Talk:Cambrian explosion

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[edit] How to make the article accessible to the lay reader whilst useful to an educated reader, and anybody in between

I intend to spend some quality time with this article over the summer, and have been thinking about the best way of making it useful to the full spectrum of complete newcomer to serious scientist. My vision is moving towards creating the in-depth and detailed discussion necessary to really grapple with the main themes and players on appropriate sub-pages, for example, at "Acritarch", and if necessary new pages such as "Organisms of the Burgess shale". This article would then serve as a brief summary of the sub-pages, introducing the lay reader to the main themes and letting them feel they know what's going on. "For further information" and "Main article" links could be provided at the start of each section to let the interested understand more of the "science behind the story". Sound sensible? Smith609 Talk 17:52, 20 May 2008 (UTC)

Count me in, provided you can promise not to duck out half-way through (as has happened on History of IBM mainframe operating systems – I should stop waiting for others and just do it).
The big questions are:
  • What's the target structure? I know it will evolve, but if we start off with no initial idea, .....
  • How do we structure the package at the intermediate stages? Philcha (talk) 18:00, 20 May 2008 (UTC)
Good! I think subpages in general is a better idea than outright deletion of material – when the material is of encyclopedic interest. However, in this case there might also be a matter of a partial misdirection of the content. Considerable parts concern "Cambrian development" or "late stage precambrian development" (e.g., Ediacaran). IMHO, much of the material had better be moved to the article Cambrian, or to subarticles of it. The "explosion" article could repeat summaries of the most relevant "explosive" findings, but otherwise mainly could refer to Cambrian or Ediacaran (or their subpages) for the biological development.
Perhaps something similar could be done to the terminology section. After all, the terminology is relevant for much more than the discussion of the possibility of a Cambrian explosion.
(By the way, as usual the simplest possibility, that there was no exceptional "explosion", seems to be played down a bit. Even the section How real was the explosion? does not discuss neither the relative occurrence of relatively well preserved strata from the Cambrian and the Ediacaran eras, nor the possibility that species of many already existing orders developed hard body parts, which would be more well-preserved as fossiles, in a parallel but not quite independent development; cf. e.g. Ediacaran#Biota. It would depend on enough calcium being available; and also be strongly favoured by the appearance of predators with hard teeth.)--JoergenB (talk) 21:01, 28 May 2008 (UTC)
Hi, JoergenB, it would be a great help to have a 3rd co-worker!
Re "but otherwise mainly could refer to Cambrian or Ediacaran (or their subpages) for the biological development", I think that's what we're aimimg for. AFAIK Wikipedia does not use the Wikimedia sub-page facility (e.g. "Main topic/Sub-topic"), but prefers linked top-level articles.
I strongly favour keeping the the terminology section, for the benefit of non-specialists. If they have to refer to another article, they'll lose their train of thought in the main article, etc. And the separate articles on these terms often explain too litte (e.g. Triploblasty is a stub), too much (Coelom is too long and technical), have unsuitable focus (e.g. Coelom is too centred on human anatomy), or omit the important points (e.g. Phylum does not mention that the concept has difficulties with modern animals and worse difficulties with long-extinct ones).
Re "the simplest possibility, that there was no exceptional “explosion”, seems to be played down a bit", AFAIK what the evidence supports is that coelomates were around from about 580 MYA and triploblastic bilaterians a lot earlier, but there was an explosion of size and disparity in the Early Cambrian. If you know of evidence that supports other views, it would be a welcome addtion to the article. Philcha (talk) 14:02, 2 June 2008 (UTC)
Re: the terminology section: I still feel that this would be a benefit to other articles in the field, as well. What about a common transcluded page, not too long, together with references to a more general terminology explanation page? Does this get too complex?-JoergenB (talk) 18:19, 4 June 2008 (UTC)
I'm all in favour of reusability (my professional background is computers), but I'd be inclined to wait and refactor when we actually see another article that could benefit from explanation of the same concepts at the same level of detail. Philcha (talk) 21:33, 4 June 2008 (UTC)
...Wouldn't a common terminology page be of some help for most Smith609 hit list items? JoergenB (talk) 12:39, 9 June 2008 (UTC)
I don't know if your mathematical background includes much computer programming. The reason that's relevant is that as far as I can see transcluded pages are rather like subroutines. I've done quite a lot of programming, and it's very difficult to decide the structure of a package of subroutines in advance. For example a high-level design might say, "sections A and B should use sub-routine X," but when you write sections A and B you find that section A needs functionality X+x1 and B needs functionality X+x2. Problems like this make code refactoring important and often time-consuming in computer projects. My hunch is that for the projected set of articles there will be very few cases where exactly the same set of words will satisfy the requirements of each "client" article. Philcha (talk) 14:52, 9 June 2008 (UTC)
Yes and no; my background includes a substantial bit of rather old-fashioned programming (mainly in "Standard Lisp"); but certainly not transclusion (if you don't count very little SGML and similar experimenting). However, as I thought my link made clear, I was not proposing any advanced programming, just making use of the existing wikimedia transclusion software; that's why I linked to WP:TRANS.
However, your opinion that "...there will be very few cases where exactly the same set of words will satisfy the requirements of each 'client' article" certainly is relevant. That would probably require at least some additions to the wikimedia package.-JoergenB (talk) 17:37, 9 June 2008 (UTC)
I've just finished replying to your comment at Talk:Emanuel Lasker. Maybe our discussions should be transcluded :-) Philcha (talk) 18:11, 9 June 2008 (UTC)
Well... possibly we could transclude Proposed applications for game theory to both articles:-) Seriously, let the idea rest. As Smith609 notes, it could always be fixed at a later stage, if that then seems desirable.-JoergenB (talk) 12:38, 10 June 2008 (UTC)
  • It is technologically simple to display subtle variants of the same block of text as required in different articles. The problem is that it is less clear for would-be editors to amend the text. The problem of "how do I edit this text" is probably the biggest argument against transcludes – even if all pages transclude the same text.
I guess the best time to think about this is when we find several articles with blocks of similarly worded definitions – or wish to try to make them. If someone's wanting to use the transclude somewhere, I'll gladly make and amend it for them, and we can see how useful it turns out: it is a trivial task to convert a transclude to plain text at a later date if it doesn't work out. Smith609 Talk 18:18, 9 June 2008 (UTC)

[edit] Proposed structure

Here's one way we could structure the article:

  • Good solid introduction outlining the concept, so a skim-reader is satisfied, while provoking the interest necessary to read the rest of the article.
  • What components of the Cambrian fauna were present in the Ediacaran? Were the bits that don't show up really absent, or can we just not see them (for taphonomic reasons)?
    • Include a BRIEF description of the Proterozoic oceans. What was their chemistry and biology?
  • What was present by the end of the explosion?
    • Brief description of the composition of the Burgess shale & the Orsten fauna. Basically we want to introduce the idea that some can be categorised into modern phyla, others are harder to do so. At most 2–3 specific examples:
      • Wiwaxia to show a debate between two placements
      • Hallucigenia to show something we don't really have a clue about
    • What does this fauna represent? More diversity than ever seen before or since, as Gould would have it, or just lots of stem groups which confound Linnean taxonomy, but in fact represent a similar diversity to the modern fauna?
  • Why don't we know what was there in between the Ediacaran and the Burgess shale? – the limitations of a poor fossil record
  • Why do we think something fundamental happened in the early Cambrian?
    • Evidence includes changes in circulation, ocean chemistry, etc.
    • Mention the Ediacara biota's extinction.
  • Was there an explosion?
    • A fossil explosion, or an organism explosion? Taphonomic explanations and the difficulty of cryptic ghost lineages
    • Evidence for explosion in the "forgotten" fossil record, i.e. trace fossils, acritarchs
    • Timing – how accurate can we be, and is it accurate enough? Brief nod to molecular clock data.
  • What caused it? Including why the causes waited until 542Ma to become important.
    • Changes in the earth system discussed earlier; link to snowballs
    • Very quick discussion of famous, but disproven, hypotheses, such as HOX genes, eyes, etc
    • Oxygen's role
    • Ecological drivers
  • Implications for our understanding of animal evolution

I think that covers the essential points; the final section would probably provide a good conclusion to the article.

Concerning logistics, Stage one of the interim would be to pad out any key articles, and construct any new ones necessary. Once that was complete, there will be a lot of duplicated information; we could probably create a very rough draft replacement article, possibly in userspace, perhaps straight into article space, making sure that it contains all the necessary links. This would enable collaborative work on the article to pad it out without leaving too much of a vacuum anywhere, while ensuring that all editors can contribute asap.

The first stage will be the most time consuming: it will require us to generate a list of articles for expansion and creation. I may propose a task force at WikiProject Geology to see if I can drum up some help.

Thoughts welcome, although I remain busy for a week or two. Smith609 Talk 13:02, 2 June 2008 (UTC)

And busy for a year or 2 if this takes off!
Re "may propose a task force at WikiProject Geology, I'm in 2 minds (again!):
  • It's a big job, and help would be useful. I'd also think Wikipedia:WikiProject Evolutionary biology could help.
  • It's been well understood since the mid-1960s that a computer project should have at most 3 lead designers. The project we're discussing is of similar complexity to the specification and design stages of a computer software project (thank goodness we don't also have to code and test), and I'm wary of too many cooks spoiling the broth. My inclination is for us few brave (foolhardy?) volunteers to set up the framework and then ask for help with more specific issues.
Re your proposed structure, can you please add a bit more detail? My concern is that (as usual) I'm keen to minimise the amount of prior knowledge required of readers. To be more honest, in the first 1/3 of your outline I can't work out where you're going! (I'm aware from our previous discussions that your detailed technical knowledge of the subject far exceeds mine). Philcha (talk) 14:02, 2 June 2008 (UTC)
I agree that many cooks could spoil the broth if everyone tries to inflict their own ideas directly on this article. However, there are a huge number of "peripheral" articles which stand to support the main one, most of which are in dire need of work. It would take a literal year or two for just a couple of us to attempt to bring all of these to bear, so we may as well direct the energy of any willing volunteers towards these. Whether or not we encourage them to get involved with the new pages which we port much of the existing content to, I'm not so sure.
Just before reading your response here I'd created this list of articles in need of work; I should perhaps de-link the page – although I still feel that if other people are willing to help out, we should encourage them to do so in any way possible!
I'll pad the outline out now.
Smith609 Talk 15:04, 2 June 2008 (UTC)
Geez, your hit list has scared the s wits out me! I see the point that "we should encourage them to do so in any way possible" but in fairness we should point out that we might come along later and refactor like mad. Even with as much help as we could reasonably hope for, we may be looking at a 2-year project.
BTW I really like your statement of objectives at the top of the "hit list". Philcha (talk) 21:33, 4 June 2008 (UTC)
Surely the nature of Wikipedia is that anyone may come along at any time and refactor like mad! But I think the bulk of the "wishlist" is of supporting articles, which will not form a part of the main "flow" of the article, in the way that an article on say "environmental conditions at the start of the Cambrian" might do. I've deliberately not listed "new" articles there yet as I suspect that these might be cases where too many cooks spoil the broth, and the focussed attention of a couple of editors would provide a better approach.
For the time being, I'm trying to perfect my citation-finding tools before adding too much new content, but it might make sense to start shipping content out to the sideline articles now – I'm going to make a gradual start nowish and you're verywelcome to help me! Smith609 Talk 18:25, 9 June 2008 (UTC)

[edit] Trace fossils

As Smith609 pointed out a while ago, strictly speaking the term "trace fossils" includes geochemical evidence (e.g. isotope ratios) as well as tracks and burrows. The section "Trace fossils" is entirely about tracks and burrows. Is there a short term for tracks and burrows that excludes geochemical evidence, so that the section can avoid repeating the phrase "tracks and burrows" once or more per sentence? Philcha (talk) 23:23, 19 May 2008 (UTC)

"Bioturbation" springs to mind; could you also use something like "animal tracks" for variety, or would that term be confusing? Smith609 Talk 07:47, 20 May 2008 (UTC)
We'd have to explain "bioturbation", which would take more space than it saves. "Animal tracks" suggests pawprints (it's that dogbot again!) and does not include burrows.
How about titling the section "Tracks and burrows" then using the same phrase once in the text and then "these trace fossils" for variety? I don't think that would imply that "trace fossils" means only tracks & burrows.
PS you mean you can't help me make up my mind(s) (previous post)? Philcha (talk) 13:46, 20 May 2008 (UTC)

[edit] Possible reason (my theory)

Didn't (large) plants appear around the same time? Even if there was already plenty of oxygen, well still wasn't there a rather big shortage of food? So there you have it. Nice and simple ;) —Preceding unsigned comment added by 80.220.63.147 (talk) 22:19, 26 May 2008 (UTC)

Afraid that was during the late Devonian. In fact, the overabundance of food caused by plants becoming large probably caused a mass extinction! Nice idea, though – it's always fun coming up with "theories of the explosion"! Smith609 Talk 07:26, 27 May 2008 (UTC)

A recent paper outlining the role of ocean circulation : DOI:10.1038/nature07072 Smith609 Talk 12:10, 29 May 2008 (UTC)

Er, wouldn't that H2S release cause a mass extinction, as suggested for the Permian–Triassic extinction event? And at present it's hard to see how a mass extinction would cause the Cambrian explosion. Or have I missed something? Philcha (talk) 21:32, 7 June 2008 (UTC)

[edit] Earth Precession

Disappointed in the article, as to not including a Cambrian rapid 90 degree precession of Earth spin. This would cause the rapid plate tectonics unique to this period, also causal for phosphate nutrient plumes. Thus, the Precambrian very small fauna/flora would have immediately grown to larger size, giving the fossil based appearance of species explosion.Morbas (talk) 20:47, 7 June 2008 (UTC)

Are you thinking of "True Polar Wander", which is an extremely accelerated rate of Continental drift? If so, the idea of such events has been questioned (see Polar Wander and the Cambrian), and it's unclear how the increase in diversity which the fragmentation of environments would cause would also lead to the observed increase in disparity (see Marshall's "Explaining the Cambrian “Explosion” of Animals", cites in the refs). I admit it might be a good idea to include "True Polar Wander" under "Environmental causes".
If you really mean that the Earth's axis shifted significantly, please supply references to relevant scientific literature which give good evidence for such events and explain why they would cause the observed increase in disparity. Philcha (talk) 21:15, 7 June 2008 (UTC)
Fun ideas, which unfortunately very few people take very seriously – too many things have to be assumed to have happened for which there is no direct evidence at any time in Earth history. Worth a passing mention at most, I suspect. Smith609 Talk 21:22, 7 June 2008 (UTC)
As the Cambrian explosion draws on analyses from so many disciplines, it's hard to present anything intelligibly in just "a passing mention" (I wish!) I think we have to cover any hypotheses half-decently or not at all. Philcha (talk) 21:28, 7 June 2008 (UTC)
I am refering to an Inertia Interchange Event (IIE), Journal of Science Kerschvink, Evans, Ripperdan: 1997. This appears to be a unifying causal to several theories (Environmental Oxygen Threshold, Fossil (size and hardness), Snowball Earth, Tectonic Arrangement, Skeletal, Predation, Genetic awakening, etc.). And to me the observation that the complex trilobite just suddenly appeared. Or is it that understanding a broad discipline is rare?Morbas (talk) 21:56, 7 June 2008 (UTC)
That's "True Polar Wander". If I understand them correctly it's unrelated to precession, as Kirschvink and co. speak of the continents moving rapidly relative to the spin axis, which (in the absence of specifc statements) I would therefore assume behaved normally (i.e. slow, small precession). Philcha (talk) 22:12, 7 June 2008 (UTC)
Back to your original comment, you suggested "the Precambrian very small fauna/flora would have immediately grown to larger size, giving the fossil based appearance of species explosion":
  • It's unlikely that a mere increase in size by itself would create the appearance of species explosion. Paleontologists have long been able to detect microscopic and near-microscopic fossil organisms, and to diagnose their features. For example: probable bacteria up to 3.5 billion years ago; acritarchs, and the increase in their size and spininess (covered in Cambrian explosion); Vernanimalcula was 0.1 to 0.2 mm in diameter (covered in Cambrian explosion – assuming it really was an animal).
  • Cambrian explosion also covers Butterfield's idea that an increase in the size of phytoplankton was an important contributor – not because the increase enabled paleontologists to see organisms they'd previously missed, but because it indirectly increased the food and oxygen available in the middle and bottom levels of the seas, and this "took the brakes off" and allowed a rapid increase in the size, diversity and disparity of animals. Philcha (talk) 22:28, 7 June 2008 (UTC)

What caused large phytoplankton? Somehow nutrients/environment favored this outcome. Acritarch are a fill in for unknown biomass evidence, probably Bacterial. Ok, why not Archaea or Eukaryotes? With all do regard...references? Precession was used to paraphrase migration of the polar mass to equatorial positions. (This term is incorrect. From Kirchvink this was an imbalance of moments of inertia in the Mantle...apologies) "True Polar Wander" period was about 15M-years. This would have atleast stirred up sea floor nutrients...Morbas (talk) 00:59, 8 June 2008 (UTC)

I think it's time for you to read Cambrian explosion thoroughly – it contains answers to most of your questions. Philcha (talk) 07:42, 8 June 2008 (UTC)

[edit] Ediacaran organisms

Hi, Smith609, for the most part I really like your abbreviation of "Ediacaran organisms". Outstanding points:

  • I've done a copyedit which I hope removes a few small glitches. Did I get it right?
  • I still have an itch to flag Parvancorina as a more promising arthropod than Spriggina – IIRC it was you who first pointed that out to me. Perhaps add the "segments not symmetrical" point to the citation of McMenamin?
  • I've changed "disparity" to diversity, because the recent report of an "Avalon explosion" said disparity was roughly constant from the start. I'll check that nothing in "Avalon explosion" needs further explanation as a result of the pruning of "Ediacaran organisms"
  • I'm still unsure about the sentence you tagged "unclear". Did you mean "most fossils in general lack the features used to diagnose the affinity of modern organisms" or "most of these fossils lack the features used to diagnose the affinity of modern organisms"? Philcha (talk) 21:34, 9 June 2008 (UTC)
Ooh, I didn't reply to these comments, did I! Yes, I think Parvancorina is a more promising arthropod, but I'm quite looking forward to delving into the literature on these two and spotting a defendable viewpoint. Re. Avalon explosion, I think your original suggestion of popping it in a new article may be a good one – or perhaps incorporating it into the Ediacara biota article. But maybe wait a while for the dust to settle? Other stuff is now all good. Smith609 Talk 17:30, 10 June 2008 (UTC)
Hmmm. "mainly because the diagnostic features which allow taxonomists to classify more recent organisms are generally absent in the Ediacarans" doesn't work for me, in fact the ambiguity of "Ediacaran" (time or taxonomy?) makes it seem perilously close to assuming what it's trying to prove (or disprove?). What does Butterfield ("Hooking some stem-group worms: fossil lophotrochozoans in the Burgess Shale") actually say about the putative molluscs / arthropods / echninoderms in Ediacaran deposits? Philcha (talk) 10:19, 10 June 2008 (UTC)
That reference is in relation to Kimberella; Butterfield's not happy that Radulichnus necessarily implies a radula.
“ dorvilleid polychaetes also scrape microbial substrates using a jaw apparatus that is strikingly convergent on the molluscan radula ”
He concludes that Kimberella "on current evidence can only be reliably identified as a probable bilaterian" – i.e. not a mollusc. Martin (2000) is also sceptical.
I agree that more references refuting the other critters would be useful. That can come in later, though (when someone's expanded Arkarua and Spriggina, I guess). Smith609 Talk 16:38, 10 June 2008 (UTC)
If I understand your last point, you want to deal with the crucial critters one at a time and then re-visit Cambrian explosion? Philcha (talk) 17:11, 10 June 2008 (UTC)
As far as content goes, I admit to being somewhat haphazard and picking what I'm in the mood to edit. But as far as referencing goes, one would hope that the sub-articles would be well enough referenced to copy references into this article. If they aren't, I (or ideally someone else!) will come across some references in the process of expanding them. I guess I'll have a concerted effort of referencing this article when it becomes necessary, but don't really want to invest too much effort into it when the article is in such a state of flux. Smith609 Talk 17:30, 10 June 2008 (UTC)

[edit] Decline of stromatolites over 1 billion years ago

Hi, Smith609. I'm concerned that your recent edit has made this section more "academic" in its prose style, which is something I specifically wanted to avoid - non-specialist readers will have to assimilate so many new facts and concepts that it would be cruel to introduce any linguistic barriers, either cognitive or emotional (PS that wiki-link is not a personal dig!). If you can spell out what you were aiming to achieve, I'll see if I can find a wording that's as simple as possible but is faithful to your aims, and will post it here first for you to check out. Philcha (talk) 17:39, 10 June 2008 (UTC)

[edit] Suggested taphonomic explanation

It took me a while to remember and find the place where I read most of the ideas I referred to supra (and then I had to look up Taphonomy in order to see if this indeed was what Smith609 was referring to; thanks, Smith609, it's always nice to learn something new). Unhappily, this was an article in a Swedish science magazine: Rovdjuren satte fart på evolutionen ("The predators speeded up the evolution"), by Jens Rydell and Per Sundberg, Gothenburg University (Göteborgs universitet), Forskning och Framsteg 2/2000, pp. 29–33; there is a summary on line, also in Swedish, here. However, I do not find a discussion of hydrochemical reasons for hard shell forming being enabled at about this time; so I think I read that elsewhere.

Here follows a brief summary of the article. (Note that the article itself is copyrighted by Forskning och Framsteg, 2000, and not under a GFDL compatible license.)

540 million years ago animals, as we recognize them, for the first time appear in the fossile record. Traditionally, scientists have assumed that this was due to the animal phyla developping from a common ancestor, almost simultaneously, by means of a fast and thorough evolution. The phenomenon is called the Cambrian explosion.
However, many scientists question this; perhaps the animals existed before, but didn't fossilise; since they lacked hard parts, and also since they were immobile, and thus did not leave traces from movement. Investigating the DNA molecular clock supports this view: the [modern separate] phyla seem to have evolved already 1100 to 600 Ma ago. Moreover, recent chinese finds seem to confirm the existence of [recent] phyla already in Precambrium. [Later, the authors thanked prof. Chen Jun-yuan at the department for geology and paleontology, Nanjing, China for permission to reproduce their photos].
There are also fossils which do not resemble anything else, the so-called Ediacara organisms. Scientists are of divided opinion whether at least some of these organisms should be classified as animals, or all as belonging to some now extinct regnum. The ediacara organisms probably were soft and immobile, obviosly living in a "Garden of Ediacara" paradise, with no predators. The early animal percursors lived in the same world. This must have been the environment in which the different animal phyla developed. The circumstances were changed totally and irrevocably with the appearance of predators (e.g., Anomalocaris).
At the beginning of Cambrium, in a few million years, animals became larger, harder, and more mobile. There are several suggestions as for why, and several causes may have contributed. However, probably the direct reason was that the animals had started to eat each others. The early predators could not have been very efficient hunters, and possibly just ate other animals incidently, while feeding on the sea bottom "biocarpet" of algae and bacteria. However, they had a large evolutionary impact. Every property making being eaten less probable, such as harder skin or greater mobility, would be favoured. So would higher ability to find and catch prey be, for the predators. This "evolutionary arms race" may be what made us acquire vertebrae, the arthropods their exoskeletons, the molluscs their shells, and the annelids their undulating movements.

Of course, this summary is less subtle than the article, which contains more descriptions of finds and more discussion of various theories, and also IMHO a better but far from perfect distinction between consensus and the authors' opinions.

Note that the authors do not propose that the differences in preserved fossiles do not correspond to a real development; on the contrary, they repeatedly speak about harder, larger, and more mobile forms, and also briefly touch a possibly accompanying development of organs of perception and nerval systems. They by no means dismiss the cambrian explosion as a mythus. However, they explicitly or implicitly indicate, that this "explosion" didn't involve the development of the present distinct animal phyla, which (they claim) probably already existed, although as small, soft, sessile, and seldom fossilised organisms; instead, the ediocara phyla or even a separate regnum went extinct. In this manner, the "cambrian explosion fossiles" more represents the various survivors of a kind of mass extinction (my term, not theirs), which however was driven not by exterior reasons, but by a predator-prey co-evolution which eventually also stimulated fast development of new forms.

What I still miss is the discussion of the sea water chemistry I've seen somewhere, explaining how both teeth and shells became much more feasible than before; I think the explanation was that there was a higher ratio or more easily accessible form of calcium. Anyhow, this is what I now can contribute to the Cambrian explosion article. I'm not going to insert any larger content directly into the article; while I of course do not consider Smith609 and Philcha as its "owners", I do recognise that they do a better work than I would, balancing material and producing references and contexts which contribute to a high quality article. I'm in no mood to lower article standard by direct contribution. Thus, you may use much, little or none of the preceeding material, as you wish – bearing in mind copyright considerations, of course. JoergenB (talk) 18:07, 10 June 2008 (UTC)

Don't despair – I think I possibly know 100x as much about the Cambrian explosion than when I started (or have I just read and forgotten 100x as much as I knew before I started?)
Butterfield, N.J. (2001). "Ecology and evolution of Cambrian plankton". The Ecology of the Cambrian Radiation. Columbia University Press, New York: 200–216.  is an article used extensively here. Unfortunately the Google scholar link has now expired and, as the paper was in a collection (book) rather than a journal, it is unlikely to be come free any time soon. However when I first read it I wanted to check that I understood it properly and summarised it, then Smith609 commented on parts where his interpretation was slightly different – it's at my Talk page.
Regarding predation, Bengtson, S. (2002), “Origins and early evolution of predation”, in Kowalewski, M., and Kelley, P.H., The fossil record of predation. The Paleontological Society Papers 8, The Paleontological Society, pp. 289– 317, <http://www.nrm.se/download/18.4e32c81078a8d9249800021552/Bengtson2002predation.pdf>  is good, and free(!) and amusing (!!! – so much for sterotypes about Swedes).
I don't remember much about a change the calcium supply being an important factor, but there's plenty about the importance of increased O2 supply allowing animals extra energy for use in activities other than basic maintenance and reproduction; two of the most commonly mentioned "extras" are the building of hard parts and the building of collagen for connective tissues (collagen is expensive; IIRC one of the reasons is that it requires an amino acid for which DNA does not code, so the synthesis is complicated). The Butterfield paper provides a mechanism by which the supply of both O2 and nutrients could have been improved quite dramatically. Butterfield also has few paragraphs about changes the mineral chemistry of the oceans in the late Proterozoic, but that got edited out of Cambrian explosion a while ago because it did not seem to be contributing much. Philcha (talk) 19:35, 10 June 2008 (UTC)
If there are any papers you'd like to access, I can happily forward you a PDF. Regarding the calcium change, there was a shift from a calcite to aragonite ocean. To try and put this concept, which usually baffles me, into comprehensible terms, there are two "polymorphs" of calcite – that is, the mineral CaCO3 can be stable in two different mineralogical states, calcite and aragonite. Calcite is very stable, whereas aragonite quickly degrades to calcite. Some time around the Ediacaran/Cambrian boundary, the polymorph which was most stable in the oceans – therefore which organisms would be able to use to form skeletons – changed from one to the other, something that has happened about half a dozen times in recorded history.
At this point my understanding grows hazy, but I think the concept goes that it's much harder to form and maintain a calcium skeleton than an aragonite one, or vice versa; so when the naturally stable polymorph changed it became much more energetically feasible for organisms to form a calcified skeleton which wouldn't just dissolve away straight away.
This is an important hypothesis, and indeed one which ought to be developed in the article; to the best of my knowledge it's still considered an important factor in the explosion. Phyla also seem to "remember" the state of the ocean when they first started calcifying.
I guess I need to read a lot more into this article to get familiar with it again and put forwards a case for its implementation, but thanks a lot for reminding me of it!
Ooh – I've just remembered, there was an article at Calcite sea which does a brief summary.
The italic text is a wonderful summary of a pretty consistent view of the explosion. However, parts depend strongly on how much you trust molecular clocks – which have been falling from fashion recently!
Thanks for getting involved, Joergen - it's nice to have a little more company!
Smith609 Talk 22:56, 10 June 2008 (UTC)