Steve Steve and end of the Cambrian Explosion as we know it (part 1)

Posted 9 January 2006 by Prof. Steve Steve

As an international, jet setting public intellectual there are many calls on my time, and I find myself rushing from pillar to post with my busy diary. However, at last I was able to take up the offer of that nice Dr. Musgrave to visit Adelaide, and amongst other things, take in Chris ("how can Nedin be trusted") Nedin's Big Dick (Chris was so excited about it, how could I resist). Despite being nearly devoid of bamboo, Adelaide is renown in song ("just another boring night in Adelaide" "people ask me, why Adelaide?") and justifiably famous for being perched on the edge of umpteen square kilometers of burning desert. But the desert holds many treasures, one of which is the finest collection of fossils from the Ediacaran period, a Precambrian era that features lots of weird, squashy creatures and mysterious animal tracks, and some things that Intelligent Design creationists don't want to talk about, because they throw doubt on the so-called "Cambrian Explosion" that they claim evolution can't explain. But now a creature has been found that wipes out the Cambrian Explosion (clue, see picture). The ID creationists like to claim that all major body plans originate in the so-called "Cambrian explosion", a period of around 30-60 million years where there is a rapid appearance of animals with hard parts. However, ID creationists ignore the fact that things like sponges, corals, echinoderms like Arkarua, and mollusks like Kimberella make their appearance long before the Cambrian Explosion, in the Ediacaran. Note that the hyperlinks are a bit cautious about these fossils, but there has been a lot more work (and better fossils) since then (the links still call them Vendian, for goodness sakes). See this excellent review on Edicarian fossils and Kimberella and its feeding tracks. There is also another, very important group that appears in the Ediacaran, which I'll tell you about later on (you'll just have to wait in suspenders, I promised Nedin I would show the Big Dick first). However, all these organisms are very small and squashy (just like evolutionary biologists predicted) and don't attract the attention that the Cambrian fossils do.

The Flinders Ranges north of Adelaide has one of the finest exposures of Ediacaran sediments, with massive fossil assemblages preserving ecological relationships, and reveals a unique window on this vanished world, so I was more that a little pleased when Musgrave (on the left of yours truly below) and Nedin (on the right below) agreed to take me to the newly opened Hall of the Ediacarans at the South Australian Museum. Now, Dr. Musgrave is a nice guy, but a bit gormless. Not only did he fail to arrange a meeting with the Museum director Tim Flannery (world renowned marsupial expert and author of "The Future Eaters") but he forgot to bring the camera tripod, which is essential for photographing flat, nearly invisible trace fossils in low light conditions. When other people have taken me to see fossils at least they looked like fossils rather than deflated toy balloons.

The entrance to the exhibit is fairly spectacular, they have dug up an entire slab of fossil seabed and set it upright. On the side facing the entrance is the ripple marks on the seabed, but on the side facing away is an amazing seafloor community, buried in time. There is a whole range of organisms on the face of the slab, worm-like things and mysterious helmet-like things, but the clearest organism on the slab is the minute worm-like Dikensonia that appear everywhere.

Dickensonia are everywhere, there are small ones, medium ones (like the one below) and big ones. There are traces of them crawling over algal mats feeding, we have fossils that suggest different growth stages and there are hints about their social behavior as well.

Finally though, I got to see Nedin's Big Dick. Dickensonia rex, a monster flat worm one meter long, the pride of the Ediacaran seas.

Typically, this is where Musgrave needed a tripod to bring out the details of Dikensonia (the awful way the fossils were lit didn't help). All you can see here is a large slab of rock with some faint striations on it, but be assured that most of that slab is covered with a giant flat worm.

And here is the nice label that shows that Nedin collected this behemoth of worminess. Even though Nedin can't spell paleontologist, he can at least find really interesting things.

Since the gormster couldn't photograph the Big Dick, here's a picture of me swimming with a nice model Dickensonia.

The paleontologists are able to reconstruct things like Dickensonia in such good 3D detail because many of the Flinders Ranges Ediacarans were presevered by rapid slumps of fine-grained sediment. Because entire assemblages were buried there are also lots of representative organisms in many different orientations so that a 3D image can be built up from examining multiple specimens.

Here is a magnificent Sea Pen (Charniodiscus) preserved in very good detail. This fossil was stolen from the Flinders Ranges but finally recovered and returned to Australia after nine years of heroic sleuthing.

Because of the fine level of detail in many Ediacaran deposits all sorts of small squashy beasties turn up. Including this one, the one that destroys the "Cambrian Explosion" beloved of ID creationists.

Yes, the strange looking groove you are looking at is related to all of us. You are looking at the first recorded Chordate. Now it's a bit hard to see here, but you can see grooves that record the record the muscle bands (there's also traces of fins, but they can't be seen in this picture. Nedin was a bit unconvinced, and thought that it might be part of a frond animal (and as Nedin is quite intimately knowledgeable about the Ediacaran fossils, you ignore him at your peril), but there are now 18 of these fossils described, preserved in every possible orientation, so they know it is not a frond animal, but a fossil of the first chordate.

Here's a reconstruction based on the 18 fossil impressions we have. A tadpole-like beastie similar to the chordate amphioxus. Clear muscle bands, small fin fringe, traces of what could be gill structures and a possible sensorium on the "head" area. This is pretty much what was predicted by scientists based on the finds of the primitive chordates Yunnanozoon and Pikaia in the Cambrian. Also, the Ediacaran chordate is consistent with several DNA studies which suggest that chordates arose in the Ediacaran. The main impact of this find is that the "Cambrian Explosion" is dead. Yes, there was a period of rapid diversification (if you want to call a period of 30-60 million years rapid) when animals developed hard parts. But this was preceded by a long period of time when basic body plans were developed. ID creationists claims that all animal body plans developed in an implausibly short period of time in the Cambrian are refuted by this small tadpole-like ancestor. That's all for now. In part 2 I will go behind the scenes at the South Australian Museum to see how these fascinating fossil critters are turned in models we can study.

39 Comments

Kevin from NYC · 9 January 2006

hey its my great x 10>55555 grandfather!

Mike Syvanen · 10 January 2006

These recent Ediacarian fossils are very exciting. However, it seems to me to be a big mistake to try to interpret them as a polemic against creationism. As a scientific interpretation that creed has been dead for over a century. There are some very interesting questions that are raised by the fact of the Cambrian Explosion. Yes, in spite of these fossils, this is something that really did happen. And that is, over a very short period of time calcium carbonate and silicate based life forms appeared in the fossil record. Because of the these Ediacarian fossils and also because of evidence from molecular evolution this is still one of the more spectacular examples of parallel evolution. This should be discussed in terms of modern evolutionary theory and not archaic religious teachings.

Nick Matzke · 10 January 2006

Dear Prof. Steve Steve,

About how long is this Ediacaran chordate fossil? It's a bit hard to tell from the photos.

Nick

Corkscrew · 10 January 2006

Even though Nedin can't spell paleontologist

What is it with you yanks? Not only do you muck up your spelling for the sole purpose of being different from the rest of the world, you then try to inflict this absurdity on us too??? Anyway, lovely article.

Dean Morrison · 10 January 2006

What is it with you yanks?

-I'm confused I always thought Prof Steve Steve was Chinese? I'm also confused about Mikes point about 'parallel evolution'? Don't these fossils show that the 'Cambrian' explosion is more of an artifact of the fossil record rather than a sudden burst of diversification? Not such a 'fact' after all? Creationism is still alive and kicking in the 21st century - and the 'Cambrian explosion' is still a commonly used criticism of evolutionary theory. What's wrong with showing the evidence aginst this?

Miguelito · 10 January 2006

Excellent article!

Can anybody comment on "The Crucible of Creation" by Simon Conway-Morris?

I thought it was a great pop-science description of the origin of many Cambrian fauna from Ediacaran fauna. But, my last paleontology course was over 10 years ago and I might have been won over by style rather than substance. How much of this is now outdated by these recent finds?

Bayesian Bouffant, FCD · 10 January 2006

You are looking at the first recorded Chordate.

No name? Does that mean it hasn't been published yet?

Michael I · 10 January 2006

Steve Steve says

first recorded Chordate

Obviously a B flat...

jim · 10 January 2006

This is OT, but this is the closest thread on PT for it.

This article just appeared on yahoo.com. It mentions ID, holes in scientific knowledge, insects, and (my favorite) flight. It's an article that discusses the mechanisms of bees flight.

Enjoy!

Corkscrew · 10 January 2006

Obviously a B flat...
— Michael I

Nah, it's obviously a C creature.

Bob O'H · 10 January 2006

Obviously a B flat...
— Corkscrew
Nah, it's obviously a C creature.

Whatever, but it was spotted by A sharp miner. Bob

jim · 10 January 2006

My parents always warned us to:
C sharp or you'll B flat.

Corkscrew · 10 January 2006

Whatever, but it was spotted by A sharp miner.

Argh! My eyes!

MrDarwin · 10 January 2006

I think it's important to stress that this fossil is being INTERPRETED as a chordate. The older these things are, the harder it is to tell. I'd like to see a better image of the fossils themselves before being too awed by the diagrams of it. This might end up being re-interpreted as a stem-group deuterostome or even arthropod (the latter was my first thought upon seeing the diagrams), which would still be pretty exciting but the creationists and ID proponents would make a pretty big deal out of any possible disagreements of interpretation (ignoring the fact that either way, it's an important fossil and not at all favorable to their own claims).

Henry J · 10 January 2006

Let's hope the topic stays on-key...

jim · 10 January 2006

or it'll become dischordant.

Corkscrew · 10 January 2006

Let's hope the topic stays on-key...
— Henry J

Yeah, we should stick to the core data

Gav · 10 January 2006

The Professor commented:

"Despite being nearly devoid of bamboo, Adelaide is renown in song "

Indeed. Beethoven himself wrote a song about Adelaide.

Kevin from NYC · 10 January 2006

Well we won't be bamboozeled if we keep our (central) nerve.

mike syvanen · 10 January 2006

Morrison wrote:

"I'm also confused about Mikes point about 'parallel evolution'? Don't these fossils show that the 'Cambrian' explosion is more of an artifact of the fossil record rather than a sudden burst of diversification? Not such a 'fact' after all? "

What these new results show is that there were many different eukaryotic lineages present before the Cambrian. What the Cambrian explosion represents is that these many different lineages learned how to make hard parts at the same time. This is classical parallelism. It is something that is seen often in the fossil record. I think this is interesting. It is totally absurd to dismiss this phenomena simply because bronze age thinking is still alive in this society.

In general, I find the debate against creationism has had some negative impacts on the developement of evolutionary thinking. It has tended to harden views and has made it more difficult to offer novel scientific explanations for phenomena that are not really explained very well. It is as if we admit to gap in our knowledge then we have conceded some point to the religious fanatics.

Dean Morrison · 10 January 2006

What these new results show is that there were many different eukaryotic lineages present before the Cambrian. What the Cambrian explosion represents is that these many different lineages learned how to make hard parts at the same time. This is classical parallelism. It is something that is seen often in the fossil record. I think this is interesting. It is totally absurd to dismiss this phenomena simply because bronze age thinking is still alive in this society.

As I understand it there aren't a lot of rocks left in the world from the Precambrian, that haven't been so heavily metamorphosised as to wipe out any posible trace of fossils. Darwin pointed out in origins that the record was incomplete - and when you get that far back there has been more time to erase the record. This is one possible explanation for an apparant 'explosion' in the Cambrian. Another explanation could be the 'simultaneous' evolution of hard parts - I see that this is what Mike meant by 'parallel evolution' - (perhaps in response to the appearance of a new type of predator? - would seem the obvious explanation to me). However this is still an explanation of why the 'Cambrian explosion' is an artifact rather than a real event - I mean we don't really think that hard parts, per se, are intrinsically important other than they fossilise more easily? - do we ?? Both possibilities could be true - and these additions to the fossil record help support the first one. Either way the 'Cambrian explosion' looks more like an artefact than a real event. Very interesting - worthy of further research - and nothing at all to do with 'Bronze Age Thinking'. Mike .. are you saying it would be wrong to interpret the evidence in this way because it might be seen as a reaction to 'Creationists'?. Are we supposed to suspend judgement so as to be 'fair' to them or something?

Ian Musgrave · 10 January 2006

Professor Steve Steve is unavailable at the moment, touring in the UK, he has asked me to respond to your comments on his behalf. In post 69462

About how long is this Ediacaran chordate fossil? It's a bit hard to tell from the photos.
— Nic Matzke

It is about 2-2.5 cm long. A titchy little thing. In post 69630

No name? Does that mean it hasn't been published yet?
— Bayesian Bouffant,

GAHHGGG!!! Professor Steve Steve and I spent over an hour talking to one of the preparators of this organism, and we forgot to ask what it was called. The descriptive paper should be out sometime mid to late 2006. In post 69686

The older these things are, the harder it is to tell. I'd like to see a better image of the fossils themselves before being too awed by the diagrams of it. This might end up being re-interpreted as a stem-group deuterostome or even arthropod (the latter was my first thought upon seeing the diagrams)
— MrDarwin

Unfortunately, I didn't bring a tripod and the images are not the best, even more unfortunately, the other 17 specimens were unavailable for photography. As noted before, the drawings are composites done by analysing all 18 specimens under different lighting conditions to ensure adequate visualization of the details. Arthropods don't have fins. Professor Steve Steve's discussion with Jo Bain, who does the 3D reconstructions of fossils at the South Australian Museum, will be up shortly.

Ian Musgrave · 10 January 2006

in Post 69453

These recent Ediacarian fossils are very exciting. However, it seems to me to be a big mistake to try to interpret them as a polemic against creationism. As a scientific interpretation that creed has been dead for over a century.
— Mike Syvanen

Standard Creationism has been scientifically dead for some time, but it is still being promoted by Answers in Genesis and ICR and so on, and needs refuting. Intelligent Design Creationism (IDC, Creationism in a cheap tuxedo), while scientifically vacuous, is being vigorously promoted at the moment. Witness the recent Dover case. The Cambrian explosion is one of IDC's key arguments. They interpret it not just as the appearance of mineralizable structures (which has precursors in the "small shelly fauna") but as the abrupt appearance of all major animal phyla. This they claim is not explainable by standard evolutionary theory and is thus evidence of an "intelligent designer". Now the ICD claims are nonsense, but the existence of major animal phyla in the Precambrian, and molecular evidence suggesting diversification took place over longer periods than the mineralizable fossils suggest, have been comprehensively ignored by the IDC's. But chordates are iconic, they can ignore worm trails, feeding scratch marks, sponges, jellyfish and Kimberella, but a Precambrian chordate crashes their argument in one fell swoop. No one disagrees that there was major, rapid diversification in the Cambrian. The development of mineralizable body parts was a major innovation which as rapidly exploited by many different organisms. However, the rapid diversification of fossiliable hard parts (which is not so different to the time scales of diversification of faunas after major extinctions) was preceded by a long period where small squashy things accumulated the modifications that would allow them to become the recognisable animals we see in the Cambrian. The Cambrian explosion (sensu IDC)is dead, long live the Cambrian explosion. in Post 69759

What these new results show is that there were many different eukaryotic lineages present before the Cambrian.
— Mike Syvanen

Don't you mean metazoan here? (yes, there were lots of eukaryotes, but the Cambrian was characterized by the expansion of eukayotic metazoans, and specifically animal, lineages). The existence of precambrian representatives of modern phyla is exactly what IDC's don't want to see. Their claim is that all the major modern phyla arose near simultanously, not that modern phyla rapidly developed hard parts.

Popper's ghost · 10 January 2006

The development of mineralizable body parts was a major innovation which as rapidly exploited by many different organisms.

Did these many different organisms all have a common ancestor? Or was there some change in the environment that was conducive to the development of mineralizable body parts? As written, this statement seems to suggest that one organism is able to exploit a development by another organism, but genetics ain't mimetics.

Henry J · 10 January 2006

Re "Either way the 'Cambrian explosion' looks more like an artefact than a real event."

To me it looks like an "arms race" of some sort, during which hard parts became necessary for survival.

Maybe several lineages had small hard parts before that (teeth or equivalent?), enough so that they only had to evolve more of it when everybody else started doing so? At least that's my impression at this point.

Henry

djlactin · 11 January 2006

?!? After all the hype, there's no recognizeable picture of the big Dick?! puh-leez post one! a foto of a collection of brown rocks was no consolation!

Bayesian Bouffant, FCD · 11 January 2006

GAHHGGG!!! Professor Steve Steve and I spent over an hour talking to one of the preparators of this organism, and we forgot to ask what it was called. The descriptive paper should be out sometime mid to late 2006.

'Steve' or 'Bruce' seem like likely names.

Michael Tuite · 11 January 2006

Creationists may dismiss the significance of the Precambrian fossil record of metazoans but some, apparently, are interested in adding such fossils to their collections.

I took this picture of a Late Proterozoic (575Mya) "pizza disk" fossil near Mistaken Point, Newfoundland last summer. A group of American creationists were caught in flagrante delicto excising the fossil with a high-powered water saw. Suspicions were aroused when one member of the group signed a guest book with an unambiguously creationist-associated email address - and then returned twenty minutes later to erase his entry. The huge plume of water from the saw was a dead giveaway to what was going on and when the eager excavators were approached by some of the locals (who take very good care of their fossils) they hastily packed up and scurried off. They were eventually apprehended by police but were released without charge because they hadn't actually transported the fossil out of the country.

MrDarwin · 11 January 2006

You know, it's just a matter of time before the creationists and IDists change their tune only slightly and say "all the phyla appeared suddenly and at the same time"... they will just push the date back sometime into the Precambrian. Mark my words.

mike syvanen · 11 January 2006

Ian wrote

Don't you mean metazoan here? (yes, there were lots of eukaryotes, but the Cambrian was characterized by the expansion of eukayotic metazoans, and specifically animal, lineages). The existence of precambrian representatives of modern phyla is exactly what IDC's don't want to see. Their claim is that all the major modern phyla arose near simultanously, not that modern phyla rapidly developed hard parts.

The mineralization occurred with eukaryotes other than the metazoa; eg the unicellular forams and the sponges discovered mineralization at this time and they are not considered metazoan. These forms appeared in the fossil record during the Cambrian. Thus the Cambrian explosion does represent a revolutionary change that happened to not only multiple metazoan lineages but even more diverse eukaryotic lineages. Skeletonization as made possible new bauplans that very much likely resulted in the formation of new metazoan phyla. Dean wrote

Mike .. are you saying it would be wrong to interpret the evidence in this way because it might be seen as a reaction to 'Creationists'?.

No. I am saying it is wrong to interpret evidence as a reaction to creationists arguments. The former should be follows the rules of science, the latter are political and theological arguments.

Dean Morrison · 11 January 2006

Mike .. are you saying it would be wrong to interpret the evidence in this way because it might be seen as a reaction to 'Creationists'?.

No. I am saying it is wrong to interpret evidence as a reaction to creationists arguments. The former should be follows the rules of science, the latter are political and theological arguments. .. Not sure I followed this - maybe you mistyped. However if our interpretation could be seen to be politically or theologically motivated by creationists; should we reject this interpretation? Or if our interpretation happens to undermine a favourite 'argument' of theirs - should we back off from it? What bearing in fact do their views, or the views of Hindus or Buddhists, have in the matter? If you think this interpretation is wrong for scientific reasons - and that these guys are motivated to make a faulty analysis because they want to 'stick one' to the creationists - then fine. But all you need to do is make a scientific case for the 'Cambrian explosion'. Isn't the 'Cambrian explosion' said to be the observation that 'all the major Phyla appeared' over a period of 30-40 million years. A chordate in the Precambrian would blow a big hole in that viewpoint don't you think? In any case I thought that Creationists thought that everything was made in a week? what is their point about the 'Cambrian explosion' any way - other than to say - oh look - there's a gap!

mike syvaneN · 11 January 2006

Dean

I did commit a typo. I will try to edit my comments better from now on.

I meant to say

"I am saying it is wrong to interpret evidence as a reaction to creationists arguments. The former should follow the rules of science, the latter are political and theological arguments."

What I am trying say is that we should interpret and discuss evidence within the rules of science. If the evidence is not easily explained within our current theories then so be it (The explanatory power of our theories are so powerful as it is that we should not worry about such uncertainties).

Let us consider an example of this problem as I see it. In 1959 there was a famous meeting in Chicago -- celebrating the 100th aniversary of the publication of "Origin of species". A number of papers were presented and these were published under the editorship of E. Mayr. One of the talks presented at this meeting was given by a paleontologist by the name of Olson (I met him once and discussed this with him). His talk focused on a number of problems that remained unexplained by the New Synthesis. I am relying on memory here but there was maybe 6 issues he raised. They included the need for an explanation of the Cambrian radiation as well as an explanation for mass extinctions. At that time these were certainly open questions.

Olson's paper was rejected by Mayr for the resulting symposium proceedings. Now why was this? I believe that he was trying to focus the attention of other evolutionist on unsolved problems as expressed in the fossil record. Yet his comments were surpressed. I think that the editors were being overly sensitive to the debate about the reality of evolution and subconsciously suppressed an open discussion on the problems with current theory. Perhaps my recollections are distorted. But this is some of the background for my opinions on this thread. I have other anecdotes that are consistent with this concern.

Dean Morrison · 12 January 2006

.. or perhaps Olson's wasn't good enough and he was sore enough to tell you? I don't see what the poit is about speculating about why paper wasn't published 50 years ago.

One person who did withold publication because of fear of upsetting the creationists was Darwin himself of course. He did his work and sat it aside for what? 15 years? - it was only when friends told him he risked being trumped by Wallace (who always seems to be forgotten in the matter) - that they jointly published. Hats off to Wallace I say - Darwin could have taken the secret to his grave, or perhaps he was planning to be published posthumously.

We should be beyond this by now - if someone makes a claim - let them make it - if it's 'dodgy', there are plenty of palaeontologists (and a paleontologist or two!); waiting to shoot them down. The creationists are irrelevant to the debate - the YEC ones don't even believe in Geology for Crisakes.

We're not even talking about a 'theory' here - just a piece of evidence. Leave the creationists to look for 'Rabbits in the Cambrian' - if they ever find one they won't hesitate to shout from the rooftops about it - trust me (and they'd be right to).

And remember Mike: 'The plural of anecdotes is not evidence'.

Scott de B. · 12 January 2006

Interesting post. I find it curious that Dickensonia is being billed as a worm. The little plastic model even shows it as being bilaterally symmetric, yet the fossils are not (instead, the segments are interleaved rather than being paired off). Similarly, if Charniodiscus is a sea pen, it is like none ever known since it too is not bilaterally symmetric.

Nathan Myers · 12 January 2006

Re: parallel evolution... At that early date, might not genetic divergence between (what we now call) orders have been smaller than is now seen between species? If so, adoption of genetic fragments that code for (e.g.) hard body parts from nominally unrelated prey might have been much easier than it is today. Defenses against contamination by foreign DNA had to evolve, too.

The Central Dogma has been under assault for a long time.

Henry J · 12 January 2006

Re "curious that Dickensonia is being billed as a worm."

So, it has to watch out for the early bird? :)

Henry

Louis · 13 January 2006

Ian, In post #69852 you wrote:

GAHHGGG!!! Professor Steve Steve and I spent over an hour talking to one of the preparators of this organism, and we forgot to ask what it was called. The descriptive paper should be out sometime mid to late 2006.

I have to read slower because I read one part of that as "...Professor Steve Steve and I spent over an hour talking to one of the PERPETRATORS of this organism...". A bold claim! Bloody quick work on that time machine. Now at least when the creationists ask "How do you know, were you there?" we can confidently answer "Yes, and I've had a chat with it's parents!". Nice (P.S. Humour disclaimer: While I am sure Ian, and indeed anyone of sound mind and mental faculties will realise I was joking, some creationists/morons may think I believe Ian really has a time machine. As far as I am aware he doesn't, nor has such a thing been made. Nor do I wish to convey the impression to creationists that the "were you there?" question is sensible or even unanswerable. Thank you for your time. Yoou may now return to your hair.)

Dean Morrison · 13 January 2006

There's something fishy going on in the Precambrian....

W. Kevin Vicklund · 16 January 2006

Interesting post. I find it curious that Dickensonia is being billed as a worm. The little plastic model even shows it as being bilaterally symmetric, yet the fossils are not (instead, the segments are interleaved rather than being paired off). Similarly, if Charniodiscus is a sea pen, it is like none ever known since it too is not bilaterally symmetric.
— Scot de B.

Are you looking at the right captions? The fossils of the Dickensonia look just like the plastic models to me. The sea pen looks bilaterally symmetric to me.