraminiferans and radiolarians) lie within the Cercozoa far divorced

from the chromists (diatoms and dinoﬂ agellates) within the Chromalveolates. (From Keeling et al.

2005.)