Cambrian explosion of life

Another Cambrian life and evolution bookmark

BBC Science pages EARTH TIMELINE

They know how to share knowledge, the people in the justly legendary BBC

From Cambrian to Concertgebouw

Salton Sea, California
Image: Aquafornia

Sitting on the shore of Cambrian sea is a very peaceful experience. There are no other humans around on the virgin beach, not even footprints of Friday. There are no dangerous animals lurking in the jungle as there are no land animals, even insects, neither any plants growing on the land. No birds are flying in the air still so thin of oxygen - it is just me and the vast ocean opening to the end of this world.

The quiet is so remarkable that my ears actully here the lack of sounds. No mocking bird singing, no wind in the willows, no grasshoppers playing their violins - nothing living at all.

The sea water is so clear that I can easily sea the many plants and animals near the shore. Somehow I have no urge to take a dip in these waters. I do know that most of those things swarming in the sea are totally harmless to me who present blood and flesh from another world yet to come. But these antennas, complex eyes, multiple legs, tails, things moving here and there, ugh... these waters are not for the casual human swimmer, nope.

So I just sit there enjoying the peace and let my mind wander without distractions.

In front of me I see what anyone with good will might call primitive life forms (or less). Yes, they are. fabulous, inventive, complicated each in its own way, funny even, but here is nothing much beyond basic necessities for the survival, various types of mouths for eating and digesting, organs for having good sex and hopefully peaceful sleeping in some safe hole on the bottom of the sea. Life, amazing life, but this could be a bit boring for me on the long term.

My mind travels forward in time and reaches Amsterdam 2012. I imagine being in the Concergebouw and seeing the grand..... grand ... grand children of these primitive Cambrian life forms sitting in the hall dressed in best clothes and ladies decorated with expensive jewels. In front of the huge organ sits a highly organized band of professional musicians each with a carefully manufactured and perfectly tuned top class musical instrument in his or her hand.

A human being standing upright on two legs called Bernard Haiting is totally concentrated in conducting Anton Bruckner's 5th Symphony and the musicians following the lead of his baton make no mistakes. Make no mistake of that, for this is the Royal Concertgebouw Orchestra.

Haitink is the embodiment of a tradition of Bruckner conducting that is fiercely true to the cleaned-up scores: there is no funny business. Nor is there any great flexibility with the tempo, no unmarked accelerandos nor exaggerated ritardandos. The markings added to the scores published in Bruckner’s day suggest that this is not how the symphonies were performed then, nor is it how Furtwängler and Barenboim have approached them. Even Abbado was not above interventions to over-highlight the second violins in the Scherzo, or to bring out the flutes towards the end of the finale coda. But from the moment you see the wonderful Concertgebouw take their seats and you realise the orchestra is exactly as Bruckner specified – no extra brass (the so-called “eleven apostles” favoured by Jochum and other conductors), not even a “bumper”, just the four horns, three trumpets, three trombones and tuba – you know this is going to be a performance with no pretensions beyond Bruckner’s own. And when Haitink raises his baton and with absolute security ushers in the disparate elements of the slow introduction, you also know that the symphony is in safe hands: no matter how discursive or episodic it may at times seem to be, the form is absolutely secure and, come the great affirmative ennobling chorale that brings this immense symphony to an end, you are gratefully aware that Haitink, like Bruckner, had this destination in mind throughout.
Ken Ward 21st May 2012

Hearing Bruckner's eerie music in my mind while sitting on the bare sand of Cambrian sea shore I say to myself "What a wonderful world!"

How all the biocomplexity and convulsed evolution of life forms from the explosion of life in Cambrian to the architectural and musical harmonies of Concertgebouw has not only produced species that are better adapted to survive in the changing environments of the Nature..

Instead of providing just the bare necessities, our good God has made planet Earth a very comfortable place to live for the humans He so loves, filled it with colours, sounds, tastes, wind in the willows, birds singing and even good tasting fish (among some killer sharks) in the much more comfortable seas for surfers and swimmers.

Of course evolutionary biologist are allowed to try to figure out in strict selective ways why that early human had made a flute of bone and carved a Penthouse style figurine of a woman and taken them to his cave some 40k years ago. My suggestion is "just for fun".

Classical music of Bruckner's complexity is rather useless from the strictly utilitarian point of view of evolutionism - and some less musical people, as well - comparing to military marches, Scottish bagpipes or the African warriors drumming themselves ready for an attack in the tribal war.

I sit quietly and wonder - from here to there.

What a trip to terrestrial life!

Robots, intelligence and Cambrian life forms

This is a bookmark to a very interesting report by Jo Pavlus in BBC Future (29 June 2012) concerning artificial intelligence and the future of robotics.

 Link

When looking at Cambrian life forms one can hardly avoid a comparison to modern efforts to create intelligently moving robots that sense the environment and make decisions on the basis of this information.

The FuRo futuristic robot Halluc II ^myBlog is an actual example of a modern robot moving in a manner that was inspired by a Cambrian life proto-type, so to say.

Trilobite life cycle

Life cycle of a trilobite

Drawing © Sam Gon III

Talking about the complexity of early life...

Sexuality is a serious challenge to evolutionary hypotheses and requires broad approach to the study of life. I think that natural selection alone is not sophisticated enough as a tool to explain the duality of Ying and Yang in nature. Better scientific explanations are needed.

But the drawing of the life cycle of Isotelus parvirugosus really hits the nail of complexity to the reconstruction of the origins and develompent of life.

Why such enormously complex and difficult to figure out system?

I do not try to explain the life cycle here - it is complex - and I only refer here to Sam's page on Trilobite ontogeny as an accurate source of information on the subject.


Here the life cycle of the Blue crab for comparison that even a child can understand

Maryland Department of natural resources (ref)

God and Cambrian sex

Personally I find it very significant that at the early stage of evolution of life on Earth we already have evidence of sexual reproduction involving handsome male and egg-bearing pretty female trilobites.

Sexuality is a very deep rooted character of living organisms. I suggest that this is one of the things that astrobiologists will notice in the species they found in space, as well.

Why such a broad claim?

Because it seems from the Bible that God of Israel, the creator of the universe, has some sort of Ying and Yang!

It is true that Lord Jesus said that in afterlife there is no more marriage.

But the first creation story in the Bible has a curious and powerful description of the creation of the image of God. That concept used here, an image, indicates that the image tells something about its target.

And God said, "Let Us make man in Our image, after Our likeness; and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth and over every creeping thing that creepeth upon the earth."

So God created man in His own image, in the image of God created He him; male and female created He them.
And God blessed them, and God said unto them, "Be fruitful and multiply, and replenish the earth, and subdue it; and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth."
Genesis 1:26-28 KJ21

One of the many wonderful things in these verses of the Bible is the complexity of the image.

Often we men think that we are the image of God.

It makes us feel that at least in this point the Bible has it right...

However, this is not what the Bible is saying here.

It says "man and woman" is the image of God.


Well. There is much to think about that!

My point is that the creation of life involves this concept from the very beginning - that there are boys and girls.

Even among the first arthropods.

Trilobite sexuality

© Fortey & Hughes 1998

Trilobite with brood pouch

Sex in the Cambrian period?

Were they not all just some organisms multiplying somehow... in a very primitive way?

Sexuality is a concept that involves usually two distinct types of the same organism we usually call in English male and female.

Sexuality suggests pairing of different body parts which is in evolutionary theory a serious complication. Why and how two different creatures must be there in the line of reproduction? How come...

Sexuality suggests much more complex social behaviour than just being there and bringing one offspring after other to this world since it has an evolutionary purpose helping the species to choose attractive partner.

It is quite a world in itself and dominates modern humans.

Well, whatever... The fact is, according to Sam Gon III, trilobites had sex in those Cambrian oceans. The evidence is there in the fossil evidence but apparently quite rare and not so simple to analyse and interpret.

Drawing ©2000 by S. M. Gon after Fortey & Hughes 1998

Trilobites are thought to have reproduced sexually, as do nearly all arthropods today.

Eggs were presumably laid, but fossilized eggs that may be of Cambrian eodiscid trilobites have been documented only once (Zhang, X. & B. Pratt. 1994. Middle Cambrian arthropod embryos with blastomeres. Science 266:637-9)..

It has recently been suggested that some trilobites may have held eggs and/or developing young within the cephalon (as horseshoe crabs do today), and anterior median swellings of the cephalon (of the preglabellar field) in some specimens are interpreted as brood pouches (e.g., Fortey, R.A. & N.C. Hughes. 1998. Brood pouches in trilobites.  Paleontology 72(4):638-49) because they appear only in holaspids (adults) and represent a dimorphism in which the swelling is the only morphological difference.

Ostracods and some other crustaceans show similar brood pouch swellings, although not at the anterior of the body. Because specimens with brood pouches appear only in natant trilobites, it is possible that the eggs or protaspids were released ventrally, anterior of the hypostome.
trilobite info pages

Horse shoe crab 

Beach chair scientist

Horse shoe crabs are sometimes met at the beaches on Earth today.

The animal helps really looks a bit like a trilobite but is not a relative. It helps scientists to understand the features on surviving trilobite fossils like in the case of suggesting that maybe also trilobite young developed within the cephalon.


As for the physical and social details of arthropod sex in general and the love life of horse shoe crabs and trilobites in special... 

Very interesting in many aspects but I skip it for now.

The important point here is the presence of sexuality in these early life forms in Cambrian seas.

First eyes - Trevor D. Lamb et al.

The evolution of phototransduction and eyes

Trevor D Lamb, Detlev Arendt and Shaun P Collin

 Royal Society Publishing October 2009.

Well, well.

Now I understand the fighting spirit in the Scientific America 2011 preview - Trevor D. Lamb is a friend of Richard Dawkin and thus presents one side in the Atheism/Creationism coin.

The publisher introduces this highly interesting book with these words (probably written by the authors)

Charles Darwin was acutely aware of the importance of explaining the evolution of 'organs of extreme perfection' such as the eye and in recent years there has been remarkable progress in understanding how the eyes of vertebrate and invertebrate animals have evolved. In this Theme Issue, leading figures in the field draw together our current understanding.

The contributions span the range - from the origin of the simplest forms of light detection in primitive organisms more than a billion years ago, through the strategies adopted to improve photoreceptors, to the origin of simple shading eyes, and their evolution into modern visual organs with outstanding performance.

A common theme running through the articles is the vast amount of information that is available through examination of the genes of different organisms.

Thus, much of the evolution of vision can be traced through the genes that specify neural development and eye development, and the genes that encode visual pigments (opsins) and other components of phototransduction (the conversion of light into a neural signal).

This collection of work represents our current knowledge of the evolution of photoreceptors and their incorporation into eyes.
Royal Society Publishing

Different ballgame altogether - DNA
The approach to understanding the origins and evolution of eye in this modern publication is different from the traditional "go and find fossil evidence" method.

Instead of hunting for those probably extremely rare survivors of early photosensors these scientists study the Book of Life, DNA, in order to reconstruct the history of the eye.

How very interesting!

I have opened another blog God, DNA and evolution because Evolutionary Genetics is a very specific and significant field of research of the origins of life before the Cambrian period.


Actively evolving organism
As for my claim that some evolution biologists project God into natural processes, read this sentence carefully from the introductory text

"through the strategies adopted to improve photoreceptors, to the origin of simple shading eyes"

It is not so far from the learned language of Sam Gon III and others who occasionally use the verb evolve in active mode. We laypeople get the impression that some trilobites evolved long spikes to balance them while swimming and others actively adapted to the environment by effacement that made burrowing life style easier ^myBlog.

These rather Promethean attitudes are prevalent today.

As an alternative I am not suggesting introducing religion into science, far from that! We have no ability to understand how God relates to His work, we can only study His work and praise His wisdom.

Instead, let us just keep the rules of the game clear: this fabulous collection of research articles is in the field of genetics and scientifically describes what may have probably taken place in the past.

A comprehensive explanation showing full understanding of why things live and grow and evolve it definitely is not.

Future generations of scientist will look at our top knowledge of the evolution of eye as we look at the knowledge of Charles Darwin and his generation... before George Mendel.



Contents:

Introduction: The evolution of phototransduction and eyes	Trevor D Lamb, Detlev Arendt and Shaun P Collin
The ‘division of labour’ model of eye evolution	Detlev Arendt, Harald Hausen and Günter Purschke
Eye evolution: common use and independent recruitment of genetic components	Pavel Vopalensky and Zbynek Kozmik
The evolution of eyes and visually guided behaviour	Dan-Eric Nilsson
The evolution of irradiance detection: melanopsin and the non-visual opsins	Stuart N Peirson, Stephanie Halford and Russell G Foster
Evolution of vertebrate rod and cone phototransduction genes	Dan Larhammar, Karin Nordström and Tomas A Larsson
Evolution of opsins and phototransduction	Yoshinori Shichida and Take Matsuyama
Evolution and the origin of the visual retinoid cycle in vertebrates	Takehiro G Kusakabe, Noriko Takimoto, Minghao Jin, and Motoyuki Tsuda
Evolution of vertebrate retinal photoreception	Trevor D Lamb
The evolution of early vertebrate photoreceptors	Shaun P Collin, Wayne L Davies, Nathan S Hart and David M Hunt
Evolution and spectral tuning of visual pigments in birds and mammals	David M Hunt, Livia S Carvalho, Jill A Cowing and Wayne L Davies
Evolution of colour vision in mammals	Gerald H Jacobs

First eyes? Scientific American 2011

We are asking the biologists to tell us who was the first one to see anything upon Earth.

We have been told that it was not Cambrian trilobite nor Anomalocaris or other creatures with complex eyes on those oceans.

Please, tell us who?

Did these earliest eyes resemble camera obscura as some sort of dark chambers with pinholes and primitive nerve sensing light and dark or what?

For if we should take the role of God the Creator and figure out how to create eyes, some hint from His work could help.


Evolution of the Eye [Preview]
"Scientists now have a clear vision of how our notoriously complex eye came to be"
By Trevor D. Lamb June 27, 2011

The human eye is an exquisitely complicated organ. It acts like a camera to collect and focus light and convert it into an electrical signal that the brain translates into images. But instead of photographic film, it has a highly specialized retina that detects light and processes the signals using dozens of different kinds of neurons.

So intricate is the eye that its origin has long been a cause célèbre among creationists and intelligent design proponents, who hold it up as a prime example of what they term irreducible complexity—a system that cannot function in the absence of any of its components and that therefore cannot have evolved naturally from a more primitive form.

Indeed, Charles Darwin himself acknowledged in On the Origin of Species—the 1859 book detailing his theory of evolution by natural selection—that it might seem absurd to think the eye formed by natural selection. He nonetheless firmly believed that the eye did evolve in that way, despite a lack of evidence for intermediate forms at the time.
Scientific American

Evolution = Natural selection
Well well, that certainly is a battle cry against all those who believe in creation or Intelligent Design!

Please note that this fighter, Trevor D. Lamb, is writing in Scientific American.

Evolution is here firmly equalled to the mechanisms of natural selection. IMHO this is a gross simplification of evolution since natural selection is only one of the tools God uses in creating life. More science, better analysis and innovative thinking is required to complete the picture of how life evolves.

But back to our question. Surely Mr. Lamb can inform us about the first eyes upon Earth!


Origins of eyes
Trevor summarizes the article continuing the trend of defending our dear Charles and equalling evolution with natural selection:

The results indicate that our kind of eye—the type common across vertebrates—took shape in less than 100 million years, evolving from a simple light sensor for circadian (daily) and seasonal rhythms around 600 million years ago to an optically and neurologically sophisticated organ by 500 million years ago.

More than 150 years after Darwin published his groundbreaking theory, these findings put the nail in the coffin of irreducible complexity and beautifully support Darwin’s idea.

They also explain why the eye, far from being a perfectly engineered piece of machinery, exhibits a number of major flaws—these flaws are the scars of evolution.

Natural selection does not, as some might think, result in perfection. It tinkers with the material available to it, sometimes to odd effect.
Scientific American

Comment: camera obscura after all?
Those 600 million years roughly mentioned in the Scientific American article would suggest that there is fossil evidence of simple Ediacaran light sensors from which the Cambrian eye evolved.

We have learned that paleobiologists tend to see a major break between the Ediacaran enigma and Cambrian explosion of life. In fact, there may have been one of those extinctions known from later periods, for example at the end of Permian or the catastrophic destruction of Mesozoic life.

But this article suggests continuity, a logical process in purely Victorian mechanical world, that somehow produces increasingly sophisticated systems given enough time and suitably changing environments.

Let us try to learn more about the fossil evidence for early light sensors and eyes and continuity - this is getting a bit confusing.


Konservat-lagerstätte?
Of course, we need to be aware that very few such delicate organs as eyes or proto-eyes if you want may have survived and the best place for hunting would be those divine nature reserves.

In fact, since God saw it good to let Adam see early bird, His masterwork, so perhaps God has also proudly preserved evidence of early eyes, His masterwork, somewhere for us to admire and to learn more and to praise Him.

Maybe that deposit has not been found yet and now would be good time as Adam is getting more understanding what that discovery would signify.

(Remember that feather, found when Darwin had published his revolutioary Origin of Species)

Anomaclocaris' eyes

Anomalocaris. An artist's view

Credit Katrina Kenny/University of Adelaide, Australia

It was the fabulous discovery in 2011 of the well preserved eyes of that strange Cambrian "shrimp" Anomalocaris that made me double interested in astrobiology and what an alien might have found on our planet when life began here in earnest ^myBlog 

As in the case of trilobites, also here we find at early stage of evolution staggeringly sophisticated and structurally highly complex eyes with close to 36.000 small lenses working together in perfect harmony to give the predator an almost 360^o view of the surrounding sea.

Such amazing eyes exist also today - the design was a success! - enabling flies to decide where to fly and dragonflies to hunt them on the fly.

Dragonfly eyes

wikimedia

Sam Gon III and proponents of Intelligent Design

When studying Trilobite evolution Sam Gon III is battling with the same Philosophical and Theological questions as everyone else.

He makes this important statement about Intelligent Design in connection with the trilobite eyes.


I use the term "design" as a lead-in to the parallels between the optic designs of humans and the remarkably evolved morphology of trilobites. 

Trilobites provide some superb examples of evolution in action (see "loss of eyes" below). 

Trilobites make it quite clear that evolution of eyes occurs, and that one does not need to evoke "intelligent design" by a creator to explain them. To do so detracts from the idea of an omniscient being. 

It would have God tinkering with many flawed and suboptimal "designs" and never developing a perfect one. Who would want to worship a god like that?

 I mention this because this page has been used (without my permission) by people espousing "intelligent design" to the public, and I want it to be clear that I do not share those opinions, nor need that flawed argument to underpin my faith. 

Evolution is a remarkable and well-documented process, and breakthroughs in our understanding of its intricacies occur every year. Evolution is not in conflict with religious belief. Ignorance and intolerance damage the benefits of faith. 
Sam Gon III



Comment
Personally I agree with most of what Sam Gon III is saying here and especially the final paragraph is essential regardless of once religion.

As he writes, we cannot and we should not invoke spirits or gods or even the One real God to explain natural phenomena as if we were able to see the relation between creation and Creator. This is the standard pit into witch both Atheists and Creationists fall, the one denying and the other enforcing such an element into rational scientific inquiry. What element? That exactly is the point!

However, Sam has this theological point also raised by Richard Dawkin

"It would have God tinkering with many flawed and suboptimal "designs" and never developing a perfect one. Who would want to worship a god like that?"

In other words, the reality does not correspond to our view of a perfect God.

Charles Darwin once wrote "I cannot believe in a God who has created cats to play with the mouse they have captured".

But the fact is that God has created cats to play with the mouse. The problem is not the reality but our image of God.

He is not some philosophical principle or logical mathematical purity but a dangerous and rather bad tempered person.

Let us worship Him as He is and not some pure good image created in our own heads "as God should be" to please us, His creatures!.

Early eyes

Holochroal eyes of the Asaphoid trilobite Isotelus

 Sam

Here he/she is looking at us from some five hundred million years ago.

Isn't early Earth so fresh and interesting!

However, our teacher Sam Gon III says that trilobites were not the first creatures on Earth to see:

Although they were not the first animals with eyes, trilobites developed one of the first sophisticated visual systems in the animal kingdom.

The majority of trilobites bore a pair of compound eyes (made up of many lensed units).

They typically occupied the outer edges of the fixigena (fixed cheeks) on either side of the glabella, adjacent to the facial sutures.

At least one suborder of trilobites, the Agnostina, are thought to be primarily eyeless. None have ever been found with eyes. In contrast, a few secondarily eyeless species (in which a clear evolutionary trend toward reduced eye size with eventual disappearence of eyes altogether) have developed within several groups, even those known for large, well-developed eyes (e.g., Phacopina).
Sam Gon III website

Classification of trilobite eyes

Scientists classify three main types of eyes found on these creatures (from Sam page):


1. Holochroal

• found in nearly all Orders
• few to very many lenses (to >15,000!)
• lenses typically small, numerous
• one corneal layer covers all lenses
• lenses in direct contact with others
• no sclera between lenses
• corneal membrane covers surface only 

2. Schizochroal

• found in some Phacopida only
• typically fewer lenses (to ca 700)
• lenses much larger, fewer
• each lens bears an individual cornea
• lenses separated from each other
• sclera between lenses very deep
• corneal membrane extends into sclera

3. Abathochroal

• found in Cambrian Eodiscina only
• few lenses (to ca 70)
• lens size small, not numerous
• each lens bears an individual cornea
• lenses separated from each other
• interlensar sclera not deeper than lenses
• corneal membrane ends at lens margin

 It is important to note that all early trilobites dating to the Cambrian period had holochroal eyes.

The picture below shows how FIRST trilobite eyes looked early in the evolutionary tree of these amazing animals.

Trilobite eyes and the optics of Des Cartes and Huygens

Clarkson, E. N. K. and R. Levi-Setti. 1975.

Nature 254 (1975): 663-667.

Yes, you heard Sam right - these highly complex eyes with thousands of lenses working together and with one corneal level covering all lenses and lenses in contact with each other (not yet contact lenses, though) are found in the FIRST trilobites.

No simple camera obscura here to start some line of evolution. Sorry.

Please, take a careful look at the Trilobite info pages to learn more about the variations, angles of view, ideas about evolution of these eyes and more.

The Eyes of Daniel C. Dennett

Daniel C. Dennett is University Professor and Austin B. Fletcher Professor of Philosophy, and Co-Director of the Center for Cognitive Studies at Tufts University. (homepage)

Like most humans, also he has two eyes in front of his face (Richard Falk aka Detective Columbo, had one eye and one glass eye). As his photo on the left shows professor Dennett enhances his eyesight with two external lenses that are held securely on place with a special frame structure for good focus. (As far as I know, this smart device, eyeglasses, was invented in late 16th century Netherlands and are a great benefit to mankind.)


Movement of eyes and the head holding them
Dennett can move his eyes synchronized (some even asynchronized depending on the genetic heritage) and the movements are controlled by the cooperation of several groups of muscles around the eye.

He has the ability to turn his look at will and turn his head in order to see something on the sides, as well. Sometimes humans use this ability to stare for a competition testing who will first turn away his or her eyes from those of the opponent. (Such staring games with wild animals such as lions or snakes or bears is not recommended, though. Not even with dogs of any size. Better to look a bit aside and not at the eyes of the animal or they mistakenly think that we are calculating the attack distance and time required to hit and may take initiative.)


Autofocus
Note that the eyes of Professor Dennett have the coveted autofocus feature. It is so important in modern digital cameras that few are made for the general public without at least a rudimentary system. Our professor can focus his eyes without steps from macro mode to infinite and the motor makes no sound and is fairly fast.


Wide angle view
His vision covers about 180 degrees, a bit less, depending on the location of the eyes and has selectivity recognizing and alerting about movement like a good security camera while providing the brain with most information about the main area of focus. This selectivity and keeping down the overall information while still sensing movement in other areas of vision is quite useful for us for example when we are hunting and simultaneously trying to survive from being hunted down in a jungle or field of war.


Automatic maintenance
The eyes of Professor Dennett are regularly watered by a reflective movement of eyelids and drops of tears for maintenance of the delicate surfaces. Tears have also another function for humans showing emotions, sorrow or happiness.


Sophisticated protection
His eyes are further protected by eye lashes that provide shade and filter out dirt from the air near by (they also enhance the beauty of women and perhaps of men too).

Eye brows are set above the safely designed deeper eye sockets and direct the salty sweat that is created by the cooling systems of human forehead away from the eyes. That cooling liquid would otherwise irritate the sensitive surfaces of the eyes.

The eyes of Professor Dennett are further protected by a sophisticated system of eyelids. Should something fly dangerously towards his eyes, even a small insect or something, the system recognizes the danger and eyelids close automatically without his being able to influence the system decision.

The closing of the lids for watering and for protection is extremely fast reaction so that we use in most of our human language the expression "in a blink of an eye" or its equivalent.


Stereo vision
The two eyes of Professor Dennett are so aligned in front of his head that they provide him with stereo vision for estimating distances. (I think that the late period dinosaurs, birds, need to turn their heads rapidly to figure out if something is approaching or getting further away because their eyes tend to be on the sides of the head.)


Senstivity to visible light
Daniel C. Dennett can distinguish an amazing range of colors from the visible spectrum of light and is somewhat sensitive to ultraviolet and infra-red so he needs to protect his eyes against such electro-magnetic radiation. (This is taken care by the system, he does not necessarily need to know what is EMR.)


Automatic sensitivity to dim and bright light
His eyes are furthermore sensitive to the brightness of light, his pupils automatically adjusting the exposure and the photosensitive cells at the back of his eyes been partly specialized for seeing in the dark night and partly in bright daylight.


Recognition and cognitive things
We have not yet even started to talk about the systems that convey light from the eyes of Professor Dennett through complicated neural systems deep into his brain where somehow a corrected, not upside down, image of the surroundings are formed.


This electro-magnetic image is somehow translated into human consciousness (and ant and butterfly and rat consciousness) to produce meaningful information about what is going on.

We know the region and we have learned a lot about the electronic signals that are generated so that there is even hope for true "mind reading" and translating of these signals into something that a handicapped person can use for his or her benefit. And the secret police, of course.


The eyes of Daniel C. Dennett
Professor Dennett is obviously a very wise and learned man who has achieved much in life. He spends time teaching other human beings Philosophy, Love of Wisdom, and is particularly interested in cognitive systems that enable humans and others to recognize things.

Dennett has figured out in his brilliant mind to his satisfaction how eyes have evolved upon Earth as a combination of just the right selective pressures from the Darwinian environment and effect of series of lucky mutations. He concludes that no spirits or gods are needed for the eyes to evolve.

This he tells in the August 28, 2005 New York Times Op-Ed Show me the Science so it is not exactly news seven years later - but still highly relevant.

I wish him well.

Although as a Theologian I am not an expert of Cognitive sciences nor of Evolutionary Biology I can still recognize the importance of systematic scientific research and give it high value. Learn from it and encourage others to study.

But unlike the famed atheist professor defending the independence of State from religion I conclude from the scientific research that I have been able to comprehend that I have even more reason to admire and praise the God of Israel, the only real God there is.

As is written in the Letter to the Romans by Saint Paul and in the Letter to the Hebrews possibly by Apollinus the immense wisdom of God can be SEEN in His works - such, I think, as the eyes of all living things - although He is Himself INVISIBLE to the eyes He has created to us.

I thank God the Creator for the eyes He has given to me as a loving gift, the ability to see, the eyeglasses that help me, the healthy vision which is not at all a guaranteed thing in these days of ours.

I recommend that you do the same and may God keep your eyesight 120!

First eyes upon Earth - camera obscura?

Planet Earth was going through many transformations climate changing, oceans rising and lowering again, land masses moving violently and rocks melting again quietly eroding... In the midst of all this life was surviving as a tiny promise for future patiently building oxygen with the power of Sun.

Evidence has shown that in the Ediacaran period there were mats of sessile organisms on the shallow seas and at some point something moved there for the first time.

But as far as we know, for very long early period in the early history of life upon Earth nobody had eyes to see nor the brains needed to interpret the significance of the electric signals produced by eyes.

Every living thing enjoyed the Sun and used the energy in the photons for their benefit and the benefit of all in one way or other - but nobody had eyes to see.


Definition of an eye
By the English word eye we commonly indicate some kind of organic thing or its mechanical equivalent that lets light in to a small space through an opening, possibly has some sort of lens(es) to focus the incoming photons on a layer acting as photosensitive layer(s) that translate the incoming light beams into some sort of electronic signals that a brain or equivalent can decipher to form a meaningful image of the surroundings.

Is that definition of an eye generic enough?

If there is no opening, no lens, no photosensitive layer, no brain wired to the thing, we call it something else but not an eye, right? At least laymen like me.


Camera obscura

Camera obscura

wikimedia

Camera obscura is the simplest of eye like devices invented by humans. It is not really an eye because although it does have a pinhole and a dark chamber for the light to enter there is no independent photosensitive surface to detect the light nor anykind of built-in or wired brain to interpret the image generated by light beams without any lens bending them on the way.

Nevertheless, camera obscura is an initial rude concept of a device that "can see" and humans are still today busy at work to create increasingly sophisticated cameras that also have sensors for detecting movement, changes in environment and for aiming weapons - of course.



Evolution of camera obscura
It took us with our highly sophisticated brains - by far the smartest upon Earth if we judge from who is the boss among the living things here - quite a long time to evolve the concept of camera obscura.

The first surviving mention of the principles behind the pinhole camera, a precursor to the camera obscura, belongs to Mo-Ti (470 BC to 390 BC), a Chinese philosopher and the founder of Mohism. Mo-Ti referred to this camera as a "collecting plate" or "locked treasure room".

The Greek philosopher Aristotle (384 to 322 BC) understood the optical principle of the pinhole camera. He viewed the crescent shape of a partially eclipsed sun projected on the ground through the holes in a sieve, and the gaps between leaves of a plane tree.

The camera obscura was known to earlier scholars since the time of Mozi and Aristotle. Euclid's Optics (ca 300 BC), presupposed the camera obscura as a demonstration that light travels in straight lines.

Early models were large; comprising either a whole darkened room or a tent (as employed by Johannes Kepler). By the 18th century, following developments by Robert Boyle and Robert Hooke, more easily portable models became available. These were extensively used by amateur artists while on their travels, but they were also employed by professionals, including Paul Sandby, Canaletto and Joshua Reynolds, whose camera (disguised as a book) is now in the Science Museum (London). Such cameras were later adapted by Joseph Nicephore Niepce, Louis Daguerre and William Fox Talbot for creating the first photographs.
wikipedia

Evolution of camera obscura took five million years
So if our species we call human has existed on this planet for about five million years (counting from the DNA based estimation of the time we separated from the chimpanzee) it took us about five million years to evolve the idea of a pinhole camera. Not by everyone  by the very smart people of ancient China and Greece. It obviously took lots of brainpower to figure it out and to build a pinhole camera.

Trilobite evolution - Pitted fringe

Harpetida   Harpes	Asaphida   Cryptolithus

Sam Gon III website

The last, but not least, evolutionary trend that Sam Gon III is discussing in his website is pitted fringe by which they mean an expansion of the cephalon into a concave chamber. 


This Big Head on the two samples shown in the drawings has numerous fenestrations. 


Why?
"In both cases the cephalon is the dominant part, with transverse thoracic segments and an unremarkable pygidium. Long genal spines or genal prolongations are also notable in this morphotype.  They are thought to help stabilize the trilobite during filter-feeding."
Sam 

Filter-feeding brings to my mind for example whales, those lazy bums that just swim around big mouth open and food enters into their system.

But what did these trilobites filter-feed themselves into?


What did trilobites eat?

"Trilobites occupied a huge set of habitats and paleolatitudes, from tropical shallows and reefs, to polar depths, and wide-ranging pelagic habitats in between.

Their diversity of form suggests a complex ecology with many modes of life, including occupation of a variety of trophic (feeding) guilds.

There has been a long history of speculation about the feeding habits of trilobites, ranging from predators, scavengers, filter-feeders, free-swimming planktivores, and even parasites or hosts of chemoautrophic symbionts.

Using modern-day crustaceans as an analog, it is reasonable to suggest that the majority of trilobites may have been predator-scavengers, as the majority of marine crustaceans are today.

Nonetheless, among today's crustaceans are filter-feeders (such as barnacles), planktivores (the majority of larval crustaceans fall into that category), herbivores (many small shrimp species), and parasites (a few copepods, isopods, and other taxa).
Sam

Comment
So my association was not completely off. Professional evolutionary biologists also look at the familiar Nature of modern world and look for analogies.

Of course, my example of whales is far off, but the quote from Sam's expert text gives a listing of closer parallels between today's world and the very first eaters on our planet.

Remarkably interesting!


Barnacle



Balanus improvisus
one of the many barnacle taxa erected by Charles Darwin
wikimedia


As for the analogue of filter-feeding barnacles:

"A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters.

Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile (non-motile) suspension feeders, and have two nektonic (active swimming) larval stages. Around 1,220 barnacle species are currently known.

The name "Cirripedia" is Latin, meaning "curl-footed".
wikipedia

Trilobite evolution - Olenimorph

Wujiajiania sutherlandii
Sam Gon III website

This evolutionary trend towards a shape called olenimorph comes from the type fossil of Ptychopariida Suborder Olenina which have thin exoskeleton, increased numbers of thoracic segments, and a widened, flat body.


Why?
Since we study using Sam's web pages the evolution of trilobites in the Cambrian period (and later) our question is naturally Why a trilobite has these attributes?
And then we explain that the subspecies has evolved these features exactly for this reason.

Right?

So Sam tells us that paleobiologists suggest that the Olenimorph have adapted to a specific environment and the "form is associated with benthic habitats marked by low oxygen and high sulphur compound concentrations"

Hmm...

What has this form to do with that environment?

Elrathia kingi

Sam Gon III website

"Fortey suggests that olenimorphs may represent the first symbiotic relationships with sulphur-eating bacteria as a feeding strategy. The numerous transverse thoracic pleurae presumeably overlaid a series of laterally extended gill exites, maximizing oxygen absorption and providing a large surface area upon (or within) which symbiotic bacteria could live."
[Fortey, R. A., and R. M. Owens. 1999. Feeding habits in trilobites. Palaeontology 42(3):429-65.]
Sam

Well well!

That is - sorry my French - bloody smart from little Ptychopariida!

I would say, that is a divinely smart plan to get more food!

No wonder they flourished all the way from Cambrian to the end of Permian.

Trilobite evolution - Pelagic morphology

Proetida Carolinites leisurely swimming upside down!
Sam Gon III website

Well, just when we thought we have it figured out... normal eyes (more about them later), no need for eyes, so skip them.

And then we get these Big Eye Carolinites as example of  the opposite of reduction of size ... Pelagic morphology.


Nature does not seem to be such a simplistic thing after all - not even at the very beginning of the history of life upon Earth!

Sam does not even try to explain, only notes the fact "There are a number of trilobites that have developed extremely large eyes and elongate, streamlined body shape associated with swimming in the photic water column."

Photic?

The photic zone or euphotic zone (Greek for "well lit”: εὖ “good” + φῶς “light") is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur.

The depth of the photic zone can be affected greatly by seasonal turbidity. It extends from the atmosphere-water interface downwards to a depth where light intensity falls to one percent of that at the surface, called the euphotic depth.

Accordingly, its thickness varies widely on the extent of light attenuation in the water column. Typical euphotic depths vary from only a few centimetres in highly turbid eutrophic lakes, to around 200 metres in the open ocean.
wikipedia

Bingo!

Ah, finally I caught Sam at the scene of the crime that I have blamed evolutionary biologists all along!

Note the active verb " trilobites that have developed extremely large eyes and..."

As if one honourable trilobite decided "now I want to develop big eyes and elongate body shape so that I can swim better in these lovely Cambrian oceans".

As if you could say "now I want to grow red hair because it attracts the kind of men I like."

Heh!

This active form where an organism actively evolves something for some purpose is often present in professional texts and is IMHO highly unprofessional as evolutionary theory emphasizes the importance of environment and selection, not the active action of an organism itself to evolve.

Trilobite evolution - Atheloptic morphology

Eyless trilobites

Sam Gon III web page

Atheloptic means something that involves eyes (optics) - in this case reduction or total loss of eyes. By the way, Sam has a very informative page on trilobite eyes here.

As for no eyes - I have heard about olms (Proteus anguinus) that are amphibians living in dark caves and have no eyes. So this phenomenon is familiar to us also from the nature of modern Europe.

So it is relatively easy to understand when Sam writes "secondary reduction and loss of eyes is thought to be a trend among benthic species living in deep, poorly-lit or aphotic habitats".

Well, the special term benthic is not familiar to me as a humanist and I need to study its meaning

The benthic zone is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers.

Organisms living in this zone are called benthos. They generally live in close relationship with the substrate bottom; many such organisms are permanently attached to the bottom.

The superficial layer of the soil lining the given body of water, the benthic boundary layer, is an integral part of the benthic zone, as it greatly influences the biological activity which takes place there.

Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud.
wikipedia

Adaptation to dark
Over here you do not need eyes so drop them!

Nature does not waist on complex things that are not needed.

Sam: "It is interesting to note that another trend of deep bottom habitat adaptation is an increase in the number and width of thoracic segments, which might be related to specialized feeding adaptations."

Trilobite evolution - Miniaturization

Ptychopariida
Acanthopleurella

We learn from Sam Gon III page on evolutionary trends that the size of some trilobites got smaller.
"Reduction in size is seen in several trilobites, such as Acanthopleurella (just about 1 millimeter at maturity)."

I am not able to argue about the chronological sequences from big Acanthopleurella to small ones. I fully trust the biologists who have studied the evidence that some did get smaller by time, let us say between Ordovici and Permian, and are not just variations of the same animal during Cambrian.


Why, Sam , why?
"The general argument for evolution of small size typically evokes the numerous microhabitats of complex marine systems, coupled with a correlation of size to rapid maturity (early maturation means smaller size at adulthood)."

Hmmm...
Thank you, I need to digest that...


AND...
"When this reduction is due to progenesis (arrested development) the trilobites may also display a reduction in the number of thoracic segments."

Okay, that is great to hear that biologists can detect progenesis...


AND...

Agnostida

Pagetia 

"The entire order Agnostida is composed of small species that may have originated as a miniaturized and specialized early offbranch of the Redlichiida or Ptychopariida."

Hmm...
Now I am a bit confused.

If so, where is the Darvinian natural selection pressure?  You say that Agnostida appear in Cambrian period and originated as mini-trilobites...

Trilobite evolution - Spinosity

Leonaspis sp (Morocco)
From Sam Gon III website

Interestingly, the development of trilobites with spines is opposite to effacement and makes it impossible to  practice the suggested burrowing lifestyle.

Variations of trilobite spines
Sam teaches us about the spines

'Spines may originate from just about any part of the exoskeleton, especially the margins. Sometimes these patterns provide consistent and diagnostic characters for higher classification (for example, the pattern of pygidial spines among odontopleuroid Lichida). However, as seen in the spinose species below, development of spines occurs in many orders of trilobites."

Phacopida	Asaphida	Corynexochida	Proetida

From Sam Gon III website

Why did Nature provide some trilobites such handsome spikes?

Self-defence

Sam gives the suggested answer in Darwin's spirit (adaptation to changing environment)


 "The development of spines is commonly thought of as primarily a defensive adaptation, and increased spinosity is seen in a wide variety of trilobite species."

This line of argumentation suggests that where trilobites were living there was someone interested in them as food. The ones with spikes survived better and increased while those without perished to the mouths or whatever it was that ate them.

In strict Darwinian explanation I guess the assumption would be rather mechanistic: those random mutation of trilobite species that got by pure chance spikes did well in the fight for survival and so they got somehow bigger and bigger until the animal was really spiky!


Alternative hypotheses
Sam is critical and continues the discussion with alternative explanations

"Alternate hypotheses for the adaptive significance of spines include
stabilization structures on a loose silty substrate, and
flotation/stabilization structures for slow-swimming taxa."


Comment
I have the personal feeling that the explanations evolutionary biologists give for the function of the spikes helping the animal to defend itself passively and to balance itself while floating or on silty surfaces. But it does not provide adequate explanation why or how they came into being.

Trilobite evolution - effacement

According to the classic theory of Darwin trilobite itself and the variations are participants in the fight for survival of the fittest. But it is, of course, possible that several variations of the basic type, more or less mutated children of the Grand daddy Redclichia, exist in the same period of life on Earth all doing well in those changing oceans that once existed.

One such example of change by adaptation into the environment is what is called the effacement of trilobite types meaning the loss of detail and complexity as in these examples (see the full article for more examples of the same)

Corynexochida   Bumastus	Agnostida   Lejopyge

I very much like the way Sam describes effacement in exact scientific language. As a simple student of his magnificent page I try to break the rather compact and hard nut into smaller and hopefully easier to digest bits and pieces:

What is effacement?
Loss of surface detail.

"In several trilobite orders, but perhaps most notably among the Agnostida, Corynexochida (Suborder Illaenina), and Asaphida, effacement of cephalic, pygidial, and even thoracic furrows is not uncommon."

Causes problem with taxonomy
Because diagnostic details disappear the established classification of types can get confused because of the missing signs.

"This loss of surface detail can be confounding to systematics, since effaced features (for example loss of glabellar details) can mask evidence of relationships."


Why this happens?
Some palaeobiologists suggest that some trilobites began to dig for food. The suggested mechanism is, I guess, that those mutants who got rid of too much surface detail were able to eat more and reproduce more efficiently and so we have this evolutionary thing.

"Some workers suggest that effacement is an adaptation related to a burrowing lifestyle, especially in Illaenina, but such effacement might also play a role in streamlining of pelagic Asaphida, and is also seen in many Agnostida (which may have been planktonic)."

Not so sure, however
Sam is an honest seeker of truth and critical as good scientists should be.

"No single selection pressure seems to have been responsible for the effaced morphotype."

Trilobite evolution - Morphology

Redlichia 

Grand daddy

Crotalocephalina  Elongated body	Harpillaenus  Transverse form	Balcoracania Increased segments	Thoracocare  Decreased segments

Sam Gon III Trilobige page

Sam's Trilobite pages contain wonderful materials that introduce the work of evolutionary biologists and teaches also us laypeople how fossil evidence is studied in detail to suggest patterns of evolution. There is beautiful, almost mathematical, logic in the variations of the forms shown in these drawings.

Sam says
Through the 300 million years that trilobites existed, prior to their extinction in the Permian, there were many opportunities for diversification of form, starting from the presumed primitive morphology exemplified by a species such as Redlichia.

This typical primitive morphotype had a small pygidium, well developed eye ridges, a simple, lobed glabella, several thoracic segments, and a rather flattened body form. The first trilobites were characterized by this primitive form.

Among the over 20,000 species of described trilobites there are species in which aspects of morphology have diverged greatly from the primitive state. Thoracic segments were reduced to as few as two or increased to over 100, overall body shape was greatly elongated in some, or rendered transverse (widened) in others.
Sam

Trilobite evolution - Origins

From Parvancorina to Trilobite in Four Easy Steps

Sam Gon III Trilobite pages

The series of ontogeny diagrams is highly illustrative and gives fundamental insight on the evolution of a significant family among Cambrian life forms upon Earth.

How do these specimens fit into the chronology of fossil discovery? For the pattern in the schematic chart could suggest that all these branches are variations of a single basic form and they could at some point exist all at the same period of time.

However, Sam tells us that these are called different species and that there is a chronological sequence:
"Taken in sequence, and with legs added to accentuate their underlying shared arthropod heritage, the links between Parvancorina, Primicaris, Naraoia, Kuamaia (a helmetid), and trilobites seem easier to visualize in the sequence below:"

Parvancorina	Primicaris	Naraoia
Kuamaia	Redlichia

The oldest Trilobite is the Redlichia that appears in the lower Cambrian (Series 2).

I understand from Sam that Parvancorina and the fellows including the helmetid Kuamaia are known from the Ediacaran period of enigmatic life forms and these do not appear in the known Cambrian record.

In my untrained eyes the sequence looks like the evolution according to the species (microevolution, in Biblical Hebrew leminehu) rather than the birth of trilobites from some very different species (macroevolution). In other words, that the DNA determining the major characteristics of the species is already locked in the Parvancorina and allows the kind of variations that the main chart is so nicely demonstrating.

Of course, it is a matter of taxonomy and what arguments we use to define a separate species, family or subordinates and so on. But the impression is given that we have something that resembles some  mathematical factor defining the evolution of these things.


Sam

An un-named "soft-bodied trilobite" from the Flinders site in Australia also might seem a reasonable Precambrian candidate antecedent to true trilobites ( Gehling, J.G. 1991. The case for Ediacaran fossil roots to the metazoan tree. Memoirs Geological Society of India. 20: 181-223. ).

At first glance, it resembles the many-segmented Redlichiida, but it also resembles small specimens of Archaeaspinus, Dickinsonia, or Vendia, which most workers do not consider to be of arthropod affinity.

Nonetheless, this taxon, as well as Parvancorina minchami (Glaessner 1980) both suggest that arthropods did not miraculously appear in the Lower Cambrian, but took form during the Precambrian. The specimen of Parvancorina to the right even bears fine lines that some workers have interpreted as evidence of paired limbs.

(Glaessner, M.F. 1980. Parvancorina - an arthropod from the Late Precambrian fauna of the Ediacara Fossil Reserve. Records of the South Australia Museum 13:83-90).

Sam Gon III


COMMENT
Okay! So Sam suggests actually the same thing, a species starting in Ediacaran and continuing in Cambrian and living all the way to the end of Permian.

This pushes the knowledge of trilobites origins forward and raises the question how then did the Parvanorina begin their life upon planet Earth.

Or to paraphrase Sam Gon III "Where did the Parvancorina come from?"

Parvancorina and Primicaris

When we read the web page where Sam Gon III discusses the origins of trilobites we also gain insight on how the curiosity built into us humans leads to a never-ending quest for knowledge and understanding. For God's creation is such that when an answer is found it frequently raises new questions. In this manner, combined with exploration and analysis, our knowledge and understanding of the matter increases.

From his presentation we learn that there is a group of fossils that may be classified as ancestors of Cambrian trilobites. If this turns out to be true the rather recent discovery is, of course, another major step forward in bridging Ediacaran enigma with the Cambrian explosion of life. Here is just a short quote from Sam's text (check the page itself for full discussion and a very illuminative chart):

Parvancorina: a Precambrian trilobite ancestor?

The similarity of the Precambrian Parvancorina to the Cambrian Chengjiang arthropod Primicaris larvaformis, and a protaspid of a Cambrian trilobite is seen to the left. [Protaspid is an early period in the growth of a trilobite in which larva lacks articulated segments]

All three have an ovoid form, and an anchor-like structure made up of an axial lobe and lateral lobes running along the anterior and lateral edges of the body.

Primicaris was first thought to be a larval naraoid (e.g., Hou & Bergstrom 1997), but it was recognized more recently as taxon in its own right (Zhang et al 2003).

Recapitulating phylogeny, the trilobite protaspid resembles Primicaris.

If the similarity of Parvancorina to Primicaris is more than superficial, it is perhaps the best candidate for an early arthropod in the Precambrian.

Two Comments
1. The text is again a good example of how research goes on in search of answers to increasingly specific questions as our knowledge increases. The many "ifs" are actually exclamation marks that here is something that should still be verified and studied carefully before we can say that we know.

2. I like very much this sentence in Sam's expert text

"Recapitulating phylogeny, the trilobite protaspid resembles Primicaris."

It is half English, half Latin and as such fully Hebrew to most people.

So where did Trilobites come from?

Trilobites are a true Leitfossil for the period of early life on planet Earth called Paleozoic which is Greek for Old Life.

"Trilobites were one of several families of arthropods in the early Cambrian oceans." But when exactly do they first appear in the fossil record and where in the arthropods tree of life did trilobites come from?


Earliest known Trilobites
Sam Gon III writes in his website and I quote (I have added emphasis. For the complete story it is highly recommended to visit the page on trilobite origins.)

The earliest trilobites appear in the lower Cambrian record.

[Note. In another page Sam tells that not in earliest Cambrian but in the so-called Series 2: 
"The first appearance of trilobites defines the start of Series 2 of the Cambrian (521 mya), and they can be found in strata up to the upper Permian (251 mya), after which trilobites (among a large number of marine organisms) went extinct in the great catastrophe that removed over 90% of all species on earth.]

These oldest trilobites include members of
Order Redlichiida, Suborder Olenellina, Superfamily Fallotaspidoidea and
Order Ptychopariida, Suborder Ptychopariina, Superfamily Ellipsocephaloidea.

Even these early representatives bear all of the defining characters of trilobites.


Probably the key distinguishing character, one that also allowed trilobites to be preserved so well (and which accounts for their sudden prominence in the Cambrian), is calcification of the exoskeleton.

It is interesting that some of the most primitive of trilobites lack a few characters that more advanced trilobites bear. Fallotaspidoids lack facial sutures, for example, and their protaspides are apparently uncalcified.

If the ancestors of trilobites in the Precambrian were uncalcified, then their preservation would be restricted to konservat-lagerstätten, which are very rare indeed. Cambrian konservat-lagerstätten such as the Burgess Shale (Canada) and Chengjiang (China) demonstrate the huge diversity of non-calcified arthropods that would have escaped detection if those sites did not exist. Many of these are arachnomorphs closely related to trilobites and relevant in a search for trilobite ancestors. But where did these arachnomorphs come from?

Three comments
1. The general observation Sam makes on the significance of what I call "Divine nature reserves" is of great importance here - the preservation of evidence. As he writes, without the Konservat-lagerstätten researchers of the origins and evolution of trilobites would be left without evidence about life forms that lack the calcified parts which survive better among the fossil record.


2. In a way it is, of course, tautology to say that first recognized trilobites have the defining characters of trilobites.

Of course! Otherwise they would not be defined as trilobites, would they?

Sam goes on describing some typical characteristics missing from the trilobites classed as Fallotaspidoidea but also these have the signs needed to make the fundamental Aristotelean classification into families, subfamilies etc.

The logic is simple
Superfamily A has characteristics ABCD
Superfamily B has characteristics ABCEFG
Specimen X has characteristics ABCD so it is an example of superfamily A.


3. It is quite remarkable that the known record of Cambrian life forms represents such a collection of "ready" organisms that then continue to live and develop from generation to generation. As Sam says, trilobites are a very successful designs and survived about three hundred million years flourishing in thousands of variations to the end of Permian.

Sam Gon III Guide to the Trilobites

Dr Sam Gon III "serves as the Senior Scientist for The Nature Conservancy's Hawai‘i Field Office in Honolulu... The [Web] site was first unveiled in August 1999 and has attracted feedback from around the world, generating ongoing updates. For all the accolades this site has gathered, Sam is not a professional trilobitologist, but a devoted trilobitophile! In 2006 this culminated in his first paleontological publication, dealing with trilobite origins."
From about the author page

Sam Gon III has created a comprehensive, very interesting, highly recommended, and publicly rewarded science site

Guide to the Orders of Trilobites 
and invites us to their fascinating world with these introductory words:

"Trilobites are the most diverse group of extinct animals preserved in the fossil record. Ten orders of trilobites are recognized, into which 20,000+ species are placed.

• Learn more about trilobite morphology, anatomy, ecology, behavior, reproduction, and development, and how they relate to trilobite origins, evolution, and classification. 
• Explore trilobite biostratigraphy, paleobiogeography, persistence across geological time, and their ultimate extinction. 
• View galleries of trilobite images from the web, examine fact sheets, pictorial guides, and an identification key for each order, 
• refer to a family listing, a genus listing, 
• or consult a trilobite glossary and bibliography, 
• tour world famous trilobite localities, 
• explore links to other web resources on trilobites, 
• and review books on trilobites, including an exclusive hardcopy pictorial adaptation of this website."

Period of the trilobites

"The first appearance of trilobites defines the start of Series 2 of the Cambrian (521 mya), and they can be found in strata up to the upper Permian (251 mya), after which trilobites (among a large number of marine organisms) went extinct in the great catastrophe that removed over 90% of all species on earth.

The Great Permian Extinction marks the end of the Paleozoic and the start of the Mesozoic.

Trilobites are one of the few major groups of organisms that span the majority of the Paleozoic Era. The greatest numbers of trilobite species occurred during the Cambrian and Ordovician periods, after which trilobite extinction trends exceeded radiation events.

Toward the end of the Devonian most of the families and orders of trilobites were gone. There were much fewer species in the lone surviving order Proetida in the Carboniferous and Permian periods.

Nevertheless, to have persisted for nearly 300 million years is a testimony to the successful design and adaptability of trilobites. Some scientists even hold out the faint hope that in poorly explored deep sea environments, trilobites may still exist, a holdover from truly ancient times."
From the Geotime page

Oldest known multi-cellular animal found in Namibia

Photo St. Andrews University

Otavia antiqua
Photo St. Andrews University

Pre-cambrian multi-cellular sponge like animal found in Namibia.

Geologist Anthony Prave has told about the discovery in January issue of the South African Journal of Science. See for more information here.