timescale. The fossil record of visible plants and animals
the Cambrian Era, nominally dated to around 540 Ma[FOOTNOTE:
the actual beginning of the Cambrian Era is determined by
Subcommission on Cambrian Stratigraphy. In
1991 they set the Cambrian boundary at the first
appearance of fossil burrows known as Trichophycus pedum, that
were obviously made by
a complex animal, probably an arthropod, dated to 590 Ma. Since that
time the date has been moved to a later time; it is still under
discussion. See the lecture, David C.
Bossard Abundant Life].
In the time between the creation of the first life (around 3,900
Ma) and the
visible, multicellular life in the Cambrian Era, a
principle task of life as it then
existed was to fill
the globe with organic nutrients in preparation for the future creation
of complex life (another task was to create an oxygen atmosphere).
These organic nutrients include, in particular, abundant
amounts of fixed nitrogen, an essential component of dna and virtually
every other molecule that participates in the central dogma of life --
the nucleotides of rna and dna, and the proteins' backbone amino acids[FOOTNOTE:
By definition all amino
acids include a nitrogen-containing amino group NH2].
Fixed nitrogen was scarce throughout the
first few billion years of Earth's existence, and had to be
manufactured from atmospheric nitrogen gas by the difficult, slow,
process of nitrogen fixing. Nitrogen fixing is done by bacteria that
specialize in that one task. They first make the complex nitrogenase
molecule, and then concentrate on the single task of fixing nitrogen
one molecule at a time -- a process that takes about 1.2 seconds per
nitrogen atom. This task is
so all-demanding that the nitrogen-fixing cells require food and energy
(in the form of ATP) provided by other cells: most nitrogen-fixing
bacteria cannot live independent lives.
The more complex the life form, the
less it can afford to take the time or energy to create its own food.
Thus there has to be readily available organic food -- amino
acids, nucleotides, sugars, etc. -- so that the complex species could
concentrate their energies on more advanced tasks[FOOTNOTE:
Until the recent manufacture of inorganic ammonia by the Haber process, the only
significant source of fixed nitrogen was organic food. Small amounts of
inorganic nitrogen are produced by lightning, but this is transitory
and not reliable. It is difficult to estimate the amount produced in
ancient times, but over the past billion years or so, the percentage of
fixed nitrogen produced by inorganic means is estimated to be under
??%??CHECK??]. This filling of the
earth took a long time, and this is the primary reason why the first
appearance of visible plants and animals in the Cambrian explosion
around 540 Ma
was over three billion years after the first living cell appeared on
The first plants and animals lived in water. They fed on dissolved
nutrients, microbes, colonies of algae and plankton, and of course on
other small plants and animals. Plants are often called "autotrophic"
meaning their principal food is inorganic, but that is a misnomer,
because all plants have to
get fixed nitrogen from organic sources (legumes get fixed nitrogen
from symbiotic nitrogen-fixing bacteria attached to their roots). Even
nitrogen-fixing bacteria must depend on other bacteria to supply
True multi-cellular species arose somewhere
between 1000 Ma
and 550 Ma.
At the beginning they had no skeletons or other hard parts, so the
are limited to burrows of worm-like animals, compressed impressions or
mats of plants, and other indirect evidence. One exception to this rule
is the rare appearance of soft-body fossils in the Burgess Shale and
Cheng-Jiang Cambrian sites, which were preserved under oxygen-free
All plants and animals at
this stage lived in the oceans. The dry land was kept relatively
sterile at this time because of the high-energy "hard" cosmic and solar
rays. The first colonizers of dry land (400-450 Ma) were bacteria which
could hide from direct sunlight -- in soils or under rocks.
Animal fossils appear suddenly in the Cambrian Era, nominally 542 to
500 Ma with the nearly-simultaneous appearance of most if not all of
the known animal body plans (phyla). With time, some early phyla
disappear, but no new animal phylum arises after the Cambrian era, with
the possible exception of Bryozoa
= "moss animals" which first appear in the fossil record in the early
Ordovician Era, about 480 Ma -- but possibly soft-bodied bryozoa may
have existed in the Cambrian Era. Plant phyla have a more variable
fossil record, many appearing much later, because of the problem of
of the first and most complex animals to appear is the trilobite, an
(joint-footed appendages), which by any reckoning must be viewed as a
complex and morphologically advanced creature. This very complexity and
appearance suggests that the true origin was earlier than the fossil
record indicates[FOOTNOTE: Some paleobiologists argue
that the real innovation in the Cambrian era was hard skeletal parts
which the fossil record preserves; prior to this innovation, the same
species existed in soft bodies that were not preserved. Until positive
evidence arises to support this (such as soft-bodied trilobites) this
seems to be a case of special pleading in the absence of evidence.
Regarding this, the Cambrian
Factsheet (Discovery Institute) remarks: "Some scientists have
suggested that fossil ancestors for the animal phyla are missing not
because the rocks have been deformed or eroded, but because animals
before the Cambrian lacked hard parts, and thus never fossilized in the
first place. According to this hypothesis, the Cambrian explosion
merely represents the sudden appearance of shells and skeletons in
animals that had evolved long before. The fossil evidence, however,
does not support this hypothesis.].
Coral reefs also appear at this time, the by-product of early
soft-bodied cnidarians who secrete calcium that forms a hard habitat in
which the coral individuals dwell (somewhat like the much earlier
stromatolyte-forming cyanobacteria). Since the cnidarians are basically
soft-bodied, it is not difficult to imagine that the coral ancestors
were soft-bodied creatures that did not secrete calcium.
and foraminifera also appear at this time.
These are single-celled
animals that build a hard skeleton and needle-like spicules [FIGURE:
radiolaria and forams].
In general, the hard parts of animals are calcium (calcium carbonate or
calcium phosphate) and silica (silicon dioxide -- quartz and sand).
Because of the soft bodies, the early plant record is less abundant,
and plants as we commonly think of them do not flourish in the fossil
record until they begin to appear on land, around 350 Ma. By this time,
an ozone layer in the outer atmosphere has built up to the point that
it can filter out the most harmful hard cosmic rays, which allows both
plants and animals to grow on dry land. Because of this late appearance
in the fossil record, we will discuss animal creation first, even
though animals are admittedly much more complex than plants.
Colonies. As we noted in an earlier
chapter, evidence of single-celled
cyanobacteria goes back to nearly the earliest stages of the Earth,
when it was first cool enough to have oceans and living cells. These,
too, left a fossil record in the form of stromatolytes which were
formed by calcium excretions of the bacteria. The
colonies made up of single-celled bacteria, in which the bacteria
specialize in various ways that benefit the colony as a whole.
Specialized forms of cyanobacteria include heterocysts which
fix nitrogen, and akinetes,
which are a dormant, protective form that can survive harsh
conditions. In addition, the layers of cyanobacteria that form the
stromatolytes have various specialized layers [DISCUSS].
All single-celled eukaryotic species live in water, or at least in
moist environments (soils or tissues). Lynn Margulis places these
species in the kingdom Protoctista.
They are sometimes called protists - protophyta (plant-like) and
protozoa (animal-like)[FOOTNOTE: See Margulis, Kingdoms and Domains, p.122].
Many of the species have complex life-cycles that include colonial
The life cycle of the slime
(Margulis' phylum Rhizopoda,
Pr-2) gives a fascinating example of something that seems
half-way between a colony and a multi-celled animal (Figure 1)[FOOTNOTE:The
discoideum, ibid., Fig. F, p. 137 (also available
here.). Ongoing reserach on this species is proceeding in a number
of areas: cellular differentiation, signaling, programmed cell death,
etc. because of its short life cycle (8-10 hrs). The DNA has been
completely sequenced.]. It is independent
single-celled amoebas at one stage. At another stage the amoebas swarm
to form a "slug". The slug looks and moves like a multi-cellular animal
-- including a slimy cellulose "skin", but in fact each of the
component amoebas retains its individual identity (CHECK). In the
reproductive stage the "slug" grows into a fruiting body -- a stalk
with a round cap that bursts into a shower of spores that produce the
next generation amoebas. At this point some of the original amoebas
undergo programmed deaths to form the stalks and other specialized
portions of the fruiting body. In the aggregated stages, the individual
amoebas appear to use chemical signalling to initiate the various
stages in the life cycle and coordinate the movements of the
Slime Mold Life
World Land Map during the Cambrian Era.
The worldwide distribution of Cambrian fossils carries with it
implications for how the continental landmass was configured during
that Era (see Figures 3a-3c).
Note that over this time the North American landmass moved
mid-Southern latitudes to equatorial latitudes. Note also the proximity
of the future (emerging) Siberia, Greenland and North America, and the
separation of these from South China (the location of the ChengJiang
Ediacaran and Cambrian fossil beds).
|Continental Formation and Tectonic Movement
The Silent Speech of Psalm 19 includes an extensive record of how the
Earth's landmass changed over the entire fossil record of life on
earth. The description of this tectonic movement combines a
number of scientific disciplines, and involves extensive information
preserved in a continuous record for over 500 million years. The
shows this in
one of the best collection of Early
available on the Internet, The fact that scientists
can form these maps of the distant past is a remarkable example of how
God has invested his Creation with a silent speech that proclaims his
glory and handiwork.
Many-Celled Plants and Animals.
What is the difference between a colony of individual single-celled
species and a multi-cellular plant or animal? Presumably the individual
cells of multi-celled species cannot enjoy an independent existence.
This situation was already seen in the heterocysts of cyanobacteria,
which depend on sustenance from adjacent cyanobacteria. The
cyanobacteria form heterocysts when they are facing a nitrogen
deficiency. The nitrogen production is destroyed by oxygen which is a
byproduct of photosynthesis, and so the heterocysts get the ATP and
sugars produced by photosynthesis from adjacent cells. See also the
Wikipedia article on the Evolution
Inventions Associated with the
Appearance of Plants and Animals.
oxygen metabolism -- requires circulation -- either osmosis or a circ
syst. sexual reproduction. Chromosomes --
The Difference between Plants and
Plant body plans are algorithmic; animal body plans are topological
(with algorithmic components)[FOOTNOTE: In Medicine,
"Topology" refers to "The anatomical structure of a specific area or
part of the body." from Answers.com)].
And therein lies all the difference.
Algorithmic body plans. An
algorithmic body plan is rule-based with random variations
superimposed. The prototype for an algorithmic plan is the "knit one,
perl two" rule for knitting. The body plans for plants are typically
algorithmic and result in the haphazard appearance of tree branches,
leaf veins. It is not that they have no systematic plan, it is that the
plan is algorithmic: put out a new branch in a random direction
according to an established rule for that species. The result is
roughly symmetric in the large but apparently haphazard in the small.
Tree shapes and leaf shapes follow a general pattern that is
Figure 3 shows an example of algorithmic growth of leaf veins.
Algorithms control the (random) placement of the main, secondary and
tertiary branching. In this instance, all of the branching occurs in
the plane of the leaf, but the spacing and orientation of the veins is
clearly random but follows definite rules.
Figure 4 shows an example of tree branching. Again note the
algorithmic placement of branches, which in this case occurs in
three-dimensions. The placement/growth algorithm is obviously
influenced by access to sunlight. Root growth also follows a similar
branching algorithm, influenced by access to water and nutrients.
An Example of Algorithmic Growth
[SUBSTITUTE MY OWN PIX]
[SUBSTITUTE MY OWN PIX]
Plant embryos immediately (??) produce cells that form a cell wall.
These do not move relative to one another. Growth occurs by cell
division interior to the cell wall (??). See also the Wikipedia article
on the evolution
Topological body plans. Topological body
plans take account of cell location within the body.
In effect, they build the body according to a 3-dimensional map, and
location: anterior/posterior (head/tail), left/right, and dorsal/ventral
(front/back), Topological plans can result in left-right body symmetry
or anti-symmetry, body segmentation (head, thorax, etc.), organ
placement, and other complex details that algorithmic plans cannot
achieve. Animal body plans are topological.
The body plan of an embryonic animal
first shows up in the blastula (a hollow sphere),
which is entirely formed of undifferentiated stem cells. All animals
(and only animals) pass through a blastula stage during their embryonic
development[FOOTNOTE: Margulis, p.233].
From this stage on the stem cells immediately begin to differentiate
based on position and orientation in the embryo, and locate the
(future) head, legs, intestine, nerve system, etc. Thus the topological
body plan is fundamental to all animals, in contrast to plants.
The body plan is
controlled by a package of genes called the homeobox (hox) genes.
The composition of this gene package varies by phylum (??). The hox
genes control gene expression, and the parameters for this gene
expression are stored in non-coding portions of the dna (i.e. these dna
do not code for genes). All hox genes are headed by a dna marker of 183
base pairs called the homeobox and the corresponding 61 amino acid
section of the hox proteins is called the homeodomain.
This uniquely identifies all hox genes, and is essentially the same
over a large swath of animal phyla "from fruitflies to man." Hox genes
across the animal species forms the subject matter of evolutionary
developmental biology (evo-devo).
The implementation of the body plan permits variation in development
within closely defined limits. This variation is called phenotype
plasticity. This variation is in addition to changes that result
from radiation damage or various types of copying errors that may slip
through the cell's error-checking machinery. Apparently a
mechanism exists to preserve some of these variations, so that it can
(occasionally) be passed on to future generations -- probably within
the non-coding portions of the dna.
The Cambrian Explosion.
The Animal kingdom appears suddenly in the fossil record over 600 My
ago, in what has come to be called the Cambrian explosion. The boundary
that defines the start of the Cambrian age is the appearance of fossil
burrows that were obviously made by a complex animal, probably an
arthropod—the name means “jointed feet”, think lobster. We will meet
trilobites, a kind of arthropod, in a minute. Animals
differ from plants in that they have a
much more elaborate body
plan that is built into the embryonic development. This plan is
incorporated into the homeobox
or "hox" genes and expression or development genes. The various animal
phyla differ in the organization of these genes, and the resulting
complexity of the species.
Trichophycus fossil burrows
that define the start of the Cambrian age
The beginning of the Cambrian age is currently set at about 590 My ago,
and marks the start of the “Phanerozoic Era”, which means “visible
animals”, ones that are visible to the unaided eye[FOOTNOTE:
In 1991 the International Subcommission on Cambrian Stratigraphy
officially set the Cambrian boundary at the first appearance of these
irony, from the perspective of natural evolution, is that
all of the basic animal body plans appear almost simultaneously within
about a 10 My span of time about 530 Ma. Recent work on
development genes indicates that at this time, a number of basic gene
packages appear which were used over and over in many combinations
during the subsequent development of animal life. For example,
there are development gene packages to control the development of
appendages, of eyes, of the nervous system. These same packages are
used repeatedly in different configurations over the next 500My.
cambrian fossils. trilobite, pikaia, arthropods, brachiopods,
eocrinoids, corals shellfish,
many become much more elaborately and characteristically formed
in ordovician (e.g. starfish) but the phylum is clearly present.
Timeline of Evolution
haploid/diploid stages of life. In sexual animals: diploid is
normal. egg and sperm are haploid, and join at fertilization to form a
haploid = only half there.
With the creation of the eukaryotic cell, multi-cellular plants and
animals can be made.
Remarkable living fossil from the Cambrian Era: Monoplacophorans
-- ancestral to later mollusc classes. 1952 Galathea expedition: 10
living species of Neopilina galathea.
PR-3 - Granuloreticulosa
(Foraminifera). First appear Early Cambrian,
about 542 Ma.
See the Foraminifera gallery
developed and maintained by Michael Hesemann.
Chlorophyta (green algae).
See also Haeckels HMS Challenger report on Radiolaria
[Some stunning pics from Cambrian are in the Lyell collection
Society, London). However this is a pay-per-view.]
Gamophyta (green algae).
Rhodophyta (red algae).
Porifera. Early Cambrian fossils include a short-lived (about
10My) but prolific blossoming of a sponge Archaeocyathans.
They are the first reef-building animals, conical shaped with a calcium
carbonate (calcite) shell -- similar in overall shape to the later rugose corals.
Because of their brief span they are an index fossil for the lower
Sponges commonly have needle-like spicules which they use for movement
and defense. The following figure shows a number of Cambrian sponges
The following Mid-Cambrian fossil sponges are listed by Charles
Walcott[FOOTNOTE, Charles Doolittle Walcott, Second
Contribution to the Studies
Cambrian Faunas of North
. Note the surface
pores of the sponges indicated in the figures.
Mid-Cambrian Sponge Leptomitus zitteli.
Georgia Formation, Parker's Quarry, Vermont
Middle Cambrian Hyalouema
showing silicious spicules. natural size.
Silver Peak, Nevada.
Note the pores in the magnified section.
Georgia Formation, Troy, NY length 0.3"
Note the pores in the magnified section.
A-4 Phylum Coelenterata
All Coelenterates have stingers called cnidaria;
hence this is an alternative name for the phylum. The phylum
includes hydras, medusas, jellyfish and corals. Often the life-cycle of
a species may pass through several of these forms.
Medusa -- Narcomedusa
Marjum Formation (Utah)
fossils up to 8mm across.
(bar = 2mm (??))
Medusas -- Scypohzoa
Krukowski Quarry, Mosinee, Wisconsin
(Individual medusas up to 2 ft. diameter)
Note water ripple marks
Cambrian "protoconodonts" are currently believed to be the unrelated
remains of chaetognaths (or "arrow worms")
A-7 to A-19 are mostly soft-bodied and many are worms
(horsehair worms). A lower Cambrian worm of
in quite remarkable preservation, was discovered in 1999 in the Chengjiang
of China (Figure ??).
A-20 Phylum Chelicerata
. The Chelicerates
include horseshoe crabs, scorpions, spiders and mites. The shells are
somewhat soft and may not fossilize well. ??Cambrian examples are
sometimes disputed. ???? CHECK ???? (especially if trilobites and
tardigrades are removed from this phylum).
[SHOW SOME FOSSILS]
. The Trilobite
the most remarkable Cambrian fossil. It appeared suddenly as a fully
formed arthropod, and lasted for over 200 My, becoming extinct in the
Permian Extinction (about 250 Ma). Trilobite fossils represent the
earliest clearly defined occurrence of compound eyes. In most
classification schemes the trilobite is placed in its own phylum
because of its unique body structure which consists of multiple
segments each with three lobes (left to right). The only comparable
animal is a newly-hatched trilobite
larva of the horseshoe crab (a Chelicerate), so-named because its body
plan resembles a trilobite. The Cambrian trilobites are mostly small,
but in later times some fossils are quite large -- up to 28 inches. See
the Chapter on Phyla for further remarks on the trilobite, particularly
the trilobite eyes.
A-21 Phylum Mandibulata
Early Cambrian Trilobite
phylum includes the classes
Hexapoda (Insecta) -- insects and spiders
, Crustacea -- crabs, shrimp and
lobsters, and Myriapoda -- centipedes and millipedes.
Orsten fauna "The initial site,
discovered in 1975 by Klaus Müller and his assistants,
exceptionally preserves soft-bodied organisms, and their larvae, who
are preserved uncompacted in three dimensions." For information
about the Orsten fauna see also
http://www.core-orsten-research.de. CHECK THIS OUT FOR MORE PIX!!
Annelida. segmented worms -- Earthworms, etc.
Spriggina is a
possible pre-cambrian annelid. It is a segmented worm about 3 cm in
length. It appears to be armored with interlocking plates. There are no
Ediacaran (pre-Cambrian) Annelid?
Mollusca. A Cambrian fossil Mollusc (class Monoplacophora)
is named Knightoconus.
This was thought to be extinct, until ten living species were
discovered in 1952[FOOTNOTE:
expedition: 10 living species of Neopilina
]. Since that time a number of other
specimens have been found. Modern species live on the ocean bed in deep
water. "All extant classes of molluscs, except Scaphopoda, began
at various times during the Cambrian."[FOOTNOTE: Lyell
Collection, citing Runnegar & Pojeta (1974). Scaphopoda may
date from the mid-Ordovician Era.]
Class Monoplacophora. Knightoconus
top: fossil; bottom: living representation
Cambrian Gastropod Mollusc
a snail, Class Gastropoda
attleborensis (Shaler & Foerste, 1888).
Phosphatocopina Müller, 1964 (Larva)
SEM micrograph, Oblique view.
Original size up to 5mm.
D. Walossek, Ulm[FOOTNOTE:
From the web page “Life in the Cambrian” at
Phylum Tardigrada. Tardigrades are
microscopic animals that range from 100 µm to 1,500 µm
A-29 Phylum Bryozoa.
Cambrian Tardigrade (530 Ma)
may begin during the Ordivician Era. ???CHECK???
. The following Mid-Cambrian shellfish are
listed by Charles Walcott[FOOTNOTE. Op. Cit.]
Numerous fossils of this sort have been found.
Lingulella caelata, 2x
Middle Cambrian, Georgia Formation
ridge East of Troy, NY
Acrotreta gemma, 3x
Antelope Springs, Utah
The genus Lingula (Bruguiere, 1797) is the oldest known animal genus
that still containins extant species. (WIKI)
Get examples from plates in Second contribution to
the studies on the Cambrian faunas of North America By Charles Doolittle Walcott (1886)
starfish, sea lilies, sea urcins, and sea
cucumbers. Most of these appear later in the Ordovician Era. The
sea lilies (Crinoids), or at any rate, crinoid-like fossils, occur in
the Cambrian Era. Gogia
is the most common example.
are (until recently) the only fossil remains of this extinct worm-like
creature. The name applies both to these bony structures and to the
They are plentiful, and amount to a trace fossil, appearing between the
mid-Cambrian to the Triassic Era. In 1952 the first
complete conodont fossil (from the Granton Shrimp Bed, Carboniferous
Era) was described in 1963
by E.N.K. Clarkson. Margullis calls the Conodont
an early chordate class -- but
not a vertebrate[
FOOTNOTE: K&D 261].
This is confirmed by some recent papers: see Conodonta: Overview at the Palaeos website. Other than these
bony structures, the first full fossil was discovered by in
1963. Since the initial description, other complete specimens
have been identified. The "switch" from phylum A-6 to A-37 was
generally accepted around the turn of the (21st) Century.
St. Peter Formation NE Iowa.
The conodont elements can be retrieved from limestone formations
dissolving the limestone in acid. The conodont elements remain and can
be used as markers to calibrate the age of other fossils by "condodont
zones" which can represent time intervals to within a small fraction of
a million years -- more accurate than any other means of dating[FOOTNOTE:
www.ferindril.org/twiki/pub/Lab/LinkList/Barrick_Conodonts.pdf. The use
of conodonts in petroleum surveys: "The petroleum industry uses
conodonts as indicators of the degree of maturation of hydrocarbons in
sedimentary basins as well as for biostratigraphy. Unburied and
unheated conodonts have a light amber color because they retain complex
organic molecules in the skeletal framework. When conodonts undergo
deep burial and heating, these organic molecules change or mature in
the same manner as do organic substances in the strata that are
transformed into oil and natural gas. As the organics in the conodonts
mature, the conodonts change color from light amber to dark amber to
brown until they turn black. Experimental work and field research shows
that when conodonts are light brown, the sediments have been buried and
heated to a degree such that hydrocarbons have fully matured into oil".
W. Britt Leatham, The Hidden World of the
Conodonta and Conodonta Overview.].
The following figure is a
reconstruction of a conodont (from the
|Conodont "teeth": Precision fossil
The soft-bodied conodonts lived
between the Mid-Cambrian and the Permian
(~520 Ma to 251 Ma). The characteristic feature of the
Conodonts (and virtually the only fossil remains) were abundant
microscopic "teeth"called Conodont elements
which apparently aided in breaking down food particles for digestion,
and have microscopic sizes up to 0.5 mm.
These phosphatic "teeth" are liberally distributed in the fossil record
over the 300 years of conodont existence, and can be used to calibrate
fossil formations worldwide to within less than a million years. This
is much greater accuracy than even the most precise dating with
radioactive half-lives. The teeth vary their appearance slowly over
time and have very distinctive shapes, so that specific
micro-formations can be correlated worldwide, providing a precise way
to date widely disperse formations, a fact that is widely used in the
examination of drill core samples in petroleum exploration.
WORKING However, a new convicing candidate for
first chordate was announced in 1999 with Haikouichys -- an early (530
MYA) Cambrian fossil found in China. These 2 to 3- cm
resemble a tiny fish -- the first such animal in the fossil record
(officially the first bony fish fossils are from the Ordovician
Better specimens were announced in 2003 which show well-developed eyes,
and other sensory structures characteristic of the cratiates, as well
as the muscle blocks typical of early vertebrates (Nature 421, pp
|The Fossil Animals of the Cambrian Era
"ammonites can be assigned, not just to
the Mollusca, but also to the cephalopods, and indeed, are close
relatives to the Coleoidea." GRAHAM E. BUDD, The Cambrian Fossil Record and the Origin
of the Phyla