Talk:Cambrian explosion/Archive 3

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)

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)

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. 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)

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 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)

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)

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)

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?)
 * 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, 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)

Section "Burgess shale type faunas"
I sympathise with the deisire to make the article a little shorter, but I think section "Burgess shale type faunas" has been amputated too drastically. The way it is now I think only someone who's read and understood e.g. Wonderful Life would understand it at all. More specifically:
 * Does Sirius Passet count as a Burgess shale type fauna? One of the things I noticed while writing the earlier version is that Chenjiang is closer in time to Sirius Passet than to Burgess Shale, but Chenjiang's fossils are much more like those of Burgess Shale. Among other things that exemplifies some limitations of lagerstätten, that they cover only a minority of the range of organisms extant at the time and this sample is biassed by preservational factors. IMO not mentioning Sirius Passet or Chenjiang hides information.
 * No mention of the critters that fired the debate. At a bare minimum it should describe and outline the significance of Marella and Opabinia – Marella is a fairly derived-looking arthropod but does not belong to one of the 4 recognised groups; Opabinia looks so wierd that it was first classified as a member of a new phylum, but is now regarded as "great-aunt" of arthropods (which means it's necessary to explain the body plan a little). In fact the pattern of the Burgess Shale is greater diversity / disparity at many taxonomic levels. IMO the anomalocarids also should be mentioned, to make the point that Opabinia was a member of a pretty successful group (in terms of duration and distribution), and because they are among the organisms most likely to be known to non-specialist readers – after all I can see no other reason for mentioning Hallucigenia. In fact the discussion of anomalocarids has to start with Pambdelurion and Kerygmachela because, unlike later relatives, their fossils show traces of legs and that is the strongest resemblance to biramous arthropods.
 * No mention of the differences in mineralization of hard parts between Sirius Passet, Chenjiang and Burgess Shale.
 * It's odd that this section spends 3 paras on a description of lagerstätten.
 * No references.

While writing this a thought has struck me – if we want to shorten the "brief history of Cambrian life", perhaps we need to structure it by what I'll call "themes", as a better words doesn't jump out at me. Such "themes" include: Right after "Small shelly fauna" because some small shellies appear to be halkieriid fragments.
 * Ediacaran and Early Cambrian diversification of trace fossils
 * Small shelly fauna
 * Molluscs, annelids or brachiopods?
 * Arthropods.
 * Trilobites.
 * Crustaceans.
 * Hard to classify, e.g. Marella.
 * Anomalocarids.
 * Other groups that are less well represented, e.g. echinoderms, chordates.
 * Apparent increase in mineralization, unless this is regarded as statistically unsound or as probalby reflecting environmental variations rather than an evolutionary trend. (The distinctive nature of the Siriuis Passet fauna suggests environmental differences).

The downside would be that this would lose chronological perspective. But perhaps this could be handled by a table-cum-timeline for the Cambrian, with columns showing:
 * Timescale (dates).
 * Major fossil beds, with bars showing the period covered.
 * A column for each major group of animals, with bars showing the time range of each. Philcha (talk) 11:42, 19 June 2008 (UTC)

The older version of the article had pics of Kerygmachela, Anomalocaris and Opabinia. From the point of view of the "themes" above, Opabinia (first analysed; big contributor to the idea that many metazoan phyla originated in the Early Cambrian) and Kerygmachela (legs and gills, like biramous arthropods) are the important ones. However we could sneak a pic of Anomalocaris into the beginning of section "Body fossils", with a caption such as "At first only fragments of Anomalocaris were found, and these were interpreted as parts of 3 different animals", to illustrate the problems of the fossil record. Philcha (talk) 11:59, 19 June 2008 (UTC)


 * I'm still trying to get a handle on how best to structure the article – perhaps I have been a bit "scissor happy" in places, but this can be easily rectified at a later stage! I've done my best to incorporate only the essentials which a lay reader would need to grasp the concept, at this stage.  I think that once non-core material is moved to sub-articles, it will be somewhat easier to shift the structure around, and work out which parts need bulking out again.  Things like references can still be found in sub-articles, so it'll be no problem to bring them back in when the content's stabilised.  I think it might work out best to mention the "fossil celebrities"  in a discussion of how diversity changed, rather than a summation of the types of evidence. Smith609  Talk  12:16, 19 June 2008 (UTC)

Sections "Comparative anatomy" and "Molecular phylogenetics"
I suggest these could be combined. Cladistics is a method of analysis that has been applied to both comparative anatomy and molecular data, and the information it can provide is much the same for both data sources: A is closer to B than either is to C; if this "family tree" says A is of an earlier "generation" than B and the earliest fossil of B is from X MYA, then A must evolved before X MYA. Philcha (talk) 11:49, 19 June 2008 (UTC)


 * Sounds good – go for it! Smith609  Talk  12:50, 19 June 2008 (UTC)

Explanation of terms
I like almost all of the recent copy edit, but I think the last change is questionable. The previous version said, "Echinoderms are coelomates; living species do not look bilaterian (they are radially symmetrical, although sea cucumbers have distinct front and rear ends), but the earliest echinoderms are still poorly understood and some may have been bilaterally symmetrical." Without this there is an apparent contradiction: coelomates are bilaterians; echinoderms are coelomates; but most echinoderms look very un-bilaterian and are usually described as "radially symmetrical" (like jellyfish). In addition, the ref at the end of the sentence is about their possible bilaterian origins, not their coelomate anatomy / embryology. Philcha (talk) 00:42, 21 June 2008 (UTC)

Feedback
I thought it might be an appropriate point to request some feedback regarding the current content and organisation. Any major points or radical suggestions? More change still to come but some external input will probably be helpful! Martin  (Smith609 – Talk)  16:25, 21 June 2008 (UTC)

Hi, I can see you've been busy. Some comments / suggestions: ✅Have you concluded that stromatolites don't provide worthwhile evidence of pre-Cambrian herbivory? I thought their inverse correlation with mass extinctions was quite suggestive.
 * After not looking at the article for a while I think it needs to explain early on what all the fuss has been about, in terms that casual readers will recognise. I'm guessing that non-specialist readers probably fall into 2 major types: those who know nothing and those who know a little based on nth hand accounts of Wonderful Life. I also suspect the latter will be the harder group to please. I suggest "History of the debate" be expanded a little to explain how unfamiliar the Burgess fossils looked to Whittington et al and to Gould. Opabinia would be a suitable "poster child" because it's wierd-looking and it was the fossil that convinced Whittington that something strange was going on in the 1st half of the Cambrian.
 * Will perhaps replace "Acritarch" with "Predation" and include them there, as well as in passing at "how real was the explosion"
 * How about title "Signs of very early predation", as there's also plenty about predation arounf the Ed-Cm boundary? Philcha (talk) 20:51, 21 June 2008 (UTC)

✅Would you like me to knock up a really simplified image of a coeolomate, as the article Coelom is far to human-based?
 * That could well be useful – illustrations are looking quite sparse now. It'd be great if you could produce it in an SVG format, perhaps using the free and wonderful Inkscape.


 * I rather fancied playing with a new toy, then I remembered something – SVG is not good news for Internet Explorer users, and the majority of readers probably use IE. I'd better stick to the usual PNG. There's a facility to make image maps so as to wikilink to articles on items in the pic, and I've used it before. Philcha (talk) 20:51, 21 June 2008 (UTC)
 * Wikipedia has a brilliant function that transforms all SVG images into PNGs before IE users see them – so that's not a worry. And see also Template:Annotated_image, as used at Permian–Triassic extinction event – preferable because it means the image can easily be used in different languages. Martin  (Smith609 – Talk)  21:41, 21 June 2008 (UTC)
 * I've produced a PNG now, and I don't fancy doing all those nested ovals again!
 * Does Template:Annotated_image allow multi-line text blocks? The way the layout has developed, that's necessary.
 * Does it provide sans-serif fonts such as Arial? Sans-serif is usually better for reading form a screen than serif.
 * If Template:Annotated_image is suitalbe, I can easily remove the graphical text. Philcha (talk) 22:25, 21 June 2008 (UTC)
 * annotated image will do the job. You may consider tagging the text-free image with "svg" so somebody with more time on their hands vectorises it at some point. (and for future reference, nested ovals are really easy in inkscape (-; ) Martin  (Smith609 – Talk) 

✅"Doushantuo Formation" should precede "Ediacaran organisms". I also suggest the title "Fossils from the Doushantuo Formation".
 * As written it refers to the Ediacarans, so needs to come after they've been mentioend – this is perhaps unnecessary but is why I re-ordered. Understanding of it is also a lot thinner than the Ediacarans, so putting it early seems perhaps a little unwise.
 * The temporal thing is just a matter of phrasing. If the article gives an impression that understanding gets better closer to the present, I'd have thought that was good. Philcha (talk) 20:51, 21 June 2008 (UTC)

✅ I think more needs to be said about the status of the Doushantuo fossils, especially Vernanimalcula, otherwise someone with a little knowledge (or perhaps lot) will insert their understanding of the debate, but possibly in an over-academic tone. I also notice the re-write has changed the tone of the section – by giving the critics the last word, it suggests that the sceptical view has the upper hand. Is that intentional?
 * I don't think this article is the place to develop a debate as to their affinities – this tells the passing reader what they need to know, while the curious can go to Doushantuo formation for the why. I sympathise with your desire to keep to brief. What about something like "Opinions differ about whether the fossil called Vernanimalcula is the remains of a minute coelomate or of a bubble"? I thing that would be more neutral. Philcha (talk) 20:51, 21 June 2008 (UTC)

✅Is Kimberella now regarded as less likely to have been a triplobastic metazoan? If it was a triplobastic metazoan it defeats almost single-handed the view that all metazoan phyla appeared in a very short part of the early Cambrian.
 * I'm not aware of anyone saying that it's not – I hadn't intended to imply that it wasn't.
 * That's why I'm suggesting it deserves a bit more prominence.


 * I'm not happy about "Burgess shale type faunas":
 * ✅The 1st 2 paras basically repeat the explanation of "lagerstätte", then the whole of the fauna and and their interpretation are compressed into the last para. This is particularly serious at present because the current version of the article does not cover Opabinia and the anomalocarids, which are fairly central to the Gould interpretation.

I suspect the "terminology" section needs a simple exmaple of stem vs crown groups, preferably wiith a diagram that works well at thumbnail size. I'll have a go at the text and diagram if you like.
 * "early offshoots from the phyla we know today" is a poor description of the stem group concept, as it implies that these taxa evloved after the modern phyla became distinct.
 * I'd actually been considering making up an image based on this – do go for that if you feel like it! Will do. The pic you cited is a beauty, very nearly the right size and very clear. Philcha (talk) 20:51, 21 June 2008 (UTC)
 * I'm having 2nd thoughts about tackling crown/stem groups. I thought I'd better get a good grasp of the concepts first, so I googled and found Valentine's On the Origin of Phyla. If I understand him correctly: there's no topological difference in the trees for crown and stem groups; the only real difference is that crown groups have living members. So: a crown group loses that status when its last member becomes extinct; the discovery of a Lazarus taxon can turn part of a stem group into a crown group, and possibly the split other (still extinct) members of the original stem group into 2 stem groups. That all seems rather unstable to me. Philcha (talk) 23:26, 21 June 2008 (UTC)
 * A very useful read is  – see especially figure 2.


 * The instability, or flexibility, is sort of the point – you can in theory define anything as a crown group, then start talking about stems to that clade.  An earthworm is in the bilaterian, lophotrochozoan, and annelid crown groups; the extinct Machaeridians are crown group lophotrochozoans, but stem group annelids.


 * It would be valid to classify a new fossil as a "stem group machaeridian" if it was more closely related to the machaeridians than any other group, but could not be placed within it.


 * The lack of topological difference is an important point: a Cambrian zoologist might call the Halwaxiids (by Caron's interpretation) a family, and would also consider the molluscs a family, with no inclination that they would go on to be classified as a phylum by holocene zoologists. Thinking of the Halwaxiids as stem group molluscs is far more helpful than thinking of each of the Halwaxiids, and for that matter Odontogriphus and Kimberella,  as separate phyla.


 * The concept of stem and crown groups is of fundamental importance to understanding the explosion – I guess the struggle is to explain the concepts in terms that mean they can be fully grasped. Martin  (Smith609 – Talk)  11:47, 22 June 2008 (UTC)

✅in "Early Cambrian crustaceans", " ... the taphonomic mode (of the Orsten) only preserved organisms smaller than 2mm, limiting the data set to juveniles and miniaturised adults" defeats me, and I have some idea what "taphonomy" means. What features of the environment or of the events / processes that preserved the fossils limits the size of the fossils? I note also that there's no ref for this point, although I doubt whether a free abstract of a scientific paper would help the non-specialist reader, assuming that there is a free abstract. ✅"Developmental Explanations" has been amputated to the point where I would not understand it if I have not written an earlier version. Also the way I understood (?) it, there are 2 distinct types of developmental explanation, Hox genes and entrenchment. ✅"Uniqueness of the explosion" is mostly very nice, and I particularly like the parallel with the radiation of land plants, but:
 * "With a wide range of empty niches, clades would be able to diversify and become disparate enough for us to recognise them as different phyla; when clades are filled, lineages will continue to resemble one another long after they diverge, as there is limited opportunity for them to change their form" appears to skip a few steps in the logic. The way i understand (?) the reasning, the full sequence is: either a change in the environment creates new niches or an evolutionary innovation makes it possible to colonise previously empty ones (the last 4 M years of hominid evolution are an example of the latter); until all the newly-available niches are filled, the severity of natural selection pressure is reduced and there is rapid diversification; when all niches are filled (not clades, that sounds like a 19th century completist theory), selection pressure returns to normal levels and incumbents have the advantage, so observed diversification drops back to normal rates.
 * It omits the key point that this reasoning explains why the Cambrian explosion happened only once.
 * What, no Avalon explosion? The idea was new when I added it earlier this year. If it has not been demolished, I think it should be included for the same reason as the Devonian radiation of land planets, to illustrate that even a genuine explosion does not need to be explained by extraordinary hypotheses. 82.34.73.184 (talk) 17:44, 21 June 2008 (UTC)
 * It's been included with "Ediacaran organisms" – it seems a little rash to build a case on a single paper. Reading through all the estimates of diversity and disparity to build on that idea I've come to appreciate how different the results of different methods are!
 * So where can I see some of these estimating methods? I remember you mentioned quantification before.
 * Looking at the Ediacaran bit, I have a feeling the diversity / disparity distinction should be defined up front. That would make it possible to say that the Ediacaran assemblages showed increasing diversity but roughly constant disparity, which is why an early explosion is suspected. Philcha (talk) 20:51, 21 June 2008 (UTC)
 * What I meant to say was that every paper I read considering Cambrian disparity/diversity seemed to give a different answer. I guess the big one is Bambach, Bush +1 2007, with their feeding-style-ecospace approach; I think Marshall 2006 came up with a different story, while Harvey 2008 mentions constant crustacean diversity; I'm sure Gould has his ideas, and I think I came across a few more in passing.  My point is that I'm uneasy saying that diversity goes up and disparity is constant based only on one paper; it would be nice to get a second opinion! Martin  (Smith609 – Talk)  15:19, 22 June 2008 (UTC)

I'm also concerned about the somewhat academic phrasing. While I was editing this item we had an update conflict and of course the situation has changed. I like you final para about the 2-phase diversification, but then the whole section looks confused as it mainly talks about the uniqueness of the CE. How about:
 * In "Uniqueness of the explosion" the statement "everything that can be done, is being done by something, leaving no space for a subsequent diverstification" strikes me as a serious exaggeration. Counter-examples include fish (it was only during the Silurian that modern-looking fish evolved, relying on more on manoeuvrability than armour or burrowing for defence, and then they rapidly became the dominant medium to large swimmers) and the various groups that evolved flight (insects, pterosaurs, birds, bats). The uniqueness of the Cambrian is a matter of degree, not kind.
 * The "Cambrian explosion" can be viewed as two waves of metazoan expansion into empty niches: first, a co-evolutionary rise in diversity as the first animals explored niches on the Ediacaran sea floor, followed by a second expansion in the early Cambrian as they became established in the marine realm.


 * The rate of diversification seen in the Cambrian phase of the explosion is unparalleled in the animal kingdom: it affected higher taxonomic levels and hence featured more radical developments in body plans; and it affected all metazoan clades of which Cambrian fossils have been found. Later  radiations, such as those of fish in the Silurian and Devonian periods, involved fewer  taxa, mainly with very similar body plans.


 * Whatever triggered the Cambrian explosion opened up an exceptionally wide range of previousy-unoccupied ecological niches. When these were all occupied, there was little room for such wide-ranging diversifications to occur again, because there was strong competition in all niches and incumbents usually had the advantage. If there had continued to be a wide range of empty niches, clades would be able to diversify and become disparate enough for us to recognise them as different  phyla; when niches are filled, lineages will continue to resemble one another long after they diverge, as there is limited opportunity for them to change their life-styles and forms.


 * There is a similar one-time explosion in the evolution of land plants: after a cryptic history beginning about, land plants underwent an explosive and unparalleled adaptive radiation during the Devonian period, about.
 * Philcha (talk) 16:01, 22 June 2008 (UTC)

I like it. but: I'd been careful to state the "marine realm"; are you sure it beats that of terrestrial animals / insects?
 * Fair point. "among marine animals"? Philcha (talk) 18:31, 22 June 2008 (UTC)

Also, at the time, the organisms weren't at higher taxonomic levels: the taxonomic rank is a function of when they appeared and how different they look from other organisms, not the other way round. Martin  (Smith609 – Talk)  16:38, 22 June 2008 (UTC)
 * Hmmm, it might depend on how "taxonomic levels" is defined. For me it works in both Linnean terms (later radiations were mainly at the class or lower levels; the CE apparently produced what are now recognised as new phyla or sub-phyla, and other critters that would be recognised in the same way if they had survived) and cladistic (the CE produced new branches a few levels / nodes closer to "Urbilateria" than later animal radiations). On either interpretation, it's not surprising that the CE apparently had more impact on body plans. So what's an accurate but intelligible way to express this? Philcha (talk) 18:31, 22 June 2008 (UTC)
 * No-one would say that the Cambrian explosion was more significant than more recent diversifications simply because it was longer ago.
 * But that is what both those viewpoints essentially boil down to.
 * A zoologist living in the Cambrian would consider the different phyla to be exactly as similar to one another as a Devonian zoologist would consider his classes of fish, or an Eocene zoologist his families of mammals. Only in the light of 530 million years worth of their descendants do they look unusual, and that's why they were termed "new phyla" for so long.
 * From a cladistic perspective, what is the significance of Urbilateria? The Ediacaran radiation was closer to Urbilateria (or Ureukarya, or Urwhatever), but no-one spills much ink about that.
 * In my opinion, the Cambrian explosion produced such an array of body plans because there were so many empty niches waiting – and waiting to be produced. The Eocene radiation of mammals produced lots of new body plans – but convergence is rife!  The marsupials produced almost exact equivalents to all types of placental mammal, because they were constrained to the same niches.  If no animals had survived the KT but mammals, there's no reason that mammals wouldn't fill the empty niches and disparity bounce back to pre-extinction levels.  The same evolutionary processes operate on clades of all sizes, from phylum to species; and at all distances from the Ur-whatever.
 * The Cambrian explosion is different to other radiations, according to Butterfield (2007), because animals are so good at creating niches (by co-evolution).
 * Martin  (Smith609 – Talk)  19:21, 22 June 2008 (UTC)


 * "Section "Uniqueness of the explosion" says, "... followed by a second expansion in the early Cambrian as they became established in the marine realm." What does "became established in the marine realm" mean? Are you trying to squeeze into 1 phrase the ideas that some occupied additional bottom-dwelling niches while others became swimmers? Philcha (talk) 22:12, 22 June 2008 (UTC)
 * Yes. is "...  in the water column" better?
 * "... in the water column" was my first thought, then I realised it's jargon that has not been explained. How about "... followed by a second expansion in the early Cambrian, which included the appearance of mid-level swimmers"? Philcha (talk) 12:34, 26 June 2008 (UTC)
 * Do you mean pelagic? --Blechnic (talk) 02:53, 27 June 2008 (UTC)
 * I'd also regard "pelagic" as jargon that has not been explained. Since most of the article is about benthic organisms, it's probably clearer to use the cicumlocution at the handful of relevant points than to define it once and hope the reader remembers the definition when it becomes relevant again a few sections later. Philcha (talk) 13:09, 27 June 2008 (UTC)

Agronomic Revolution
There's no doubt this happened, but the section currently does not say enough about causes or effects. In fact if I hadn't just found and read Bottjer, Hagadorn Dornbos' paper The Cambrian Substrate Revolution and some lecture notes I I would not understand a word of it. To be of any help to non-specialist readers it needs to explain:
 * The physical and chemical (H2S v O2) differences between miocrobial mat and "modern" muddy seafloors.
 * Why animals started burrowing into this hostile (H2S) environment and, if possible why it happened in the early Cambrian.
 * What new opportunities the change presented. (Bottjet et al says more about how the change exterminated "sea-floor stickers" and restricted mat-grazing proto-molluscs, and little about new opportunities)

At present the topic looks to me more like it should be in "See also". Philcha (talk) 01:02, 28 June 2008 (UTC)


 * I'd be inclined to fit this in with "burrowing". Did the revolution present, or represent, new opportunities - perhaps provided by in increased organic flux to the sea floor (due to mesoplankton)? Martin  (Smith609 – Talk)  10:56, 28 June 2008 (UTC)

We're going wrong
I just realised why I'm unhappy about the way this revision is going. We're not following your proposal of 13:02, 2 June 2008 (UTC) - "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." Philcha (talk) 22:46, 3 July 2008 (UTC)

Some comments
Section "Fossils of the Doushantuo formation" says "These fossils form the earliest hard-and-fast evidence of animals, as opposed to other predators" - but there are other interpretations of the "embryos" and of Vernanimalcula. Philcha (talk) 19:31, 3 July 2008 (UTC)
 * I gather that at least some of the embryos are pretty definitely embryos; there don't seem to be any contemporary references denying this.Martin  (Smith609 – Talk)  19:54, 3 July 2008 (UTC)
 * Do we have a ref for someone who is sceptical about some "embryos" but admits others? Philcha (talk) 21:02, 3 July 2008 (UTC)
 * We do; |ref 36 has a good array. Specific to your query would be
 * Martin  (Smith609 – Talk)  21:45, 3 July 2008 (UTC)
 * Martin  (Smith609 – Talk)  21:45, 3 July 2008 (UTC)

Section "Small shelly fauna" says "... allow the fossil ranges of many groups to be extended." Apart from archeocyathids and the presumed sclerites of halkeriids, how many later groups have been confidently identified? Philcha (talk) 19:31, 3 July 2008 (UTC)
 * The SSF are something I wish I knew more about; wikipedia's not a great place to start on these beasties! I think the significance is more that they are pretty much the only reliable fossil record for this time period. A re-wording may be necessary. Martin  (Smith609 – Talk)  19:54, 3 July 2008 (UTC)
 * I'd drop that para unless we intend to do something with the halkeriids. Philcha (talk) 21:02, 3 July 2008 (UTC)
 * So long as the shellies' significance remains clear.Martin  (Smith609 – Talk)  21:45, 3 July 2008 (UTC)
 * What is their significance? To me it's: halkeriid sclerites; tiny snail-like organisms. Philcha (talk) 22:32, 3 July 2008 (UTC)
 * I don't pretend to know the first thing about the shellies, but going by Butterfield 2003 and Budd's comment below, I guess the significance is that they are part of the conventional fossil record that underwent an explosive increase in diversity during the early Cambrian. [Citation needed]! Martin  (Smith609 – Talk)  22:48, 3 July 2008 (UTC)

Section "Early Cambrian trilobites and echinoderms" says "These (530MYA) provide firm data points for the "end" of the explosion, or at least indications that the crown groups of modern phyla were represented". Problems with this:
 * That would imply that the lagerstatten (518-505 MYA) are irrelevant? Considering Gould thought the Burgess Shale (505 MYA) was very relevant, explanations and citations are needed.
 * I'm still not sure the Burgess and friends tell us anything much about the explosion. Butterfield (2003) says as much.
 * Is that the general opinion? Wonderful Life (p. 24) says, "The Burgess Shale is our only extensive, well-documented window upon ... the Cambrian Explosion". Since that's the nearest we can expect to a preconception in non-specialist readers, we have to deal with it. Philcha (talk) 21:02, 3 July 2008 (UTC)
 * I'm not sure we should write the article around a dated 20 year old text. I think it's more important to keep the article focussed on the current state of affairs than to think about every query or misconception a Wonderful Life reader may be left with. Martin  (Smith609 – Talk)  21:45, 3 July 2008 (UTC)
 * Hmmm, I haven't quoted Locke's "under-labourer" sentence at you recently, have I? :-) Philcha (talk) 22:32, 3 July 2008 (UTC)
 * Hmmm, I haven't quoted Locke's "under-labourer" sentence at you recently, have I? :-) Philcha (talk) 22:32, 3 July 2008 (UTC)


 * What is the criterion for defining the start and end of the CE?
 * It depends how you define the CE... what do we say in the article? Martin  (Smith609 – Talk)  19:54, 3 July 2008 (UTC)
 * The lead says "... the seemingly rapid appearance of most major groups of complex animals around 530 million years ago .." and IIRC that's the nearest we get to offering a date. But IIRC nothing in the article specifically supports that date, and most of the article argues that the "CE" started earlier and ended later. ''Wonderful Life' says (p. 55) "The Burgess fauna does not lie within the explosion itself, but marks a time soon afterward, ...". Other pages indexed for "Cambrian Explosion" do not give dates.
 * And we don't give a phylogentic or morphological criterion (such as "from earliest fossil of X to earliest fossil of Y") - does anyone? Philcha (talk) 21:02, 3 July 2008 (UTC)
 * I have hazy memories of a discussion with Graham (Budd) on these pages about the difficulty (/futility) of defining the explosion. Putting dates to it is as good as meaningless, especially given the difficulty of dating the Cambrian, and the fact that it wasn't "switched on" - it was more like a dimmer switch being turned up (to use a rather poor analogy). Martin  (Smith609 – Talk)  21:45, 3 July 2008 (UTC)
 * Graham Budd (Talk archive) about the difficulty (/ futility) of defining the explosion: "Dating the "speed" of the "explosion": this is highly constrained by the exceptional preservations. All we know is that by Sirius Passet/Chengjiang time (c. 516 Ma or so), loads of stuff was around, and that in Doushantuo time (perhaps around 580-560??), nothing was. In between we have increased diversity of small shellies and trace fossils, plus things like trilobites and echinoderms coming in at around 520 Ma. I don't think one can pull out an arbitrary chunk of 10 million years from this interval and say that THAT was the "explosion"..." Did he write anything similar anywhere that's citable? Philcha (talk) 22:32, 3 July 2008 (UTC)
 * This looks hopeful but I can't access page 2 on the limited preview. Perhaps Google's semi-random preview will favour you? Martin  (Smith609 – Talk)  23:22, 3 July 2008 (UTC)
 * See also the below. Martin  (Smith609 – Talk)  23:28, 3 July 2008 (UTC)
 * "it was more like a dimmer switch being turned up" - great phrase. Email it to Bengtson, he might use it, then you can cite it. Philcha (talk) 22:32, 3 July 2008 (UTC)
 * "it was more like a dimmer switch being turned up" - great phrase. Email it to Bengtson, he might use it, then you can cite it. Philcha (talk) 22:32, 3 July 2008 (UTC)


 * "crown groups" not defined anywhere. Philcha (talk) 19:31, 3 July 2008 (UTC)

Section "Burgess shale type faunas" says, "Since a large part of the ecosystem is preserved, the ecology of the community can also be tentatively reconstructed." That appears to contradict the comments about the limitations of lagerstatten in section "Body fossils". Explanations and citations are needed to explain why the Burgess Shale might provide more info about ecosystems than most lagerstatten. Philcha (talk) 19:31, 3 July 2008 (UTC)
 * I've been struggling to get into this paper, which answers that question quite nicely. Perhaps you'll have better luck!
 * I've had good look at the abstract, which says, "Overall, our data suggest that transport was trivial and the traditional distinction between a pre- and postslide environment is unnecessary. It is likely that all specimens present at the time of burial would have been preserved independent of their original tissue composition and degree of preburial decay." "Qualitative comparisons of the degree of preservation of 15 species ..." hardly constitute an entire ecosystem. I'm suspicious of any claim that a fossil bed preserved everything and in good enough order for us to reconstruct the entire eco-system - I'm not sure neontologists can reconstruct entire eco-systems. "all specimens present at the time of burial" also looks suspicious to me - a specimen is something that has been recognised as representing something of interest (Rumsfeld was right about the unknown unknowns!).
 * OTOH the last item looks like a useful ref for how the Cm Substr Rev end ed Burgess-type preservation.
 * Of course that's just based on the abstract. Full PDF is at http://www.eeb.utoronto.ca/system/files/publication_caron_2006_2.pdf Philcha (talk) 21:25, 3 July 2008 (UTC)
 * "Isolated or broken parts of unidentified taxa, and isolated sclerites of Wiwaxia or Chancelloria, were excluded" may be a smoking gun - if there's another undiagnosed comedy of errors like Anomalocaris, it's been excluded. I wish this paper had been published in Science, where "technical comments" are provided with each article. Philcha (talk) 21:38, 3 July 2008 (UTC)
 * Thoughts about rotifers kept bugging me while I was reading the article, and I've realised why - the most Caron & Jackson can prove is that each assembly probably represents the ratios of living organism for animals that have been diagnosed and were at least as durable as polychaetes, in other words it does not cover less durable organisms, and assumes that their estimates of each species' durability are accurate. Philcha (talk) 22:32, 3 July 2008 (UTC)
 * Thoughts about rotifers kept bugging me while I was reading the article, and I've realised why - the most Caron & Jackson can prove is that each assembly probably represents the ratios of living organism for animals that have been diagnosed and were at least as durable as polychaetes, in other words it does not cover less durable organisms, and assumes that their estimates of each species' durability are accurate. Philcha (talk) 22:32, 3 July 2008 (UTC)

Section "Burgess shale type faunas" does not explain well enough why these lagerstatten are worth mentioning. Philcha (talk) 19:31, 3 July 2008 (UTC)
 * You've got me there... I'm not entirely sure why they're worth mentioning myself! (Apart from their historical value.)
 * I ought probably work that out pronto, considering I start working with the stuff at the end of the summer... Martin  (Smith609 – Talk)  19:54, 3 July 2008 (UTC)
 * OK, leave it until Jan 2009, then you can be the resident expert - provided you don't appear as lead author in any papers!
 * More seriously, "Burgess shale type faunas" are part of the evidence that there was a lot going on - but the current version does not explain in any way. Philcha (talk) 21:02, 3 July 2008 (UTC)

Disparity
Section "How real was the explosion?" says,
 * There is little doubt that disparity – that is, the range of different organism "designs" or "ways of life" – rose sharply in the early Cambrian.

The statement creates and exploits an ambiguity in "disparity", with one sense referring to morphospace and the other to ecospace, and the citation deals only with ecospace. However AFAIK the Cambrian explosion debate is about morphological disparity and its implications for phylogeny. -- Philcha (talk) 09:53, 10 July 2008 (UTC)


 * Hi Philcha. I'm no pro on this topic (to say the least), but my understanding concurs with your's: that the disparity discussed in relation to the Cambrian Explosion is primarily morphological rather than ecological (though these are obviously not entirely uncoupled).  Cheers, --Plumbago (talk) 10:13, 10 July 2008 (UTC)

Metamorphosis or Metamorphism?
At the start of http://en.wikipedia.org/wiki/Cambrian_explosion#Body_fossils, it's claimed "Fossilisation is a rare event, and most fossils are either destroyed by erosion or metamorphosis before they can be observed". I'm no expert on the subject, but I think the editor probably intended to use metamorphism (the geological transformation of rocks), rather than metamorphosis (the biological process of, e.g., caterpillars becoming moths). See Metamorphism and Metamorphosis. Balfa (talk) 13:46, 17 July 2008 (UTC)


 * And while I'm here, if anyone who understands the subject feels this change is useful, may I suggest they also swap the order of "either" and "destroyed" in the above sentence :) Balfa (talk) 13:49, 17 July 2008 (UTC)


 * Good catches Balfa. I've made the changes that you suggest above.  Cheers, --Plumbago (talk) 13:55, 17 July 2008 (UTC)

"Theistic Evolution" Section
The section has some good information, but the title of it doesn't reflect the content of it at all. It looks like someone just threw it in there. Maybe it should be renamed?Punkrockrunner (talk) 01:22, 18 August 2008 (UTC)punkrockrunner


 * I got deleted this section. All it said was, "Like Darwin said the explosion may not fit with the theory of pure evolution." I don't see how this (unsupported) claim belongs in the article. Xerxesthepersian (talk) 02:50, 18 August 2008 (UTC)


 * It's been added again. The author has done some research, so I'm reluctant to delete it immediately. But it's in the wrong article - there's one on the debate about evolution, which would be a good place for this content. I'll remove the "Theistic Evolution" section in a week. -- Philcha (talk) 06:02, 19 August 2008 (UTC)


 * I've also deleted the section. It was simply a tick-list of names associated with theistic evolution, with no strong connection to the Cambrian explosion (and almost certainly nothing published in the scientific literature).  In passing, while the Cambrian explosion was once read as evidence against evolution (i.e. everything seemed to arrive at once), this view is no longer tenable, as the article is testament to (scientifically speaking, of course; if you're a creationist, well, anything goes).  This view of the Cambrian explosion (which already appears in the article) is worth noting in the context of the history of evolutionary thought, but it's not in the least obvious why modern theological views need noting, and certainly not from the deleted text (i.e. what have they added to the discussion that wasn't there before?).  Cheers, --P LUMBAGO  08:53, 19 August 2008 (UTC)

Removed "under construction" tag
I removed this tag according to the instructions in the template itself - the article hasn't undergone any major changes in the past 7 days plus. It looks like there is a long-term project focusing on this article, and the task force notice on the talk page is appropriate to advertise that. However, there's no need to have the "under construction" notice up for regular readers, since the article is in pretty good shape and it's no more under construction than any other article. -- Beland (talk) 01:23, 13 September 2008 (UTC)
 * Fair enough. And thanks for your edits, at WP:CEX and elsewhere - my watchlist is pleasantly bloated with small fixes (-: Martin  (Smith609 – Talk)  03:10, 13 September 2008 (UTC)

Orphaned references in Cambrian explosion
I check pages listed in Category:Pages with incorrect ref formatting to try to fix reference errors. One of the things I do is look for content for orphaned references in wikilinked articles. I have found content for some of Cambrian explosion's orphans, the problem is that I found more than one version. I can't determine which (if any) is correct for this article, so I am asking for a sentient editor to look it over and copy the correct ref content into this article.

Reference named "Budd1996": From Evolutionary history of life:  From Opabinia:  

I apologize if any of the above are effectively identical; I am just a simple computer program, so I can't determine whether minor differences are significant or not. AnomieBOT ⚡ 16:36, 17 October 2008 (UTC)


 * ✅ Martin  (Smith609 – Talk)  19:47, 25 October 2008 (UTC)

Molecular clocks
Martin, can you please explain "However, the clocks can give an indication of branching rate, and when combined with the constraints of the fossil record, recent clocks suggest a sustained period of diversification through the Ediacaran and Cambrian.":
 * "branching rate" suggests something to do with time, which is the controversial issue about molecular clocks.
 * If "when combined with the constraints of the fossil record, recent clocks suggest a sustained period of diversification through the Ediacaran and Cambrian" means some molecular clock estimates are consistent with the fossil record: some are not (I remember seeing one with error margins so wide they overlapped into the Ordovician); the fossil record is so scrappy that it does not present much in the way of constraints. -- Philcha (talk) 16:28, 17 October 2008 (UTC)


 * The fossil record does provide some constraint, as explained in the ref. As I recall, in simpler terms, the argument was that given the constraints that could be put into place on the clocks, they show that more diversification happened during the Cambrian explosion than usual.


 * Incedentally, 10.1641/B580912 might be of interest: it is an overview of the Cambrian explosion whose structure bears uncanny resemblance to this article. It may contain some snippets worth including or ideas for how to contract/expand the main article. Martin  (Smith609 – Talk)  19:53, 25 October 2008 (UTC)


 * I can't access the full text of 10.1641/B580912. Does it bear an uncanny resemblance to Petersen et al (2008) or to "our" Cambrian explosion?
 * Just read Petersen et al (2008). There's a lot I don't understand, especially how they can set the "root prior" (Fungi-Metazoa split) to 100MYA (probably not a misprint, it's in there twice and their central case was 1,000MYA).
 * I'm impressed with the point that they got consistent results out of 2 different software packages and that the results were stable and consistent from the deuterostome-protostome split onwards irrespective of whether they constrained the age of the origin of crown-group demo sponges.
 * I'll have to re-read Petersen et al (2008) to make sure I understand the reasoning behind all the constraints / timimg points they set, and to work out which are most "vulnerable" to unexpected discoveries.
 * BTW I now understand your interest in whether ocean chemistry favoured aragonite or calcite, as the development of stereom can't precede the switch from aragonite to calcite. -- Philcha (talk) 22:18, 25 October 2008 (UTC)


 * 10.1641/B580912 is also at The Cambrian explosion: how do we use the evidence


 * The new animal phylogeny: Reliability and implications (2000) argues that, since mol phylo can distinguish beteeen deuterostomes, ecdysozoa and lophotrochozoa but can't determine the branching order within any of these:
 * These three clades were well established but not diverse before the Cambrian.
 * They all diversified rapidly and simultaneously.
 * Hence the trigger must have been external, i.e. ecological, rather than genetic. --Philcha (talk) 16:34, 27 November 2008 (UTC)
 * OTOH Lack of Resolution in the Animal Phylogeny: Closely Spaced Cladogeneses or Undetected Systematic Errors? concludes that poor resolution of basal metazoa is caused by taxa whose genomes have high "noise-to-signal" ratios, and proposes various methos to get round this, including not using fast-evolving Caenorhabditis as a representative of nematodes. --Philcha (talk) 18:18, 27 November 2008 (UTC)

Darwin and sudden appearance of life
The reference [7] appears to cite pp. 315–316 of the first edition of On the Origin of Species, but the relevant pages seem to be pp. 306–311. Note that it's in with other grave objections, which he answers by appealing to the imperfection of the fossil record on the precedent set by Charles Lyell, so the chapter is not devoted to this one aspect of prehistory. In that edition he refers to the Silurian strata, as that seems to have included the Cambrian when he wrote the first edition, and in the 6th edition pp. 285–289 he presents the same argument with reference to the Cambrian. . dave souza, talk 17:48, 21 April 2009 (UTC)

Permian comparison
What's a 'new type of animal'? Martin  (Smith609 – Talk)  15:14, 24 April 2009 (UTC)


 * The source says no new phyla and very few new classes or orders. I was trying to avoid going into the whole Linnean taxonomic hierarchy, which in any case doesn't work that well in paleo.
 * BTW the point of this item is that the "vacant spaces" idea is not pure speculation, and in particular the CE increase in disparity was not due simply to lower species count. --Philcha (talk) 15:23, 24 April 2009 (UTC)


 * Then the source is attaching a significance to phyla and classes which is entirely inappropriate (Budd & Jensen 2000). It might be worth developing the idea in terms of morphospace, but I'm not convinced that I agree with the implication that the Cambrian radiation was any different to the Permian one.  Martin  (Smith609 – Talk)  15:29, 24 April 2009 (UTC)


 * Is your dissatisfaction conceptual ("attaching a significance to phyla and classes ...") or factual?
 * Re morphospace, IIRC someone estimated the CE filled about 80% of it for marine animals. That might be useful, if we can explain "morphospace" to readers. --Philcha (talk) 16:01, 24 April 2009 (UTC)


 * If the only reason to think that the CEx is different to the Triassic radiation is because the T.R. didn't produce new phyla, then both. The reference you are referring to is probably Bambach and Bush - try the Jan 2008 issue of Palaeontology? Martin  (Smith609 – Talk)  19:00, 24 April 2009 (UTC)


 * I think "If the only reason to think that the CEx is different to the Triassic radiation is because the T.R. didn't produce new phyla, then both" is rather an over-reaction, as we know the T.R. started in a bombed-out environment while evidence for an end-Ediacaran extinction is less certain (taphonomic artefact?) and even less for its magnitude if any. The source's argument is that paucity of species is not a sufficient condition for the CE, as shown by the TR.
 * I'll try to remember Bambach and Bush (2008), thanks - but I've seen an earlier one in the last few days, probably while hunting sources for Burgess Shale. Yep, it's The evolution of morphological diversity (M. Foote; Annual Review of Ecology and Systematics, 1997; doi: 10.1146/annurev.ecolsys.28.1.129) - "about 90% of designs ultimately used by animals (considered as pairwise combinations of skeletal features) had already been exploited rather early in animal history". --Philcha (talk) 19:45, 24 April 2009 (UTC)
 * Can't be a taphonomic artefact. Calcareous organisms go; Ediacarans are known from burgess-shale type preservation, and microbial mats do not appear overnight at 542Ma.  I don't quite follow the point you are extracting from the (rather old) source, and I certainly don't think that the statement currently in the article is particularly helpful. TBH I'm not sure it's necessary... Martin  (Smith609 – Talk)  20:19, 24 April 2009 (UTC)

images, chart or whatever in the lead
That chart thingie is kinda huge in the lead, and.. isn't terribly aesthetic, not to put too fine a point on it. An image is much more appealing. I moved one up, but was reverted by an IP. Aesthetics are not a trivial issue. The IP said "it belongs in the significancse [sic] section anyhow"/ That's a rather stovepiped way of looking at things. I would just.. you know... move it back up and move the chart thing elsewhere, but I'm trying to be nice and all. Ling.Nut (talk) 14:33, 15 August 2009 (UTC)


 * I think the Opabinia pic is best placed with the para about the 1970s part of the debate, see Opabinia for reasons. The timeline isn't particularly useful where it is, largely becuase of its contnet - the various lagerstätten show the results of the process rather than the process, i.e. even the earliest was after the real action. This version of the article is a holding operation anyway, see WP:CEX - we concluded that giving more detail made the article too long, so we want to build up a supporting package of articles, e.g. Fossils of the Burgess Shale and articles about the most important critters. Then we can worry about a lead image. --Philcha (talk) 18:41, 15 August 2009 (UTC)
 * I dunno. I hate to argue with you, partially because these discussions on Wikipedia last half a lifetime. But I would think that the Opabinia image goes in the lead because (as the caption says) it "made the largest single contribution to modern interest in the Cambrian explosion". That makes it relevant to the entire article. Moreover, it's simply an attractive image; too nice to be wasted in the nether portions of the article. But whatever. Ling.Nut (talk) 00:18, 16 August 2009 (UTC)

Stromatolite image
Wilson44691 replaced the pic of living stromatolites with a pic of fossil ones. I prefer the living ones, as they give non-specialists some idea of what sort of life was the latest and greatest for most of Earth's history. Anyone else want to comment? --Philcha (talk) 21:10, 17 August 2009 (UTC)
 * Have boldly added the modern pic, so that readers can compare and contrast. Looks better to me. . dave souza, talk 21:28, 17 August 2009 (UTC)
 * Looks good to me too! Wilson44691 (talk) 22:33, 17 August 2009 (UTC)

Global glaciation on the Ediacaran-Cambrian boundary and Cambrian explosion

 * Aleksey (Alnagov (talk) 14:21, 22 November 2009 (UTC))
 * Aleksey (Alnagov (talk) 14:21, 22 November 2009 (UTC))

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 : 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)
 * A mass extinction before the Cambrian explosion can not be ruled out, though there is not enough data to suggest it happened. But the complexity of the Ediacara biota and its vague relationship with the Cambrian biota may suggest that it might have happened. As to the cause of such a mass extiction, who wants to guess? Enlil Ninlil (talk) 00:52, 30 June 2008 (UTC)
 * I'll take a stab at it... how about the Cambrian substrate revolution? Although you raise a good point; I guess that article ought to mention the loss of the Ediacara biota as well as Cloudina and other mat-sticking calcifiers. And a mass extinction could have triggered a radiation of some degree (although I agree it's unlikely to explain the whole explosion!) Martin  (Smith609 – Talk)  10:10, 30 June 2008 (UTC)

I didn't start this topic, but here's my theory. It was a large radiation event kicked off by activity of a "nearby" star. My thinking is that radiation inspires mutation. 199.172.169.35 (talk) 12:07, 8 December 2009 (UTC)
 * Indeed, it might've been so. Also, quasars and stars explosions may reach a certain level of radiation that would kill most living beings. Maybe a mass extinction followed by intese genetic mutation? All is possible. That's why it's so beautiful. Mr.Smith 1:07, 23 October 2010 (UTC) —Preceding unsigned comment added by 187.20.165.146 (talk)

A Silent Darwinian Fundamentalism
This article seems to have a prejudice against the evidence of chordates having evolved around this time period. It is mysteriously silent on the subject and pushes the radiation of early fish to the Silurian and Devonian periods:


 * "The rate of diversification seen in the Cambrian phase of the explosion is unparalleled among marine animals: it affected all metazoan clades of which Cambrian fossils have been found. Later radiations, such as those of fish in the Silurian and Devonian periods, involved fewer taxa, mainly with very similar body plans." (Subsection: Uniqueness of the Explosion, lines 3-5)

In the rest of the article, chordates are not mentioned to be within the Bauplan with the rest of animal life. There is fossil evidence that they were part of that plan. I'm sensing a hint of a silent adaptationism within this article. Consider revising. -Ano-User (talk) 00:18, 12 March 2010 (UTC)


 * The problem is shortage of fossils - one of the sources says only about 10 of about 30 phyla have left fossils. So "it affected all metazoan clades of which Cambrian fossils have been found". Last time I looked, there were 2 possible chordates in the Fossils of the Burgess Shale while  Chengjiang shows 8 possible chordates including 2 possible fish - but jawless and with gelatinous skeletons, so having almost zero chance of being found outside the lagerstätten. However, if you can provide good citations (see WP:RS) for further Ediacaran or early Cambrian chordates that would be seriously exciting. --Philcha (talk) 04:08, 12 March 2010 (UTC)


 * The fossil record of deuterostomes and molecular clock estimates of divergence times. http://www.nhm.ac.uk/resources-rx/files/swallasmith08-18122.pdf Aleksey (Alnagov (talk) 12:37, 12 March 2010 (UTC))


 * I think the above link proves my point. Namely about the main deuterostome phylogenies (tunicates, craniates, etc.) diverging at similar times, but even earlier than that, the ancestral phylums of Chordata and Ambulacraria diverge from each other around the same time (the Ediacaran), and not one leading to the other.  The evolutionary process is more like a bush than that of a tree, when put into picture.  But that it is more like a tree is apparently what the main article is saying.


 * However, I am not trying to suggest that there were chordates during the Ediacaran period. Forms during that time, as far as I know, were too primitive and mostly soft-bodied to have been chordates.  --Ano-User (talk) 04:54, 13 March 2010 (UTC)

Information Landscape Change as Cause
HI, recent paper in Paleobiology arguing for the role of information landscapes in causing the evolution of complex sense organs and possibly the explosion itself. Should be listed under causes of explosion.

DOI: 10.1666/08062.1

PDF: https://pantherfile.uwm.edu/sdornbos/www/PDF%27s/Plotnick.et.al.2010.pdf —Preceding unsigned comment added by Joseph.9371 (talk • contribs) 16:31, 7 June 2010 (UTC)


 * I agree, environment does play a big role in the evolution of species, which is what I was trying to get at in the comment above yours. Causes for the explosion may not have been due entirely to the "inherent" Bauplan of living organisms, but as the Paleobiology article states, by "external environment changes" (Plotnick, et. al., p. 304).  The organism "must continually obtain new information in order to reduce uncertainty and make the most advantageous decisions."  The article continues, "It can be assumed that there should be strong selection for features that reduce uncertainty; the more signals that can be detected and analyzed (the more information) the greater the ability to make the ‘right decision'" (p. 304).


 * Information landscapes are defined as environments that "are heterogeneous in some property over space" (p. 305). The development of complex sensory organs may have been due to these information landscapes available in the early Cambrian.  As you said, this should be listed under [possible] causes of explosion.  -Ano-User (talk) 07:48, 21 July 2010 (UTC)


 * Thanks, Joseph.9371 and Ano-User. All this looks interesting, and with a good citation (the PDF) - do you have any others like that? Go for it. --Philcha (talk) 12:01, 21 July 2010 (UTC)

Oxygen point bummer
The section Increase in oxygen levels perfectly misses the point. It approx claims that the rise in size of the sea critters has no correlation with the oxygen levels. That's off-topic, since the Cambrian explosion is a rise in number of fossils, not specifically a rise in size. Those who claim an oxygen increase as the reason for the Cambrian explosion claims that the rise in oxygen levels in any way enabled the animals to grow hard exoskeletons that can fossilize. The theory is not uncontested but I believe it has many adherents. The explanation why increased oxygen levels created this fossil explosion varies from this to that more precise theory:
 * 1. (mainly deprecated:) the increase in oxygen levels enabled the monstrous critters to grow larger than before,
 * 2. (still valid) the increase in oxygen levels enabled the monstrous critters to grow calcium carbonate based fossilizable (exo)skeletons from oxygen and other ingredients,
 * 3. (still valid) the increase in oxygen levels enabled the monstrous critters to grow fossilizable (exo)skeletons, and still not be suffocated because of a decreased skin respiration.

The section in question only relates to theory 1, and believes that being sufficient. Rursus dixit. ( m bork3 !) 19:39, 2 November 2010 (UTC)

Reference list
I suggest the implementation of  on this article, because of the length of the reference list. Opinions, rejections? —bender235 (talk) 19:49, 19 December 2010 (UTC)

Section on explanation of terms.
I might suggest adding the tag to the section called "Explanation of a few scientific terms". The article is significantly wikified enough that a user will be able to deduce what the various terms mean by following the hyperlinks already present in the article. It is out of place in terms of historical scientific context describing the Cambrian explosion and is an abrupt change in subject when reading the article top down. Altogether, the section (IMHO) could be deleted or rewritten.


 * I've disabled the request tag because I think that some will disagree with you - a discussion here might be appropriate, though. Martin  (Smith609 – Talk)  13:40, 8 December 2008 (UTC)
 * I don't see why not... There is a bit of reason to put it on, and it wont hurt anyone. 173.183.66.173 (talk) 05:58, 30 January 2011 (UTC)

They fed above the sediment surface, but were forced to burrow to avoid predators
4.3 Burrows

The traces of organisms moving on and directly underneath the microbial mats that covered the Ediacaran sea floor are preserved from the Ediacaran period, about 565 million years ago. They were probably made by organisms resembling earthworms in shape, size, and how they moved. The burrow-makers have never been found preserved, but because they would need a head and a tail, the burrowers probably had bilateral symmetry – which would in all probability make them bilaterian animals.[49] They fed above the sediment surface, but were forced to burrow to avoid predators.[50]

It is erroneous citing of the primary source (bold). The special case has been transformed into the characteristic of all Ediacaran or Сambrian burrows.

Remark to primary source
 * Dzik talk about special case – the trace fossils from Kessyusa formation, Mattaia Creek, Khorbusonka River area, which he has collected at time the single visit of this locality. Dzik has studied trace fossils Podolodes, Treptichnus (Manykodes), Dydymaulichnus (Mattaia) only.


 * He does not mention about such traces as Planolites, Palaeophycus and others, which are available in the studied by him deposits and in more ancient deposits of the Khorbusonka River and in Ediacaran-Cambrian beds somewhere else in the World. These traces (burrows) without doubts belong to animals feeding in sediment rather than to animals feeding above it and burrowing only to avoid predators.

Aleksey (Alnagov (talk) 13:35, 25 December 2010 (UTC))
 * He could not collect and has not collected all variety of trace fossils and not ascertained the cases of their first occurrence in this locality. Dzik has incorrectly defined age of the studied deposits on base of the first case of occurrence of Treptichnus traces in the studied outcrop which has been known to he. The deposits on the Mattaia Creek where Dzik has collected trace fossils are Tommotian age rather than of boundary Ediacaran-Cambrian or lowermost Cambrian. That is known for a long time and it is confirmed by new detailed long-term (2006-2010) researches of this Ediacaran-Cambrian deposits.

Stratigraphy of the Vendian-Cambrian succession along Khorbusuonka and Olenek Rivers Aleksey (Alnagov (Alnagov (talk) 17:14, 7 March 2011 (UTC))

Over a period of many millions of years
This ridiculous parenthetical seems like a preemptive attack on creationists that doesn't deserve the focus it has. Anyone who has a grade school understanding of evolution will know that "relatively rapid" doesn't mean over a few decades. Saying it is a transparent attack on a fringe position that isn't explicitly involved. Is it absolutely necessary? I mean, I for one am sick of every topic pertaining to prehistory being framed by people who still believe in gods and monsters. Twin Bird (talk) 23:29, 30 November 2011 (UTC)
 * I think you might be reading too much into it, in my opinion. I think relating time scales to evolutionary speed is a basic task for the lead here. Jesanj (talk) 21:42, 31 December 2011 (UTC)

Animal groups did NOT form in the Cambrian Explosion
I changed the topic sentence to "seemingly rapid diversification of life" from "seemingly rapid formation of most major animal groups". Birds, Mammals, Amphibians, and Reptiles ALL formed a long time after the Cambrian Explosion! To claim that "most major animal groups" formed during it is misleading nonsense. In fact, it reeks of the usual misinformation spread by Creationists. InterwebUsr (talk) 02:10, 3 March 2009 (UTC)


 * I'm afraid your comment suffers from vertebro-centrism (a wider form of anthropocentrism). The groups you list are Classes or Orders within 1 sub-Phylum, Craniata, within Phylum Chordata. Chordates, Annelids, Arthropods and many other phyla are first seen in rocks from the Early Cambrian. Hence "seemingly rapid formation of most major animal groups" is accurate, and is expressed in plainer language. In addition "seemingly rapid diversification of life" is inaccurate because there important higher level groupings are known from earlier rocks, in some cases back to at least 3,000 M years ago e.g. - e.g. plants, fungi, protists at the Kingdom level; and eubacteria, archea and eucaryotes at the Domain level - see Evolutionary history of life for a quick gallop through that long span of time. You may have noticed I did not mention Mollusca - the Ediacaran critter Kimberella may have been a primitive mollusc, although there's debate about that. In the light of all this, I'm going to undo your change.
 * But thanks for your interest in this article. Please comment on this Talk page if you think parts need to be improved - including not giving encouragement to Creationists. You mignt also like to take a look at WP:CEX, a project to produce a supporting package of decent articles about the fossils and other evidence relating to the Cambrian explosion, so that Cambrian explosion can refer to these for details and stick to the most important aspects - it's a huge subject. --Philcha (talk) 13:53, 3 March 2009 (UTC)

Sorry, you are right, thanks for informing me. InterwebUsr (talk) 01:59, 4 March 2009 (UTC)
 * One of my books on Earth history speaks of "the origin of most animal phyla". Should the word "groups" be replaced by "phyla"? Woodwalker (talk) 10:19, 4 March 2009 (UTC)
 * I'd avoid that issue as it's contentious - some fossils from about 580 MYA are thought to represent Cnidarians, and there are also Late Ediacaran fossils that may be arthropods (Spriggina, Parvancorina), another that may be an echinoderm (Arkarua), and I've even seen an article that suggested some sessile "frond animals" (that looked a bit like ferns in shape, and filter-fed), of a type seen in both the Ediacaran and Early Cambrian, may have been early Ctenophores. Considering that fossils have been found for only about 10 of the about 30 known phyla, we have early candidates for about half of these. I also remember an article last year that spoke of a possible "Ediacaran explosion", as most of the forms often classified as Vendobionta seem to appear about 570 MYA and chages after that were minor. Who knows, perhaps the "Cambrian explosion" will be an obsolete concept 10 years from now. --Philcha (talk) 11:16, 4 March 2009 (UTC)
 * Thanks for the reply. I read through some literature given in the refs this morning. It already gave me the feeling the sentence "most phyla have their origin in the Cambrian explosion" is getting more and more outdated with the new Ediacaran claims. I am myself not a palaeontologist, but I think you and the other guys from WP:CEX are doing a great job. I'll keep the article on my watchlist because I think it's interesting to see it develop. Regards, Woodwalker (talk) 14:36, 4 March 2009 (UTC)

Currently, the lead sentence says most (major) phyla arose in the Cambrian explosion, presenting it as the most important fact to glean from this article. In contradiction, the phyla article only mentions this topic once and only to say that many modern phyla did not appear until long after the Cambrian.

Surely, if the point is important enough to be in the lead, then it warrants more detailed discussion in the body? The idea that most phyla appear in one explosion is widespread, and is even employed as an argument by creationists (such as L. Brand, who neglects to explain to his lay-readers that phyla are a completely different level from the groups of birds, fish, etc), which is another motivation to try to be more accurate and understandable here. One of the complicating issues seems to be that the classification of phyla has altered in the past (as relationships are determined more accurately), and in fact that the very concept of phyla (i.e., of assigning ranks to clades) is being depreciated as arbitrary.

To me, it seems it would be better if we explicitly listed which clades did appear around the explosion and which did not appear until later (and which were already observed earlier). Such a section would also accord with the convention that the lead should summarise the body rather than itself need referencing. Is there already a list summarised someplace? Cesiumfrog (talk) 00:40, 2 February 2012 (UTC)


 * You will find answers to these questions in the article: S. V. Rozhnov (2010). "Combinatorial Model for the Formation of Body Plans in Higher Metazoan Taxa: Paleontological Insight". Paleontological Journal 44 (12): 1500–1508. Aleksey (Alnagov (talk) 07:08, 4 February 2012 (UTC))

Avalon explosion
So, what's the relationship, if there is one, between the Cambrian explosion & the Avalon Explosion?76.246.45.160 (talk) 06:56, 5 July 2012 (UTC)

All present phyla?
I'm about confused about this article because the lead says that All present phyla appeared within the first 20 million years of the period, with the exception of Bryozoa who made its earliest known appearance in the upper Cambrian but the section "How real was the explosion?" says the conventional view that all the phyla arose in the Cambrian is flawed. Which statement is correct? --Cerebellum (talk) 03:49, 7 March 2013 (UTC)


 * "All present phyla appeared within the first 20 million years of the period, with the exception of Bryozoa who made its earliest known appearance in the upper Cambrian" This phrase only means that fossils of nearly all animal phyla what known from Cambrian deposites appeared within the first 20 million years of the period. It is important to remember that the fossil record of this phyla begins with the appearance of species with mineral skeletons what can be preserved in carbonatic and phosphatic sediments, and with the appearance of Lagerstattens in which a soft parts of the body can be well-preserved - NOT from the time of phyla origin.


 * "view that all the phyla arose in the Cambrian is flawed". This means that the time of origin of phyla precedes the time of appearance of its fossils in the Cambrian. For example see

~35 modern animal phyla are accepted. Fossils of ~16 modern (see list) and several extinct animal phyla are known from Cambrian deposites. The fossil record is very incomplete, usually only mineralized and resistant chitinous remains of animal can be fossilized. Fossil record of soft body animals (marked by bold ) are unbelievably prodigy and known from several Lagerstatten only (for example, Burgess Shale).
 * Arthropoda
 * Brachiopoda
 * Bryozoa
 * Chaetognatha
 * Cnidaria (known also from Ediacaran)
 * Echinodermata
 * Mollusca
 * Porifera (Criogenian?, Ediacaran)
 * Hemichordata
 * Annelida
 * Chordata
 * Ctenophora (Ediacaran)
 * Entoprocta ?
 * Onychophora/Lobopodia
 * Priapulida
 * Sipunculida
 * Tardigrada

Aleksey (Alnagov (talk) 22:24, 7 March 2013 (UTC))

Fixed footnotes
I have finally fixed the footnotes after they were broken in 5 years ago! For comparison was the last one with footnotes working. Quietbritishjim (talk) 18:00, 9 June 2013 (UTC)
 * Someone had partially fixed the mess by moving the two footnotes in the lead inline in text, so I've moved them back out. I'm not convinced they're actually better as notes, but now any move can at least be a conscious decision rather than out of necessity.
 * There was also commented out text in the lead that I've now put in a new footnote.
 * Most importantly, I fixed the two footnotes in the body of the article, which appeared as orphaned notes all this time. The one in the "How real was the explosion?" section was "fixed" to point at the wrong reference, which explains the confusion in the last point in User:TDurden1937's comment higher up this page.
 * Thank you! Danger High voltage! 19:24, 9 June 2013 (UTC)

How real was the explosion? and Possible causes of the “explosion” seriously flawed
This page, the "Cambrian Explosion" is riddled with qualifying clauses such as "may" and "might." In my opinion, this page very nearly reduced to speculative anthropology/geology.

Speculation is poor science. Although, I see no problem speculating (its fun!), when science (anthropology/geology in this case) is speculative, it should be prominently marked as speculative. As scientists (either professionally or laymen) we must take great care in how we present ourselves and our arguments lest we leave ourselves open to anti-scientific criticism.

Now I will list some of the most egregious examples of the qualified statements:

1) "The explosion may not have been a significant evolutionary event. It may represent a threshold being crossed: for example a threshold in genetic complexity that allowed a vast range of morphological forms to be employed."

WTF. Well. . . without ANY supporting material for these two sentences, anyone reading this with any kind of critical reasoning could think, "The explosion may have been a significant evolutionary event. It may not represent a threshold being crossed, but represent a very real and unexplained explosion."

2) "As a simple example, the evolution of predation may have caused one organism to develop defence (sic) while another developed motion to flee."

My God. . . is there any evidence other than speculation that this actually happened Metazoans in these circumstances?

3) "The initial herbivorous mesozooplankton were probably larvae of benthic (seafloor) animals. A larval stage was probably an evolutionary innovation driven by the increasing level of predation at the seafloor during the Ediacaran period."

Is this anything other than a wild, very wild guess? Is there any evidence at ALL? Both these sentences depend on "probably" as assurances. Probably? This is not science but pure and simple speculation! I am embarrassed.

4) "If any of these remains sank uneaten to the sea floor they could be buried; this would have taken some carbon out of circulation, resulting in an increase in the concentration of breathable oxygen in the seas (carbon readily combines with oxygen)."

Yet, under "Increase in Oxygen levels" it is explicitly pointed out that ". . . animals are not affected when similar oceanographic conditions occur in the Phanerozoic; there is no convincing correlation between oxygen levels and evolution, so oxygen may have been no more a prerequisite to complex life than liquid water or primary productivity."

How can we let contradictory evidence like this co-exist in the same page?

How can it be justified that approx. 180 words in the above mentioned section is dedicated to how oxygen levels might have influenced the Cambrian explosion, yet during the "Phanerozoic . . . there is no convincing correlation between oxygen levels and evolution . .. "

As a believer in the scientific method. . . this is just embarrassing.

Finally, I would like to point out the following statement: "The presence of Precambrian animals somewhat dampens the "bang" of the explosion: not only was the appearance of animals gradual, but their evolutionary radiation ("diversification") may also not have been as rapid as once thought. Indeed, statistical analysis shows that the Cambrian explosion was no faster than any of the other radiations in animals' history."

The citation appears to cover the paragraph to its beginning. However, examining the article (it is available in pdf on a Google of the article name), there is absolutely, as far as I can tell, no mention of statistic analysis that shows the Cambrian explosion no faster than any other radiation in animals' history. To the contrary, this study shows a extraordinary increase in morphological disparity during the Cambrian explosion! There is a serious problem here. Indeed, the above citation from the page seems to drastically misrepresent what conclusions to "Macroevolution and macroecology through deep time" are arrived at in the article by Butterfield.

These are only some of the problems I found in this page. IMO, this page is highly flawed and in need of significant revision.

As a scientist and a contributor to Wikipedia, I am embarrassed that such a page on such an important subject could be so riddled in mistakes and unqualified speculation. — Preceding unsigned comment added by TDurden1937 (talk • contribs)
 * You seem to be new here. First, anyone can contribute to any article.  If you find flaws, make changes.  I don't know anything about a lot of articles I help edit, but I learn.  Use reliable sources to support anything you write.  Your personal synthesis or opinion is not useful, only what can be verified.  So, you seem to have some good ideas, go for it.  By the way, these articles aren't written in a scientific method...they just use citations that do.   Orange Marlin  Talk• Contributions 00:24, 23 March 2011 (UTC)


 * You may find my toolbox useful, including 2 for building citations. --Philcha (talk) 08:29, 23 March 2011 (UTC)
 * As you look back over time, the quality and quantity of fossils decreases. Hence there are a lot of "maybe"s in the early history of metazoans. --Philcha (talk) 08:29, 23 March 2011 (UTC)

98.165.76.78 (talk) 16:09, 3 April 2011 (UTC)TDurden1937
 * Thank you for your comments and encouragement to refine this page. I do not take lightly the action of editing contribution to a Wiki article. However, I am committed to quality in all the Wiki articles . . . so I will do my research to the best of my ability. Any changes I make will be done with a "do no harm" philosophy, and I will as clearly as I can make a notation in the discussion page (this page) as to what I change a why. I have watched Wiki grow over the years and I love what it has become. I thank all the people who cared enough to invest the time and energy to make contributions to this particular page. BTW, I have been following this page for a time now, but it is true that this is the first time I posted a comment.

Just a few things I'd suggest. First register a user name. I want to say hi to someone, not a number. LOL. That's just me. Also, remember to sign using the 4 tilde's. Indents use ":". The asterisk "*" is for lists. Finally, as long as you don't push a POV, I personally enjoy new editors joining in the articles that I watch. Everyone was a brand new editor once. And remember Wikipedia has a lot of stuff from templates to codes. I learn new ones almost every day. I forget old ones every day too. :)  Orange Marlin  Talk• Contributions 19:24, 3 April 2011 (UTC)
 * Can the title of this section be changed to "how sudden was the C. E.?" Maybe "how unusual was the..." I think most people think of "real" as a Boolean. Fotoguzzi (talk) 19:25, 9 July 2013 (UTC)

Cambrian Explosion: Yes? Or No?
I'm your standard "lay reader" and after reading through this entire article, I am more confused than before I read it.

Was or wasn't there a Cambrian explosion? You argue for both sides (offering multiple pieces of evidence for why there was and why there wasn't) but it would be helpful to come down on one side or the other as the general consensus of the academic community. I mean, it can't be an even 50/50 split between the two camps, right? So, do most paleontologists and geologists believe there was a Cambrian explosion or do they think there is insufficient evidence to warrant this claim? Hopefully, some knowledgeable editor can make a deft editing so that this is clearer.

It's fine if there is still an ongoing debate about this question. But to lay out all of this evidence both for and against and not draw a conclusion at the end of the article just ends up confusing the average reader. If it's undecided, say it's undecided. But have some kind of conclusion. 68.197.234.170 (talk) 18:16, 8 July 2012 (UTC)


 * There is an ongoing debate. It's hard to draw conclusions when you've got multiple schools of thought drawing different conclusions - all you can do is reference each of them. Drawing a conclusion on who is "right" is beyond Wikipedia's remit. Sakkura (talk) 18:02, 6 October 2012 (UTC)


 * There really isn't a debate on the reoccurring fossil patterns of those known from the 1980's which produced this enigma in the first place. If anything those patterns have only amplified. If you cut out all of the wild speculation attempting to downplay or 'dampen' the Cambrian explosion then people probably wouldn't be so confused. 64.222.209.188 (talk) 18:12, 22 June 2014 (UTC)

Were these animals edible?
If a human went back in time 500 million years could they survive by eating the Dickinsonia creatures? — Preceding unsigned comment added by OMPIRE (talk • contribs) 16:37, 5 September 2014
 * Assuming that one could handle the oxygen content of the period during harvest, they were wafer-thin (~0.5 cm at most) pancake-like organisms who ranged in size from a few milimeters in diameter to at most twenty centimeters. Presumably if they were abundant enough, one could scrape enough of them out of sediment and consume them. That said, while amusing, it would be irresponsible (but entertaining) to speculate on the specific nutrient quality of said critters. Aderksen (talk) 16:47, 3 November 2014 (UTC)

Creationism influence
Creationism is a uniquely American phenomenon and it is clear by reading this article that their influence is all over it. Someone please sort this out. It is making the article below par. It gives the false impression there is 'debate' within science about the causes and origins of life based on the 'explosion' (which took 25 million years by the way.. hardly an explosiion). Wikipedia is better than this. — Preceding unsigned comment added by 92.54.152.90 (talk) 12:17, 18 February 2015 (UTC)


 * I don't read it that way. The term "Cambrian explosion" is generally what it's called - it may be a misnomer, but it's use in so many scientific papers and books is what we follow here. There is definitely still debate about the causes of this rapid radiation. Do you have an alternative wording that you would like to see? Mikenorton (talk) 12:56, 18 February 2015 (UTC)
 * Anonymous Wikipedia editor! Please register an account for yourself, and help to improve this page! I am curious what your specific objections or suggestions are. I can assure you that this page is regularly updated with recent and relevant research, and that there are a number of geologists and phylogeneticists who monitor the page for abuse. If anything, I read the article as revealing "early controversies" (brought up by folks like Darwin), and how they were gradually and comprehensively addressed over the next two centuries. Please join us and let us know what else we might do to improve the article! Aderksen (talk) 19:54, 5 May 2015 (UTC)

History and significance
I'm not sure "spiny slug-like Wiwaxia" helps here. The paragraph is about how so many Burgess animals did not fit into known taxa, and "slug-like" blurs this. IIRC Wiwaxia was not one of the fossils that drove Whittington and co. to a more radical view (Marella and Opabinia were the main factors), and I'd omit Wiwaxia for now and discuss the Halwaxiids later. Philcha (talk) 00:44, 28 June 2008 (UTC)


 * Please feel free to correct me, but (while interesting in their own right) I'm not sure how important the "Halwaxiids" are in understanding the Cambrian explosion. I suspect that there would be a good sub-article on "History of research on the Cambrian explosion" (I need to develop my skills as writing snappy titles!), but this article should attempt to be up to date, and my feeling is that "Wonderful Life" and the Burgess shale now only represents a tiny part of the available evidence. Martin  (Smith609 – Talk)  10:52, 28 June 2008 (UTC)


 * I agree that "Wonderful Life" and the Burgess shale now only represents a tiny part of the available evidence (how could I not!) but, if some of our readers have any prior knowledge, those are probably what it's based on. And the stars of Wonderful Life and of the research by Whittington & co. are Marella and Opabinia - they were the fossils that caused the paradigm shift. Philcha (talk) 00:10, 30 June 2008 (UTC)

I think the whole paragraph "dating the Cambrian written in a imprecise way ". This gets in the way of understanding. Radiometric dates for much of the Cambrian, obtained by analysis of radioactive elements contained within rocks, have only recently become available, and for only a few regions.


 * Sentences using "relative time" (words like recently) should probably be avoided.
 * What is a Radiometric date?
 * For much of the Cambrian "what"?
 * When is recently and where is the source?
 * What regions?

"Therefore, dates or descriptions of sequences of events should be regarded with some caution until better data become available."


 * "Relative time" phrase (until better data...)
 * What is meant my "dates" in this context?

Glennbech (talk) 22:36, 2 July 2015 (UTC)

jnfobox
Could the hallucigenia image be reworked to suit current images of the creature? Jackiespeel (talk) 00:09, 13 March 2016 (UTC)

External links modified
Hello fellow Wikipedians,

I have just modified one external link on Cambrian explosion. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
 * Added archive https://web.archive.org/web/20090226122725/http://www.vend.paleo.ru/pub/Fedonkin_2003.pdf to http://www.vend.paleo.ru/pub/Fedonkin_2003.pdf

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

Cheers.— InternetArchiveBot  (Report bug) 23:06, 25 May 2017 (UTC)

Simplifying the lead.
My recent changes removed nothing from the article. Every word from the lead was moved down below. WP:BRD. Thanks. BeenAroundAWhile (talk) 20:45, 11 December 2017 (UTC)


 * Hmm. If you'd moved all the refs out of the lead, I'd have understood and approved of what you were doing. But you've left 8 of them, so that obviously wasn't your beef. If the lead had been ridiculously long and complicated, too, I'd have understood and sympathised: but it was 3 paragraphs, and it was clear, helpful, and straightforward. And if you'd left the lead in a state which elegantly and tersely summarised the sections of the article—its History and significance, Precambrian life, Ediacaran skeletonisation, Cambrian life, Stages, Possible causes, Uniqueness—I'd have admired and approved. But you didn't. What we now have is indeed skeletal, but it mentions history and significance not at all; nor the Precambrian life; nor the skeletonisation; nor the stages. Instead, all that's left is three too-short paragraphs. These don't even mention that the explosion was brief. In a word, it was better before. I see that the in-work tag has vanished, but perhaps you're planning to work on it some more? It certainly needs improvement. Failing that, we should probably revert. Chiswick Chap (talk) 21:20, 11 December 2017 (UTC)

Incomprehensible sentence
The article includes the following sentence today which does not make sense to me:
 * The intense modern interest in this "'Cambrian explosion" was sparked by the work of Harry B. Whittington and colleagues, who in the 1970s re-analysed many fossils from the Burgess Shale (see below) and concluded that several were complex as but different from any living animals.'

Someone who knows what it should say, please correct it. Perhaps it should read: "were as complex as" instead of current "were complex as"? WilliamKF (talk) 06:31, 1 December 2008 (UTC)


 * Edited to "... several were complex as but different from any living animals" - "as a complex as" would bw wrong. Thanks for pointing out the problem. --Philcha (talk) 09:38, 1 December 2008 (UTC)


 * That is certainly more grammatically correct, but I can't comment on its correctness with respect to the citation. WilliamKF (talk) 03:43, 3 December 2008 (UTC)


 * I restored "that several were as complex as, but different from, any living animals" which is perfectly grammatical and means something different from "complex but different". The second comma is a matter of taste but IMO makes the relations clearer 194.174.76.21 (talk) 16:17, 2 January 2018 (UTC) Marco Pagliero Berlin

And here is another one with grammar issues which I am unclear on what is intended:
 * A stem group is offshoots from members of the lineage earlier than the last common ancestor of the crown group; it is a relative concept, for example tardigrades are living animals which form a crown group in their own right, but Budd (1996) regarded them also as being a stem group relative to the arthropods.

"Is offshoots" makes no sense. WilliamKF (talk) 07:05, 1 December 2008 (UTC)


 * Edited to "A stem group is a set of offshoots from the lineage at a point earlier than the last common ancestor of the crown group." Does that work for you? --Philcha (talk) 09:38, 1 December 2008 (UTC)


 * Again, that is now grammatically correct, but I can't speak to its correctness. WilliamKF (talk) 03:43, 3 December 2008 (UTC)


 * They're as correct as such short summaries can be. Thanks for pointing out the prose issues. --Philcha (talk) 08:29, 3 December 2008 (UTC)