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MeargleSchmeargl

Floyd County Cambrian: Any clues?

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MeargleSchmeargl

As you are all probably aware, I have been to the Chatsworth Conasauga exposure multiple times, and have gotten some stellar stuff from the formation. Recently, I have been seeing a lot about another exposure of the Conasauga in Floyd County near Rome somewhere along the Coosa river that produces a different trilo species (Elrathria Antiquata), as well as a species of primitive sponge, Brooksella (which I have yet to get, or any sponge material for that matter). Any tips on Floyd's Conasauga material? :D

 

Brooksella, my primary interest:

post-4301-0-60657800-1384225207.thumb.jpg.048ff7f2dbb4c1a9edb33fb37acce44b.jpg

 

 

 

Elrathria antiquata, another objective:

IMG1.jpg.577d94f564244c61c85278dfa1437152.jpg.9f4325f8a58371c0b7f696c2a5793c13.jpg

 

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Tidgy's Dad
13 hours ago, MeargleSchmeargl said:

As you are all probably aware, I have been to the Chatsworth Conasauga exposure multiple times, and have gotten some stellar stuff from the formation. Recently, I have been seeing a lot about another exposure of the Conasauga in Floyd County near Rome somewhere along the Coosa river that produces a different trilo species (Elrathria Antiquata), as well as a species of primitive sponge, Brooksella (which I have yet to get, or any sponge material for that matter). Any tips on Floyd's Conasauga material? :D

 

Brooksella, my primary interest:

 

 

Elrathria antiquata, another objective:

 

I presume you've read Doctor Schwimmer's paper on 'The Exceptional Preservation" of fossils from this site? 

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Tidgy's Dad
11 minutes ago, Spongy Joe said:

Ah, Brooksella... alas, it's about to get booted out of everyone's fossil collections again!

https://gsa.confex.com/gsa/2016AM/webprogram/Paper279168.html

 

It's a strange thing, and there's still no explanation, really. If it's a concretion, why doesn't it turn up more widely? If it's some sort of fossil, why doesn't it have any consistent morphology, or indeed any diagnostic features of a particular group? I've never been happy with it being a sponge, though, and there's really no evidence in favour. Since this is a new locality, though, it's possibly that the diagenesis or taphonomy was a little different, and it preserves some slightly different details. Any chance of getting one cut and polished to see the interior?

Boooooo! 

What a shame. :(

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WhodamanHD
9 minutes ago, Spongy Joe said:

any consistent morphology

I’m not expert in the area, but to my untrained eye, this seems like a soft bodied critter. It reminds me of certain medusazua. Then again, that’s probably to the scientists to determine.

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Spongy Joe
5 minutes ago, WhodamanHD said:

I’m not expert in the area, but to my untrained eye, this seems like a soft bodied critter. It reminds me of certain medusazua. Then again, that’s probably to the scientists to determine.

The problem is the symmetry: the number of lobes, relative size of them, and so on. Look at a medusozoan, and you'll find it's tetraradially symmetric, with only superficial variations on a theme, because the basic symmetry is defined genetically and can't be easily altered. Admittedly there are a few animals that manage some randomness (sun stars, for example, and some sponges), or even complete blobbiness (placozoans), but normally consistent symmetry is there. Then there's the problem of the compound one to the right side of the pic: that just doesn't look right...

 

Concretion, based around a trace fossil? That I could believe. Seilacher was a wonderful eccentric, but he really did know his traces.

 

Piranha: yes, sorry - I spotted that after posting. It needed repeating here, anyway. :-)

 

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Tidgy's Dad

Hooorrrrrrraaaaaayyyyyy!!!!!!!!!!!!!

Ichnofossil is much better than concretion. :)

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Wrangellian

If it's a concretion, it's a weird one! I've never seen any like that anywhere else.

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Ludwigia

I also wanted to ask if anyone knows of other sites around the world that produce such forms?

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doushantuo

posting something hopefully/potentially useful here(Ciampaglio et al/2006):

tra53l.jpg

 

Richter's(contra Kinkelin's* interpretation) "Pleurodictyum" interpretation(PZ/1925)

 

tra53l.jpg

 

*Kinkelin(Devonian Orthoceras-shale/Germany):

 

tra53l.jpg

so: a "medusoid(coelenterate)"

 

Gamez et al(Geobios,2006--///CAMBRIAN,Pedroche Fm)

Specimens do NOT overlap,suggesting phobotaxis)

Not suggesting any taxonomic affinity,BTW

 

tra53l.jpg

 

trilobites&Brooksella

Conasauga spicules:

 

tra53l.jpg

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WhodamanHD
7 hours ago, Spongy Joe said:

The problem is the symmetry: the number of lobes, relative size of them, and so on. Look at a medusozoan, and you'll find it's tetraradially symmetric, with only superficial variations on a theme, because the basic symmetry is defined genetically and can't be easily altered. Admittedly there are a few animals that manage some randomness (sun stars, for example, and some sponges), or even complete blobbiness (placozoans), but normally consistent symmetry is there. Then there's the problem of the compound one to the right side of the pic: that just doesn't look right...

I just thought maybe it drecomposed in strange ways after death, thought I guess that would be more uniform. Anyway, trace fossil makes sense. Reminds me of those ones that people mistake for crinoid holdfasts (I forget what they call them)

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Spongy Joe

Thanks for adding those links, Doushantuo! B)

 

I'm going to try to be restrained here. Schwimmer & Montante's work on the Conasauga stuff doesn't fill me with a warm, fuzzy feeling. The last link, to the presentation, is actually pretty informative... but not in the way he might like. Trying to call those little spherical 'sponges' Eiffelia globosa shows a substantial failure of understanding as regards what Eiffelia is actually like, irrespective of interpretations. The one with 'possible surface expression of spicules' can only work if it had completely different spicules (and arrangement) to Eiffelia, for example. You can't recognise Eiffelia globosa purely on the basis of globosity. It just ain't so!

    Some of the other bits are dodgy too (that "arthropod appendage"... hmm...), but the sponges take the biscuit entirely.

 

The 'spicule' evidence is also really unconvincing. The main problem is that it's very easy to see cross-shaped structures, or even just lines, and say you've found spicules. One of the classics were the ones described by none other than Martin Brasier (et al., 1997, image below) that held the record as the earliest reliable Precambrian sponge remains... before they turned out to be arsenopyrite crystals when re-examined twenty years later. Don't believe that there are spicules just because someone claims it and shows a low-res image... 

 

And this, of course, is why Brooksella is still such a delicious controversy, all those years after it was first discovered. It probably is a concretion growing around a trace fossil, but the waters have been so muddied by other claims that nobody's sure of anything any more! :oyh:

 

pseudospicules.jpg

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doushantuo

I can recommend Uriz's work on spicules,BTW..

wholeheartedly

BTW,what do you know of Eiffelia,anyway?:ninja:

nudge,wink

 

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Spongy Joe

Eiffelia? Absolutely nuffink, guv. But I can bluff with the best of 'em! :P

 

Maria Uriz's stuff, though... yeah, that's really very good. Sally Leys as well - definitely worth reading taking seriously.

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doushantuo

minor threadjack:it seems this is the largest known spicule!

tra53l.jpg

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MeargleSchmeargl

Then what on Earth is Brooksella, seeing scientists can't make up their minds?

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doushantuo

Science is an ongoing process.......

 

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Spongy Joe

Ooh, Monorhaphis... that's a pretty big threadjack, Doushantuo, but always worthwhile! :D

 

After all, that is the longest-lived organism yet discovered (although it's probably beaten by some other deep-sea sponges that are much harder to age). Eleven thousand years isn't bad, really - twice as old as bristlecone pines.

 

https://www.researchgate.net/publication/256681133_Siliceous_deep-sea_sponge_Monorhaphis_chuni_A_potential_paleoclimate_archive_in_ancient_animals

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FossilDAWG

I've been working with Sally Walker and her students on the Brooksella question.  A paper will be forthcoming eventually.

 

I collected a specimen of Brooksella that has a complete trilobite embedded in one of the "lobes".  If I subscribed to the same thought process that led to Brooksella being declared a hexactinellid sponge, then I would have to say Brooksella is a trilobite, which it obviously is not.  Clearly it is a trace fossil in which the radial feeding traces nucleated concretion formation, which grew to incorporate surrounding sediment and whatever organic remains (spicules or trilobites) happened to be in that sediment close to the feeding trace.  Seilacher's description seems reasonable to me.  Also they underwent a complex geochemical history; the concretions were originally carbonate but they were later replaced by silica.

 

Don

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piranha
9 minutes ago, FossilDAWG said:

...I may try to have a CT scan done to see if we can image the trilobite inside the Brooksella...

 

 

th_detective.gif   mail?url=http%3A%2F%2Fmail.yimg.com%2Fok%2Fu%2Fassets%2Fimg%2Femoticons%2Femo57.gif&t=1526088763&ymreqid=2b37d289-e028-403a-1c09-a1000201e400&sig=rvrlLtlrx_NiHubfnmAiBA--~C :popcorn:

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MeargleSchmeargl

>Starts with a site search near Rome.

>Ends with discussion on what on Earth Brooksella is.

 

 

 

I think this can be called a good day. :D

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Spongy Joe
5 hours ago, David Schwimmer said:

Hello:

 

I see a number of discussions about the ID of Brooksella, and a figure from one of my papers.  I think a fairly simple answer to many of the questions is that "Brooksella" is not a unitary thing.  I have seen literal hundreds in the field and examined thousands, and I noted a lot of variability, including many in situ aligned with sedimentary bedding.  We have sectioned many of them and observed inclusions and sedimentary bedding parallel to the enclosing strata in many, suggesting they were simply silica cemented sedimentary structures.  Some also contain trilobite fragments.  I suspect the specimen with a complete trilobite on it was simply some sticky substrate which hardened into the stricture.  It would be interesting to know if the trilobite was complete (i.e. dead) or a molt.

   Many are clearly sponges, given the presence of symmetrical oscula on the lobes.  I am not sure the argument that they are hexactiellids is definitive: they could also be siliceous demosponges. I was originally considering Seilacher's argument for trace fossil affinity for some of them, but we have collected "Brooksella" with both negative and positive structures: that is, a 5-pointed mold rather than a cast: I'm not sure how you get that by filing a trace.  I have also worked for decades in the Conasauga and never found traces in the shales enclosing the "Brooksellas" other than tubular and branched shapes.  One would think a few unhardened lobed traces might be seen if they were feeding structures. 

  One more point: one comment was why scientists can't make up their minds about this.  The answer is that science is the process of searching for information, not the data itself. Complicated questions are often open ended, like this discussion.  Identifying "Brooksella" definitively has some open ends, so it still counts as science. If we ever establish precisely and definitively what something is, it becomes a fact to use for additional science, but is no longer science.

 

Cheers.

Hi David! Good to see you here! :D

    Sorry, but I'm going to have to take issue with the statement bolded. If they had oscula, then yes, they're sponges -  by definition, because oscula are a particular morphological feature of sponges. Unfortunately, what they have (in some cases - see below image from the link above), seems to be small rounded protuberances on the lobe apices. I cannot see how these can possibly be called oscula. In this example, the left-hand one is broken off, but the right-hand shows the continuous surface. If it were, you'd see a rounded gap in the body wall, where it just stops and allows continuity between interior and exterior. There's no osculum here, in my view.

 

   So, what else have we got? Internally, these are sediment-filled, with occasional fractures, tubular voids (burrows?), inclusions etc. Some of these features look vaguely like spicules, but I've not seen any evidence suggesting that they really are anything of the sort. There are bigger problems for a sponge interpretation, though: where is the skeleton? There is a clear surface, and yet the spicules are entirely lost, and the interior filled with sediment? Even if the spicules were dissolved, where is the mould of the skeletal wall that held the form open long enough for it to be infilled? In siliceous concretions (for example at Llandegley Rocks, in flints, and in cherts generally), sponges are preserved with some degradation of the skeleton, but to lose all trace of it..? Nah, that just doesn't work. Not and still have a fossil with a definite shape at the end of it. In order for this to be a body fossil, there must be some skeletal structure maintaining the wall long enough to preserve it. Are there any sponge spicules at all in the surrounding sediment, by the way? If so, it tells you how they should have been preserved, had they been there in the fossil.

 

    Furthermore, how did the sediment get inside to completely fill the interior? The 'oscula' were open holes, and there's no trace of sponge skeletal texture on the surface of the bodies - so it would have to have been formed in its entirety before compression, and before sufficient decay to reveal the skeleton beneath the surface soft tissue - and yet still, in every case, have been completely filled by sediment internally, with no sign of any visible opening to the exterior.

 

    So, we have no features of sponges, and we do have features (lots of them) that appear to preclude sponges. Ergo, these quite simply ain't sponges, IMO. If you have any evidence that really does point spongewards, though, I'd really love to see it!

 

Finally, I'm uneasy believing that we have a morphological continuum of 'weird things', abundant in a couple of places, but virtually unknown anywhere else, and ascribing multiple, very different origins to them rather than trying to find a single formation mechanism that covers it all. I'm not a great fan of Occam, but he really wouldn't like that.

 

 

Brooksella.jpg

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