Talk:Ediacaran biota/Archive 2

GA

I'm sorry, but there are major POV problems in this article. Take reference 28: "N.J. Butterfield & G. Narbonne, pers. comm" - you can't use a personal communication as a reference in Wikipedia, it has to be limited to Peer-reviewed articles. There also dubious statements like "It was not until 1989[15] that it became clear that the standard Linnean method of classification was inadequate to deal with these bizarre organisms, although doomed attempts to cling to this system remained until a 2000 paper in plain English[16] clarified the failings of the system, and helped to provide a new framework from which to hang the fossils." Reference 15 claims to be a weblink, but is not linked; reference 16 does not support the text, being a discussion on Cambrian fossils, with a brief discussion of Edicarnean fossils that is, as far as I see on a quick skim, entirely compatible with the Linnaean system.

This article needs a lot of work before it can be GA. While parts of it are good, it has a strong tendency to simplify genuine debates to a single issue, and mischaracterise the side the author does not support.

Hence, I must fail it from GA, and put a POV tag up. Adam Cuerden ^talk 11:30, 19 May 2007 (UTC)

I've marked up the parts that worry me. I would like to get some other people in to also have a close look, though: The presence of a few errors spotable by a biology undergraduate (admittedly, one with a strong interest in the subject), leads one to worry what an expert would find. Failing that, just a careful source-checking would probably suffice for now. Adam Cuerden ^talk 11:56, 19 May 2007 (UTC)

Thanks for your comments! I'm quite concerned that you've flagged quite so many issues - I'll do my best to look further into them. I tried to only insert information extracted from primary sources, although I must admit that I only checked the abstracts of some. As the article's only major contributor I suppose it's no great surprise that some POV has arisen, as I've only had any significant degree of exposure to two sides of the argument — who by the sounds of it have presented a different impression on the firmness of some of the arguments than some of the literature holds to be the case.

The remark to the Linnaean system was badly worded. To clarify, I intended to convey the fact that people were trying to push things into crown groups where the organisms should fairly certainly be put in stem groups.

Which link was it that didn't work? The references seem to have been renumbered after your comment, and the current [15] works fine - on an institutional computer, at least.

Verisimilus T 12:20, 19 May 2007 (UTC)

I've addressed the issues that you flagged, with the exception of the dodgy "animal" which no-one seems to have published a response to yet. Would you mind checking that you agree with the new wordings? If there are any other issues in need of addressing, I'd be grateful if you pointed them out too! I'll have a further look at the way I've presented some of the other arguments. Thanks, Verisimilus T 12:52, 19 May 2007 (UTC)

Alright, sure! And I'm sorry if I was unpleasant while being critical: I have some rather bad food poisning just now, and my painkillers hadn't fully kicked in. I will say that on rechecking carefully, I'm a lot less worried than I thought I'd be. Adam Cuerden ^talk 14:21, 19 May 2007 (UTC)

Right. Let ma go through in detail... Fiurst of all, best note [1] - I cut the badly worded Linnaean bit, but now that I see what you were getting at, I don't see any reason why - appropriately rewritten - it couldn't be restored. I'd be careful, though: Realise that paper's actually on classifying Cambrian organisms, and while it's a great analysis of that, it doesn't actually say all that much about Ediacarans (at least, from a skim), so it might be overreaching a bit unless other references show his insights (and they are good insights) being applied to the Ediacarans.

I'm just going to list everything that strikes me - we can worry about if it matters afterwards.

LEAD

• "Seilacher has placed many in their own kingdom Vendobionta (now Vendozoa),[2] but this is not universally accepted." - It'd be worth saying who Seilacher is, and tying this in with Narbonne's theory (as they are, of course, related: Both are saying that the Ediacarans are profoundly different from what came after.)

History

• In 1933, Gürich's discovery of specimens in Namibia[7] brought about a similar situation: the strong consensus that life originated in the Cambrian resulted in the designation of a Cambrian age to the fossils, which were promptly forgotten, and never linked to Aspidella. I don't doubt it, but it'd be good to point out someone who pointed out the connection between Gürich's discovery and the later Ediacaran fossils.

• The following two paragraphs:

In 1946, Reg Sprigg noticed "jellyfishes" in the Ediacara Hills of Australia's Flinders Ranges.[8] These rocks were then dated as Early Cambrian, and the reports did not receive much attention[9] until 1959,[10] when amateur collection and improved stratigraphic dating made it apparent that the Ediacaran fossils provided evidence of Precambrian multicellular animals.[11]

This reinterpretation was undoubtedly prompted by the 1957 discovery of Charnia in England's Charnwood Forest.[12] The detailed geologic mapping of the British Geological Survey left no doubt that these fossils sat in Precambrian rocks. With an impetus to search Precambrian rocks for life, many more finds ensued, all in sandstone with such coarse grain size that fine details were never preserved and interpretation remained difficult. Mistra's 1967 discovery[13] of fossiliferous ash-beds at the Mistaken Point assemblage in Newfoundland[14] rejuvenated the field; the fossils were preserved in enlightening detail in the fine ash.

are choppy, leaping back and forth in time, and neglecting to mention Charnia until after the events that Charnia triggered. Indeed, the whole history section could have its flow improved. Also, while "This reinterpretation was undoubtedly prompted" is accurate and perfectly correct, it's... phrased in such a way to make it look like a massive POV/OR violation. Better to just say something like "In 1946, Reg Sprigg noticed "jellyfishes" in the Ediacara Hills of Australia's Flinders Ranges,[8] but they were then presumed to be from the Early Cambrian and largely ignored[9] However, the 1957 discovery of Charnia in England's Charnwood Forest,[12] which the detailed geologic mapping of the British Geological Survey unambiguously dated as Precambrian, led to the reintepretation of the Edicaran finds in 1959,[10] aided amateur collection and improved stratigraphic dating.[11] With these impetuses to search Precambrian rocks for life, many more finds ensued; however, all finds in coarse-grained sandstone which prevented fine details being preserved,until Mistra's 1967 discovery[13] of much better preserved fossiliferous ash-beds at the Mistaken Point assemblage in Newfoundland[14], which rejuvenated the field."

• The section beginning In 1922, Amadeus Grabau named the Precambrian strata the Sinian, based on the Yangtze Gorges locality; is... perhaps a little too listy. Could we make that a side table?

• "The debate has now moved to fixing the end of the Ediacaran, with the current Ediacaran-Cambrian boundary unsatisfactory for a number of reasons, and the advantages of the Russians' nomenclature becoming clear as their science opens up to the West." This sentence is... completely unrelated to what came before, and has no source for the assertaion of the benefits of the Russian system (and doesn't actually explain what the Russian system is, which is worse.)

 Done — Although I still don't like the etymology paragraph. Verisimilus T 15:34, 23 May 2007 (UTC)

Preservation The main problem in this section is presuming too much knowledge.

• "The Ediacaran biota had soft bodies, which makes their abundant preservation surprising. The absence of vertically burrowing infaunal creatures undoubtably helped;[16] after these evolved in the Cambrian, soft-bodied impressions were disturbed before they could fossilize." Presumes people know that soft-bodied organisms rarely fossilise. I'm not sure that's a safe presumption.

• "Very few Ediacaran age strata with the "elephant skin" texture signifying a microbial mat are devoid of fossils, and Ediacaran fossils are almost never found in beds not containing microbial mats" Presumes people know what a microbial mat is. This one can probably be fixed by rearrangement.

• "Microbial mats were widespread until the Cambrian radiation of grazing organisms,[18] which now limit their distribution to refugia where no predators can survive long enough to eat them." - "Cambrian radiation" and "refugia" are dicey terms to use for the general public.

• "Sedimentary environment" - awkward title.

• "trapping their mould against the muddy or microbial substrate on which they lived." - I'm not entirely sure the word "mould" is accurate in this particular case, as the mould's what you get after they start fossilising. There's some other weird language in this paragraph: "can be dated accurate to the nearest million years" (dated accurate to?) "during a turbidite event (an offshore high-discharge "flood")" (I'm not sure that parenthetical explanation actually explains)

• "Soft-bodied organisms today almost never fossilise under such events; it is likely that the presence of widespread microbial mats aided preservation by preserving their impressions in the sediment below.[21]" - this is the sort of information that we ought to have explained right at the start.

• The section "What is preserved?" comes before an explanation of what there is to be preserved.

 Done — Except for the Turbidity current. These are hard to explain to the scientist, let alone the layman! Verisimilus T 15:58, 23 May 2007 (UTC)

MORPHOLOGY

• Symmetry ranges from radial, and pentameral to bilateral and trigonal; rigidity from sturdy and resistant to jelly-soft." - Too much terminology.

• "...presence of motile, probably bilateral..." - We need to say what a bilaterian is for the importance of this to register.

• "common in the Phanerozoic" - "Phanerozoic" is an excessively difficult term when you could get away with "common later"

• "Some Ediacaran fossils, especially discs..." The description of discs isn't until the next subsection, so the reader isn't yet primed to understand this. Actually, can't the section on trace fossils be moved to just before or just after "non-Ediacaran Ediacarans"? Because if they are evidence of Bilateria, that makes them non-Ediacaran anyway.

• Subsection "Discs" - needs citing.

• Subsection "Quilted" - Accurate, but not as clearly written as it might be.

• "the reputed bilaterian Vernanimalcula, now widely held to represent the diagenetic infilling of an egg-sac or acritarch." - I think that perhaps that might be just a smidgen too much jargon for one sentence.

• "Small, shelly fossils" - This term is too important to let it be seen as a mere description of the fossils, and the wiki page on Small shelly fossils is simply terrible. It's not immediately obvious that "small shelly fossils" actually refers to organisms using lots of small shells for armour plating or other purposes, and that we're referring to them, not just small shells.

 Done - I've had a look at this section; it's still not perfect but I hope I've addressed all these points to a suitable degree.

Classification and interpretation

• Adolf Seilacher responded by suggesting that the Ediacaran sees animals usurping giant protists as the dominant life form.[43] - It's less than clear how this is a response to Glaessner's theory. Is Selacher proposing, say, that Charnia is a giant multi-nucleate protist? Anyway, we need to explain what a protist is: It's a term that swung into popularity briefly, but seems to have swung out of favour again.

• Subsection "New phylum" - I'm not entirely clear what's being explained here. In what kingdom did Seilacher put his phylum? Animalia? What led him to stop calling them a kingdom?

• Subsection "Lichens" - This has some odd wording, though it's understandable enough.

• "a view which is supported by molecular clocks." - The layperson's not going to know what a molecular clock is.

I'm going to break here for a bit. Adam Cuerden ^talk 14:21, 19 May 2007 (UTC)

Wow. Thanks so much for providing such a comprehensive list!

Regarding the Budd paper, I feel it's just as relevant to the Ediacarans, even if it does barely mention them. But I take your point on not being able to prove it's affected research on them. I'll have a think about how to incorporate it; there's a 36 page paper from 2006 that I've not got round to reading yet (apparently it's quite a tough read!) which may cover that area. I'll look at the other points when I've a bit more time. Verisimilus T 16:51, 20 May 2007 (UTC)

It's a very interesting paper, and probably correct, at least for some phyla, but without showing it affected research on the Ediacarans, it's overstating the impact. Adam Cuerden ^talk 20:34, 20 May 2007 (UTC)

GA - Continuing

Origin

• Frankly, this whole section lacks focus and is probably only really comprehensible if you know what it's getting at already. Needs organised in a more logical manner, with less presumption of pre-extant knowledge, e.g. Don't presume people know the age of the earth, explain about the early development of unicellular life, as that explains why the delay in multicellular life is odd, etc.

Disappearance

• Lacks an introduction: It leaps straight into theories about their disappearance, but doesn't actually talk about them disappearing first. Also, consider removing some or all of the subsection headers.  Done

• Subsection "Preservation bias" A little oddly written, but that may just be an impression from the use of that dramatic dash ("— unless such assemblages represent an environment never occupied by the Ediacaran biota.") "Lagerstätten" is a very obscure word, and should be explained.  Done | I agree that the dash is a little overdramatic, I'd've preferred a normal dash but that's against the MOS...Verisimilus T 14:55, 25 May 2007 (UTC)

• Subsection "predation and grazing": "higher trophic level" obscure, for that matter, so is "biota". Odontogriphus is undescribed on first appearance, it's not until "These grazers first appeared as the Ediacaran biota started to decline" that we learn that it's a grazer. Time of the appearance of grazers is somewhat obscure: It could be read as late Ediacaran or early Cambrian, though Odontogriphus itself is middle Cambrianish, at least according to Wikipedia, and thus, if Wikipedia's information is accurate and not superceded by later discoveries, probably a poor example. Simplify language a bit for laypeople. Clearly identify Kimberella as Ediacaran; people won't remember.  Done | As "biota" is in the title I'd argue we can get away with using it in the article. Verisimilus T 14:55, 25 May 2007 (UTC)

• Subsection "Competition" is... kind of awkwardly written, or, more accurately, written a bit too much in the format preferred in scientific papers. Add a bit more padding to ease in the layperson. Try to avoid the "it is possible" opening.

• Subsection "Change in environmental conditions" Perfectly fine, except for the word "biomineralisation". I suppose you could add more detail, but isn't that always true?

Assemblages

• Slightly obscure paleontological term for the section title, also "depositional". Otherwise, it's pretty good. Consider putting NArna before Avalon (which refers to Narna); the use of "rangeomorph" is valid, but not all that emphasised in the description of rangeomorphs themselves (indeed, It doesn't even look like Rangea is mentioned) - but that's more another thing to do up in the descriptive section than a problem here.

• "Palæolatitudes", "sedimentary basins" obscure, though not all that awful. "Lifestyles occupied to rise to 30" could use a bit more reference back to the explanation of lifestyles, briefly reminding the reader what that means. Also, spell out numbers.

Sources

Some of the sources have "retreived on" dates, but no links to where they can be retreived. Either give a link, or, if it's through your university, drop the confusing "retreived on" date, which is more for web sources than published works. Adam Cuerden ^talk 20:32, 20 May 2007 (UTC)

Proarticulata?

Is there room in the article for a reference to Mikhail A. Fedonkin's Proarticulata? References on the web are a bit thin, and I can't judge the relative prominence of Proarticulata to other theories/classifications of Ediacaran biota. -- Donald Albury 14:21, 20 May 2007 (UTC)

In my opinion, so long as Fedonkin's theory has been published and peer reviewed, and is not actively getting dismissed as the ravings of a crank, it's likely that it's notable enough to mention. There's not a huge number of prominent scientists dealing with the Ediacaran, and classification and so on is still very much up in the air, so we ought to mention all reasonable interpretations. I'm not quite sure that the commentary on that wikipedia article about chordates is correct, though, but I'll see what I think after I read the paper in full. Adam Cuerden ^talk 15:40, 20 May 2007 (UTC)

Thanks for the link, it should certainly be incorporated - Fedonkin is one of the five big players in the field! Again, I'll do it once I've read the paper! Verisimilus T 16:45, 20 May 2007 (UTC)

The article I linked to in the Proarticulata article only mentions the phylum in passing. More important would be:

• Fedonkin, M. A.. 1985a: Precambrian metazoans: the problems of preservation, systematics and evolution. Philosophical Transactions of the Royal Society, London, vol. B311, p. 27-45.
• Fedonkin, M. A., 1985b: Non-skeletal fauna of the Vendian: promorphological analysis. In, Sokolov, B. S. and Iwanowski, A. B. eds., The Vendian System, vol. I, Paleontology, p. 10-69. Nauka, Moscow (In Russian), and
• Fedonkin, M. A., 1987: Non-skeletal Fauna of the Vendian and Its Place in the Evolution of Metazoans, 175 p. Transactions of the Paleontological Institute, vol. 226. Nauka, Moscow (in Russian)

None of which I have access to. And 1985b and 1987 were published in Russian. Sigh! -- Donald Albury 17:28, 20 May 2007 (UTC)

I *think* I can get 1985a through my university. I'll try tomorrow. Adam Cuerden ^talk 20:35, 20 May 2007 (UTC)

I have to ask

What is the meaning of the edit summary "de-POV ստատէմէնտ" What language is that, anyway? Adam Cuerden ^talk 12:23, 21 May 2007 (UTC)

Tch. The lovely university computers change the input language when you press Shift and Alt without an S or P... so whenever I'm just about to save and realise I've not put in a suitable edit summary, it changes to Armenian! I usually catch myself in time but that one slipped away... Verisimilus T 12:35, 21 May 2007 (UTC)

Minor problem

"although the possibility that it represents the diagenetic infilling of an egg-sac or acritarch has not yet been considered in print"

I know what you're getting at, it's a fair critique, but we probably need to wait for the research to be published (or at least have a researcher's webpage we can link to - if the researcher's notable, as it appears he is, his speculations are worth mentioning. But we can't just bring something up, then promptly say that we can provide no evidence for it - it looks like WP:OR, even if I know, from the old reference, that it's actually an unpublished belief of a notable scientist. Adam Cuerden ^talk 12:29, 21 May 2007 (UTC)

There are reasons for this restriction on Wikipedia, by the way. Sure, you can be trusted, but I don't think everyone can. In days Wikipedia would grind to a halt from the most surprising personal communications... Adam Cuerden ^talk 12:32, 21 May 2007 (UTC)

I've now found it in print (and referenced); Google Scholar didn't flag the article correctly... My faith in science has been restored, I was getting a bit worried that something so blatantly false could go so long unchallenged! Bengtson and Budd to the rescue, thank goodness. Verisimilus T 12:40, 21 May 2007 (UTC)

Excellent! I have to admit I don't know enough about microfossils to really adjudicate on these: Indeed, the terms "diagenetic filling" and "acritarch" are not ones I'm familiar with (we ought to simplify or explain those...) How big are these supposed embryos, anyway? It doesn't actually say. As I said, I'm an undergraduate with an interest - I can point out what seems odd to me, and probably identify POV, but please don't ask my opinion on the grand debates without a lot of time to read up. Adam Cuerden ^talk 12:54, 21 May 2007 (UTC)

Request for new section

Could we have a paragraph or two, fairly early on, perhaps even before most of the current introduction, briefly putting the Ediacaran itself in context? There's references to the Cambrian, Cryogenian, and so on, but we don't actually explainn the Cambrian explosion or snowball earth - we're just presuming people know about them. Adam Cuerden ^talk 18:15, 21 May 2007 (UTC)

Isn't that what hyper-links are for? :-) Seriously, though, that's a good point. Not everybody is willing to jump around in links to find out what a term means. And suitable hyper-links are not always available, as some of the terms used are not well covered in WP, or even in other general interest sources. I recently struggled with making "symmetry of gliding reflection" (as it applies to some Ediacaran fossils) more intelligible to the general readership. -- Donald Albury 11:43, 22 May 2007 (UTC)

Aye, the early geology articles are pretty bad. I had a bit of a go at Cryogenian, but my Geology knowledge is weak, and I didn't get far. I think we basically just need to explain the Cryogenian hyperglacation, and explain the Cambrian explosion that sprung out of the Ediacaran, with a quick overview of the Ediacaran in between. But I don't feel knowledgable enough to write it. Adam Cuerden ^talk 12:34, 22 May 2007 (UTC)

On my to do list. Theoretically, I should be able to do that with my eyes closed. It's probably not going to be that easy...Verisimilus T 12:53, 22 May 2007 (UTC)

Is this edit accurate?

[2] I've tried to simplify language and draw readers in without distorting the information, but there's always the risk of accidental distortions when you're not rock-solid on the material. It still doesn't explain the Cambrian explosion, of course, which still needs fixed.... Adam Cuerden ^talk 13:56, 22 May 2007 (UTC)

Looks great. I'm not too sure about the "bits and pieces" wording but can't think of anything better that's non-technical. Verisimilus T 17:07, 22 May 2007 (UTC)

That paragraph may be too simplistic. Fedonkin, in Precambrian metazoans : the problems of preservation, systematics and evolution, states that the second half of the Vendian (Ediacaran) is greatly impoverished of fossils compared to the first half, and adds that this "suggests a mass extinction of many groups of invertebrates long before the beginning of the Cambrian period." It would be interesting if there are other sources for that. This interpretation would also affect the section on "Disappearance". -- Donald Albury 23:29, 22 May 2007 (UTC)

We can probably leave it a bit simplistic in the introduction, but should *definitely* explain in full by the end of the article.

Also, I've finished revising the introduction, save for the bit on context. I'm afraid the end of the second paragraph gets... very... literary. I just can't help but being saddened by the loss of the Ediacarans, and, under the logic that, so long as it's accurate, engaging the reader can only be a good thing, got a bit literary with the description of their loss. A little information was cut (it appears later), and I simplified everything (again, checking we covered it in more detail, with all proper terminology, later). Check me for accuracy. Adam Cuerden ^talk 00:06, 23 May 2007 (UTC)

Well, I find the whole topic very exciting, but then people do look at me funny. Unforunately, my writing (for WP) tends to be dry, and biology was not one of my majors. I need to find some time to read more and digest the info before I try adding to the article. -- Donald Albury 01:27, 23 May 2007 (UTC)

Regarding the lack of fossils in the second half of the Ediacaran - How sure are you that that's not simply due to sampling bias? It's not something I've heard mentioned at all, and the increasing diversity with time doesn't seem to tie in with it. Verisimilus T 09:14, 23 May 2007 (UTC)

As I indicated, there's the comment by Fedonkin, butI really would like to see what other workers in the field have to say. It does seem odd that there would a blooming of forms, and then a die off with not much new filling in for a while. However, if the second half of the Ediacaran is impoverished of fossils, then the Ediacaran-Cambrian boundary relates only to the widespread appearance of Cambrian forms, and doesn't provide any insight into the fate of the Ediacaran forms. -- Donald Albury 10:42, 23 May 2007 (UTC)

Presumably shelled fossils such as Cloudina and Namacalathus are found in sufficient abundance to infer an extinction. But I agree - it's impossible to tell to what extent this affected the "Ediacarans". Verisimilus T

..I've had another go, but I think there's problems

I've added a context, but I may be muddling it; is it safe to presume the Ediacaran biota were either animal or other, but not plant or fungi? If so, I should be mostly correct, or at least, it will be salvagable when I look it over in the morning. If not, the new first paragraph probably degrades into absolute muddle.

Anyway, I need to look at it again in the morning anyway: I suspect it's not actually that good. Adam Cuerden ^talk 02:39, 23 May 2007 (UTC)

"Plant" would be a misleading irrelevance and should not appear anywhere in a Pre-Cambrian/Cambrian article, where the photosynthesizers were bacterial, single-cell, colonial, or multicellular. They are not "plants.' It is not safe to assume anything about fungi, pro or con: much better to quote some recent articles. --Wetman 07:56, 23 May 2007 (UTC)

Wetman hits the nail on the head there. There are several slight issues with your new introduction, all of which are understandable - I've tried to provide a rationale for my revisions here.

• The extent of the Cryogenian glaciation is disputed; glaciers may not have stretched quite as far as you suggested - the jury is somewhat out. Whilst some still push the idea that the entire Earth was solid (and the Wikipedia perhaps leaves that as the conclusion), in my POV this is very improbable.
• The Cambrian Explosion didn't start at the base of the period - at least, not in the body-fossil record. But the base of the Cambrian (542 million years ago) marked the extinction of Cloudina and Namacalathus, as well as a huge diversification in trace fossil (burrow) diversity and behavioural complexity.
• The "rise of the phyla" argument, which you've implied, is very much Gould's idea — but it's likely that the phyla diverged long before the Cambrian, which is when we first see (or at least recognise) them.
• The Twitya Nimbia discs are probably not Ediacarans - the first proper Ediacarans appear at about 600.
• They probably didn't remain that much the same - the earliest forms are the Avalon-type assemblage, which is restricted to rangeomorphs (charnia etc); motile things (e.g. Dickinsonia, Yorgia, Kimberella) don't appear until later. This may be sampling bias but Occam's razor would suggest otherwise.
• The survivors aren't DEFINITE survivors - they (probably) can't both be Ediacarans and Sea pens, as Simon Conway Morris suggested for Thaumaptilion. He's not quite sure what to make of it any more, I feel (unfortunately, because it would make a great story otherwise) it's more likely to be an early sea pen converging on the Ediacaran form. Reconstructions of their range have a dashed line with a question mark on it after the end of the Ediacaran.
• Spelling out numbers - I think the MOS advocates consistency here, so I've redigitised ninety (and changed it to 60).
• Stem groups/Crown groups - this is an important concept - Kimberella was far more likely to be a stem group mollusc than a crown group one.
• I've tried to avoid brackets.
• Evolutionary path that "Led to us" - ouch. Evolution doesn't "lead" anywhere. Besides, everything else alive today is on a path that didn't lead to us. I think this may give confusing vibes off about how evolution works, so I've rephrased.

However, on the whole, the tone is much more engaging, and it reads a lot better.

And re. your sadness. Maybe they didn't disappear, they just "evolved into" something that's alive today?

But a better tonic is the melancholy serendipity of Ginkgo biloba, which I'm just about to add to its article if it's not already there (I'm sure it will be...)

Verisimilus T 10:15, 23 May 2007 (UTC)

Weel, in my defense, a couple of the problems were me attempting to understand ambiguous wording in the original, but most of that is a completely fair cop. Ah, well, at least between us we can get it right.

I do think that we need to explain Narbonne's theory a bit more: It's probably not immediately apparent what is meant by a "failed experiment". Adam Cuerden ^talk 13:39, 23 May 2007 (UTC)

Of course! Please don't take it as a personal slating, they're common misconceptions shared by a great many! I just intended the list to clarify the errors to avoid them being inadvertently made again.

Re. Narbonne's experiment, your amendment seems to sum it up nicely. Verisimilus T 14:17, 23 May 2007 (UTC)

Aye, no personal insult seen - just glad to be able to cooperate, so if I do mess up, it gets caught. Oh, yes, best warn you: the article on the Cryogenian explicitly says glaciers reaching the equator. It does say the Snowball Earth hypothesis is disputed, but gives the impression the dispute was between "Glaciers reached the equator, but not all parts of the equator" vs. "yes, all parts of the equator". If that isn't right... Adam Cuerden ^talk 14:32, 23 May 2007 (UTC)

Yikes. That article was a mess! There are still those that maintain that glaciers didn't quite reach the equator (at sea level, at least - mountain glaciers don't count) but the main crux of the argument does centre on the two points you make. However, I think it's better to leave an air of "mystery" about it until the doubters are vanquished (or proven right!). Verisimilus T 16:13, 23 May 2007 (UTC)

Aye. I don't think the coverage of any geology before the Ediacaran is very good on Wikipedia. It might be worth thinking of as the next project. Adam Cuerden ^talk 18:36, 23 May 2007 (UTC)

Did a little more revision. I've presumed the Primordial strata was the Cambrian - I may be wrong on this; clarify it as best you may. Adam Cuerden ^talk 11:31, 24 May 2007 (UTC)

Left a few "clarifyme" tags about, with comments as to bits I didn't know enough to speak of. Notably the Charnia paragraph, and the Mistaken Point description.

Sorry!

Sorry to disappear like that: As you may have seen, Evolution just hit FAC, and I wanted to help out a bit there.

Actually, we might be fairly near FAC for this article, if we play it right. Looking it over now, there's only a few minor things:

• "The absence of vertically burrowing infaunal creatures undoubtedly helped" (Preservation section). I've never seen the term "infaunal" before, and I'm a biology major... What... does this mean, exactly? I mean, I know roughly what it means: burrowing activity became much more common in the Cambrian, and, presumably, much of the burrowing in the Ediacaran was... at a shallow angle, maybe? Ah, well. I'm going to leave this one to you. Adam Cuerden ^talk 10:04, 7 June 2007 (UTC)

• "They may appear to migrate upwards when covered by a thin layer of sediment;" followed by "being unable to move" (Microbial mats) - Which is it?

• "muddy or microbial substrate" (Sedimentary setting) - an awkward phrase.

• "Dating is easiest in ash beds, which can readily and precisely dated to the nearest million years or better." - This is by radiometric dating, right? I didn't want to just guess... Adam Cuerden ^talk 10:04, 7 June 2007 (UTC)

No problem. I've had 2 weeks of intensive examination so haven't been too active either! I'll clarify these points in the main text soon (last exam finishes in 3 hours...)

• Infaunal is a term used extensively to describe anything living within the sediment - I'm surprised you haven't come accross it! It's in pretty standard use in our Ecology, Zoology and Geology courses.

• Odd, then. Mind you, given the focuses of the courses I've taken, I could see how I'd miss that term - there's only really one course it could have come up in, and that was a pretty broad-reaching survey of the Metazoa phyla. Edinburgh's policy is to try and get a very broad range in courses, so I've done everything from mathematical modelling of ecology to botany to a survey of the metazoa to parasite biology to mammalian reproduction to microbiology. I have another half-year of the depth courses to go (I missed half of this year to illness), so it'll probably come up in the standard ecology course. Adam Cuerden ^talk 13:07, 7 June 2007 (UTC)

• They *appear* to migrate upwards, as new organisms originate on the new surface.
• Yes, radiometric.

Verisimilus T 12:30, 7 June 2007 (UTC)

I've changed the first to "The absence of burrowing creatures living in the sediments undoubtedly helped;" - is this accurate? I seem to recall there being worm-tracks in the ediacaran, but I'm not sure if these were on the surface or below it. Few other changes, check me for accuracy as always: I don't want to mess this up. Adam Cuerden ^talk 12:31, 8 June 2007 (UTC)

Timeline

Can we do something about the timeline? It's kind of ugly-looking, like the fonts are badly pixelated... Adam Cuerden ^talk 12:08, 8 June 2007 (UTC)

It's difficult to do anything whilst retaining an easily editable wiki syntax - which I feel is vital given the certainty that details'll change significantly as time goes on. Unless I were to write a new "timeline" template.... *lighting up of eyes in slightly manic fashion* Verisimilus T 07:25, 9 June 2007 (UTC)

Heh heh. Oh, dear. Adam Cuerden ^talk 08:02, 9 June 2007 (UTC)

Nama-type assemblage

Did some more editing. I've changed "sandbars in the mouths of a delta's distributaries" to "sandbars in a river delta". This is certainly simpler, but it's not quite as specific. change it back if you think this removes too much information.

The two environments are subtly different - one is marine, one is freshwater. Verisimilus T 16:32, 17 June 2007 (UTC)

Good point. What about "sandbars at the mouth of a river delta"? Adam Cuerden ^talk 17:26, 17 June 2007 (UTC)

Also, there's a citation needed tag in there. Can you get that? Adam Cuerden ^talk 03:43, 17 June 2007 (UTC)

I found a source! Adam Cuerden ^talk 02:48, 18 June 2007 (UTC)

Also, I've tried to clarify the underside/upperside preservation. in "What is preserved?" I think this is right: "The rate of cementation of the overlying substrate, relative to the rate of decomposition of the organism, determines whether the top or bottom surface of an organism is preserved. Most disc-shaped fossils decomposed before the overlying sediment was cemented, and the ash or sand slumped in to fill the void, leaving a cast of the underside of the organism." Adam Cuerden ^talk 03:48, 17 June 2007 (UTC)°

I might have to look into some of Narbonne's stuff to clarify properly. On it. Verisimilus T 16:32, 17 June 2007 (UTC)

I've checked the original: It looks like that's right. "In the simplest case, a bulb seated with the basal protuberance in clay, suffers burial under a layer of sand at least as thick as the exposed height of the bulb. Collapse or decay of a hypothetical upper surface would allow sand to cast the basal impression in the underlying clay" Adam Cuerden ^talk 02:48, 18 June 2007 (UTC)

Lastly, should

"Mark McMenamin goes one step further, and claims that Ediacarans could not be animals because they did not possess an embryonic stage." read "Mark McMenamin goes one step further, and claims that Ediacarans could not be animals because, as far as is known, they did not possess an embryonic stage.

I'm not sure. The claim is based on the assumption that they do not have an embryonic stage; if it's proven that they did, it's invalid. I suppose that the claim is that they don't have an embryonic stage, and the (a?) logical conclusion is that they're not animals. Verisimilus T 16:32, 17 June 2007 (UTC)

Aye. But at the moment, we state their lack of embryonic stages as a fact, is this definitely true, or is it a presumption of McMenamin that we have to mark as such? Adam Cuerden ^talk 17:26, 17 June 2007 (UTC)