Talk:Small shelly fauna

Comments pasted in from user Talk pages

{{Cambrian explosion calling card }} The following copied here from user Talk pages -- Philcha (talk) 20:18, 31 July 2008 (UTC)

This looks pretty comprehensive now, although I'm certainly no expert. The one criticism I'd make is that it's a little piecemeal. I'm not sure if there's much that can be done about this – the list of different shells is by its nature very bitty. But I do think the structure needs a bit of a look at – I'd put the list later and introduce the concept of skeletonisation, and perhaps their significance, sooner. It doesn't really flow or "tell a story" at the moment. And one other thing – the iron pyrite gastropod is an very interesting aside, but does it really have a place in this article? Perhaps Exoskeleton#Evolution would be a more worthy home. (Oh – you got there first!)

Keep up the good work,

Martin (Smith609 – Talk) 14:01, 31 July 2008 (UTC)

Thanks for the comments, I'll take seriously your proposal that the big ideas should come first in Small shelly fossils. The point of the snail with the pyrite mini-skirt is that it uses a "traditional" material for the usual shell and what's handy for the new-fangled pelmet. Does that not come over clearly enough? -- Philcha (talk) 15:47, 31 July 2008 (UTC)

I'm just not sure it's 100% relevant – maybe it's a flow issue but it strikes be as misplaced. If you want to keep it then don't let me stop you! :Martin (Smith609 – Talk) 16:02, 31 July 2008 (UTC)

I've restructured Small shelly fauna as you suggested. Time to get it promoted? -- Philcha (talk) 17:56, 31 July 2008 (UTC)

I'm taking a more thorough look through now, and think I would like to see the "minerals used" section expanded a little. I guess that's why the mollusc stood out – you've given the reader some good information about a living creature, but very little about the topic of the article. Why would calcite be easier to precipitate than aragonite, and what would cause the regional differences you seem to have inferred? How did the organisms precipitate the minerals in the first place? What are the roles of structural proteins? Martin (Smith609 – Talk) 19:53, 31 July 2008 (UTC)

I'm not sure about the relevance of how variations in ocean chemistry make it easier to precipitate calcite or aragonite. In fact I don't understand why organisms apparently prefer aragonite in favourable chemical situations, or what general principle of evolution it highlights. So in oceano-chemical Philistine mode I simply said sometimes they use this, sometimes that. Can you explain it to this ignoramus in words of 1 syllable?

OTOH to me the snail with the pyrite mini-skirt makes a point about conservatism re existing features versus opportunism re new features. -- Philcha (talk) 20:33, 31 July 2008 (UTC)

Also, I'm curious as to how "non-mineralised tubes" fall under the juristiction of the small shelly fossils? Martin (Smith609 – Talk) 20:07, 31 July 2008 (UTC)

(P.S. done reviewing)

Good question. Bengtson's article was "Small Skeletal Fossils", and "non-mineralised tubes" fall into that category, but probably not into small shellies. It's all the fault of these boring predators that didn't fancy Sinotubulites. I suppose If I delete "non-mineralised tubes" and the description of Sinotubulites I could get away with no further description of Sinotubulites in the bit about boring predators' attacks on Cloudina and their distaste for Sinotubulites. What do you think? -- Philcha (talk) 20:33, 31 July 2008 (UTC)

You could probably do away with the generic name altogether and just say "other organisms" where necessary. Martin (Smith609 – Talk) 19:06, 1 August 2008 (UTC)

Evolutionary significance

I'm still a little concerned that outlining Budd's argument in so much detail risks appearing to conflict with Kimberella - Budd doubts whether any pre-Cambrian critter were triploblastic, mainly on methodological grounds ("parsimony"), while AFAIK no-one has recently explicitly questioned that Kimberella is a genuine triploblastic bilaterian. The origins of triploblastic bilaterians are to complex an issue for Small shelly fauna to go into, e.g. which came first, triploblasts or bilaterians?

I'm also concerned that readers whose mental tool-kits don't already include cladograms will be confused by the notion of different levels of stem group, which Budd's analysis implies. I'll see if I can come up with a suitable annotated image that doesn't occupy half the page. -- Philcha (talk) 12:13, 1 August 2008 (UTC)

Which timeline?

Porter, S.M. (May 2004). "Halkieriids in Middle Cambrian Phosphatic Limestones from Australia". Journal of Paleontology. 78 (3): 574–590. doi:10.1666/0022-3360(2004)078<0574:HIMCPL>2.0.CO;2. Retrieved 2008-08-01. reports 1 new genus plus 2 other unclassified species from Mid-Cambrian rocks of the Georgina Basin in Australia – so a family that produced many SSFs has been found later than the range of the current SSF timeline. I'm beginning to think Small shelly fauna should use the Halkieria timeline, which should then be extended to 585 MYA to include all Ediacara biota). -- Philcha (talk) 15:48, 1 August 2008 (UTC)

Just a guess, but were the sclerites of the post-SSF Halkeriids not preserved as small shellies, due to the closure of the taphonomic window? Hence the animals were still about without appearing as SSFs. Martin (Smith609 – Talk) 19:05, 1 August 2008 (UTC)

It appears the closure of the phospatisation window was protracted and geographically patchy: "Phosphatized fossils occur throughout the Monastery Creek Phosphorite Member" (Porter, 2008) -- Philcha (talk) 12:54, 17 August 2008 (UTC)

What's the link for Porter 2008 again? I can't find it anywhere. Martin (Smith609 – Talk) 13:03, 17 August 2008 (UTC)

It would help if I got the date right - Porter (2004) above, mea culpa. (2008 was on similarity of halkiierid and chancelloriid sclerites) -- Philcha (talk) 13:26, 17 August 2008 (UTC)

Initial Impressions

Just quickly, since I have to get going soon:

1. The lead covers a bit of information (groups, problems with working with SSF) that isn't in the article.

• Info about groups now in "Cambrian forms".
• re problems, "Although most of the SSFs are difficult to identify ..." in section "Evolutionary significance". -- Philcha (talk) 16:49, 27 August 2008 (UTC)

2. Much of the article is written in a list format that looks like it's just a skeleton and could be fleshed out. For example there should be more to say about what it means to have a supportive skeleton beyond just an example of an organism that had one. Parallels to existing fauna (if they exist), especially fauna that your average high-schooler would recognize, would be great.

• I hoped 1st sentence of section "Explanations for development of mineralized hard parts" would cover what it means to have a "skeleton", including a few non-support functions.
• Re "Parallels to existing fauna ..." do you mean specifically with the list of potential benefits? If so, Bengtson (2004) doesn't link the benefits with specific living animals. Otherwise we may have to handle this point case by case - and the results may often be negative, as most of these critters don't fit into extant taxa.-- Philcha (talk) 16:49, 27 August 2008 (UTC)

• Looking at it, it might make sense the "Explanations for development of mineralized hard parts" section into the list instead of making it a separate section. I'm also not really all that clear on exactly what the boundaries of SSF are: is it "organisms from a specific period that have hard parts?" As the article currently states, SSF is not a "does exactly what it says on the tin" description. SDY (talk) 17:08, 27 August 2008 (UTC)

• Incorporate the "Explanations for development of mineralized hard parts" section into which list?
• Theres's fair range of theories about the onset of skeletonization, and I this this is too big to nest inside another section. -- Philcha (talk) 17:50, 27 August 2008 (UTC)

• More or less what I'm proposing is a "here is how we think it works, here is an example of an organism that used it." The list of examples of SSF as it stands is just a list appended to the article. Part of my confusion comes back to the inclusion/exclusion: is the list as it stands comprehensive, or is it just a group of examples? I'm currently reading it as a group of examples, which is possibly just an indication that I'm living up to my username. SDY (talk) 17:58, 27 August 2008 (UTC)

You've already confessed that your username is as much a misnomer as "small shelly fauna". :-)

"The list of examples of SSF as it stands is just a list ..." goes with the territory. The majority have not been identified. Even where there are good grounds for saying "fossils A, B and C all belonged to animal X", it's often unknown how it worked - see for example the account at Halkieria of how Conway Morris got lucky. This not "business-as-usual" paleontology - paleontologists have to be grateful for what little they can get from the Ediacaran and early Cambrian. --

• SSF is not a "does exactly what it says on the tin" description - is more or less what Bengtson says up-front (quoted). The time range was initially defined to be "Cambrian but before earliest trilobite fossils" - the people spoiled it by making new discoveries, e.g.: Cloudina is small and shelly but Late Ediacaran; at the other end, halkieriid sclerites probably belonging to 3 different species have been found in mid-Cambrian rocks (post-Atdabanian) from Oz; and some sessile forms grew up to a meter wide. AFAIK no-one has actually tried to give an up-to-date or even out-of-date formal definition of "small shelly fauna". Guess what kind of tin it is :-) -- Philcha (talk) 18:41, 27 August 2008 (UTC)

• The lack of a formal definition should be prominent in the lead. Why they're considered as a group (i.e. their significance to the Cambrian Explosion) should also be given a bit more prominence there and also in the article itself (i.e. earlier). Given the lack of formal definition, what is Bengston's source of the dates used you're using in the timeline? Giving a sourced example of a popular informal definition would be helpful. SDY (talk) 20:10, 27 August 2008 (UTC)

Sounds like you would agree with Gould’s assessment that the term is "a catchall name that spells frustration" (book Wonderful Life, 1989, quoted by Bengtson).

Why considered as a group - I don't have access to the full text of Matthews and Missarzhevsky (1975), which coined the term, and the abstract doesn't explain.

Re dates:

• The earliest recognised SSF is Cloudina but it's in the Nama Group (548.8 ± 1 to 543.3 ± 1 MYA) and I can add the ref for that (Grotzinger, JP, SA Bowring, BZ Saylor & AJ Kaufman (1995), Biostratigraphic and geochronologic constraints on early animal evolution. Science, 270: 598-604.)
• I cut off the top of SSF bar on the timeline at 518 MYA because that's the date of the Sirius Passet lagerstätte where the only articulated halkieriid specimens were found. Porter (cited at Halkieria doesn't give a date for her "Mid Cambrian" Ozzie halkieriids because Oz is "poorly constrained" (some things never change). I could extend the SSF bar to the top of the timeline to represent "Mid Cambrian", but that might be misleading as most of the SSF were extinct by then, apparently killed in the end-Botomian extinction (Porter, op. cit.) - apart from the doubts about opening and closing of the phosphatic preservational window mentioned in Small shelly fauna.
• Bottom line - pick a plausible end-date and there's probably a ref for it somewhere. I'm not being flippant (if only!).

Re "sourced example of a popular informal definition" - "Neoproterozoic to Early Cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the Yangtze Platform (China)" (Michael Steiner, Guoxiang Li, Yi Qian, Maoyan Zhu and Bernd-Dietrich Erdtmann; Palaeogeography, Palaeoclimatology, Palaeoecology Volume 254, Issues 1-2, 8 October 2007, Pages 67-99; doi:10.1016/j.palaeo.2007.03.046 ) says, "... neither Matthews and Missarzhevsky (1975) nor any later authors have given a definition for the terms “small shelly fossils” or “small skeletal fossils”." -- Philcha (talk) 21:17, 27 August 2008 (UTC)...

Added lack of formal definition as new 2nd para of "History of discovery", with cite quoted above. Preceded by point about diversity. Condensed version of this added to lead. -- Philcha (talk) 09:02, 28 August 2008 (UTC)

3. Some jargon issues, for example "This gives the impression that the first SSF animals, from the late Ediacaran, were basal members of later clades, with the phyla subsequently appearing in a "rapid, but nevertheless resolvable and orderly" fashion, rather than as a "sudden jumble",[21]:163 and thus reveals the true pace of the Cambrian explosion." This sounds like it's quoting someone.

Attempted clarification at User:Philcha/Sandbox/SSFs#Evolutionary_significance. -- Philcha (talk) 17:44, 27 August 2008 (UTC)

Just to clarify, the parts in quotation marks are quotations from the citation quoted immediately after them. I couldn't put the phrasing any better myself. Martin (Smith609 – Talk) 18:56, 27 August 2008 (UTC)

Mostly I'm just trying to figure out if we can turn the language on cladistics into something more accessible to an average reader. The diagrams should help with this. SDY (talk) 20:10, 27 August 2008 (UTC)

Would you like me to put in the sandbox version for now, or would you rather wait and see if further simplification is possible without a mini=-article? -- Philcha (talk) 21:22, 27 August 2008 (UTC)

Is it possible to avoid the terms basal, crown group, etc... and still give an adequate description? If not, I'm wondering why there's a green spot in the diagram and what the strange hieroglyphs are next to crown and stem. "Total" is not really explained: total of what? The diagram is potentially very helpful. I have some quibbles with the language, but it'd be easier to fix them than explain them if we decide to use the paragraph. SDY (talk) 00:41, 28 August 2008 (UTC)

• You know from previous discussions that I share your desire to avoid jargon wherever possible - I (?convergently) coined the term "evolutionary “aunts” or “cousins”" to describe stem groups and have used this anology in several articles. I think this case is exceptional because Budd describes a progression of stem group members and eventually some crown group members. Circumlocutions for the various stem groups, each closer to the crown group than the last, would involve hyphenated "aunts" and "cousins" more obscure than the definitions of "xxx group"; and I think the explanation I've given of crown group is about the most concise circumlocution that can be accurate, but it's still too long to use in mid-sentence. I haven't defined "basal", but I hoped the explanation that it is also a relative term would do the job.
• Teaching the terms "crown group" and "stem group" is also beneficial to the reader because these terms occur more often in paleo journal articles on most metazoan taxa than "phylum", "class" and other Linnean terms - it's simply how paleontologists think these days. I think the basic concepts are simpler than e.g. the obscure anatomical features that one has to refer to in comparing A's and B's theories about the phylogeny of of organism Z - see Halwaxiid for examples; without the features it's just "he said ..., she said...".
• "Total group" is valid but simpler than Budd's "zygotaxon", and simply refers to all animals, extinct or extant, under consideration - but that explanation / circumlocution is too long to fit in the diagram.
• The green and pale blue patches are "plesion" and "scion" respectively. I can't remember seeing these in papers I've read, and simply copied them from Budd. If you like I can upload a version of the diagram without these features.
• I don't understand "strange hieroglyphs ... next to crown and stem" - can you give me a clue, e.g what colours are they? -- Philcha (talk) 04:50, 28 August 2008 (UTC)

• On a different computer now so it displays a little differently. "Group" is wrapping around and overlapping the equal sign. Given the explanation, it does sound simpler to just define it rather than avoid it. SDY (talk) 05:12, 28 August 2008 (UTC)

The screen on the earlier compuiter may have some faulty pixels.

I reproduced the overlap by telling my browser to increase font size 1 step - the annotations are actual text. I've revised the diagram to give more space between annotations and this works if I tell my browser to increase font size by 3 steps - 4th step still causes overlap. What do you think? -- Philcha (talk) 09:25, 28 August 2008 (UTC)

It's clean now. The green and blue should probably become extinct if we aren't going to use them. SDY (talk) 17:42, 28 August 2008 (UTC)

4. Some of the language sounds speculative, such as "This gives the impression that the first SSF animals, from the late Ediacaran, were basal members of later clades." If the reality is that no one currently knows, attribute that admission of lack of knowledge to a source.

The current text summarises Budd's "Rather, the impression rather is of a rapid, but nevertheless resolvable and orderly appearance, starting with the earliest skeletal forms such as Cloudina that are reasonably assignable to a diploblast grade (i.e., stem- or crown-group cnidarians or basal stem-group bilaterians). These are followed by taxa that lie in basal positions within bilaterian clades, and (in general) considerably later by representatives of the crown-groups of phyla." (Budd 2003, p.163) -- Philcha (talk) 17:44, 27 August 2008 (UTC)

Perhaps best to just attribute it, i.e. "a guarded interpretation of the available fossils is that the first SSF from the late Ediacaran were basal members of the later clades. (Budd 2003, p. 163)" Looking for a better word than guarded, but the article should be clear that it's Budd's impression, not Wikipedia's. SDY (talk) 20:10, 27 August 2008 (UTC)

How about this?

Budd (2003) cautiously interpreted this as indicating "a rapid, but nevertheless resolvable and orderly appearance, ..." -- Philcha (talk) 21:26, 27 August 2008 (UTC)

Sounds fine. SDY (talk) 00:41, 28 August 2008 (UTC)

Inserted into sandbox version while we resolve the jargon issue. -- Philcha (talk) 04:57, 28 August 2008 (UTC)

5. A quick and dirty (i.e. two sentences tops) description of how skeletons and shells are formed would be helpful. It's hinted at in some sections of the article, but how modern creatures do it would give useful perspective and contrast.

"two sentences tops" description of how skeletons and shells are formed - wow!

• The cap-shaped shells at the ends of Halkieria were formed by "accretionary growth" (without further explanation. If I understand this, it's addition of material from underneath, which produced growth rings round the edges as the critter and its shell-secreting surfaces grew. AFAIK bivalve shells are similar; that's guesswork, though hopefully refs should be easy enough.
• Halkieria′s sclerites may have grown rather like our teeth, being secreted from fleshy material inside (see diagram there)
• I've seen no suggestions about how the molluscan SSFs like the rather gastropodish Helcionellids grew their shells. Extrapolation from modern gastropods would be very speculative - especially as some Helcionellids have "exhaust pipes" that break the "spiral symmetry" (?? terminology) of the modern gastropod shell.
• IIRC sponges have spicule-secreting cells that move around a bit - I'd have to look it up.
• Don't know about corals yet, but I bet it's different - and there's no guarantee that their process was used by any SSFs.
• That's the end of the simple stuff - see for example Butterfield vs the rest on the sclerites of Wiwaxia (admittedly not an SSF, but it illustrates how complex this can get; details may be moved to Halwaxiid shortly). -- Philcha (talk) 18:10, 27 August 2008 (UTC)

• "It varies widely and the exact mechanisms are not well known" may be the best nutshellesque description to put in. The main challenge for articles like this is explaining that the article is incomplete because no one knows for certain rather than because the article is written vaguely. An "evidence of absence" if you will, rather than "absence of evidence." SDY (talk) 20:10, 27 August 2008 (UTC)

OK as long as I don't have to find a citation for that! I suggest the best place would be at end of section "Minerals used in shells", as that's the only one that goes into any detail about formation of shellies. -- Philcha (talk) 21:31, 27 August 2008 (UTC)

Sounds good. SDY (talk) 05:12, 28 August 2008 (UTC)

Added, with qualification "in most cases" since e.g. quite a lot is known about halkieriid sclerites.

More later, just some things to start with. SDY (talk) 15:59, 27 August 2008 (UTC)

Hi, SDY, nice to see you again.

I'm looking forward to seeing more of your comments. -- Philcha (talk) 16:49, 27 August 2008 (UTC)

Timelines

Bizarrely enough, at home on firefox/vista I see the timeline clearly, but on this computer with IE/2k XP I see strange overlaps. SDY (talk) 17:08, 27 August 2008 (UTC)

I'll call the engineer. -- Philcha (talk) 17:51, 27 August 2008 (UTC)

Which IE, and what specifically is the problem? Looks fine in IE7/Vista. Martin (Smith609 – Talk) 18:04, 27 August 2008 (UTC)

(pasted in by Philcha (talk) 18:13, 27 August 2008 (UTC))

6.0.2900.2180.xpsp_sp2_gdr.070227-2254 is the full version, at 1024x768 resolution. The tag "cambrian explosion" is below the relevant arrow instead of next to it, and it covers up the pink block and the tag for the pink block (Tommotian). SDY (talk) 18:19, 27 August 2008 (UTC)

A line by line review

User:Somedumbyankee/SSF. This is a bit of an experiment on the review process, mostly just my comments on reading through the text. A lot of it is style stuff, some of it is just flagging jargon. Comments are generally marked with triple asterisks ("***") so that the page is searchable.

I'm still a little uneasy with the list and I'd like to find some way to incorporate it into a narrative format or at least make the list "jive" with the narrative a little better.

I'm curious if this is helpful. If not, tell me, because I'll probably be reviewing Opabinia when we get done here. SDY (talk) 17:39, 28 August 2008 (UTC)

Apart from making my eyes blur, I think the experiment has serious disadvantages:

• Strikeouts ambiguous. I hope most mean "this is OK", but some, e.g. "The great majority ..." in section "History of discovery", look like things you dont't like. And where does that leave the bits w/o/ strikeouts.
• Nightmare to maintain if we go through a few rounds of discussion, as we have occasionally.
• Might make a bad impression on a reviewee who doesn't know you well enough.

Of the formats I've seen, the ones used by Wikiproject Chess seem to work best, see e.g. Talk:Alexander_Alekhine#GA_review. Based on this, with a few embellishments, I suggest the review should have the following sections:

• General. Should be as short as possible and only refer to things that occur at many points, e.g. "please use cite templates". Must be specific, e.g. "there are style issues" would be totally unhelpful.
• Article structure, if there serious doubts.
• A section for each section of the article, in that order, using the article's section titles.. One exception: I'd leave the lead until last, in case the content changes noticeably during the review.

Other techniques I like (mainly from chess):

• Use the  Done {{done}} template to make resolved items clear. If an item generates sub-items, as a few of ours have, mark {{done}} from the bottom level upwards. Check out Template:Done, which lists a few related templates you might find useful.
• State up front the rules about who uses {{done}}. At Wikiproject Chess the convention is that the reviewee can use only if it's beyond reasonable doubt. With reviewees you don't know, might be best to insist that only the reviewer can use it.
• If some completely {{done}} sections are really long and make it hard to see what else is outstanding, wrap a hide / show template or table round them, e.g. Template:Hide with the section heading as the caption.
• If the review results in a significant restructure, it might be best to hide all the preceding stuff and start another cycle of "general", "structure", one per section, and "lead".
• Quote wording you're unhappy with. The reviewee can copy and paste into his / browser's "find" facility.

Hope this helps.

If we can reach a good layout in this and Opabinia, should we write a reviewer's guide? -- Philcha (talk) 18:23, 28 August 2008 (UTC)

Helpful to know. I can rehash the thoughts into a "distilled version", but the general points essentially just boiled down to a couple of rambling sentences, a few more bits of jargon, and trying to get full names of the relevant people. SDY (talk) 18:34, 28 August 2008 (UTC)

• re the names of Matthews and Missarzhevsky, S.C. Matthews and V.V. Missarzhevsky are the best I can do. Citations only quote initials, so does the abstract and I don't have access to the full text. No existing Wikipedia articles for a Missarzhevsky, and the Matthews don't match the initials. Hold the press: I Googled for "Matthews Missarzhevsky" and Samuel Crosbie Matthews - publications gives the title of the 1975 paper, so I'm confident that's a match; is it WP:RS enough? Neither "Matthews Missarzhevsky" nor "Missarzhevsky paleontologist" nor "Missarzhevsky obituary" got anything useful for Missarzhevsky (and yes, he's dead).
• Likewise nothing doing for Durham.
• That leaves us with a problem: the "History" section will look odd of some get full nmaes and others don't. As a matter of interest, what's supposed to happen for literature with umpteen authors, which seems to be common for paleo reports from China and for mol phylo articles?

• Bizarre. Probably need dead tree editions for some of these. I'd like to get those names into the article somehow. When there are a billion authors, it's probably best to do some nonjargonish equivalent of et al. such as "a team led by soandso." SDY (talk) 21:15, 28 August 2008 (UTC)

• Re "The great majority of all the features ..." Bengtson says, "Thomas et al. (2000) applied the concept of “skeleton space” (Thomas and Reif, 1993) to an analysis of Cambrian faunas. The “skeleton space” is an array of general characters and character states of animal skeletons, nearly all of which appears to have been filled by animals at one time or another. Thomas et al. found that in the earliest Cambrian (Tommotian Stage of the Lena River) about half and in the Middle Cambrian (Burgess Shale, British Columbia) more than 80% of this “skeleton space” had been utilized."

• Mostly I just had an issue with "great majority" since "majority" should be sufficient. Purely word-wrangling and nothing important. SDY (talk) 21:15, 28 August 2008 (UTC)

• Re "Specimens and sometimes quite rich collections of these fossils were discovered between 1872 and 1967 ...", Bengtson says, "... elements and even rich faunas of this type had been previously reported from early Cambrian beds ..".

• Again, more of a word choice issue rather than a concern about content. SDY (talk) 21:15, 28 August 2008 (UTC)

• Re "In the late 1960s Soviet paleontologists discovered even richer collections of SSFs in beds below and therefore earlier than those containing Cambrian trilobites. Unfortunately the papers that described these discoveries were in Russian, and the 1975 paper by Matthews and Missarzhevsky first brought the SSFs to the serious attention of the non-Russian-reading world" which you've struck out, the Cold War did serious harm to paleontology, see for example Origin_of_birds#Heilmann_and_the_thecodont_hypothesis.
• Re the Gould quote "... frustration ...", perhaps the top of "Evolutionary significance" would be better because the would give contrasting view. Then start the rest, "However Budd (2003) ...".
• Re the theoretical scene (explosive vs long cryptic history), what's wrong with it? That's why people paid attention to the SSFs. Bengtson follows this with a 1976 quote from Steven M. Stanley that appears to endorse the view Gould took of the Cambrian explosion in Wonderul Life.

or am I totally misinterpreting the strike-outs? -- Philcha (talk) 20:45, 28 August 2008 (UTC)

Most of them are just places where I'm quibbling about the wording rather than actual problems with the content. SDY (talk) 21:15, 28 August 2008 (UTC)

Might be best for you to paste them here in bite-size chunks, than we can discuss thme individually, then check the result for consistency, internal linkages, etc. -- Philcha (talk) 21:21, 28 August 2008 (UTC)

The list:

Awkward phrasing or other purely style quirks where I will probably make changes myself rather than try and explain.

• "...more familiar fossils such as trilobites."
• "On the other hand mineralized..."
• "It is still true that the animals used minerals that were most easily accessible."
• "they have the great advantage..."
• "The great majority..."
• "...sometimes quite rich..."
• "trilobites, archaeocyatans, etc."
• "non-Russian-reading"
• "...without requiring that it should have joints."
• "This evidence of selective..."
• "...thus reveals the true pace of the..."
• "These are a really mixed collection."
• "...animals or were inherited from a common ancestor."
• "...although they have been more closely related to halkieriids."

There are also a fair number of sentences that I'd just replace commas with periods and break up a bit, but this is also a style issue.

Random comments-

• arthropods -> arthropods

Done -- Philcha (talk) 22:46, 28 August 2008 (UTC)

• "Small shellies" is used in the article before it is defined as a common nickname. It also isn't listed as a nickname.

changed to "they" in lead. -- Philcha (talk) 22:46, 28 August 2008 (UTC)

• "all-organic skeleton" is listed in the lead. An example would help.

Added "like those of insects" - but the ref (Cohen) doesn't give examples. -- Philcha (talk) 22:46, 28 August 2008 (UTC)

• "Hard to work with" should be more specific (i.e. hard to isolate, hard to recover, hard to identify, etc...)

"makes it difficult to identify and classify them" -- Philcha (talk) 22:46, 28 August 2008 (UTC)

• "Nearly continuous record" doesn't quite line up with the headache of nonspecific definition and the concerns about false absences from the fossil record because of recovery technique problems.

In practice non-specific definition doesn't stop them from being labelled as SSFs. The concerns about false absences from the fossil record because of recovery technique problems apply to periods before and after that in which SSFs are common, so don't raise problem of discontinuities. -- Philcha (talk) 22:46, 28 August 2008 (UTC)

• First names for folks.

Done where possible. -- Philcha (talk) 06:30, 29 August 2008 (UTC)

• "...may therefore be an illusion" should specify why. It's clearer later in the paragraph, so it may just be a shuffling issue.

Had a go at simplifying. And there's a bonus: more recently I found a ref for Mid Cambrian (i.e. later) halkieriid sclerites in Oz. The dates of Ozzie rocks are little vague, a problem we discussed in Kimberella. -- Philcha (talk) 23:33, 28 August 2008 (UTC)

• "...mobility and acute senses..." is listed as if it might be a single item. It should be clear if it is.
• There's an easter egg link to Ontogeny recapitulates phylogeny, which is not something I'm comfortable to just "sneaking in" when it's mostly a discredited explanation for both ontogeny and phylogeny.

Haeckel was too dogmatic and may have "enhanced" his drawings, but a more refined form, "embryos go through stages that resemble embryos of living representatives of successively more recent ancestral stocks" (draw breath) is still regarded as useful - see Recapitulation theory (lead) and, for a recent example, Dinosaur_physiology#The_crocodilian_puzzle. -- Philcha (talk) 23:33, 28 August 2008 (UTC)

• There's a "Cambrian forms" section on the list portion of the article which seems out of place, everything else is classified by anatomy.

It's hierarchical, with "Ediacaran forms" and "Cambrian forms" at the same heading level. "Ediacaran forms" has fewer sub-levels because less diverse. -- Philcha (talk) 23:33, 28 August 2008 (UTC)

Jargon-

• "...selection for size..." (selection in the context of evolution means more than it does in general discussion)

Google agrees.

How about replacing whole sentence with "In addition larger holes appear in larger shells, which suggests that the predators preferred targets of a certain size relative to themsleves" (Hua, H., Pratt, B.R., and Zhang, L-Y. (October 2003). "Borings in Cloudina Shells: Complex Predator-Prey Dynamics in the Terminal Neoproterozoic". Palaios. 18 (4–5): 454–459. doi:10.1669/0883-1351(2003)018<0454:BICSCP>2.0.CO;2. Retrieved 2008-08-29.{{cite journal}}: CS1 maint: multiple names: authors list (link)) -- Philcha (talk) 07:11, 29 August 2008 (UTC)

• "Chancelloriids produced star-shaped composite coelosclerites..." (coelosclerite is defined, but what is a composite coelosclerite?)

The best concise description of the shape is "caltrop", but that's not exactly a common word. How about "Chancelloriids produced star-shaped coelosclerites with a spike projecting from the middle"? -- Philcha (talk) 23:40, 28 August 2008 (UTC)

• "...independently developed phosphatic scleritomes..."

"phosphatic" and "scleritome" are both defined a few sentences earlier. "independently of each other"? -- Philcha (talk) 07:11, 29 August 2008 (UTC)

I think that's a full list, though I may have left out a few of the "break up the long sentence" comments which are style and readability issues and no big deal. SDY (talk) 22:23, 28 August 2008 (UTC)

Outstanding items from earlier

There are a few points from before "A line by line review" that are not fully resolved. Since you should be fast asleep now, this might be a good time for me to pull them together: -- Philcha (talk) 08:44, 29 August 2008 (UTC)

• what it means to have a supportive skeleton - quite a lot there
• Why considered as a group
• Date range for SSF
• Clarification of stem group etc. NB: my sandbox also contains what we agreed re "This gives the impression that the first SSF animals, from the late Ediacaran, were basal members of later clades."
• Timeline display problem
• Simplify stem group diagram?

Stem group image updated. -- Philcha (talk) 09:55, 1 September 2008 (UTC)

Two other points: first names and a cleanup of the list section, which is too verbose for a list and too brief for narrative. SDY (talk) 17:01, 29 August 2008 (UTC)

Re first names, that's all I can find - I even tried Googling for an obituary for V.V. Missarzhevsky (that's how I got Durham), but no joy (I'd have taken Russian and got it translated, but didn't even get that lucky). -- Philcha (talk) 17:28, 29 August 2008 (UTC)

Re lists, have a look at User:Philcha/Sandbox/SSFs#Types_of_small_shelly_fossil. -- Philcha (talk) 17:40, 29 August 2008 (UTC)

Looks better. Some copyediting (Canada, Canada, Canada is a little jarring) but nothing major. Real life is being complicated currently, so I may be a little slow to respond. Most of this is at least polished enough to incorporate into the article. SDY (talk) 17:02, 5 September 2008 (UTC)

I've copied User:Philcha/Sandbox/SSFs#Types_of_small_shelly_fossil into the main article now and made a few tweaks. -- Philcha (talk) 17:20, 5 September 2008 (UTC)

Realities

I'm not going to be able to get into actively doing anything here until at least 09/20 or so, so I'm going to take my name off of as reviewer. If it's still listed when I get back I'll finish it, but there are still some things to work on and I'm not comfortable passing it at this point. SDY (talk) 21:48, 9 September 2008 (UTC)

Another review

On the GAN page this article is not tagged as in review, so I reviewed it. Here is my review. --Una Smith (talk) 16:37, 15 September 2008 (UTC)

•  DoneExplanation of the paleontological meaning of "skeleton" (now at the start of Explanations for development of mineralized hard parts) needs to occur earlier in the article.

I'm not sure about this. I put it where it is because section "Explanations for development of mineralized hard parts" goes into the advantages of "skeletons", some of which do not relate to the popular conception of a jointed assembly. I deliberately avoided the term in the main text until this section, to avoid confusion with "jointed assembly". Before this the term is only used in the lead (3 times; 1st is wikilinked). If the use in the lead is a problem, I'd rather replace the instances in the lead with e.g. "mineralized hard parts". -- Philcha (talk) 18:11, 15 September 2008 (UTC)

Use of "skeleton" in the lead is confusing. How about qualifying it there as "skeleton (any mineralized part)"? --Una Smith (talk) 19:12, 15 September 2008 (UTC)

How about:

Some of the fossils represent the entire skeletons - in other words rigid frameworks - of small organisms, including the mysterious Cloudina and some snail-like molluscs. (2nd para of lead)

"skeleton" is not necessarily mineralized, e.g. insects' chitin-protein exoskeletons. And I don't want to associate "skeleton" too closely with "mineralized parts", as some of the mineralized fragments are not frameworks, e.g. Halkieria's chain mail. -- Philcha (talk) 20:31, 15 September 2008 (UTC)

I see. In this article, "skeleton" has two meanings. One is rigid framework per Skeleton; the other is a much narrower meaning. So the real problem is that in the "Explanations" section the second meaning is used without being flagged as a new meaning. So that's where the fix belongs. I will take a stab at it myself. --Una Smith (talk) 01:42, 16 September 2008 (UTC)

No, that's not quite right either. On editing the article I saw the problem was in part the tangent re joints. I moved that to Skeleton, and made some other edits. Are they acceptable, Philcha? --Una Smith (talk) 02:11, 16 September 2008 (UTC)

It's no so much that "skeleton" has two meanings as that SSFs are so heterogeneous - some are skeletons (e.g. Namacalathus dwelling, various tubes, Helcionellid shell) or parts of skeletons (echinoderm shell fragments), while other are not (e.g. Halkieria "chain mail" of sclerites). Sadly even the academics slide from one to the other, e.g. Bengtson (2004) lists these advantages of skeletons then goes on to talk about various types of armour, without explicitly signalling the switch.

I'm not sure your explanatory sentence was needed, as the section explains later that mineral-organic composites are cheaper and more rigid than all-organic materials.

I think your recent change from "Hard skeletons have a wide range of possible advantages ..." to "A harder skeleton has a wide range of possible advantages" is actually misleading, as it suggests that these advantages are provided only by the harder type. Non-mineralised sleletons have done quite well, from Kimberella to modern insects. I think the section was better as it originally was: first, advantages of skeletons, irrespective of material; then possible reasons for mineralisation. If that logic is not expressed clearly enough, then we should look at ways to make it clearer. -- Philcha (talk) 02:20, 16 September 2008 (UTC)

This discussion shows that the logic is not clear. --Una Smith (talk) 02:59, 16 September 2008 (UTC)

I've started a sub-section "Skeletons" of this review, to save us from indenting all the way to China.

•  Done Merge the Notes and References. Possibly add a paragraph (to the lead) along the lines of "The fossil record of SSF has been the subject of numerous important studies." followed by numerical citation of all sources currently in References.

I found that only Matthews & Missarzhevsky (1975) was already cited. So I: removed it from "References"; retitled "References" to "Further reading"; put all the remaining items into citation template format.

I have reservations about adding a paragraph / sentence to the lead along the lines of "The fossil record of SSF has been the subject of numerous important studies." The truth is that paleontologists' views range from "...frustration..." (Gould, Wonderful Life) to Budd (2003)'s enthusiam. The number of currently active paleontologists who've done serious work on the actual fossils (as opposed to discussing their implications, like Cohen in 2005) is not large. -- Philcha (talk) 18:11, 15 September 2008 (UTC)

So put those sources somewhere else. The point is to use those sources in a more meaningful way than dumping them in a "Recommended reading" section. Such sections are a cop-out, and they tend to accumulate cruft. --Una Smith (talk) 19:12, 15 September 2008 (UTC)

I like your "accumulate cruft", it make me chuckle. However I would not say it's true in absolutely every case. Now for the challenge:

(1) Bengtson, (1992) "The Cap-Shaped Cambrian Fossil Maikhanella and the Relationship Between Coeloscleritophorans and Molluscs" could be used to support an additional sentence at the end of section "Cambrian forms":

Such discoveries may in turn enable paleontologists to make sense of other similar fragments, such as those labelled Maikhanella.^[ref]

(2) Haas (1981) "Evolution of Calcareous Hardparts in Primitive Molluscs" is widely cited but I can't find the paper itself in Google Scholar. Possibly only of historical interest, I would shed no tears over deleting it.

(3) Found Runnegar (1992) "Evolution of the Earliest Animals" at Google books. It looks waffly - the first third is history of ideas about Pre-Cambrian paleo, the next about the Ediacara biota, lost interest beofr ehte final third. Scrap.

(4) Google scholar got me nothing about the content of Valentine (1995), "Late Precambrian bilaterians: Grades and clades", and the title looks very theoretical. Scrap.

If you're happy with proposal 1, we have a deal - the rest of the section is scrapped. Thanks for the challenge, I'll remember it.-- Philcha (talk) 20:19, 15 September 2008 (UTC)

Sounds good, but the article still has the section. Philcha, did you forget to save? --Una Smith (talk) 02:11, 16 September 2008 (UTC)

No, I was waiting for your response. Done now. -- Philcha (talk) 02:28, 16 September 2008 (UTC)

•  Done The article text mixes numerical and Author (year) citation styles, which can confuse the reader. Eg, I tried to find Cohen (2005) in the References. To merge these into a single style, instead of "Bernard Cohen (2005)" at the start of a paragraph and numerical citation at the end, try "Bernard Cohen" followed immediately by the numerical citation.

"Cohen (2005)" could indeed be confusing, so I've removed "(2005)", which was only a comment. Cohen's paper of 2005 is cited at end of para. Otherwise dates are not in parentheses, and I hope it's clear that they're there just to track the history of research. -- Philcha (talk) 18:11, 15 September 2008 (UTC)

Okay. --Una Smith (talk) 19:12, 15 September 2008 (UTC)

Keep in mind Wikipedia:Good article criteria; per my review above, this article falls short of GA only in criterion 1 and only on the three points above. GA is not perfection. Fix those points and I will pass this article to GA. --Una Smith (talk) 16:51, 15 September 2008 (UTC)

Skeletons

First, I think "not necessarily jointed" or similar is necessary for non-specialist readers, as most will be familiar with vertebrate skeletons, some will also be familiar with arthropod exoskeletons, but few will be aware of the generalised "framework" sense in paleo articles.

The logic of the section is meant to be:

• Advantages of skeletons, irrespective of whether mineralised. Asides: some of this segues into "armour" even in academic articles, because this article is all about invertebrates, and invertebrate skeletons are primarily external; I admit the most recent cephalopods (Coleoidea) are an exception, but these are offspring of an ancestral cephalopod stock with external shells.(end of asides)
• Possible reasons for evolution of skeletons and other armour in Late Ediacaran and Early Cambrian.
  • Old theory that they are a way of sequestering excess calcium carbonate. I think Fedonkin's theory should be included here, as it's refinement on the basic idea.
  • This idea has 2 weaknesses: skeletons and armor plates of various materials appear at this time, not just calcium carbonate, and one these materials contains no calcium; it does not explain why excess minerals were incorporated into skeletons (rather than e.g. excreted), as the organic components of the composite materials are relatively expensive.
  • Skeletons and armor plates of various materials appear at this time, and in at least one case armour is gathered rather than organically built. Defence looks a more likely driver. This idea is supported by the increase in burrowing at the same time. The Cloudina / Sinotubulites comparison suggests an evolutionary arms race was in progress.
  • However there are other defensive strategies, so perhaps another explanation should be sought. Mineralised composite skeletons are cheaper and more rigid than all-organic ones. The greater rigidity enabled animals to grow larger and more powerful.

Apart from the misplacement of Fedonkin's explanation, which I intend to re-locate as a variant of the "sequestration" hyptothesis, where do you think the logic becomes unclear? -- Philcha (talk) 03:54, 16 September 2008 (UTC)

The "rigid framework" idea is in the lead of Skeleton, if that helps. The idea is not specifically paleontological, by the way. I am returning to the view that if skeleton needs to be explained in this article then it needs to happen closer to the start of the article. The Explanations section is rather tangled, perhaps because it starts off by explaining "skeleton", skipping over the larger idea of hard parts in general. I don't know exactly how to untangle it, but I do know usually it helps to sleep on it. --Una Smith (talk)

Okay, the explanation section has two main themes (so maybe should be two sections): evolutionary arms race and epoch of unusual preservation (a major problem for taphonomy). Try writing it by stating the theme first, then explaining the reasoning and evidence for it. --Una Smith (talk) 15:06, 16 September 2008 (UTC)

Eh? There's a separate "Mode of preservation" section 2 above "Explanations for development of mineralized hard parts", and as far as I can see "Explanations for development of mineralized hard parts" contians nothing about taphonomy - unless you're interpreting "mineralization" in "Explanations for development of mineralized hard parts". If so, pehaps I should use "biomineralization" throughout except when discussing taphonomy. -- Philcha (talk) 17:42, 16 September 2008 (UTC)

Hm. How about this? You write a topic sentence for the section, then another for each paragraph. Then examine the paragraphs for ideas that are tangential or even not related, and remove those ideas. Consider also introducing the section with a clear explanation of the limits of evidence re the evolution of mineralized hard parts, due to preservational bias (Cambrian having a different chemistry). You are correct, the section does not discuss taphonomy, but it should, to the extent that taphonomy is an important context. Does that make sense? --Una Smith (talk) 14:28, 17 September 2008 (UTC)

There's a revised version at User:Philcha/Sandbox/SSFs#Explanations_for_development_of_biomineralized_hard_parts, and I hope it clarifies the themes in the way you suggest. As part of this I suggest moving the bit about Cloudina and Sinotubulites to section "Evolutionary significance", which is mainly about the contribution of SSFs to understanding the Cambrian explosion. I've also changed all instances (I hope) of "mineralized" to "biomineralized", to distinguish this from the post mortem mineralization that produces / preserves fossils.

I have not mentioned taphonomy in the revised version, because it does not have a bearing on the reasons and mechanisms behind biomineralization - I've seen no such association in the cited sources. Phosphatic preservation was operational from at least 580 million years ago, became wide-spread some time between then and the end of the Ediacaran period 543 million years ago, and remained common until the end of the Early Cambrian, after which it declined rapidly but not uniformly - e.g. Porter's Mid Cambrian halkieriids from Australia were preserved this way. Previous sections comment on how the decline of phosphatic preservation may give a false impression of extinction of the animals that produced SSFs. -- Philcha (talk) 15:34, 17 September 2008 (UTC)

It may seem like a small point, but navigational aids for the reader are important. For example, the section header refers to "biomineralized hard parts" yet the section begins with discussion of skeletons, a subset of the above. See? Either the heading is misleading, or the section lacks some introductory information. --Una Smith (talk) 22:05, 17 September 2008 (UTC)

Re-titling the section "Explanations for development of skeletons and biomineralization" would be more accurate, but rather long. Skeletons and biomineralization appeared at about the same time; most fossil skeletons are biomineralized, but that may be due to preservational factors; some biomineralized parts are not skeletons (frameworks), e.g. halkieriid sclerites. As a result writers sometimes slide between the two ideas.

A new draft User:Philcha/Sandbox/SSFs#Explanations_for_development_of_skeltons_and_biomineralization has the title I've just suggested and distinguishes between skeletons and biomineralization. What do you think? -- Philcha (talk) 10:19, 18 September 2008 (UTC)

I revised that section in your sandbox, expanding the lead paragraph. Here is the diff. How do you like it?

Two big problems jumped at me. "Thus, the fossil record shows that skeletons and biomineralization evolved together" is almost certainly false - they may have evolved at the same time, but there's no evidence for this. "This could be an artifact of the preservational environment, however; skeletons without biomineralization could have evolved first, but left no fossil record" gets into worse trouble:

• Cloudina is the earliest known biomineralised animal - Skeletogenesis and asexual reproduction in the earliest biomineralizing animal Cloudina (2005), which says "The tubular fossil Cloudina is emerging as an important Ediacaran index fossil," i.e. useful for dating fossil beds, which implies it had a fairly narrow time range.
• Proterozoic Modular Biomineralized Metazoan from the Nama Group, Namibia confidently dates Cloudina at 549 million years ago, as there's an overlying volcanic ash be that allows radioactive dating to 548.8 million years ago.
• However Kimberella is similarly dated to 555 to 558 million years ago, and had a cuticular but unmineralised shell - New data on Kimberella, the Vendian mollusc-like organism (White sea region, Russia): palaeoecological and evolutionary implications (2007).

I also think it's a mistake to drag taphonomy into this:

• Phosphatic preservation is known from 580 million years ago onwards (see e.g. Vernanimalcula).
• Typically Ediacara biota are preserved in environments where they are buried quickly by undersea sandstorms - New data on Kimberella, the Vendian mollusc-like organism (White sea region, Russia): palaeoecological and evolutionary implications. If biomineralized animals like Cloudina had been present, they would also have been preserved by such events. They could not have been washed out by acid, because of the lack of phosphatic protection, but their presence would have been noticed.

But I think I see where you're going, and it's a good idea. The source of the difficulties you want to sort out is the combinations of skeleton or not and biomineralized or not. I've produced a new sandbox version at User:Philcha/Sandbox/SSFs#Evolution_of_skeletons_and_biomineralization_v_2. -- Philcha (talk) 08:56, 19 September 2008 (UTC)

Bingo. Put that in the article and I'll close the GA review. Great job! --Una Smith (talk) 20:49, 19 September 2008 (UTC)

Sorry for taking so long to catch on.

Before we hang the flags out, you might want to check the result of moving the bit about predator selectivity to the start of section "Evolutionary significance". -- Philcha (talk) 00:01, 20 September 2008 (UTC)

It reads okay. I could pick several nits with it but that would be beyond the GA target. In fact, much of the article could use some nit picking but there is something to be said for closing this GAN. Technically, the GAN has been open a month, between the other reviewer opening it and me finishing it. I would prefer to finish it. How about you? --Una Smith (talk) 01:09, 20 September 2008 (UTC)

That would be good, as I'm tring to get Paleontology fit for v 0.7, and then a few others -- Philcha (talk) 07:48, 20 September 2008 (UTC)

Current status

GA pass --Una Smith (talk) 14:58, 20 September 2008 (UTC)

Rename this article to correctly "Small shelly fossils"

Real and typical meaning of the term SSF it is Small Shelly Fossils. There is no specifically united "small shelly fauna" what once has appeared and disappeared.

Small Shelly Fossils assemblage(s) = small shelly fauna(s). The Small Shelly Fossils form several small shelly fossils assemblages (small shelly faunas).

SSF=Small Shelly Fossils has priority over SSF=small shelly fauna.

Small skeletal fossils are present in sediments of the whole Phanerozoic, but only in Late Precambrian-Early Cambrian these fossils are dominating and are of great importance to stratigraphy. Therefore the term "Small Shelly Fossils" is used only for Late Precambrian-Early Cambrian.

I consider that it is necessary rename this article: "Small shelly fauna" to correctly "Small shelly fossils".

Aleksey (Alnagov (talk) 12:55, 11 April 2009 (UTC))

Small shelly fossils redirects here. If this article were renamed, Small shelly fauna would have to redir to it - not worth the trouble as only WP editors would notice the difference.

The article mentions that originally the term applied only to fossils of Tommotian Age, but some authors have widened the meaning to incl e.g. Ediacaran Cloudina and some post-Tommotian fossils. --Philcha (talk) 16:54, 11 April 2009 (UTC)

I've seen SSF stand for both. 'Fauna' has a slightly larger scope as it allows speculation on the lifestyles of the animals while they were alive. I can't see a strong case for moving to fossils, especially when 'SS fossils' redirects here. Martin (Smith609 – Talk) 16:00, 12 April 2009 (UTC)

OK. Perhaps it is really senseless. I have reviewed articles about SSF in Russian and there name/phrase "мелкораковенная фауна" (the exact translation from Russian - "small shelly fauna") is used for rich assemblage/complex of small shelly fossils (Nemakit-Daldynian – Early Botomian -- less for Botomian-Toyonian for the objective reasons). In articles in Russian the English abbreviation "SSF" is often used but only as "small shelly fossils" for fossils (Early Cambrian -- for classical Early Cambrian small shelly fossils from Early Cambrian,…). Aleksey (Alnagov (talk) 18:54, 12 April 2009 (UTC))

Megabias

I reverted your paragraph about megabias as sections "Occurrence" and "Mode of preservation" already describes the unexpectedly late halkieriids from Australia, using citations by Porter and a couple of other authorities. --Philcha (talk) 19:08, 14 October 2010 (UTC)

Question

What's the relationship (if there is one) between the small shelly fauna and the Ediacara biota? —Preceding unsigned comment added by 71.142.240.36 (talk) 11:35, 13 December 2010 (UTC)

The terms Small shelly fauna and Ediacara biota are both ambiguous. See the timeline at Ediacaran period.

Most of the "Ediacara biota" fossils come from the range 555MA to 542MA and include animals that look like possible ancestors of Cambrian animals (Kimberella was a bilaterian and possibly a mollusc; Arkarua may have been an echinoderm; etc.), some possible animals with "symmetry of gliding reflection" (for example Yorgia) and some organisms whose classification is unclear.

Most of the fossils of the small shelly fauna come from the Tommotian stage of the Cambrian, but Bengston included in "SSF" Ediacaran fossils like Cloudina and post-Tommotian fossils like Microdictyon from the Maotianshan shales lagerstätte - but Microdictyon is now regarded as an "armoured worm". On the other hand some small shelly fauna fossils are easily diagnosed, for example Helcionellids was snail-like molluscs.

Confusing, isn't it? --Philcha (talk) 22:25, 15 December 2010 (UTC)