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As per to do list - I have some stuff I can put here when I have a moment!
Grahbudd 07:00, 25 January 2007 (UTC)
I've replaced Graham's timeline with a wikified one that's easier to read on the page (and a bit more colourful). I've also amended a couple of the dates where new data has allowed their refinement. Verisimilus 18:03, 10 March 2007 (UTC)
Nice, Verisimilus. But there some minor mistakes. Since you have the source file, please correct the timeline figure: there should be Chengjiang, not "Chengjang" (add missing "i"), and correct the "Cambrian Era" to "Cambrian Period" or "Pal(a)eozoic Era".
Body ridges are a common feature in organism fossils of the period, suggesting possible external food intake.
This doesn't sit too comfortably with me... there are many other possible reasons for ridges (e.g. gas exchange, structural support, artefacts of segmentation, hydrodynamics?) that don't fit this hypothesis; indeed other animals (trilobites, earthworms) are 'ridged' whilst not having this mode of life. I'm not convinced this is factual enough to be considered Encyclopædic content... whilst there is one prevailing view that they did have this mode of life I don't think a ridged appearance is necessarily evidence for it. Verisimilus 21:09, 15 March 2007 (UTC)
Alternatively, some new form of microbial or viral infection agent may have developed which could transfer genes between species, speeding up evolution by "sharing" useful features. This is somewhat comparable to the Recombinant DNA process in sexual reproduction, but on a cross-species level.
After a quick search I can't find anything in the literature (or even in the link supplied) that suggests this hypothesis is anything more than an interesting but entirely unsupported and loosely defined conjecture... Hence I don't feel it should be included here as 'encyclopaedic content' unless a reliable source is found.
Verisimilus 13:21, 5 April 2007 (UTC)
The structure of the article could be improved considerably. The "Dating the Cambrian" section serves little purpose; that topic is covered throughout the article, and what is not could be merged into the "Significance of the explosion" section. I also suggest putting the history section immediately after the intro, before the Significance section. Also, "Timing of the Cambrian Explosion" seems to be more or less dealing with the same issues as "Causes of the Cambrian Explosion". I would suggest removing the causes section from "Significance of the data" and putting it in it's own top-level section, and using a trimmed-down version of the timing section as an intro to the causes section.-- ragesoss 23:55, 19 April 2007 (UTC)
I mean, write for the intelligent lay person. Please write where someone can actually learn something.
Wikipedia is still in the process of becoming. It might make it, it might not, it needs some help! For example, bluebirding--writing just to string together blue words that refer me elsewhere, rather than talking to me when I’m right here. I’m here and now, and I’m interested, please teach me. Use Carl Sagan or any other good writer as a model (maybe James Trefil, the guy who wrote “A Scientist in the City”), rather than using some artificial, formalistic style.
Maybe at the beginning of the article, talk just like you would if an intelligent, interested 10th grader were right in front of you.
Later on, as if I was an intelligent college student.
Later on, as if I was an intelligent younger colleague.
And later on, toward the end of the article, talk to me about the cutting edge of research going on right now as if I am your fellow colleague.
This will give the article a sense of development, and please do not do this mechanically. Surprisingly, if you allow the writing to stay a little unfinished, it’s often better. The article does not need to be perfectly consistent in any regard. It just needs to be good. Good is better than perfect (in this context, and in many other contexts as well!). Write just a little bit more formally than how you would simply talk to me. That’s what would help me to learn the subject matter and really get a lot out of it.
Okay, the part on the Ediacaran fossils: “In addition, in the Ediacaran Period immediately preceding the Cambrian, apart from the trace fossils and tubes previously mentioned, the record contains the highly enigmatic “Ediacaran” biota, which despite decades of study and a flurry of recent intense interest, remains very hard to place in the context of animal evolution.”
(That’s vague, that’s hedging your bets. That is “safe” writing. At issue is whether the Ediacaran creatures died off or not. Go ahead and say it.)
“Some taxa such as
Kimberella are thought by some to represent bilaterians . . .”
(And I’m not sure whether these are part of Ediacarans or not.)
(next paragraph) “Perhaps the most promising area for study is the Doushantuo Formation of China, spectacular fossils from which are probably around 580 million years old or younger.”
(So I realize now it’s probably other early fossils (or fossil traces), but . . . more bluebirding! So, the purpose of a wikipedia article is just to bluebird, it’s not actually to teach anything.)
I think about two whole paragraphs on the Ediacaran fossils would be a lot better. It’s important enough. It’s a relatively known precursor. And for me personally, writing that builds on something I already know often makes for very satisfying reading. And afterall, the Cambrian Explosion is perhaps the greatest mystery in the history of life on Earth, and it’s a major issue in SETI and astrobiology and how likely life elsewhere in the universe might be. It’s worth spending some time on the precursors. And long is good. If it’s going to be a real teachful article, it’s probably going to have to be long. So a couple of paragraphs on Ediacarans, with the single bluebird if I want to learn even more. Now, discrete footnotes are fine, and are in fact good as long as they don’t interfere with the flow of the writing. For example, here are two websites on Ediacaran fossils (and good websites at that, at least to my untutored eye!) [1] [2] .
If someone says something like ‘appropriate for an encyclopedia,’ I’m going to say you’re letting a formalistic standard stand in the way of communication.
(I realize this may not be the most good-natured piece I’ve ever written. But it's frustrating when you look something up and you don’t learn anything.) FriendlyRiverOtter 20:45, 20 April 2007 (UTC)
It's quite a challenging set of demands, which I mainly agree with in principle. The balance I think that needs to be struck is one between an article that is concise enough to be readable without the attention wandering, and yet in depth enough to capture the imagination. One could argue that to discuss the Ediacaran biota at length would be to stray unnecessarily from the subject - and one could argue that the interested will follow the 'bluebird' whilst the uninterested will not be distracted from the main flow of article. Regarding the levels of 'in depthness' - I agree with this in principle, but it would be quite difficult to fit into the current article, which has several distinct sections. I feel that to a degree the article already does mention points in brief before expanding on them; but there could well be scope for improvement. I'd wholeheartedly encourage you to have a dabble with the article, if you feel able! | Verisimilus T 09:54, 21 April 2007 (UTC)
First off, VerisimilusT, thank you for your very gracious response. You took it better than I hoped (and I was frustrated when I wrote it), this was a post I was a little bit worried about, so thank you for your thoughtful response. However, I cannot take you up on your generous offer. I do not feel at this time I have the kind of readable writing style that will be acceptable to the majority of wiki users (people will be editing out what I think are my best parts and it will just drive me crazy), and besides that, I don’t feel I know enough about evolution! What I do hope is that I will be appreciated as someone on the other side, because it sure seems like everyone and their brother wants more formality in the writing. More formality? I ask, why can’t we explain it in plain English and introduce the occasional technical term that sincerely advances understanding? I think we can.
Okay, as an example, take Thomas Kuhn’s THE STRUCTURE OF SCIENTIFIC REVOLUTIONS. We could give a good meaty description in four sentences. And not a baby description, but a good description for a college audience. Four sentences. And I think that good description would have zero or maybe one technical terms. The technical terms are not what’s paramount. It’s explaining it to someone just as smart as you are (you’ve got to give your reader that respect), but just someone who doesn’t happen to know this particular area.
Okay, the Ediacaran animals, and the picture looks kind of like a sand dollar, but with lines radiating out from near center. Alright. Well, to an order of approproximation, all species are extinct. Appropriately 99% of all species that have ever lived are extinct. And evolution is bushy. Looking backwards, you can see a main line. But at any particular time, it’s bushy and going in all kinds of different directions and you have no way of knowing what’s going to end up being the future main line. So, it would be no great surprise if the Ediacarans had gone extinct. FriendlyRiverOtter 09:39, 27 April 2007 (UTC)
I'd have to disagree heartily on your 'main line' point. Evolution is indeed 'bushy', and just like a bush, there is no 'main line' - just twigs and twigs. It's popular - and easy - for humans to think that all evolution was directed towards them, but that's not how it works - things 'devolve' as fast as they 'evolve', and 'progress' can only be defined and measured by us, it's not an inherent property of the system. Evolution is change, and it takes us to decide when to call it 'progress'...
Re. the 'not unlikely' extinction of the Ediacarans: Species could be thought of as being a little like needles on a pine tree. It's not a perfect analogy, but an extinction of an entire clade would be like removing every single pine needle from an entire bough - if just one remains, the clade remains extant (i.e. non-extinct). Other, better documented mass extinctions have hit the pine tree like a strong wind - needles have fallen largely at random, and whilst sometimes one branch is decimated more than another, a major bough being completely stripped is incredibly rare. Twigs may be stripped (and go extinct), but larger boughs would always keep a few needles...
I suppose the counter-argument would go that the branches were twiggier back in those early days. Most people expect the 'Ediacarans' to be a major bough on the tree, but maybe at the time this was no bigger a branch than the trilobites', which went extinct at the end of the Permian... | Verisimilus T 12:26, 27 April 2007 (UTC)
And if bears had developed as the dominant intelligence, the “main line” would have gone to them. If it had been small dinosaurs, a la Harry Turtledove’s very imaginative colonization series, they would have been the “main line,” and mammals would have been just a little curious offshoot.
And if we were polar bears, seals would occupy a very central part of our mental lives. If we were antelopes, we would be disproportionately interested in the health of grasses in fields, and so on, and so forth. (And if we were insects, well, I don’t know if I can even imagine that, what kind of consciousness would we have?)
All well and fine, as long as we keep it in balance, that our main issues are not necessarily the only things of significance, nor of value (and that is a whole other discussion! we’re only recently deciding/discovering that whether animals think (like us) may be only one issue in the question of how we should treat them).
The Cambrian explosion was a step forward in complexity, although not necessarily in robustness, biomass, etc. In fact, Stephan Jay Gould said, “There are as many ways to adapt to local environments by becoming less complex is by getting more complex . . .” [3] .
Now, whether intelligence/language is a similar major step forward in complexity, that is a fascinating question of both philosophy and science, and I’m not sure the answers we might possibly get can be more than simply tentative (although we can get into emergent properties and lots of other cool stuff).
And regarding the Ediacarans, is there a good estimate of how many species, and how many separate families? 206.106.1.64 22:37, 30 April 2007 (UTC)
At the beginning of the Ediacaran, the sideshoots are going to be awfully close to the trunk as you say, and it’s going to be awfully hard to tell between them and the trunk itself. Some of the sideshoots will develop into big bushy branches, but still, isn’t the default for any particular early species is that it’s more likely to be a sideshoot than an ancestor of a later species, isn’t evolution is that bushy?
As I understand it, species are coming and going all the time, and the average lifespan for a new species, within an order of magnitude, is approximately 10 million years?
Thank you for the part about oxygen levels. That’s exactly the kind of thing I need to start learning (oxygen first building up to a higher level, then stablizing at a more medium level, along with, I’m sure, a lot of bumps along the way). I know the feedback mechanisms of ecology can be very complex, and with a lot of different feedback mechanisms going on at the same time. So, I embrace the complexity (I mean, what else can I do!).
Now, I understand that sometimes (certainly not always) life is most bushy during the middle stages of colonizing a new ecological niche, and becomes less so as one or several species becomes dominant. An example of this might be the evolution of horses. And another example might be the evolution of us humans. At the time of Australopithecus and as one species was evolving toward (through intermediary first?) Homo habilis, there may have been half a dozen species living at the same time (Australopithecus africanus . . . afarensis . . . boisei . . . robustus . . . and probably several other cool ones as well). And considerably later on, we and the neaderthals were two branches. We did not have the relationship of ancestor-descendant, but rather of cousins. We both evolved from Homo erectus. (Arguably, one of the saddest things parts of evolution is that our cousins the neanderthals are no longer here.)
And to keep all this in time perspective, this is the last (approximately) 3 million years of human evolution compared to the 542 million years since the Cambrian Explosion. FriendlyRiverOtter 02:45, 8 May 2007 (UTC)
The best visible example might be beetles. Beetles have radiated in many and sundry directions, many, many thousands of species, running into the hundreds of thousands. And yet, it’s not really a question of “progressing.” The different species of beetles are merely different.
And on the microscopic scale, bacteria do the same thing to an even greater extent.
And as far as familiar animals, okay, how about Darwin’s finches? Most probably, the branch started with a single species from the South American mainland, and from there bushed out with different species on different islands and in different niches [4] .
Or, how about the carnivorous mammal that was the ancestor of whales? And from this one species, life bushed out to a number of species, with two main branches, the toothed whales and the baleen whales.
Of course, with the exception of bacteria, the Cambrian period was before all of this. The animals of the Cambrian are less familiar, so we’re going to need to take more time in description and be more generous with photographs. FriendlyRiverOtter 00:29, 21 May 2007 (UTC)
From the timeline at the beginning of our article, the Burgess Shale fossilizations happened approximately 505 million years ago, which is thirty-seven million years after the start of the Cambrian. That’s something that needs to be pointed out, because sometimes the Burgess Shale is so emphasized that it feels like it happened at the beginning. And it didn’t.
And, regarding our topic of life being bushy, I have long heard that a number of creatures found in the Burgess Shale were unique, never to be seen again, including having bodily architecture different from all other animals that have ever walked, creeped, crawled, or swum about the Earth. Now, frankly, looking at the photos of the fossils, that’s not immediately obvious to me. But I am willing to listen to arguments and perhaps become convinced. For example, there’s a little creature that looks like a worm with spines. Okay, it’s interesting. If I saw a creature like that swimming in a pond today it would certainly get my attention, but I’m not entirely convinced that it has a unique bodily architecture.
What I do understand is that one species of worm—with the three bodily layers of ectoderm, mesoderm, and endoderm—became the blueprint for many, many later animals (including all the familiar ones!). FriendlyRiverOtter 05:28, 29 May 2007 (UTC)
This article appears to lack a clear statement of how long the Cambrian explosion took to occur. Was it 100,000 years, 1 million years, or 10 million years? TimVickers 02:31, 14 May 2007 (UTC)
If we don't know we should say we don't know and give the outer limits of the estimates. An uneducated reader might think it happened in a year or less, since "explosion" is usually kept for very rapid events indeed! TimVickers 20:21, 14 May 2007 (UTC) How about (using numbers from top of my head): Estimates of the length of time over which these changes occurred vary and the Cambrian explosion may have only taken 10,000 years or been as slow as 10 million years.
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Verisimilus
T 15:12, 17 May 2007 (UTC)Sounds great, "estimated to have taken about ten million years" would be suitably cautious. I'd suggest putting this in the lead somewhere, to give the casual reader a clear idea of what "rapid" means in geological terms! TimVickers 12:49, 19 May 2007 (UTC)
I can accept that. That’s reasonable. The fossil record is incomplete, and the rock record perhaps even more so, especially rock layers from 542 million years ago (I mean, a lot of plate tectonics come and gone!). What I would ask, could we take three examples and explain them in some detail. For example, I’m going to assume the Burgess Shale is fine-grained. And I seem to recall reading that it happened in a slump, so that a bunch of little animals were trapped all at once. I would like to have that confirmed.
Again, our article has a lot of ‘bluebirding!’ We don’t really explain things, don't really teach things, don't really describe things. We mainly just mention things. FriendlyRiverOtter 05:28, 29 May 2007 (UTC)
Does learning on a Dvorak keyboard slow you down and get in your way when you are later trying to learn on a regular Qwerty keyboard, or vice versa? No, studies have been done and it’s just the opposite. Learning on either keyboard helps you if you later move to the other. There is a positive transfer of learning.
I figure it’s probably the same with writing. So, if one has spent time on the formal style most common on wikipedia, there will be positive transfer as one makes the transition to a more communicative style. And I urge you all in fact to make the transition to a more communicative style!
Take a look at Richard Dawkins. Or look at COSMOS (the book) by Carl Sagan, and compare it to any introductory astronomy textbook for that time period, or even for the following ten years. I would suggest that it’s so much better in large part because Carl took the risk of being criticized. He wrote in his own voice. So if you do a good job of communicating with the interested lay person (and I hope that’s one of your prime audiences), you will probably be criticized as sounding too much like an essay or sounding too much like a magazine article. Please take those as compliments!
Learn from good writers like Dawkins, but mainly find and develop your own voice. For example, Richard uses the method of rephrasing something in different words. This can be useful in that it kind of puts up an intellectual signpost and makes the terrain more understandable, but then he kind of overdoes it. So, if you keep working on your writing and allowing your own unique voice to continue to develop, you might even become a better writer than Richard Dawkins. How about that! Please do not let any artificial constraints hold you back. FriendlyRiverOtter 00:29, 21 May 2007 (UTC)
I can't get the Ediacaran, as presented here, to match the Ediacaran biota tineline. which is right? Adam Cuerden talk 19:07, 28 June 2007 (UTC)
Some private correspondence gave me the initial impression that this article needed major improvements in content, but after reading it twice I think the content is good (of course there's room for improvement in anything, and it will have to be updated to take account of new discoveries and analyses).
By far the largest difficulty is the article's academic vocabulary and style, which will put off non-specialist readers, who should be Wikipedia's target audience. So it needs lot of re-phrasing.
I also think minor re-structuring would help, for example:
I have a suspicion that a cladogram would be helpful, but wonder:
Other points to be resolved:
Related WP articles:
I think that since I originally re-wrote this article, it has (inevitably) become more fractured in its viewpoints - ie it has steadily got less coherent. This is not a trouble as long as the article still holds together - otherwise it will never make FA status - something that seems very distant right now.
When I re-wrote the article, I certainly and deliberately downplayed the "sensational" aspects of the CE, as typified by Gould's book, and still (apaprently) the majority view of popular understandings of the subject. But this viewpoint only ever had limited purchase in academic study of the CE, and it is certainly completely obselete now. Specifically: i) Things do not suddenly appear "explosively" except under the influence of taphonomic windows (ie the reason everything appears around Chengjiang time is preservational); but trace fossils and other information inform us pretty clearly that crown group bilaterians did not evolve until late Ediacaran time; ii) similarly, trace fossils do not "explosively appear" at the base of the Cambrian, but rather, diversify rapidly from latest Ediacaran time onwards ; iii) the whole debate between molecular clocks and the fossil record has almost collapsed as MC's have been adjusted to give dates close to that of the fossil record.
As fas as "bluebirding" goes: I am not sure exactly what this means, but I think that one of the things that needs to be corrected about the Cambrian Explosion is that we know everything about it. In fact, almost every aspect of it is the subject of ongoing research; and it is right to reflect these uncertainties rather than present a misleadingly simplistic "solution" to whatever the problem is meant to be. We do not know what the Ediacarians are: indeed, I would say that we have little clue at all. We do not know if oxygen was important. We do not know the phylogeny of most of the major groups involved, so this makes interpreting their fossil record problematic. And so on.
A minor point: the dating of the lagerstätten in the text is inconsistent with the dating in the diagram. The dating of the Sirius Passet is uncertain given that it is based on a Holmiid-like trilobite which is pretty dissimilar to the other holmiids: but if this is broadly right, then SP is probably end Atdabanian; and almost certainly considerably older than the age given in the diagram. It could actually be considerably older than this, ie basal Atdabanian. Chengjiang is, as far as I understand based on the brachiopods, probably early Botoman.
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"...
Grahbudd 18:19, 19 July 2007 (UTC)
This has been my "next project" on Wikipedia for a long time, and it's about time I got stuck in! I'd be very grateful if you'd keep a critical eye on my efforts and expose any errors that creep in!
Graham - "Bluebirding" (as far as I can gather) is the practice of using a link to another wikipedia page in place of a full definition. Ideally the naïve reader should be able to follow the whole article without clicking elsewhere - which is probably an ambitious target in an article such as this!
I'll try and reflect the "Cambrian effervescence" viewpoint more strongly - I've been wary of avoiding "Point of View" discussions, for as you say there still seems to be a large portion of scientists that haven't come round to your point of view yet. I suspect that any eventual Featured Article reviewers would pick up on this strongly, since Gould's views probably represent most people's familiarity with the subject.
Philca - I hope you don't mind if I add to your proposed article structure above!
Verisimilus T 21:04, 20 July 2007 (UTC)
I'm not sure that the Cambrian Explosion was purely an animal phenomenon, and had carefully worded the introduction to avoid giving that impression. The planktonic realm also underwent a rapid diversification - see reference in lede. Certainly Butterfield's theory of trophic cascades as an amplifying factor requires there to have been one. [1] It may be worth adding a small section discussing this - but I'm not sure that it needs dwelling on. Verisimilus T 12:39, 19 August 2007 (UTC)
Just scanning through your additions, your "Why is it such a big issue" section, whilst a great addition to the article, may not stand up to close scientific scrutiny.
For starters, the analogy with the mammals - whilst interesting, and possibly helpful - is not without caveats. For example, it's recently become apparent that the mammals diverged long before the end of the Cretaceous, and the extent of the diversification may not be as large as it has been thought. (A little like the Cambrian, I suppose...)
Also, I'm a little wary of the picture you paint of the phyla - it perhaps paints a misleading picture. Yes, interest in the subject arose because of the "appearance of phyla", but the concept of stem groups (see Budd 2000, in the article references, for a good explanation) is more useful in geological terms than the Linnean hierarchy. Perhaps a tighter or more thorough discussion has a place in the article, as this is an interesting area that can spark some confusion about the explosion? Certainly Gould put across the "phyla appearing at once" argument, and it may be worth dismantling that.
Estimates of the Cambrian explosion's duration range from about 10M years (from 530 to 520M years ago) to about 80M years (starting about 580M years ago, in the Ediacaran age).
I've already struggled with putting a length on the explosion, and decided against it, as per Grahbudd's comment above. I'm not sure that it's helpful to pigeonhole time into "before and after the explosion". It was a smooth curve, and different definitions will cover different amounts of it...
All but an insignificant amount of fossils are marine, as terrestrial settings only fossilise in exceptional circumstances. It's not cover by more recent rocks that is an issue, but the total sedimentary rock volume preserved; this follows an exponential curve into the past, as rocks are eroded or metamorphosed over time.
The paucity of body fossils is probably a combination of taphonomic factors and a lack of hard parts.
Worth clarifying too that it's only the MIDDLE Cambrian that contains lagerstatte - after the explosion had died down.
And of course lagerstatte don't display first or last occurrence dates - but the scarcity of fossilisation means that the usual record doesn't usually contain such dates either.
A trace fossil is any trace of an organism other than its body itself - and not restricted to burrows, as your introduction seems to suggest.
Do you have a citation for the necessity of Earthworm complexity? I suspect you're probably right but would like to be sure.
What does one mean by "comparable complexity to an Earthworm"? it's perhaps worth clarifying this.
You're trying to summarise a huge amount of information in a short section.
The pitfalls of the molecular method can probably be covered with a link, and a statement that "Molecular estimates have dated the explosion at dates ranging from 1Ga to 500Ma ago, and should thus be treated with caution".
Given that one of their assumptions is often that of a constant rate of evolution, their application may be more in spotting something abnormal happening in the Cambrian, such as Butterfield's 10-fold increase due to trophic cascades, than to providing a date for the explosion, which we know anyway to have happened long before the divergence of lineages.
I hope not to cast a negative view - there are many improvements in terms of style and some content - but there are also many small but significant errors. I'm wary of straying too far from Budd's version of the article without good reason, as it's very easy for a non-expert author to add small comments which turn out to portray an incorrect or misleading impression on the reader. Verisimilus T 10:59, 20 August 2007 (UTC)
I do not wish to sound argumentative, but. The original article was one reviewed by Nature; and was found to contain a substantial number of errors. As this was the case, and as the structure was a complete hotch-potch, I totally rewrote it. I agree that the version I produced was somewhat stodgy and academic; but it was, I modestly suggest, both comprehensive and accurate. I have watched this article evolve away from what I wrote with a mixture of some dismay and amusement. Now it contains about as many mistakes as it did before. For example:
i) "The Cambrian explosion describes a profound and very rapid diversification of life[1] on Earth that occurred more than half a billion years ago."
First, how can "the Cambrian explosion" "describe" anything? And now the opening paragraph makes no reference to what the Cambrian explosion is about, ie the rapid expansion of the _fossil record_; but rather talks about several layers of inference from it, including the idea that "evolution would accelerate by an order of magnitude" - Butterfield sourced and respectable, but what does it *mean*?
ii) History of the concept: Darwin's difficulty was increased by the fact that in his time no sedimentary rocks much older than 500M years had been reliably identified, and Darwin regarded the Silurian as the earliest known geological period.[5]
But this is a misleading statement. Darwin was well aware of Sedgwick's work on the Cambrian (indeed, he accompanied him on his fieldwork to North Wales). It is true that in the 1850's the high-water mark of Murchison's Silurian concept was reached; but this paragraph makes it sound as if rocks as old as the Cambrian were not known to Darwin: they were.
iii) "Why is it such a big issue?" My original effort was stuffy, but this is too far too far in the opposite direction. And what follows is both misleading and a more or less complete non sequitor. " So at first sight a wide range of complex animals evolved from "blobs" in under 30M years". Why reference Cohen's out of date text book here, when there are zillions of more up to date works? And who says they were blobs anyway? And the misleading discussion of phyla is out of place.
iv) Duration of the explosion. I've already commented on how misleading this is. Any case, the whole idea of "Even if the process took 80M years, it would still be exceptionally fast - for comparison, the much less radical evolution of mammals from therapsids took about 70M years. " begs several questions. Says who? If one had a time machine and could watch what was going on, I expect it would not seem bizarre at all.
v). "Body fossils Body fossils preserve all or significant parts of organisms and are therefore the most informative type of evidence. Unfortunately they are increasingly rare as one looks further back in time: The rocks in which they are buried are usually covered by more recent rocks. All life in the early Cambrian was marine, and subduction destroys marine sediments within 200M years of their formation, unless they are raised above sea-level by other tectonic processes such as orogeny (mountain-building)."
It is misleading to state that fossils get rarer as rocks get older. Number of fossils is controlled by outcrop area of fossiliferous rocks; and this is controlled in turn by tectonic cycles: rocks get buried and then exhumed over a few hundred million years. Even if one accepts that _on average_ older rocks are less likely to be preserved, this does not mean necessarily that the quality of the fossil record gets worse (see eg Benton et al. Nature 403, 534-537 (3 February 2000)).
vi) Oceanic floor is destroyed by subduction; but the continental shelves where diversity is highest are continental, and thus do not get subducted in general.
lagerstätten: one needs to qualify this term to show that you mean conservation rather than concentration deposits.
vii) "Trace fossils. Trace fossils consist mainly of tracks and burrows on and a few centimeters under what was then the seabed. Animals under a centimeter long are unlikely to leave tracks or burrows on the surface; and burrows under the surface suggest the presence of animals which were almost as complex as earthworms..."
Trace fossils can in general go down a metre or more (Cambrian ones are much less tiered). Plenty of organisms smaller than a few cm can leave trace fossils; and you do not need to be particularly complex to burrow under the surface per se (e.g. the cnidarian "sea pansies" do it).
viii)"Molecular phylogenetics can provide interesting suggestions about the phylogeny ("family trees") of organisms provided one can avoid the difficulties created by saturation. But many paleontologists believe that fossils are still the best form of evidence and should take precedence if there is any conflict between the results of fossil-based and molecular analyses."
Name names! I think this sets up a false dichotomy.
ix) Triploblastic. Trichoplax is an example of a taxon that is not sponge or cnidarian but is not triploblastic; and ctenophores are not usually counted as triploblastic either.
x) Diploblastic. It is increasingly being recognised that anthozoan cnidarians are essentially bilaterian in many ways; but are not triploblasts.
xi) Coelomates. Not all Cambrian fossils are coelomates. E.g. the cycloneuralians.
xii) Trace fossils 1000M years ago?
Even the principal author of this report (Dolf Seilacher) has abandoned the idea that they are biogenic.
xiii) Ediacaran organisms.
This section is highly biased. E.g. Spriggina is "probably a trilobite" - I would just flatly disagree with this and many other people would too. Citing MacMenamin on this topic does not, alas, fill me with confidence.
xiv) "If traces such as Cruziana and Rusophycus were produced by arthropods, that would indicate that arthropods or their immediate predecessors had developed exoskeletons, although not necessarily as hard as they became in the Cambrian.[22]"
Both these _are_ Cambrian fossils, as this section states itself.
xv) "The earliest Cambrian trilobite fossils are about 530M years old, but even then they were quite diverse and world-wide, which suggests that these arthropods had been around for quite some time.[32]"
Most people would date the oldest trilobites to be beginning of the Atdabanian, ie around 520 million years ago or so. Look at http://www.palaeos.com/Timescale/timescale.html - the timescale given here is, I note, not in accord with this. Incidentally, the Burgess Shale is middle Cambrian, but sites in the Lower Cambrian in the time scale!
xvi) Sirius Passet fauna.
Again, I dispute the age, it is probably 10 million years younger than this.
xvii) "The strangest-looking animals from Sirius Passet are Pambdelurion and Kerygmachela. They are generally regarded as anomalocarids because they have long, soft, bodies with a series of broad fin-like flaps along each side. The fossils found so far show no trace of gills or other breathing apparatus and no trace of segmentation. Both were apparently blind, as the fossils show no trace of eyes. Pambdelurion had a large mouth on the front of its head, flanked by a pair of thick, segmented appendages slightly longer than the swimming flaps and equipped with a flexible spine on each segment. It may have fed on plankton. Kerygmachela had a pair of long, slender trailing appendages at the rear end, and a small conical mouth flanked by robust, unsegmented appendages which had short spines on the front edge and were tipped with longer spines. The spiny front limbs suggest that it may have been a predator, but its small mouth suggests it would have been restricted to very small prey."
Kerygmachela was described with gills: indeed the title of the first paper to describe it was "a Cambrian gilled lobopod from Greenland". I should know, as I wrote it. In the fuller description it is described as possibly possessing eyes too. It is highly misleading to say that neither show any traces of segmentation; au contraire, they are both clearly segmented. ii) Pambdelurion's mouth is not terminal, but ventral. And the idea that is was a planktivore is fanciful (whether or not it is actually true). (eh, I described this fossil too).
xviii) Chengjiang.
e.g. "Chenjian contains other animals which have puzzled paleontologists but are now regarded as lobopods and fairly closely related to arthropods. Anomalocaris was a mainly soft-bodied swimming predator which was gigantic for its time (up to 70cm = 2.1 feet long; some later species were 3 times as long); the body had a series of broad fin-like flaps along each side, and at the rear a pair of "fans" arranged in a "V" shape. The fossils found so far show no trace of gills or other breathing apparatus and no trace of segmentation. ".
Again, gills were described by Whittington and Briggs )185) and the animals are clearly segmented. Not even I have claimed that Anomalocaris in the strict sense is a lobopod: it is clearly not, in fact!
xix) Misszhouia is not a "soft-bodied trilobite".
xx) "analyses of both of these animals were hilariously wrong, but they are now regarded as lobopods, and Anomalocaris is very similar to Opabinia in most respects (except the eyes and feeding mechanisms) - see above."
Unfair: both accounts were excellent given the material at hand. And Anomalocaris is not a lobopod. And it is not really fair to call Odontogriphus a mystery any more.
Again, I do not want to be argumentative: but I think that the current version of the article now contains even more mistakes than before the rewrite. Further, it puts far too much emphasis on the various exceptionally preserved faunas, which after all all date from after the period of the most important evolution events. Thus, the overview of the whole thing is now missing, but rather the article is evolving into a list of dubious facts about the exceptionally preserved fauna. Finally, it is too much in thrall to the Gould view which is not really held to be true by most palaeontologists.
cheers
Graham Grahbudd 14:12, 26 August 2007 (UTC)
"Today, creationists with a poor grasp of science maintain public interest in subject, highlighting the Victorians' concerns about its incompatibility with evolution."
I have to agree with removing "with a poor grasp of science." It seems unverifiable and pov. I would have taken this out myself, but it seems that has already been done and undone. Momo Hemo 09:48, 22 September 2007 (UTC)
Just to point out that Knoll's paper post-dates Conway Morris's. No-one really believes that Thaumaptilion is an Ediacaran any more (it's probably not an Octocoral either) and a mass extinction is almost universally accepted at the base of the Cambrian. Verisimilus T 14:43, 22 December 2007 (UTC)
The Cambrian explosion is obviously a very important subject, but the page as it stands is forbiddingly long. Would it be possible to summarize and redirect to subpages to make this page more inviting to the paleontology non-specialist? — vivacissamamente ( talk) 16:30, 30 December 2007 (UTC)
Hi,
My initial thoughts after a first read through is that the length, unfortunately, needs reducing a lot. While there may be a case for explaining every scientific concept within the article, there are many sidetracks that are given undue weight - for example, far too much time is spent describing individual organisms, which are interesting - but stray from the central point of the article. In a shorter article, the descriptions would make interesting asides, but I think that it is important to keep as close to the subject as possible. The first paragraph of "How fast did the main metazoan groups evolve?" is the meat of the story, and the previous dozen sections could almost be omitted in favour of a modest expansion of this.
Also, there's a lot of repetition - much of the previous version appears to have barely been touched, where incorporation may have been more useful.
I think there's a difficult balance to strike between engaging the non specialist by explaining unfamiliar concepts, and keeping the article short enough to be readable within the short attention span of the average reader. As it stands, it perhaps lies a little on the former side, and a more concise style of writing may help balance the scales.
The other thing that perhaps gets lost in the size of the article is a central line of argument - the article doesn't seem to "flow" comfortably, and the reader isn't really led from one section to the next.
I hope these comments are helpful, sorry if they're a little vague at this stage! After a significant trimming, this article should well be on the right tracks...
All the best, Verisimilus T 18:55, 30 December 2007 (UTC)
A few more points:
Verisimilus T 18:01, 6 January 2008 (UTC)
The info bar appears corrupted, there seems to be code overtop of it. 207.6.125.46 ( talk) 22:59, 27 January 2008 (UTC)
I've just removed a new section suggesting that "Although no direct evidence exists, a new kind of viral or microbial infection process is one possible route that genetic material may have taken in exchanges between early species." As far as I am aware this idea doesn't have any evidence in its favour, nor support from the scientific community; I feel this article should restrict itself to scientifically supported ideas, as there are thousands of intriguing but un-testable ideas out there, and we can't reasonably expect to cover them all. Comments in its defence are welcome!
Verisimilus T 09:20, 10 February 2008 (UTC)
After reading through the article, at present I'm willing to remove:
After that I find it difficult to identify content that can be removed, since: the pre-Cambrian content shows that complex metazoans did not originate in the early Cambrian and their emergence was probably not sudden; the descriptions of early Cambrian animals illustrate the exceptionally high level of disparity.
Of course I'm not best placed to be objective about this because I wrote most of it. Constructive comments and suggestions would be very welcome! Philcha ( talk) 12:40, 21 February 2008 (UTC)
I notice no-one has so far suggested ways of making this long article significantly shorter without sacrificing important content. I've had a crazy idea that might help general readers while keepng the details that armchair paleontologists like me will want to see: place the analysis (starting with "How real was the explosion?" before the potted history of life from 1BYA to 500MYA; if necessary clarify the issue first by defining the 3 main views that have been historically important (that there were no pre-Cambrian metazoans; that coelomates and possibly triploblasts evolved and diversified extremely fast in the early Cambrian, as Gould and Whittington argued; and that triploblasts and probalby coelomates were present a lot earlier, although there was a surge of diparity in the early Cambrian). So the order of the main sections would be: Intro; history of the debate; definitions of terms used commonly in the analysis (e.g. triploblast); the analysis ("How real was the explosion?", etc.); definitions of terms used in surveying the evidence; types of evidence; potted history of life from 1BYA to 500MYA? Would that work as a method of presentation? And would it be intellectually satisfactory? Philcha ( talk) 19:54, 14 March 2008 (UTC)
Philcha ( talk) 19:33, 28 March 2008 (UTC)
I've reinstated this section. The idea is quite new (Jan 2008), and may get its own Wikipedia article in time. Meanwhile mentioning it briefly in this article will: (a) remind editors to check up on whether it gets enough scientific support and additional info to merit its own Wikipedia article; make the CE seem less surprising because there's evidence of another explosion. If the idea of an Avalon explosion survives scientific investigation, eventually someone will use the 2 explosions as the basis of some principle in evolutionary theory, then we can produce an article about that too (unless they are simply taken as examples of Valentine's "empty niches" theory and its consequence that explosions at each grade happen only once). Philcha ( talk) 18:45, 28 March 2008 (UTC)
I'm sure sure if this has been discussed previously, but the Definitions section seems a little misguided. The beauty of a hyperlinked encyclopedia is that a reader can instantly go to the article of an unfamiliar word. If the reader is unfamiliar with a word, such as phylum, they can go to the relevant article, fill in any gaps in their knowledge and then return. Ashmoo ( talk) 13:26, 7 April 2008 (UTC)
Someone has recently added a section "Quantum Evolution":
I can see a few things wrong with this:
I will remove the section in about a week if those objections are not met. Philcha ( talk) 18:07, 9 May 2008 (UTC)
I've removed these sections plus the stump of some old content about molecular phylogeny; this material had caused confusion because it was commented out. To make matters worse, the stupid doibot inserts HTML comments but is not smart enough to leave commented-out content alone, so it creates nested HTML comments and therefore a real dog's doo-doo. The last version containing the whole of the commented out material is [26] in case anyone wants to mine the old stuff for additional info. Philcha ( talk) 12:08, 11 May 2008 (UTC)
A 2nd para has recently been added to "Increase in abundance and spininess of acritarchs":
The way I read the cited paper (Stanley (2008). "Predation defeats competition on the seafloor" (extract). Paleobiology. 34: 1. doi: 10.1666/07026.1.), it attributes the drop in species durations for Proterozoic Phytoplankton to "protistan herbivory", and the next sentence, "Not surprisingly, the average duration of acritarch species declined further when metazoans diversified, being less than 10 Myr for species that arose in the Early Cambrian," does not commit itself about when metazoan herbivory / predation became significant. Philcha ( talk) 19:20, 13 May 2008 (UTC)
I thought I'd better read the reference supporting paragraph one, and thought I'd "return fire"... I think this article is being over-interpreted too, without mention of its caveats.
“ | Their increasingly spiny forms in the last 1 billion years probably result from the need for defense against predators, especially predators large enough to swallow them or tear them apart. | ” |
— Current article - italics don't appear to have support from article |
“ | Processes may be of different kinds and of different functional significance (for example, they may also be selected for as a means to increase water friction or adhesiveness).
The presence of process-bearing acritarchs is therefore not a definite indication of the presence of predators/grazers. |
” |
— Bengtson (emphasis mine) |
This article probably isn't the place for a full-blown discussion, but I think that the presentation of facts as it stands is a little skewed. I would be tempted to move it to a new section at Acritarch, and to take this opportunity to slim the C-ex article slightly.
How about combining the stromatolite and acritarch sections into a new, brief "Proterozoic microorganisms" subsection, and using a sentence along the lines of:
“ | Marine organisms ( acritarchs and stromatolites) show signs of increased predation pressure around 1,000 million years ago, which may reflect predation by protistan microorganisms. They suffer a sharp decline in abundance at the start of the Cambrian period, which has been linked to the raditaion of metazoan grazers. | ” |
— Just a rough idea |
This tells the casual reader everything they need to know in a concise form (concision being my main concern for this article at the moment, as you know!); the current, more detailed discussion can then be moved to Acritarch and Stromatolite for the interested - a "further information" link could be provided to emphasise this point. Moving the discussion to the acritarch page will allow us to expand the discussion of the papers a little more in the article, to give the readers a fairer reflection of what is and isn't being asserted, without scaring off the casual reader of this article. Smith609 Talk 10:16, 14 May 2008 (UTC)
My thoughts on how this affects Cambrian explosion:
For the reasons described in a previous post (Thread "Increase in abundance and spininess of acritarchs", post by Philcha at 14:05, 14 May 2008 (UTC)) I'm very reluctant to drop significant chunks of the potted history of life in the last billion years. But in re-reading the article I think there parts than can be dropped or shortened without serious harm:
Comments welcome! Philcha ( talk) 18:08, 14 May 2008 (UTC)
“ | the Early Cambrian adaptive radiation of several eukaryotic clades, including the Metazoa, documented by the truly rapid expansion in the fossil record of characteristics such as large size, morphological complexity, skeletalization, and infaunal activity. | ” |
— Source |
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As per to do list - I have some stuff I can put here when I have a moment!
Grahbudd 07:00, 25 January 2007 (UTC)
I've replaced Graham's timeline with a wikified one that's easier to read on the page (and a bit more colourful). I've also amended a couple of the dates where new data has allowed their refinement. Verisimilus 18:03, 10 March 2007 (UTC)
Nice, Verisimilus. But there some minor mistakes. Since you have the source file, please correct the timeline figure: there should be Chengjiang, not "Chengjang" (add missing "i"), and correct the "Cambrian Era" to "Cambrian Period" or "Pal(a)eozoic Era".
Body ridges are a common feature in organism fossils of the period, suggesting possible external food intake.
This doesn't sit too comfortably with me... there are many other possible reasons for ridges (e.g. gas exchange, structural support, artefacts of segmentation, hydrodynamics?) that don't fit this hypothesis; indeed other animals (trilobites, earthworms) are 'ridged' whilst not having this mode of life. I'm not convinced this is factual enough to be considered Encyclopædic content... whilst there is one prevailing view that they did have this mode of life I don't think a ridged appearance is necessarily evidence for it. Verisimilus 21:09, 15 March 2007 (UTC)
Alternatively, some new form of microbial or viral infection agent may have developed which could transfer genes between species, speeding up evolution by "sharing" useful features. This is somewhat comparable to the Recombinant DNA process in sexual reproduction, but on a cross-species level.
After a quick search I can't find anything in the literature (or even in the link supplied) that suggests this hypothesis is anything more than an interesting but entirely unsupported and loosely defined conjecture... Hence I don't feel it should be included here as 'encyclopaedic content' unless a reliable source is found.
Verisimilus 13:21, 5 April 2007 (UTC)
The structure of the article could be improved considerably. The "Dating the Cambrian" section serves little purpose; that topic is covered throughout the article, and what is not could be merged into the "Significance of the explosion" section. I also suggest putting the history section immediately after the intro, before the Significance section. Also, "Timing of the Cambrian Explosion" seems to be more or less dealing with the same issues as "Causes of the Cambrian Explosion". I would suggest removing the causes section from "Significance of the data" and putting it in it's own top-level section, and using a trimmed-down version of the timing section as an intro to the causes section.-- ragesoss 23:55, 19 April 2007 (UTC)
I mean, write for the intelligent lay person. Please write where someone can actually learn something.
Wikipedia is still in the process of becoming. It might make it, it might not, it needs some help! For example, bluebirding--writing just to string together blue words that refer me elsewhere, rather than talking to me when I’m right here. I’m here and now, and I’m interested, please teach me. Use Carl Sagan or any other good writer as a model (maybe James Trefil, the guy who wrote “A Scientist in the City”), rather than using some artificial, formalistic style.
Maybe at the beginning of the article, talk just like you would if an intelligent, interested 10th grader were right in front of you.
Later on, as if I was an intelligent college student.
Later on, as if I was an intelligent younger colleague.
And later on, toward the end of the article, talk to me about the cutting edge of research going on right now as if I am your fellow colleague.
This will give the article a sense of development, and please do not do this mechanically. Surprisingly, if you allow the writing to stay a little unfinished, it’s often better. The article does not need to be perfectly consistent in any regard. It just needs to be good. Good is better than perfect (in this context, and in many other contexts as well!). Write just a little bit more formally than how you would simply talk to me. That’s what would help me to learn the subject matter and really get a lot out of it.
Okay, the part on the Ediacaran fossils: “In addition, in the Ediacaran Period immediately preceding the Cambrian, apart from the trace fossils and tubes previously mentioned, the record contains the highly enigmatic “Ediacaran” biota, which despite decades of study and a flurry of recent intense interest, remains very hard to place in the context of animal evolution.”
(That’s vague, that’s hedging your bets. That is “safe” writing. At issue is whether the Ediacaran creatures died off or not. Go ahead and say it.)
“Some taxa such as
Kimberella are thought by some to represent bilaterians . . .”
(And I’m not sure whether these are part of Ediacarans or not.)
(next paragraph) “Perhaps the most promising area for study is the Doushantuo Formation of China, spectacular fossils from which are probably around 580 million years old or younger.”
(So I realize now it’s probably other early fossils (or fossil traces), but . . . more bluebirding! So, the purpose of a wikipedia article is just to bluebird, it’s not actually to teach anything.)
I think about two whole paragraphs on the Ediacaran fossils would be a lot better. It’s important enough. It’s a relatively known precursor. And for me personally, writing that builds on something I already know often makes for very satisfying reading. And afterall, the Cambrian Explosion is perhaps the greatest mystery in the history of life on Earth, and it’s a major issue in SETI and astrobiology and how likely life elsewhere in the universe might be. It’s worth spending some time on the precursors. And long is good. If it’s going to be a real teachful article, it’s probably going to have to be long. So a couple of paragraphs on Ediacarans, with the single bluebird if I want to learn even more. Now, discrete footnotes are fine, and are in fact good as long as they don’t interfere with the flow of the writing. For example, here are two websites on Ediacaran fossils (and good websites at that, at least to my untutored eye!) [1] [2] .
If someone says something like ‘appropriate for an encyclopedia,’ I’m going to say you’re letting a formalistic standard stand in the way of communication.
(I realize this may not be the most good-natured piece I’ve ever written. But it's frustrating when you look something up and you don’t learn anything.) FriendlyRiverOtter 20:45, 20 April 2007 (UTC)
It's quite a challenging set of demands, which I mainly agree with in principle. The balance I think that needs to be struck is one between an article that is concise enough to be readable without the attention wandering, and yet in depth enough to capture the imagination. One could argue that to discuss the Ediacaran biota at length would be to stray unnecessarily from the subject - and one could argue that the interested will follow the 'bluebird' whilst the uninterested will not be distracted from the main flow of article. Regarding the levels of 'in depthness' - I agree with this in principle, but it would be quite difficult to fit into the current article, which has several distinct sections. I feel that to a degree the article already does mention points in brief before expanding on them; but there could well be scope for improvement. I'd wholeheartedly encourage you to have a dabble with the article, if you feel able! | Verisimilus T 09:54, 21 April 2007 (UTC)
First off, VerisimilusT, thank you for your very gracious response. You took it better than I hoped (and I was frustrated when I wrote it), this was a post I was a little bit worried about, so thank you for your thoughtful response. However, I cannot take you up on your generous offer. I do not feel at this time I have the kind of readable writing style that will be acceptable to the majority of wiki users (people will be editing out what I think are my best parts and it will just drive me crazy), and besides that, I don’t feel I know enough about evolution! What I do hope is that I will be appreciated as someone on the other side, because it sure seems like everyone and their brother wants more formality in the writing. More formality? I ask, why can’t we explain it in plain English and introduce the occasional technical term that sincerely advances understanding? I think we can.
Okay, as an example, take Thomas Kuhn’s THE STRUCTURE OF SCIENTIFIC REVOLUTIONS. We could give a good meaty description in four sentences. And not a baby description, but a good description for a college audience. Four sentences. And I think that good description would have zero or maybe one technical terms. The technical terms are not what’s paramount. It’s explaining it to someone just as smart as you are (you’ve got to give your reader that respect), but just someone who doesn’t happen to know this particular area.
Okay, the Ediacaran animals, and the picture looks kind of like a sand dollar, but with lines radiating out from near center. Alright. Well, to an order of approproximation, all species are extinct. Appropriately 99% of all species that have ever lived are extinct. And evolution is bushy. Looking backwards, you can see a main line. But at any particular time, it’s bushy and going in all kinds of different directions and you have no way of knowing what’s going to end up being the future main line. So, it would be no great surprise if the Ediacarans had gone extinct. FriendlyRiverOtter 09:39, 27 April 2007 (UTC)
I'd have to disagree heartily on your 'main line' point. Evolution is indeed 'bushy', and just like a bush, there is no 'main line' - just twigs and twigs. It's popular - and easy - for humans to think that all evolution was directed towards them, but that's not how it works - things 'devolve' as fast as they 'evolve', and 'progress' can only be defined and measured by us, it's not an inherent property of the system. Evolution is change, and it takes us to decide when to call it 'progress'...
Re. the 'not unlikely' extinction of the Ediacarans: Species could be thought of as being a little like needles on a pine tree. It's not a perfect analogy, but an extinction of an entire clade would be like removing every single pine needle from an entire bough - if just one remains, the clade remains extant (i.e. non-extinct). Other, better documented mass extinctions have hit the pine tree like a strong wind - needles have fallen largely at random, and whilst sometimes one branch is decimated more than another, a major bough being completely stripped is incredibly rare. Twigs may be stripped (and go extinct), but larger boughs would always keep a few needles...
I suppose the counter-argument would go that the branches were twiggier back in those early days. Most people expect the 'Ediacarans' to be a major bough on the tree, but maybe at the time this was no bigger a branch than the trilobites', which went extinct at the end of the Permian... | Verisimilus T 12:26, 27 April 2007 (UTC)
And if bears had developed as the dominant intelligence, the “main line” would have gone to them. If it had been small dinosaurs, a la Harry Turtledove’s very imaginative colonization series, they would have been the “main line,” and mammals would have been just a little curious offshoot.
And if we were polar bears, seals would occupy a very central part of our mental lives. If we were antelopes, we would be disproportionately interested in the health of grasses in fields, and so on, and so forth. (And if we were insects, well, I don’t know if I can even imagine that, what kind of consciousness would we have?)
All well and fine, as long as we keep it in balance, that our main issues are not necessarily the only things of significance, nor of value (and that is a whole other discussion! we’re only recently deciding/discovering that whether animals think (like us) may be only one issue in the question of how we should treat them).
The Cambrian explosion was a step forward in complexity, although not necessarily in robustness, biomass, etc. In fact, Stephan Jay Gould said, “There are as many ways to adapt to local environments by becoming less complex is by getting more complex . . .” [3] .
Now, whether intelligence/language is a similar major step forward in complexity, that is a fascinating question of both philosophy and science, and I’m not sure the answers we might possibly get can be more than simply tentative (although we can get into emergent properties and lots of other cool stuff).
And regarding the Ediacarans, is there a good estimate of how many species, and how many separate families? 206.106.1.64 22:37, 30 April 2007 (UTC)
At the beginning of the Ediacaran, the sideshoots are going to be awfully close to the trunk as you say, and it’s going to be awfully hard to tell between them and the trunk itself. Some of the sideshoots will develop into big bushy branches, but still, isn’t the default for any particular early species is that it’s more likely to be a sideshoot than an ancestor of a later species, isn’t evolution is that bushy?
As I understand it, species are coming and going all the time, and the average lifespan for a new species, within an order of magnitude, is approximately 10 million years?
Thank you for the part about oxygen levels. That’s exactly the kind of thing I need to start learning (oxygen first building up to a higher level, then stablizing at a more medium level, along with, I’m sure, a lot of bumps along the way). I know the feedback mechanisms of ecology can be very complex, and with a lot of different feedback mechanisms going on at the same time. So, I embrace the complexity (I mean, what else can I do!).
Now, I understand that sometimes (certainly not always) life is most bushy during the middle stages of colonizing a new ecological niche, and becomes less so as one or several species becomes dominant. An example of this might be the evolution of horses. And another example might be the evolution of us humans. At the time of Australopithecus and as one species was evolving toward (through intermediary first?) Homo habilis, there may have been half a dozen species living at the same time (Australopithecus africanus . . . afarensis . . . boisei . . . robustus . . . and probably several other cool ones as well). And considerably later on, we and the neaderthals were two branches. We did not have the relationship of ancestor-descendant, but rather of cousins. We both evolved from Homo erectus. (Arguably, one of the saddest things parts of evolution is that our cousins the neanderthals are no longer here.)
And to keep all this in time perspective, this is the last (approximately) 3 million years of human evolution compared to the 542 million years since the Cambrian Explosion. FriendlyRiverOtter 02:45, 8 May 2007 (UTC)
The best visible example might be beetles. Beetles have radiated in many and sundry directions, many, many thousands of species, running into the hundreds of thousands. And yet, it’s not really a question of “progressing.” The different species of beetles are merely different.
And on the microscopic scale, bacteria do the same thing to an even greater extent.
And as far as familiar animals, okay, how about Darwin’s finches? Most probably, the branch started with a single species from the South American mainland, and from there bushed out with different species on different islands and in different niches [4] .
Or, how about the carnivorous mammal that was the ancestor of whales? And from this one species, life bushed out to a number of species, with two main branches, the toothed whales and the baleen whales.
Of course, with the exception of bacteria, the Cambrian period was before all of this. The animals of the Cambrian are less familiar, so we’re going to need to take more time in description and be more generous with photographs. FriendlyRiverOtter 00:29, 21 May 2007 (UTC)
From the timeline at the beginning of our article, the Burgess Shale fossilizations happened approximately 505 million years ago, which is thirty-seven million years after the start of the Cambrian. That’s something that needs to be pointed out, because sometimes the Burgess Shale is so emphasized that it feels like it happened at the beginning. And it didn’t.
And, regarding our topic of life being bushy, I have long heard that a number of creatures found in the Burgess Shale were unique, never to be seen again, including having bodily architecture different from all other animals that have ever walked, creeped, crawled, or swum about the Earth. Now, frankly, looking at the photos of the fossils, that’s not immediately obvious to me. But I am willing to listen to arguments and perhaps become convinced. For example, there’s a little creature that looks like a worm with spines. Okay, it’s interesting. If I saw a creature like that swimming in a pond today it would certainly get my attention, but I’m not entirely convinced that it has a unique bodily architecture.
What I do understand is that one species of worm—with the three bodily layers of ectoderm, mesoderm, and endoderm—became the blueprint for many, many later animals (including all the familiar ones!). FriendlyRiverOtter 05:28, 29 May 2007 (UTC)
This article appears to lack a clear statement of how long the Cambrian explosion took to occur. Was it 100,000 years, 1 million years, or 10 million years? TimVickers 02:31, 14 May 2007 (UTC)
If we don't know we should say we don't know and give the outer limits of the estimates. An uneducated reader might think it happened in a year or less, since "explosion" is usually kept for very rapid events indeed! TimVickers 20:21, 14 May 2007 (UTC) How about (using numbers from top of my head): Estimates of the length of time over which these changes occurred vary and the Cambrian explosion may have only taken 10,000 years or been as slow as 10 million years.
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Verisimilus
T 15:12, 17 May 2007 (UTC)Sounds great, "estimated to have taken about ten million years" would be suitably cautious. I'd suggest putting this in the lead somewhere, to give the casual reader a clear idea of what "rapid" means in geological terms! TimVickers 12:49, 19 May 2007 (UTC)
I can accept that. That’s reasonable. The fossil record is incomplete, and the rock record perhaps even more so, especially rock layers from 542 million years ago (I mean, a lot of plate tectonics come and gone!). What I would ask, could we take three examples and explain them in some detail. For example, I’m going to assume the Burgess Shale is fine-grained. And I seem to recall reading that it happened in a slump, so that a bunch of little animals were trapped all at once. I would like to have that confirmed.
Again, our article has a lot of ‘bluebirding!’ We don’t really explain things, don't really teach things, don't really describe things. We mainly just mention things. FriendlyRiverOtter 05:28, 29 May 2007 (UTC)
Does learning on a Dvorak keyboard slow you down and get in your way when you are later trying to learn on a regular Qwerty keyboard, or vice versa? No, studies have been done and it’s just the opposite. Learning on either keyboard helps you if you later move to the other. There is a positive transfer of learning.
I figure it’s probably the same with writing. So, if one has spent time on the formal style most common on wikipedia, there will be positive transfer as one makes the transition to a more communicative style. And I urge you all in fact to make the transition to a more communicative style!
Take a look at Richard Dawkins. Or look at COSMOS (the book) by Carl Sagan, and compare it to any introductory astronomy textbook for that time period, or even for the following ten years. I would suggest that it’s so much better in large part because Carl took the risk of being criticized. He wrote in his own voice. So if you do a good job of communicating with the interested lay person (and I hope that’s one of your prime audiences), you will probably be criticized as sounding too much like an essay or sounding too much like a magazine article. Please take those as compliments!
Learn from good writers like Dawkins, but mainly find and develop your own voice. For example, Richard uses the method of rephrasing something in different words. This can be useful in that it kind of puts up an intellectual signpost and makes the terrain more understandable, but then he kind of overdoes it. So, if you keep working on your writing and allowing your own unique voice to continue to develop, you might even become a better writer than Richard Dawkins. How about that! Please do not let any artificial constraints hold you back. FriendlyRiverOtter 00:29, 21 May 2007 (UTC)
I can't get the Ediacaran, as presented here, to match the Ediacaran biota tineline. which is right? Adam Cuerden talk 19:07, 28 June 2007 (UTC)
Some private correspondence gave me the initial impression that this article needed major improvements in content, but after reading it twice I think the content is good (of course there's room for improvement in anything, and it will have to be updated to take account of new discoveries and analyses).
By far the largest difficulty is the article's academic vocabulary and style, which will put off non-specialist readers, who should be Wikipedia's target audience. So it needs lot of re-phrasing.
I also think minor re-structuring would help, for example:
I have a suspicion that a cladogram would be helpful, but wonder:
Other points to be resolved:
Related WP articles:
I think that since I originally re-wrote this article, it has (inevitably) become more fractured in its viewpoints - ie it has steadily got less coherent. This is not a trouble as long as the article still holds together - otherwise it will never make FA status - something that seems very distant right now.
When I re-wrote the article, I certainly and deliberately downplayed the "sensational" aspects of the CE, as typified by Gould's book, and still (apaprently) the majority view of popular understandings of the subject. But this viewpoint only ever had limited purchase in academic study of the CE, and it is certainly completely obselete now. Specifically: i) Things do not suddenly appear "explosively" except under the influence of taphonomic windows (ie the reason everything appears around Chengjiang time is preservational); but trace fossils and other information inform us pretty clearly that crown group bilaterians did not evolve until late Ediacaran time; ii) similarly, trace fossils do not "explosively appear" at the base of the Cambrian, but rather, diversify rapidly from latest Ediacaran time onwards ; iii) the whole debate between molecular clocks and the fossil record has almost collapsed as MC's have been adjusted to give dates close to that of the fossil record.
As fas as "bluebirding" goes: I am not sure exactly what this means, but I think that one of the things that needs to be corrected about the Cambrian Explosion is that we know everything about it. In fact, almost every aspect of it is the subject of ongoing research; and it is right to reflect these uncertainties rather than present a misleadingly simplistic "solution" to whatever the problem is meant to be. We do not know what the Ediacarians are: indeed, I would say that we have little clue at all. We do not know if oxygen was important. We do not know the phylogeny of most of the major groups involved, so this makes interpreting their fossil record problematic. And so on.
A minor point: the dating of the lagerstätten in the text is inconsistent with the dating in the diagram. The dating of the Sirius Passet is uncertain given that it is based on a Holmiid-like trilobite which is pretty dissimilar to the other holmiids: but if this is broadly right, then SP is probably end Atdabanian; and almost certainly considerably older than the age given in the diagram. It could actually be considerably older than this, ie basal Atdabanian. Chengjiang is, as far as I understand based on the brachiopods, probably early Botoman.
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"...
Grahbudd 18:19, 19 July 2007 (UTC)
This has been my "next project" on Wikipedia for a long time, and it's about time I got stuck in! I'd be very grateful if you'd keep a critical eye on my efforts and expose any errors that creep in!
Graham - "Bluebirding" (as far as I can gather) is the practice of using a link to another wikipedia page in place of a full definition. Ideally the naïve reader should be able to follow the whole article without clicking elsewhere - which is probably an ambitious target in an article such as this!
I'll try and reflect the "Cambrian effervescence" viewpoint more strongly - I've been wary of avoiding "Point of View" discussions, for as you say there still seems to be a large portion of scientists that haven't come round to your point of view yet. I suspect that any eventual Featured Article reviewers would pick up on this strongly, since Gould's views probably represent most people's familiarity with the subject.
Philca - I hope you don't mind if I add to your proposed article structure above!
Verisimilus T 21:04, 20 July 2007 (UTC)
I'm not sure that the Cambrian Explosion was purely an animal phenomenon, and had carefully worded the introduction to avoid giving that impression. The planktonic realm also underwent a rapid diversification - see reference in lede. Certainly Butterfield's theory of trophic cascades as an amplifying factor requires there to have been one. [1] It may be worth adding a small section discussing this - but I'm not sure that it needs dwelling on. Verisimilus T 12:39, 19 August 2007 (UTC)
Just scanning through your additions, your "Why is it such a big issue" section, whilst a great addition to the article, may not stand up to close scientific scrutiny.
For starters, the analogy with the mammals - whilst interesting, and possibly helpful - is not without caveats. For example, it's recently become apparent that the mammals diverged long before the end of the Cretaceous, and the extent of the diversification may not be as large as it has been thought. (A little like the Cambrian, I suppose...)
Also, I'm a little wary of the picture you paint of the phyla - it perhaps paints a misleading picture. Yes, interest in the subject arose because of the "appearance of phyla", but the concept of stem groups (see Budd 2000, in the article references, for a good explanation) is more useful in geological terms than the Linnean hierarchy. Perhaps a tighter or more thorough discussion has a place in the article, as this is an interesting area that can spark some confusion about the explosion? Certainly Gould put across the "phyla appearing at once" argument, and it may be worth dismantling that.
Estimates of the Cambrian explosion's duration range from about 10M years (from 530 to 520M years ago) to about 80M years (starting about 580M years ago, in the Ediacaran age).
I've already struggled with putting a length on the explosion, and decided against it, as per Grahbudd's comment above. I'm not sure that it's helpful to pigeonhole time into "before and after the explosion". It was a smooth curve, and different definitions will cover different amounts of it...
All but an insignificant amount of fossils are marine, as terrestrial settings only fossilise in exceptional circumstances. It's not cover by more recent rocks that is an issue, but the total sedimentary rock volume preserved; this follows an exponential curve into the past, as rocks are eroded or metamorphosed over time.
The paucity of body fossils is probably a combination of taphonomic factors and a lack of hard parts.
Worth clarifying too that it's only the MIDDLE Cambrian that contains lagerstatte - after the explosion had died down.
And of course lagerstatte don't display first or last occurrence dates - but the scarcity of fossilisation means that the usual record doesn't usually contain such dates either.
A trace fossil is any trace of an organism other than its body itself - and not restricted to burrows, as your introduction seems to suggest.
Do you have a citation for the necessity of Earthworm complexity? I suspect you're probably right but would like to be sure.
What does one mean by "comparable complexity to an Earthworm"? it's perhaps worth clarifying this.
You're trying to summarise a huge amount of information in a short section.
The pitfalls of the molecular method can probably be covered with a link, and a statement that "Molecular estimates have dated the explosion at dates ranging from 1Ga to 500Ma ago, and should thus be treated with caution".
Given that one of their assumptions is often that of a constant rate of evolution, their application may be more in spotting something abnormal happening in the Cambrian, such as Butterfield's 10-fold increase due to trophic cascades, than to providing a date for the explosion, which we know anyway to have happened long before the divergence of lineages.
I hope not to cast a negative view - there are many improvements in terms of style and some content - but there are also many small but significant errors. I'm wary of straying too far from Budd's version of the article without good reason, as it's very easy for a non-expert author to add small comments which turn out to portray an incorrect or misleading impression on the reader. Verisimilus T 10:59, 20 August 2007 (UTC)
I do not wish to sound argumentative, but. The original article was one reviewed by Nature; and was found to contain a substantial number of errors. As this was the case, and as the structure was a complete hotch-potch, I totally rewrote it. I agree that the version I produced was somewhat stodgy and academic; but it was, I modestly suggest, both comprehensive and accurate. I have watched this article evolve away from what I wrote with a mixture of some dismay and amusement. Now it contains about as many mistakes as it did before. For example:
i) "The Cambrian explosion describes a profound and very rapid diversification of life[1] on Earth that occurred more than half a billion years ago."
First, how can "the Cambrian explosion" "describe" anything? And now the opening paragraph makes no reference to what the Cambrian explosion is about, ie the rapid expansion of the _fossil record_; but rather talks about several layers of inference from it, including the idea that "evolution would accelerate by an order of magnitude" - Butterfield sourced and respectable, but what does it *mean*?
ii) History of the concept: Darwin's difficulty was increased by the fact that in his time no sedimentary rocks much older than 500M years had been reliably identified, and Darwin regarded the Silurian as the earliest known geological period.[5]
But this is a misleading statement. Darwin was well aware of Sedgwick's work on the Cambrian (indeed, he accompanied him on his fieldwork to North Wales). It is true that in the 1850's the high-water mark of Murchison's Silurian concept was reached; but this paragraph makes it sound as if rocks as old as the Cambrian were not known to Darwin: they were.
iii) "Why is it such a big issue?" My original effort was stuffy, but this is too far too far in the opposite direction. And what follows is both misleading and a more or less complete non sequitor. " So at first sight a wide range of complex animals evolved from "blobs" in under 30M years". Why reference Cohen's out of date text book here, when there are zillions of more up to date works? And who says they were blobs anyway? And the misleading discussion of phyla is out of place.
iv) Duration of the explosion. I've already commented on how misleading this is. Any case, the whole idea of "Even if the process took 80M years, it would still be exceptionally fast - for comparison, the much less radical evolution of mammals from therapsids took about 70M years. " begs several questions. Says who? If one had a time machine and could watch what was going on, I expect it would not seem bizarre at all.
v). "Body fossils Body fossils preserve all or significant parts of organisms and are therefore the most informative type of evidence. Unfortunately they are increasingly rare as one looks further back in time: The rocks in which they are buried are usually covered by more recent rocks. All life in the early Cambrian was marine, and subduction destroys marine sediments within 200M years of their formation, unless they are raised above sea-level by other tectonic processes such as orogeny (mountain-building)."
It is misleading to state that fossils get rarer as rocks get older. Number of fossils is controlled by outcrop area of fossiliferous rocks; and this is controlled in turn by tectonic cycles: rocks get buried and then exhumed over a few hundred million years. Even if one accepts that _on average_ older rocks are less likely to be preserved, this does not mean necessarily that the quality of the fossil record gets worse (see eg Benton et al. Nature 403, 534-537 (3 February 2000)).
vi) Oceanic floor is destroyed by subduction; but the continental shelves where diversity is highest are continental, and thus do not get subducted in general.
lagerstätten: one needs to qualify this term to show that you mean conservation rather than concentration deposits.
vii) "Trace fossils. Trace fossils consist mainly of tracks and burrows on and a few centimeters under what was then the seabed. Animals under a centimeter long are unlikely to leave tracks or burrows on the surface; and burrows under the surface suggest the presence of animals which were almost as complex as earthworms..."
Trace fossils can in general go down a metre or more (Cambrian ones are much less tiered). Plenty of organisms smaller than a few cm can leave trace fossils; and you do not need to be particularly complex to burrow under the surface per se (e.g. the cnidarian "sea pansies" do it).
viii)"Molecular phylogenetics can provide interesting suggestions about the phylogeny ("family trees") of organisms provided one can avoid the difficulties created by saturation. But many paleontologists believe that fossils are still the best form of evidence and should take precedence if there is any conflict between the results of fossil-based and molecular analyses."
Name names! I think this sets up a false dichotomy.
ix) Triploblastic. Trichoplax is an example of a taxon that is not sponge or cnidarian but is not triploblastic; and ctenophores are not usually counted as triploblastic either.
x) Diploblastic. It is increasingly being recognised that anthozoan cnidarians are essentially bilaterian in many ways; but are not triploblasts.
xi) Coelomates. Not all Cambrian fossils are coelomates. E.g. the cycloneuralians.
xii) Trace fossils 1000M years ago?
Even the principal author of this report (Dolf Seilacher) has abandoned the idea that they are biogenic.
xiii) Ediacaran organisms.
This section is highly biased. E.g. Spriggina is "probably a trilobite" - I would just flatly disagree with this and many other people would too. Citing MacMenamin on this topic does not, alas, fill me with confidence.
xiv) "If traces such as Cruziana and Rusophycus were produced by arthropods, that would indicate that arthropods or their immediate predecessors had developed exoskeletons, although not necessarily as hard as they became in the Cambrian.[22]"
Both these _are_ Cambrian fossils, as this section states itself.
xv) "The earliest Cambrian trilobite fossils are about 530M years old, but even then they were quite diverse and world-wide, which suggests that these arthropods had been around for quite some time.[32]"
Most people would date the oldest trilobites to be beginning of the Atdabanian, ie around 520 million years ago or so. Look at http://www.palaeos.com/Timescale/timescale.html - the timescale given here is, I note, not in accord with this. Incidentally, the Burgess Shale is middle Cambrian, but sites in the Lower Cambrian in the time scale!
xvi) Sirius Passet fauna.
Again, I dispute the age, it is probably 10 million years younger than this.
xvii) "The strangest-looking animals from Sirius Passet are Pambdelurion and Kerygmachela. They are generally regarded as anomalocarids because they have long, soft, bodies with a series of broad fin-like flaps along each side. The fossils found so far show no trace of gills or other breathing apparatus and no trace of segmentation. Both were apparently blind, as the fossils show no trace of eyes. Pambdelurion had a large mouth on the front of its head, flanked by a pair of thick, segmented appendages slightly longer than the swimming flaps and equipped with a flexible spine on each segment. It may have fed on plankton. Kerygmachela had a pair of long, slender trailing appendages at the rear end, and a small conical mouth flanked by robust, unsegmented appendages which had short spines on the front edge and were tipped with longer spines. The spiny front limbs suggest that it may have been a predator, but its small mouth suggests it would have been restricted to very small prey."
Kerygmachela was described with gills: indeed the title of the first paper to describe it was "a Cambrian gilled lobopod from Greenland". I should know, as I wrote it. In the fuller description it is described as possibly possessing eyes too. It is highly misleading to say that neither show any traces of segmentation; au contraire, they are both clearly segmented. ii) Pambdelurion's mouth is not terminal, but ventral. And the idea that is was a planktivore is fanciful (whether or not it is actually true). (eh, I described this fossil too).
xviii) Chengjiang.
e.g. "Chenjian contains other animals which have puzzled paleontologists but are now regarded as lobopods and fairly closely related to arthropods. Anomalocaris was a mainly soft-bodied swimming predator which was gigantic for its time (up to 70cm = 2.1 feet long; some later species were 3 times as long); the body had a series of broad fin-like flaps along each side, and at the rear a pair of "fans" arranged in a "V" shape. The fossils found so far show no trace of gills or other breathing apparatus and no trace of segmentation. ".
Again, gills were described by Whittington and Briggs )185) and the animals are clearly segmented. Not even I have claimed that Anomalocaris in the strict sense is a lobopod: it is clearly not, in fact!
xix) Misszhouia is not a "soft-bodied trilobite".
xx) "analyses of both of these animals were hilariously wrong, but they are now regarded as lobopods, and Anomalocaris is very similar to Opabinia in most respects (except the eyes and feeding mechanisms) - see above."
Unfair: both accounts were excellent given the material at hand. And Anomalocaris is not a lobopod. And it is not really fair to call Odontogriphus a mystery any more.
Again, I do not want to be argumentative: but I think that the current version of the article now contains even more mistakes than before the rewrite. Further, it puts far too much emphasis on the various exceptionally preserved faunas, which after all all date from after the period of the most important evolution events. Thus, the overview of the whole thing is now missing, but rather the article is evolving into a list of dubious facts about the exceptionally preserved fauna. Finally, it is too much in thrall to the Gould view which is not really held to be true by most palaeontologists.
cheers
Graham Grahbudd 14:12, 26 August 2007 (UTC)
"Today, creationists with a poor grasp of science maintain public interest in subject, highlighting the Victorians' concerns about its incompatibility with evolution."
I have to agree with removing "with a poor grasp of science." It seems unverifiable and pov. I would have taken this out myself, but it seems that has already been done and undone. Momo Hemo 09:48, 22 September 2007 (UTC)
Just to point out that Knoll's paper post-dates Conway Morris's. No-one really believes that Thaumaptilion is an Ediacaran any more (it's probably not an Octocoral either) and a mass extinction is almost universally accepted at the base of the Cambrian. Verisimilus T 14:43, 22 December 2007 (UTC)
The Cambrian explosion is obviously a very important subject, but the page as it stands is forbiddingly long. Would it be possible to summarize and redirect to subpages to make this page more inviting to the paleontology non-specialist? — vivacissamamente ( talk) 16:30, 30 December 2007 (UTC)
Hi,
My initial thoughts after a first read through is that the length, unfortunately, needs reducing a lot. While there may be a case for explaining every scientific concept within the article, there are many sidetracks that are given undue weight - for example, far too much time is spent describing individual organisms, which are interesting - but stray from the central point of the article. In a shorter article, the descriptions would make interesting asides, but I think that it is important to keep as close to the subject as possible. The first paragraph of "How fast did the main metazoan groups evolve?" is the meat of the story, and the previous dozen sections could almost be omitted in favour of a modest expansion of this.
Also, there's a lot of repetition - much of the previous version appears to have barely been touched, where incorporation may have been more useful.
I think there's a difficult balance to strike between engaging the non specialist by explaining unfamiliar concepts, and keeping the article short enough to be readable within the short attention span of the average reader. As it stands, it perhaps lies a little on the former side, and a more concise style of writing may help balance the scales.
The other thing that perhaps gets lost in the size of the article is a central line of argument - the article doesn't seem to "flow" comfortably, and the reader isn't really led from one section to the next.
I hope these comments are helpful, sorry if they're a little vague at this stage! After a significant trimming, this article should well be on the right tracks...
All the best, Verisimilus T 18:55, 30 December 2007 (UTC)
A few more points:
Verisimilus T 18:01, 6 January 2008 (UTC)
The info bar appears corrupted, there seems to be code overtop of it. 207.6.125.46 ( talk) 22:59, 27 January 2008 (UTC)
I've just removed a new section suggesting that "Although no direct evidence exists, a new kind of viral or microbial infection process is one possible route that genetic material may have taken in exchanges between early species." As far as I am aware this idea doesn't have any evidence in its favour, nor support from the scientific community; I feel this article should restrict itself to scientifically supported ideas, as there are thousands of intriguing but un-testable ideas out there, and we can't reasonably expect to cover them all. Comments in its defence are welcome!
Verisimilus T 09:20, 10 February 2008 (UTC)
After reading through the article, at present I'm willing to remove:
After that I find it difficult to identify content that can be removed, since: the pre-Cambrian content shows that complex metazoans did not originate in the early Cambrian and their emergence was probably not sudden; the descriptions of early Cambrian animals illustrate the exceptionally high level of disparity.
Of course I'm not best placed to be objective about this because I wrote most of it. Constructive comments and suggestions would be very welcome! Philcha ( talk) 12:40, 21 February 2008 (UTC)
I notice no-one has so far suggested ways of making this long article significantly shorter without sacrificing important content. I've had a crazy idea that might help general readers while keepng the details that armchair paleontologists like me will want to see: place the analysis (starting with "How real was the explosion?" before the potted history of life from 1BYA to 500MYA; if necessary clarify the issue first by defining the 3 main views that have been historically important (that there were no pre-Cambrian metazoans; that coelomates and possibly triploblasts evolved and diversified extremely fast in the early Cambrian, as Gould and Whittington argued; and that triploblasts and probalby coelomates were present a lot earlier, although there was a surge of diparity in the early Cambrian). So the order of the main sections would be: Intro; history of the debate; definitions of terms used commonly in the analysis (e.g. triploblast); the analysis ("How real was the explosion?", etc.); definitions of terms used in surveying the evidence; types of evidence; potted history of life from 1BYA to 500MYA? Would that work as a method of presentation? And would it be intellectually satisfactory? Philcha ( talk) 19:54, 14 March 2008 (UTC)
Philcha ( talk) 19:33, 28 March 2008 (UTC)
I've reinstated this section. The idea is quite new (Jan 2008), and may get its own Wikipedia article in time. Meanwhile mentioning it briefly in this article will: (a) remind editors to check up on whether it gets enough scientific support and additional info to merit its own Wikipedia article; make the CE seem less surprising because there's evidence of another explosion. If the idea of an Avalon explosion survives scientific investigation, eventually someone will use the 2 explosions as the basis of some principle in evolutionary theory, then we can produce an article about that too (unless they are simply taken as examples of Valentine's "empty niches" theory and its consequence that explosions at each grade happen only once). Philcha ( talk) 18:45, 28 March 2008 (UTC)
I'm sure sure if this has been discussed previously, but the Definitions section seems a little misguided. The beauty of a hyperlinked encyclopedia is that a reader can instantly go to the article of an unfamiliar word. If the reader is unfamiliar with a word, such as phylum, they can go to the relevant article, fill in any gaps in their knowledge and then return. Ashmoo ( talk) 13:26, 7 April 2008 (UTC)
Someone has recently added a section "Quantum Evolution":
I can see a few things wrong with this:
I will remove the section in about a week if those objections are not met. Philcha ( talk) 18:07, 9 May 2008 (UTC)
I've removed these sections plus the stump of some old content about molecular phylogeny; this material had caused confusion because it was commented out. To make matters worse, the stupid doibot inserts HTML comments but is not smart enough to leave commented-out content alone, so it creates nested HTML comments and therefore a real dog's doo-doo. The last version containing the whole of the commented out material is [26] in case anyone wants to mine the old stuff for additional info. Philcha ( talk) 12:08, 11 May 2008 (UTC)
A 2nd para has recently been added to "Increase in abundance and spininess of acritarchs":
The way I read the cited paper (Stanley (2008). "Predation defeats competition on the seafloor" (extract). Paleobiology. 34: 1. doi: 10.1666/07026.1.), it attributes the drop in species durations for Proterozoic Phytoplankton to "protistan herbivory", and the next sentence, "Not surprisingly, the average duration of acritarch species declined further when metazoans diversified, being less than 10 Myr for species that arose in the Early Cambrian," does not commit itself about when metazoan herbivory / predation became significant. Philcha ( talk) 19:20, 13 May 2008 (UTC)
I thought I'd better read the reference supporting paragraph one, and thought I'd "return fire"... I think this article is being over-interpreted too, without mention of its caveats.
“ | Their increasingly spiny forms in the last 1 billion years probably result from the need for defense against predators, especially predators large enough to swallow them or tear them apart. | ” |
— Current article - italics don't appear to have support from article |
“ | Processes may be of different kinds and of different functional significance (for example, they may also be selected for as a means to increase water friction or adhesiveness).
The presence of process-bearing acritarchs is therefore not a definite indication of the presence of predators/grazers. |
” |
— Bengtson (emphasis mine) |
This article probably isn't the place for a full-blown discussion, but I think that the presentation of facts as it stands is a little skewed. I would be tempted to move it to a new section at Acritarch, and to take this opportunity to slim the C-ex article slightly.
How about combining the stromatolite and acritarch sections into a new, brief "Proterozoic microorganisms" subsection, and using a sentence along the lines of:
“ | Marine organisms ( acritarchs and stromatolites) show signs of increased predation pressure around 1,000 million years ago, which may reflect predation by protistan microorganisms. They suffer a sharp decline in abundance at the start of the Cambrian period, which has been linked to the raditaion of metazoan grazers. | ” |
— Just a rough idea |
This tells the casual reader everything they need to know in a concise form (concision being my main concern for this article at the moment, as you know!); the current, more detailed discussion can then be moved to Acritarch and Stromatolite for the interested - a "further information" link could be provided to emphasise this point. Moving the discussion to the acritarch page will allow us to expand the discussion of the papers a little more in the article, to give the readers a fairer reflection of what is and isn't being asserted, without scaring off the casual reader of this article. Smith609 Talk 10:16, 14 May 2008 (UTC)
My thoughts on how this affects Cambrian explosion:
For the reasons described in a previous post (Thread "Increase in abundance and spininess of acritarchs", post by Philcha at 14:05, 14 May 2008 (UTC)) I'm very reluctant to drop significant chunks of the potted history of life in the last billion years. But in re-reading the article I think there parts than can be dropped or shortened without serious harm:
Comments welcome! Philcha ( talk) 18:08, 14 May 2008 (UTC)
“ | the Early Cambrian adaptive radiation of several eukaryotic clades, including the Metazoa, documented by the truly rapid expansion in the fossil record of characteristics such as large size, morphological complexity, skeletalization, and infaunal activity. | ” |
— Source |
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