Et Tunc Nulla Erat III

Et tunc nulla erat III
 (And Then There Was)

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.
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.

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.

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. 

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.

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. By the end of the Cambrian, as in the illustration found to the right, many animal classes had gone extinct including, Anomalocaris, the eel-like Pikaia and the trilobite order Redlichiida.

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.
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.
Silurian landscapes; Left: Early Right: Mid
Major volcanism causing extensive outgassing during this time frame, was balanced by weathering in the uplifting orogeny of the Appalachian Mountains sequestering carbon dioxide. 

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.

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
The development of the jaw is what rifled fish into a very successful story. As a secondary component the jaw allowed fish to take in more oxygen serving as a buccal pump when opening and closing in alternating fashion. Excess oxygen availability allowed fish to live in more oxygen depleted domains and more energy to grow stronger, larger and faster.

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.

By the Devonian Period, eurypterids had gone from the deeper seas to the shallows and even inland lakes. Representatives of these eurypterids, such as hibbertopterids had eight large legs capable of land locomotion. From these evolving eurypterid arthropods, the first spider-like terrestrial true arachnid, trogontarbid made its appearance around 400-399 mya. By 380 mya the first true arachnid spiders arise in the fossil record. These first spiders such as uraraneids and Attercopus could produce silk with spigots, but did not possess spinnerets as modern spiders do.

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
Eventually, the crossopterygians relied more on lung capacity in the adult stage and began evolving a foot as opposed to a fin, yet still maintaining the same fin bone configuration. Plant life had invaded vast swaths of land during the Devonian. A foot replacing a fin was far more superior in traversing land with all types of entangled low lying plants and plant impediment parts.

With all this going on, the crossopterygian had evolved into a totally new species, the labyrinthodont at the end of the Devonian 365 mya. The earliest and most primitive labyrinthodonts were still throughout all stages waterbound, but in the later forms only the larval stage was dependent on an aquatic environment. The first tadpole had made its appearance.

Labyrinthodont: Ichthyostegalia
The labyrinthodont is the direct ancestor to all extant land living vertebrates. Although with short stubby legs ending in webbed feet, primitive labyrinthodonts were the first vertebrate to truly walk land with a mastered gait as the earth’s first true tetrapod that all other land vertebrates would carry in situ and in various forms. They were fully geared for walking with a complex vertebrate spinal column composed in four pieces as the intercentrum, two pleurocentras and a vertebral arch. The skull was massive with two nostril holes, openings for the paired eyes and a third photo receptive parietal eye. Skull shape was flattened covered in dermal armor and possessed a pair of otic notches functioning as a spiracle in the primitive forms and more as auditory structures for picking up airborne low energy sound vibrations in later labyrinthodonts.         
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. 
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,