Et tunc nulla erat III
(And Then
There Was)
Being:
As we left off in ‘Et Tunc Nulla Erat
II’ life had conquered into being here on Earth around 3.8 billion years ago
(bya) as definitive proof in the form of the Kingdom, Archaea. With geochemical
variability and geophysical constants favorable to the polymerizing building
blocks of amino acids into peptide chains, along with the encapsulation of
ribose (a monosaccharide), repetition began performing inside a cell wall. Once
nucleic acid was captured and transformed into a nucleotide, a portion of RNA
(ribonucleic acid) was transposed originating into a double helix structure
known as DNA (deoxyribonucleic acid). The remaining RNA became the messenger
for the encoded genetic messages from DNA. These instructions became the
building block for all cellular development and functioning.
The earliest evolvement of cells had a
watery origin. That is why the human body averages 53% by weight of water. All
cellular activity utilizes water today as it did in Earth’s primeval oceans.
Chemical and metabolic reactions via water transports are cell life. That is
also why all land organisms evolved body coverings to retain internal watery
components.
Archaea for sure was not the very first
of life, for there was an unknown marine ancestor base that Archaea and
Bacteria arose from. This base of life goes back to at least 4 bya and in
accommodating mostly hot environmental conditions were thermophiles. But with
no fossil affirmation to go by the actual time frame is conjectural.
Nonetheless, empirical evidence points to a basal cellular ancestor.
Cellular
Eternal Essence:
From this proto-cell to unicellular base
structure that now housed a nucleoid and protoplasm, the biological building
block for all life on Earth had arrived. Gathering environmentally available
ions, monosaccharaides, amino acids and water the protoplasm is the living
contents of a cell where replication and metabolic pathways occur. With no
nuclear membrane, as in further evolved eukaryotes, the prokaryote nucleoid in not quite a
nucleus still consists of approximately 60% DNA with the remaining components
divided up by RNA and protein. Most all single celled life is prokaryotes (Greek prefix
for: ‘before a nucleus’) while all
multicellular and some unicellular life like protozoa are known as eukaryotes
(Greek prefix for: ‘true nucleus’).
The karyote suffix literally translates into ‘kernel.’ That’s it…all life
exists with only two types of cells.
Don’t want to jump ahead just yet, for
multicellular organisms did not make an appearance until 100s of millions of
years later, but eukaryotes, such as animals, plants, fungi and protists have a
nucleus derived from the prokaryotes’ nucleoid and it is surrounded by a double
membrane while comprised of linear DNA called chromosomes where prokaryotic
cells’ DNA is circular within an imaged nucleoid.
Eukaryotes house more material so
therefore are much larger. Eukaryotic DNA is also complexed with proteins
called ‘histones’ that form chromosomes. Prokaryotic cells are considered
‘naked’ in this regard for they have no histones to form complex chromosomes in
having only one circular but convoluted chromosome.
Despite a few of the differences we’ve
just mentioned, there are many similarities. First, both cell types perform the
same functions in the same ways. Prokaryotes possess simplified ribosomes,
eukaryotes have complex ribosomes. Above all though, they are clearly
evolutionarily related. DNA in both cell structures is identical in physical
form, components and replicates in the same manner.
During cellular replicative initiation,
proteins bind to the duplicate sites, while the enzyme, helicase begins
unwinding the DNA helix structure forming two forks at the origin of
replication.
Next, during elongation of the helix
structures into straighter strands, a primer sequence is added with
complementary nucleotides later to be replaced by DNA.
Still in the elongation process, the ‘leading’ strand is being continuously
made, while the ‘lagging’ strand is
made in pieces through a process known as ‘Okazaki
fragmentation.’
During the final stage, termination of
the process commences with primers being removed and replaced by new DNA
nucleotides sealed by the DNA enzyme, ligase.
A cell is and has always been the
smallest unit of life to replicate independently. Once life in the cell took
hold, this process has been going on in the exact same sequence throughout the
eons. This is continual life in blueprint form.
Microorganism
Eternal Essence:
From the basal cellular ancestry, a
bacterium was the first to diverge away carrying with bacteria the more primal
form of replication. On the other hand Archaea groups began modifying before
totally branching from the base stem.
The copy replication of prokaryotic
cells is known as ‘mitosis.’ The more
involved and evolved form of eukaryotic replication is ‘meiosis’ essentially being, in using the catchphrase, “mitosis on
steroids.” Archaea possesses fully neither one of these choosing a simpler go
between ‘binary fission’ form as the
route to replication. This asexual process of replication, not quite mitosis,
but not fully meiosis either, is the parasexual (replication of recombinant
genes without meiosis) base that ultimately led to eukaryote evolvement.
Parasexual cycles do not involve eukaryotic meiosis, but have similar genetic
developments.
 |
| Archaean theromophile sulfolobus |
Archaea metabolism and operon gene
organization is shared with bacteria derived from their base ancestry, but archaean
factors for transcription, translation and DNA replication is akin exclusively
to eukaryote cellular activity.
Archaea truly is an ancient relic of
life and have survived to the present for logical reasons, for they have
adapted well to adverse environments and conditions.
Based on their habitat, there are three
main archaean groups:
1.
Halophiles
(hal-oh-files) — live in salty environments.
2.
Thermophiles
(ther-mo-files) — live at extremely hot temperatures.
3.
Psychrophiles
(sigh-crow-files) — live in frigid cold temperatures.
In addition, a fourth group known as Methanogens
(meth-an-oh-jins) produce methane as a by-product in digesting or creating
metabolic energy, much like eukaryotic animals do.
 |
| Archaean Methanogen |
Archaea diets are another survival strategy as it varies from what is available from hydrogen and carbon dioxide gases to sulfur and decaying organic material. With a salty environmental preference, certain archaeans use sunlight in the manufacture of ATP (adenosine triphosphate), an energy molecule.
So, archaeans and bacteria, although both
arose from a common ancestor, developed and split off separately. Hundreds of
millions of years later, the early ancestors of eukaryotes had split off from
archaeans. Due to this, even though they are single celled life, archaeans are
more closely related to us as eukaryote animals than archaeans are to bacteria.
In other words, archaeans’ genetic recipe and metabolic pathways are more
similar to ours than to bacteria. Further, the archaean phylum, Crenarchaeota contains groups that the
shapes of their ribosomes are more similar to eukaryotes than to bacteria or even
to other archaean phyla.
Don’t feel as though bacteria are left
out. Bacterium forms of replication have also been a success story in being one
of the oldest extant life forms on Earth. Although we tend to look at bacteria
as simply pathogens, we along with the rest of eukaryotes could not survive
without them.
Bacteria aid in our digestion, as
chemo-synthesizers break down elemental compounds for plant usage, are utilized
in pest control such as Bacillus
bacteria attacking mosquito larvae, degrades toxic materials from soils and
waterways and turns waste into energy.
 |
| Anaerobic rod-shaped bacterium |
There are ten times more bacterial cells
on us and inside us than there are human cells that make us. But, bacteria are
not only utilized by us they are in a sense part of us. In fact bacteria are
the origin of mitochondria within each and every animal eukaryote cell and the
origin of chloroplast in plants. Without mitochondria housed in each cell, all
animals would die. Without mitochondria/chloroplast in each cell, all plants
would die. Mitochondria and chloroplast is the energy powerhouse of each
eukaryotic cell and without these ‘organelles’
(specialized structures within a cell) all animals and plants would cease to
exist.
Mitochondria and chloroplast were once
aerobic (oxygen loving) bacteria that were engulfed by an early anaerobic
(oxygen repulsive) bacteria. The storyline goes as follows…
The larger bacterial host cell ingested
the smaller aerobic bacterial cell, but the consumed bacteria couldn’t be
digested and did not succumb finding its new environ compatible with its needs.
The aerobic bacteria found a protective home and a supplied source of nutrients
while the anaerobic bacteria realized a built-in energy factory powerhouse
since aerobic respiration on a cellular level is much more efficient than
anaerobic. The eukaryote cell evolved with this mitochondrion and chloroplasts
arrangement and is where cellular respiration occurs to this day. This is
endosymbiosis where in a symbiotic relationship both organisms mutually
benefit, but instead of both being free form, one lives or exists inside the
other.
Ever heard of the old and tiring catchphrase,
“It’s just a theory.” In everyday speech with the layman, supposedly ‘theory’
is simply an opinion or speculation. In science circles though, a theory that
has been proven through empirical observation and controlled experimentation,
scientists accept the theory as factual.
So it is with the mitochondria and
chloroplast organelles endosymbiotic theory. With snippets of circular DNA that
is unrelated to the whole cell’s DNA, but distinctly related to bacteria leads
to substantive proof. Mitochondria and chloroplast make their own DNA even
though they are housed within a cell that manufactures DNA. Both organelles use
their DNA to produce their own proteins. They also replicate and direct
replication division separate from the cell. Finally, a double membrane
surrounding the organelles, strongly suggests that each are the cell envelope
of a prokaryote composed of the cell wall and plasma membrane. This arrangement
was to be the precursor to eukaryote evolution.
Whether it is prokaryotic or eukaryotic, replication or reproduction is tantamount to life in its continuance. The route taken in this process is through gene expression via either fission or fusion. All organisms that have swam, walked or flew Earth have around 350 genes that are common to all life; a threaded throwback to the original 4 bya basal cell.
Whether it is prokaryotic or eukaryotic, replication or reproduction is tantamount to life in its continuance. The route taken in this process is through gene expression via either fission or fusion. All organisms that have swam, walked or flew Earth have around 350 genes that are common to all life; a threaded throwback to the original 4 bya basal cell.
 |
| Extant Stromatolites |
By 3.5 bya along shorelines, cyanobacteria as a biofilm began accreting sedimentary grains into structures known as ‘stromatolites.’ In the bio chemical process, stromatolites began pumping out oxygen into the atmosphere. They are very successful and spread to all existing shorelines.
Before we close out the cell, I would
like to give a mention as to why viruses weren’t included in the discussion.
The simple fact is because they are not life. Viruses are simply a gene junket
not quite complete, therefore is why viruses must invade a host’s cells to gain
access to the cellular machinery before it can ever duplicate its genome and
replicate.
Viruses lay dormant in a primary host
lying in wait to infect its secondary host to replicate and once activated
creates cellular mayhem. Viruses either have RNA or DNA but never both. That is
why they need a host cell to fool the cell in giving up its RNA and/or DNA via
transcription of a code. The host cell has a lock, but the virus has the encoded
key. Only in this way can a virus replicate by stealing a single strand of its
hosts’ RNA or DNA to duplicate with its single strand and indeed do viruses
invade. In losing RNA or DNA strands, the host cell loses its ability to
perform its assigned tasks creating the disease. There is not one organism,
microscopic or cetacean (whale) that has not been virally infected. Even other
viruses are not immune to viral infections. Without the proper host though, a
virus is essentially an inanimate object just like a rock.
 |
| Influenza RNA Virus |
Outside of any host, whether lying
dormant in a primary or active in a secondary host a virus simply perishes
within a couple of days. Today, each and every one of us carries what are known
as retroviruses. These viruses once invaded our ancestors and most likely were
catastrophic on the poor caveman, but the ones who had a genetic mutation, the
virus key could not unlock the host’s lock. So now, as prodigies of the
survivors, these viruses are still genetically passed onto the next generation
but remain permanently dormant. In fact 8% of our genome is viral. Kind of
makes one ponder a bit on what it truly means to be human.
There is no one set theory on how viruses
arose and evolved. With mobility and encoded genetic material they do have the
ability to move within cells, suggesting their evolvement came after cells
arose where viruses adapted a parasitic lifestyle. On the other hand, since RNA
as a replicating molecule developed long before DNA, which is a by-product of
RNA, single stranded RNA viruses may be the descendants of these pre cellular
RNA molecules. Only in the ongoing studies of molecular biology, genetics and
structural etiology will time reveal the answer to viruses’ evolved
origins.
Animalia
Eternal Essence:
Due to the envelopment of mitochondria
and chloroplast of one anaerobic cell over an aerobic cell, the arrangement
began replicating itself into daughter cells from which the eukaryote cell
arose with a true nucleus and enveloped organelles. This led the way to
multicellular plant and animal life. Below is a phylogenetic tree displaying
what we have discussed thus far and where we will go to plants and animals.
So with prokaryote ancestry in a unique
arrangement, the eukaryote had arrived some 1.7 bya, but still as a unicellular
unit. Today’s representatives of eukaryotic unicellular organisms are yeast, ‘independent’ protists and ‘colonialists’ protists where collections
of independent protists exist as multicellular without specialized tissue or
organs.
Now don’t jump to conclusions in
thinking that multicellular evolvement was a one step process. Multicellular eukaryotic organisms had to
first evolve strategies to meet internal biological and external environmental
conditions. This involves a lot of complexity in steps that evolutionarily
speaking could not have evolved over night. In fact, multicellularity has
evolved independently at least on forty-six occasions over time.
The hypothesis for multicellular origins
is three pronged. The symbiosis of the same cell species when colonizing took
the evolutionary path to multicellularity as a result of cells failing to
separate following division. Later, this action was bolstered by cells
separating successfully but then rejoining as today’s current ancient slime
molds do today. Slime molds nowadays do this on land, although are still restricted
to a wet environment.
This initial transformation is not quite
yet true multicellularity, but is rather known as ‘pluricellular’ where a collection of function specific cells
aggregate forming a slug-like mass known as a ‘grex’ moving as a multicellular unit. Amoebas from the genus, Dictostylium do this today when
migrating from a poor environment to a more suitable one.
As adaptation occurred with conjoined
individual cells, single unicellular cells within the aggregate, whether
through mutation or daughter cell twinning, developed multiple nuclei with a
partitioned membrane around each nucleus.
As aggregate mutualism growths occurred,
a symbiotic relationship came about with unrelated cellular species co-opting
into the aggregate introducing their specialized functions into the colonial
admixture.
Over time colonies became totally
dependent on the individuals making up the colony that none could survive
without the others’ specialized services and functions. Within this close
proximal relation, eventually through some as yet unknown mechanism, perhaps
osmosis, the individual cells began sharing the same DNA. A single genome had
thus been incorporated constituting a single species that had derived from
unicellular collections.
This is not so farfetched as it sounds.
No matter the millions of cells that comprise us as a single distinct organism,
we all started out as one singular fetal cell once the parental haploid male
and female cells fused into the diploid embryo.
Organ systems evolved with specialized
cells to take on specific loads while evolving into a network of systems to
keep the whole alive in its functional needs and environmental settings.
Varying tissue comprised of specific tasked cells came together forming
specific organs that were task specific.
One of our own organs is the skin and
being the largest organ, covers our entire body as sheets of cells aligning
over external and internal body parts as connective tissue…the glue that binds
together and supports other tissues. All nerve tissue is considered an organ
that has highly excitable plasma membranes with chemical/electrical signals
stimulating other cells.
Within this multicellular fold many
strategies for specialized function unfolded. Defense systems for protections
against foreign invasion developed. Receptors became specialized such as photo-reception
for lightness/darkness distinction then later for visual imaging.
Noci-receptors detect stimuli that are injurious or painful. Many more, such as
mechano-, electro-, thermo- and chemo-receptors evolved.
Gene regulation, homeostatic and system controls, bonding/unbonding cues of molecules and reproductive strategies evolved. Life now had evolved from a single cell to a multicellular organism.
Gene regulation, homeostatic and system controls, bonding/unbonding cues of molecules and reproductive strategies evolved. Life now had evolved from a single cell to a multicellular organism.
With the advent of a multicellular
organism, unicellular replication was revised to organism reproduction and
thusly, sex had arrived.
 |
| Vernanimalcula animal eukaryote |
Through the fossil record, it appears
plants were the first multicellular organisms to replicate through sexual
reproduction in the sharing and fusing of two individual haploid gametes. In
the phyla, Chlorobionta and Rhodophyta marine multicellular green and red algae
abound 1.4 bya, where reproduction alternates from generation to generation in
reproducing by the fusion of identical cells (isogamy) to the variant fertilization
of a non-motile cell with a motile cell. Green alga is the stem base of all
chlorophyll plants.
 |
| Soccer /baseball-like Metazoan embryos |
Full plant spore/gamete reproduction
occurs 1.2 bya in the fossil record from unidentified plant sex cells. Though
well preserved, these are marine microfossils of reproductive plant cells but
with no vestiges of the actual parent plants. These microfossils though, with
further study are appearing to have come from algae or seaweed. Thallophytes,
marine seaweed plants that are sessile but not rooted have well preserved
sexual reproduction fossils showing up ~ 1 bya.
In China’s Doushantuo formation laid
down 635-551 mya after retreat of the Ediacaran glaciation, many fossils are
extremely well preserved from micro to small bodied.
 |
| Doushantuo mitotic algal spores |
Besides plants in this formation, animal fossils have been intricately preserved as well and considering the amount appear to have been well established by 650 mya.
Doushantuo fossils were all flora and
fauna microscopic marine life. Though the preserved findings are of eggs,
embryos and pieces of body parts, it is first evidence in the fossil record of
animal life. This direct empirical evidence confirms expectations that a major
evolutionary event had occurred long before the explosive diversification of
animal life forms at the onset of the Cambrian Period. It also points to the
fact that more remote forms of ancestral phyla had previously existed.
 |
| Doushantuo embryo cells |
Doushantuo fossils include the microscopic
animal, vernanimalcula and eggs, embryos and larvae of ciliates and coelenterates.
The fossils are so well preserved, embryos exhibit cell division. In addition,
soft body parts from an array of adult sponges, cnidarians and tabulate corals
have been excavated.
Possibly as far back as 700 mya,
cnidarian belled jellyfish are the first creatures to evolve muscle tissue for
mobility.
The photo below is of an amoeba
like-cyst captured in the process of producing cells and even though cells were
dividing and growing the cyst did not. The cyst appears to have released cells
as if they were reproductive spores. Perhaps this amoeba-like organism was a
precursor to animals. All conclusions are from the results of x-ray tomography
where the original thought was that it was an animal embryo.
 |
| Doushantuo amoeba-like cyst |
The one early animal we’ll discuss fully
here are tardigrades. For some 530 million years, this 1mm/.04in diminutive
animal has been roaming Earth by sea and land. The more than 900 species have
conquered from 6096m/20,000ft Himalayan mountain tops to the Indian Ocean abyss down to
4690m/15,387ft. From the Arctic to the Antarctic, to coastal tropical shores
and deserts, tardigrades dwell quite well. They live in freshwater or on dry
land in damp mossy and lichen covered environs.
Most species graze on plants, some
ingest bacteria while a few are predaceous on smaller animals than they like
rotifers and nematodes.
Terrestrial tardigrade species can be gray, brown, red, pink, orange, yellow, green and black whereas marine ones are off-white.
Tardigrades have a lobed brain connected with a nervous system composed of ganglia segmentally repeated while connected throughout the body. This may be a convergent evolutionary precursor to a more advanced nervous system found in cephalopods such as octopi that exhibit intelligence. The possession of ‘malpighian tubules’ in some tardigrade species is also convergent with current arthropods.
Terrestrial tardigrade species can be gray, brown, red, pink, orange, yellow, green and black whereas marine ones are off-white.
Tardigrades have a lobed brain connected with a nervous system composed of ganglia segmentally repeated while connected throughout the body. This may be a convergent evolutionary precursor to a more advanced nervous system found in cephalopods such as octopi that exhibit intelligence. The possession of ‘malpighian tubules’ in some tardigrade species is also convergent with current arthropods.
Tardigrades appear as some kind of blimp
in body shape and are bilaterally symmetrical with normally four pairs of unsegmented
legs terminating in pairs of claws or suction pads. The body is housed in a jointed
exoskeleton. The tubular mouth possesses dagger like teeth that they will eject
outwards to capture prey or plant material.
Some of the earliest tardigrade fossils
from the early Cambrian of northern Europe had only three pairs of legs like
insects.
Tardigrades are not the first common
ancestor to the Panarthropoda base,
but based on DNA sequences and morphologies most certainly are the sister stem
to arthropods such as crabs, lobsters, spiders,
scorpions, centipedes, insects and the extinct trilobite. Through molecular lab studies, tardigrades
are also related to onychoporans (velvet worms).
All they need anywhere they choose to
inhabit is a drop of water. No water, fine, they will dehydrate losing up to
99% of body moisture and may remain in a torpid state for years. An experiment
on a dehydrated induced tardigrade was conducted for 120 years and once a drop
of water was applied, it bounced back to life, though shortly died. Even so,
after ten years of continuous dehydration, once the drop of water was applied
they sprung back to life and went about their merry business. What is
astounding here is that the tardigrade’s natural life span is one year only.
When natural conditions dry up the
animal becomes a ‘tun’ that can
easily be dispersed by wind, animal or in an animal’s gut (yepper, they survive
being digested too) to be transported to more favorable habitat. The cellular sugar,
trehalose appears to be the secret in surviving desiccation by protecting body
membranes.
These creatures can go for up to five days
in a hypoxic (oxygen depleted) environment. 5000grays/570,000rads of ionizing
radiation doesn’t faze the animal where a mere 13.2grays/1500rads is lethal to
humans. They can withstand atmospheric pressure 6,000 times that at sea level.
From boiling temperatures to near
absolute zero, tardigrades can withstand high temperature variables. This is
simply amazing, for the cold extreme of -272° C/-458° F where
tardigrades’ survival supersedes liquids turning into solids and gases turning
into liquids, tardigrades do quite well. Even surviving the boiling point 100° C/212° F where water
turns into vapor, tardigrades go on about their business.
 |
| orange tardigrade |
 |
| yellowish-green tardigrade |
In 2007, the European Space Agency launched some tardigrades into low orbit space exposing them to high UV radiation, cosmic rays and the space vacuum for twelve consecutive days. 68% of them returned to Earth unharmed. Man could only withstand this exposure for ninety seconds.
Due to the ability to enact a ‘cryptobiotic’ state, tardigrades can
adapt to these extreme environments by lowering their metabolism to 0.01% of
normal activity. Now think about that for a second. These animals living on a
mere one hundredth of metabolic rate, is much lower than metabolism still being
conducted in a human that just got killed.
The pair of pigmented cupped eyes is
located dorsally on the anterior end. Tardigrade eyes are one of the first
complex eyes to be developed for usage in sensing motion, detecting shape and
distinguishing color. Unicellular organisms had already developed eyespots for
detecting darkness/lightness, but around 540 million years ago, the complex eye
had developed around the same time tardigrades came about.
Besides the phenomenal tardigrade
characteristics described above what is even more interesting in my viewpoint
are these two features. One is there reproduction.
A few species do exhibit asexual
parthenogenesis, but the vast majority is sexual. One mode practiced by a few
is for the female to simply lay eggs on substratum or in her discarded molted
cuticle whereupon a male, through happenchance comes by to fertilize the eggs.
Most species though fertilize the female internally by the male’s gonophore
inserted into the female’s cloacal genital papilla.
For me, this is extraordinary. With the
tardigrade, internal sexual reproduction strategies have been going on for at
least 530 million years, an astronomical time span.
Further though, the tiny tardigrades
hatch as miniature adults (just as reptiles and mammals) forgoing any larval
stage and are ‘eutelic’ in retaining
the exact number of cells throughout life; the cells simply grow larger as the
infant tardigrade matures. Pretty much this is the same case for humans. Until
age two a few regions of the brain grow new nerve cells, but this is primarily
further fetal development outside the womb, since a human mother cannot give
birth to a fetus much older than nine months due to physical constraints and
limits.
Lastly, tardigrades possess a
buccopharyngeal apparatus to differentiate among various tardigrade species. The
early human embryo also possesses a buccopharyngeal membrane located between
the developing endoderm and ectoderm skin layers, but is eventually absorbed
once it has formed a septum dividing the primitive mouth and pharynx. A
biological throwback tool derived from much earlier times now used in humans
for a different purpose.
Fish
Eternal Essence:
[Cambrian Period
541-485.4 mya]
 |
| Precambrian/early Cambrian sea life |
 |
| Early Cambrian landscape |
At the beginning of the Cambrian, land
continents were dry and barren, but the seas exploded from primarily
microscopic and diminutive life to large animals.
Before we start the Cambrian Period,
below are a few fossils and illustrations by paleoartist Quad Paul of some
marine creatures that roamed the Cambrian seas.
 |
| From L-R Diania, Odontogriphus, Opabinia |
Platyhelminthes flatworms had already
arose 550 mya bringing with them bilateral symmetry in having a front and back
and a brain organized with a primitive nervous system transmitted through a
neural cord, precursor to the notochord.
By the time the Cambrian Period arrived
543 mya, life was beginning to proliferate, but only small skeletalized
sponges, molluscs, shrimp, brachiopods, small arthropods and archaeocyathids (early
reef builders) were prevalent. But on into the middle half of the early
Cambrian, the ‘epeiric’ seas (continental
inland shallow seas brought about by warmed rising oceans) were teeming with
life.
Evolving from green algae that had arose
1.2 bya, spore bearing embryophytes had invaded environmentally moist land 540
mya such as hornworts, liverworts and mosses.
The first evidence of animals stepping
on dry land is in the 510-500 million year old orthoquartzite shoreline trace
fossils of euthycarcinoid tracks in present day Blackberry Hill, a quarry
region in central Wisconsin.
Tunicates (urochordates) first appeared
in the early Cambrian. Tunicate larvae possess a stiffened but supportive
notochord that contracts freely allowing mobility of the larva. Once undergoing
drastic metamorphosis, the notochord and tail are lost with adults acquiring an
external cellulosic ‘tunic’ utilized
in protecting soft body parts.
The cephalochordate, lancelet (also
known as amphioxus) showing up a little later in the Cambrian was a step above
in notochord evolvement in that the notochord is retained throughout life.
Tunicates and lancelets species as
living fossil relics are still with us today, with lancelets serving as an
important proteinaceous food source in Asia.
 |
| Conodont |
The first true chordates (possessing a
notochord) in the form of the eel-like conodonts had made their appearance.
Conodonts were also one of the first to use teeth for biting. Trilobites
abounded along with other arthropods and diversified mollusk, brachiopod, and
echinoderm species. 510 mya barnacle species appear.
The first fish ancestors could have
arose from Pikaia, Haikouichthys and Myllokunmingia. These three genera all appeared around 530 mya. Unlike
the other fauna that dominated the Cambrian, these groups had a basic
vertebrate fish-body plan: a proto-notochord in Pikaia
and a notochord, rudimentary vertebrae, and a well-defined head and tail in the
other two. All of these early vertebrates lacked jaws and relied on filter
feeding close to the seabed.
 |
| Myllokunmingia |
Stromatolites had spiked 1.2 bya and by
the time of the Cambrian were only at 20% of their peak numbers. The
stromatolite reign had done its job in approximating the required amount of atmospheric
oxygen of ~ 21%. If they had continued to proliferate, oxygen levels could have
risen to dangerous levels for life. Although stromatolite numbers did rise at
the end of the Ordovician and Permian, it appears competing animal organisms
kept stromatolite proliferation in check never exceeding in number enjoyed
during pre-animal life.
An event occurred towards the end of the
mid Cambrian causing the first mass extinction.
 |
| Extinct after Cambrian |
The event most likely was a glacial
advancement lowering oceanic levels and draining shallow seas. Extinction
occurred in olnellids (the oldest trilobites) and the archaeocyathids.
A second mass extinction is actually a
collection of three that occurred between the late Cambrian to the Cambrian/Ordovician border. Trilobites, brachiopods and conodonts were severely impacted
in speciation and number of families.
Again, glaciation was the event responsible possibly along with the creation of hypoxic marine conditions where cooler waters caused a stratification effect depleting oxygen in certain water layers.
Again, glaciation was the event responsible possibly along with the creation of hypoxic marine conditions where cooler waters caused a stratification effect depleting oxygen in certain water layers.
[Ordovician
Period 485.3-443.7 mya]
By the time the Ordovician Period had
arrived 485.4 mya, most all the older animals had become extinct with newer
forms more tolerant of cooler waters taking over. Cephalopods increase with
many nautiloid species showing up. Planktonic groups were multiplying
increasing the food chain. Crinoids, sessile stemmed filter feeders began to
dominate in both shallow and deep sea floors, while articulated brachiopods
were beginning to replace trilobites as filter feeders increased.
The Ordovician did not experience the
explosion of life as the Cambrian did, but a strong adaptive radiation occurred
in organisms rapidly diversifying into new species, such as an increase in
bryozoan families.
 |
| Ordovician sea life in the shallows |
The agnathid ostracoderms, the first true
jawless fish and precursor to bony fish had made its appearance around 500 mya
in the late Cambrian surviving the cooling period. They had an armored head
that was composed of thousands of compacted teeth fused together cemented by
calcite obtained from calcium carbonate oolite sedimentary rock. This head
shield was a secondary use of teeth.
 |
| Early Ordovician Ostractoderm |
Ostracoderms or fish in general may have
evolved from existing little animals similar to sea squirts during the Cambrian.
Sea squirt larvae are very similar to primitive fish in many aspects and the first
fish may have been their larvae that retained the larval stage into adulthood. For
sure though, fish are not monophyletic in evolving from one ancestor, but were
paraphyletic in having multiple ancestral bases.
Jawless agnathid species with true vertebrae
begin proliferating throughout the Ordovician.
Plants first invade land ~ 470 mya as evidenced from early monad (singular), diad (pairs) and tetrad (groups of four) cryptospores. These cryptospores are similar to liverwort spores. Trilete spores which are similar to vascular plants, like bushes and trees appear soon afterwards.
Plants first invade land ~ 470 mya as evidenced from early monad (singular), diad (pairs) and tetrad (groups of four) cryptospores. These cryptospores are similar to liverwort spores. Trilete spores which are similar to vascular plants, like bushes and trees appear soon afterwards.
 |
| Ordovician landscape |
It is in the Ordovician around 450 mya that
witnessed the first walk on land for life-kind. Arthropod tracts are evident in
shoreline fossils within the Kingston, Ontario area’s Ordovician Nepean
formation that was originally aeolian rippled marine sand dunes. Tracks are
trace fossils where footprint trackways are known as ‘protichnites.’
Evolving from a predatory arthropod, which lived 510 mya ago in
Cambrian seas, strictly marine eurypterids make their first appearance crawling
over the shallow sea floors in the mid to late Ordovician. The horseshoe crab (Limulidae), close cousins to Eurypterida had already made an
appearance 450 mya.
 |
| Protichnites: fossilized animal trackways |
Some fish that only have fossil records
in the Ordovician are the species Tsakoviaspis
concentria in the genera Apedolepis,
Sacabambaspis and Stroinolepes and all members belonging to the order Eriptychiida.
[Silurian Period
443.6-419.2 mya]
During the late Ordovician early
Silurian boundary another extinction event ensued 443.4 mya wiping out more
than 60% of all marine invertebrates.
The reason for the massive extinction
event was geological, which took a couple of million years. As the supercontinent
Gondwana began drifting towards and over the South Pole, ice caps began forming
locking up water from the earth’s oceans draining shallow seas. Also, carbon
dioxide in the atmosphere diminished further creating a cooling effect. Deep
cold ocean currents ceased to flow creating colder environs with anoxic
conditions devastating bottom and filter feeders.
Major volcanism causing extensive
outgassing during this time frame, was balanced by weathering in the uplifting
orogeny of the Appalachian Mountains sequestering carbon dioxide.
 |
| Silurian landscapes; Left: Early Right: Mid |
The event had decimated speciation in
brachiopod, bryozoan, conodont, graptolite (small colonial animals) and
trilobite families.
The Silurian though also introduced new
species. The largest arthropod known in the euypterid genus, Eurypterus lived throughout the Silurian
from 432-418 mya reaching lengths of 2.5m/8.2ft in the species Jaekelopterus rhenaniae.
 |
| J. rhenaniae |
Scorpions evolving from freshwater
eurypterids 430 mya still possessed gills. It is this aquatic scorpion itself
that didn’t evolve into land animals but simply adapted to the new environment
replacing the gills with book lungs later in the Devonian Period.
The terrain fungus, prototaxites appearing during the late Silurian reached heights of
8m/26.4ft but could not compete with vascular plants and went extinct.
 |
| Prototaxites Lft: fossil Rt: illustration |
Once the Silurian Period had arrived
443.4 mya, fish were accelerating in evolving new features. Originally gills
were used for filter feeding, but in the Cambrian jawless ostracoderms, fish were
already using them to breathe with. The one great leap in evolutionary terms
though was the jaw. With a jaw, an animal no longer relied on filter feeding,
vacuuming up seafloor muck or rely on chance for prey to get close enough to
suck up for nutrition. The jaw allowed an animal to now bite grasping onto prey
and holding them to either swallow whole or in bitten off chunks.
 |
| Acanthodids |
We have the fish to give thanks for our jaw and that first jawed fish was in the class Acanthodii first appearing in the early Silurian 438 mya. This fish was also caught between Teleost (bony fishes) and Chondrichthyes (cartilaginous fishes) in possessing both spiny bones and cartilage. Although acanthodians were streamlined as sharks and even are commonly referred to as ‘spiny sharks’ they predate sharks by 50 million years.
 |
| Jaw evolvement from gill arches |
Fish jaws most probably derived from the
front two gill arches in agnathids. Jawless fish gills are located directly
behind the mouth supported by a series of cartilaginous arches with the gill
slits in between. Working jaws most likely evolved from the top and lower first
two gill arches that began to fold over from vertical to horizontal positioning
but joining at the midline forming an upper and lower jaw.
Teeth were developed from rasping skin
known as denticles that had originally lined the mouth. I would like to note
here that shark skin is entirely made up of denticles. If one dared to get
close enough to a shark and brush up against, the denticles could very well cause
a sore rasping scrape. Denticles are like a rough file. Both fish teeth and
denticles are constantly being replaced. Rapid replacement can lead to quicker variation
as in the jawless fish mouth’s denticles into teeth.
As stressed before, with this new biting
mouth, the fish owner no longer relied on minute food particles to float their
way, or accumulate on the seafloor, they now could pursue dinner.
 |
| Silurian bony fishes: Lft: agnathid Pharyngolepis Rt: gnathostome Panderichthys |
By the end of the Silurian, a myriad of
both bony and cartilaginous fish species had taken up the biting jaw.
A few million years after Acanthodians’
arrival around 430 mya, the jawed and armored fish class, Placodermi made their appearance and were very successful with one
placoderm species, Dunkleosteus
reaching lengths of 10m/33ft becoming an apex predator during its time.
Osteoichthyes, the class of
bony fish make their permanent appearance at the end of the Silurian 419 mya
and with streamlined fish morphology and a toothed jaw, the order Teleosti (modern ray finned fishes)
become one of the most successful animal lineages throughout the geological
time scale.
No matter if you possess a smart mouth,
loud mouth, smack gum or eat with an open mouth, in the ability to do so…paying
homage to the fish jaw is due. So, next time you yank the hook out of that
hooked jaw, a little reverence please.
[Devonian Period
419.2-358.9 mya]
 |
| Placoderm Dunkleosteus and skull with human for comparison |
Once the Devonian Period came around,
placoderms with their biting mouth inhabited and dominated all the known period’s
aquatic systems in both sea and freshwater.
 |
| Early Devonian agnathid Doryaspis |
Sarcopterygii (lobe finned fish) show up at the beginning of the Devonian in which the extant but rare coelacanth and lungfishes is a member of. Lobe finned fish had a pair of pectoral and a pair of pelvic fleshy lobed fins joined to the body by a single hinged bone underlying basic wrist bones. This is the most rudimentary form to tetrapodal mobility.
These long, muscular and fleshy lobe
fins are supported by a central core of bones that individually articulate with
one another. The first front lobe articulates with a sturdy shoulder girdle
bone. These bones are precisely the limb-bones that make up all land animals
both extinct and extant.
 |
| Sarcopterygian fins to Tetrapodal limbs |
Early shallow sea colonial coral
ancestors that were not reef builders but ‘phaceloid’
in possessing corallites uniform in height adjoined toward their base but
solitary in having separate walls, made an appearance in the fossil record.
With the arthropod’s exoskeleton acting
as protection from dessication and jointed appendages ideal for walking, Mother
Nature favored arthropodal land exploitation and sure enough around 407 mya,
insects that had evolved from shoreline arthropods such as euthycarcinoids, are
the first true animals to have conquered land as evidenced in the world’s
oldest known insect, Rhyniognatha hirsti
found in Scottish Rhynie sedimentary chert.
 |
| R. hirsti |
Rhyniognatha already
possessed characteristics of having wings. Insect wings likely developed due to
mobility in skipping across water surfaces once transitioning from the aquatic
larval stage to a terrestrial adult stage.
The first insects were plant feeders as
plants were well established in the Devonian period with seed ferns, under the
term, pteridospermphyta showing up in
the late Devonian that was a base ancestor to the ginkgo and cycad families.
Now extinct trimerophytes and zoesterophylls had spread vegetatively
without spores or seeds far inland by the mid Devonian.
With developed book lungs, the aquatic
scorpion forgoes gill breathing adapting to an existence on land 370 mya.
 |
| Trogontarbid |
Another Devonian arachnid appearance was
in the form of the mite, possibly the first parasite infecting land plant and animal
hosts. One thing curious is that today’s dust mites have parasitic ancestors.
This is ‘reverse evolution’ and
possibly arose due to their ancestors switching of hosts. This perhaps has
given the ability of the dust mite to rely on skin flakes, chitinous nail, hair
and feather bits as opposed to being totally dependent upon a specific host as
most parasites are.
Ammonites make their appearance in the
mid Devonian, which are cephalopods related to octopi, squids and cuttlefish.
Ammonites were so successful in radiating out that ammonite species are used as
fossil indexes in linking rock layers to specific geological time periods.
Chondrichthyes, a cartilaginous
fish class consisting of sharks, rays, skates and chimeras show up 395 mya. Acanthodii seems to be their immediate
ancestors.
 |
| Placoderm battling Devonian sharks |
One of the most important developments
to have evolutionarily occurred is the step of fish from water to land. Crossopterygians are a subclass of sarcopterygians
and in addition to a branchial (gill) system, possessed a pulmonary (lung)
system for engulfing atmospheric air. The Devonian known as the ‘Age of Fishes’ had experienced advanced
forms of predators roaming all the seas. To escape the predation,
crossopterygians began living along shorelines in waters that prevalently
experienced hypoxic (low oxygen) conditions, thus the need for a second source
of breathing.
 |
| Crossopterygian Tiktaalik |
In living near shore, they observed an
untapped food resource on land from the established insect and plant life. With
their sarcopterygian lobed, but weight support fins acting as legs, they
ventured onto land enticed by the abundant food sources. Further, they migrated
to nearby freshwater pools and ponds and migrated even further inland to other
bodies of freshwater when the ones occupied dried up.
 |
| Early labyrinthodont: Acanthostega |
 |
| Acanthostega |
 |
| Labyrinthodont: Ichthyostegalia |
 |
| From top to bottom early, mid, late Devonian |
During the Devonian the world’s terrain
collected into the two supercontinents of Gondwana and Euramerica. Both were
vast land masses and besides a few isolated islands the rest of Earth was ocean
covered. Throughout the Devonian the land masses experienced very warm arid
climates with virtually no glaciation until the very tail end of the Devonian
when two consecutive great mass extinctions occurred. The first lasted two
million years while the second lasting a million years of the period, decimated
life. Nearly 70% of all marine life had become extinct by the end of the
Devonian.
The cause again was glaciation taking up
water affecting most of shallow water marine life, but glaciation had help. In
the first episode, large volcanic eruptions in eastern Siberia had its effect
on climate change. There is evidence of meteor or asteroid impacts during this
period. In the last Devonian million year period, Gondwana had drifted back
over onto the South Pole creating an intense cooling effect.
 |
| Devonian trees |
Although limited to shallow water or
water logged regions, Lepidodendrales
and the genus, Archaeopteris a tree
like plant with fern shaped leaves were well established as forests by the end
of the Devonian. These Devonian forests, along with their Carboniferous
depositions, are the results of the vast coal deposits found today. With their
introduced capability in sequestering carbon and weathering of land surface
rock in rooting, the carbon sink action and introduced nutrient runoff aided in
cooling climate and creating hypoxic ocean dead zones.
With these Devonian extinctions, gone
were the placoderms, ostracoderms and all other agnathids except for ancestors
to the cyclostomes (lamprey, hagfish) that had split from the rest of agnathans
in the Devonian.
During the two late Devonian extinctions
there was a rapid drop in sea level followed by a rapid rise in sea level
decimating benthic shallow sea life. Reef building sponge stromatoporoids,
rugose and tabulate corals became extinct. The event impacted trilobites and
ammonoids that never fully recovered to become extinct in the following
Carboniferous Period. Brachiopods would never be prevalent again, although they
have even hung on in a few representative species found in the oceans today.
From acritarchs and planktonic graptolites to 75% of fish species, all became
extinct.
 |
| Cephalaspis, one of last Devonian ostracoderms |
With this tremendous stress on life, if
much of the Silurian and Devonian had only witnessed marginal success in
radiative speciation, animal life may have become extinct period during the late
Devonian mass extinction episodes. For sure though, if any had survived, it
would have evolved differently in possibly excluding the human factor.
Regardless, the labyrinthodonts had made
their appearance in the late Devonian and were the progenitors and architects
of what tetrapodal land animals were to become.
Coming
Together:
We have to understand all aspects that
at the right place at the right time in comprehending what true speciation is
all about. In understanding the mechanism (ecology) in its effects on the
process (natural selection) we can attempt to discern the particular trend in a
resultant pattern (evolution), as well as understanding the wrong place at the
wrong time in decline (extinction).
Evolution sires diversity with lineage,
adaptation and biomass having impact on ecological biomes. It may be beneficial
or deleterious. When it comes to man, the mass extinctions we have been
discussing are basically two. In the geological and fossil record there were
three more making a total of five mass extinction episodes.
During the Anthropocene, the ‘Age of Man,’ humans have already been the sole
reason in causing species extinctions. This is a double barrel shot gun effect
as once a species is gone, so too goes its genetic phyla for future
descendants.
A recent University of Wisconsin study’s
conclusion from fossil studies suggests that as humans advanced into other
lands, they hunted the larger animals into extinction. Evidence rules out
climatic, geological or calamity events such as a meteor impact and points to
the arrival of early man with the larger animals disappearing a few thousand
years afterwards.
 |
| Dodo Bird |
Also, as humans migrated, they took with
them diseases that could infect secondary hosts. It was always thought that the
three tapeworms infecting man came from cows, pigs and dogs once man began raising
livestock 10,000 years ago. It has been now proven that the opposite actually
occurred. T. saginata, T. solium and D. caninum tapeworm species have been infecting humans and their
ancestors since 1.7 million years ago. Once animal husbandry began the tapeworm
parasites made the jump to man’s domesticated animals.
 |
| Atlas Bear |
Recently in the last couple hundred
years, sixty-one species are gone forever due to man’s activity. From the
killing of the Mauritius endemic dodo bird and introduction of rats to its island
habitat eating its eggs and young to the last atlas bear, Africa’s only native
bear, being shot in 1890 by Moroccan hunters. The most recent extinction is of
the Yangtze River dolphin owed to manmade pollutants and the construction of
dams. Sixty-one species within a couple centuries have become extinct strictly
due to man’s careless actions. Click here to see the list.
.jpg) |
| Yangtze River dolphin |
University of California Berkeley paleontologist,
Anthony Barnosky estimates that if all things proceed as they are, 75% of
existing species today will be extinct within 300 years. More than the animals
already extinct, he bases it on living species that are at their tipping
points.
Barnosky is the one who coined the
phrase the “McDonaldization of nature,” as a play on the American sociologist,
George Ritzer’s “McDonaldization of society.” What he means in his expression
is that many species are habitat specific and when man introduces himself, his
development and invasive species, it stresses those endemic species to the point of extinction due to the inability to fully adapt. This is similar to what has
happened in nature. When the jaguar crossed the Central American land bridge from
North America into South America, the large carnivore proceeded eating up much
of the native fauna causing extinction in species.
 |
| A young Yangtze River dolphin one of the last of 13 in '90s population |
Some may whine and say nature does this,
so what’s wrong if man does it too? I wish oblivious naivety wasn’t so
prominent. For man to realize an alarming rate of animals going extinct or on
the verge, it is senseless to accommodate the scenario. Whether you have a
sense of appreciation for wildlife or not we are bound by all life. We’re all
in life’s threaded web; unravel one thread and the whole thread begins unraveling.
Who cares about a little minnow in a
stream? Who cares about some desert tortoise, or frog, or butterfly, or…right? Another
animal also fits this mindset. The microscopic 4.5mm/0.18in Turritopsis jellyfish, otherwise known
as the immortal jellyfish has the ability to reverse age becoming younger. When
stressed from disease, pain or damage this diminutive jellyfish has the ability
to revert itself into a polyp rejuvenating itself as young again. Wow, who
cares about some tiny jellyfish that just happens to be the elixir for the
fountain of youth we’ve been vainly seeking for ages? Hmm…
Natural History Museum of London
paleontologist, Professor Norman MacLeod stresses, “Life is very robust and it
takes a sequence of events to produce large-scale extinctions. If you add up
the numbers of species that have been wiped out over the past few hundred
years, then you find the figures fall well short of a mass extinction. It is
only when you look at the numbers of creatures that are poised at the brink of eradication does the
picture become alarming.”
Today, habitat loss is the major
concern, but what is worse is not simply climate change, but our ignorant
refusal based on economic ineptitude to deny it is egregious. Climate change
and habitat loss along with the aid of man’s spears and guns…coral reefs and
all the marine life they support, tigers, amphibians, desert tortoises, shark
species, orangutans, mountain gorillas, the marine iguanas of the Galápagos,
albatrosses, chimpanzees and thousands of other creatures now face obliteration
from extinction.
How we live our lives in choice and
decision means more than merely how long we live.
This is the third segment of ‘Et Tunc
Nulla Erat.’ Picking up from labyrinthodonts, the fourth and last segment will
conclude the series discussing amphibians to mammals and man’s evolution. Hope
that ya join me…
In Evolutionary
Reporting,
BJA
05//2014
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