Re-posting this Indiana limestone in HCL bath producing soft micro-specimens of unknown organisms found floating in the bath(released from limestone!)

[Derk]

I am hoping that by re-posting this thread that someone will know what these are that were released from within the limestone during an HCL bath to dissolve out its internal fossils. I was not expecting to find floating in the acid wash, bits of tiny ancient 'squid-like' organisms that were made delicately soft and squishy as if they were alive earlier that day, and were not encased within a rock millions of years old(but that's where they did come from!).

No one has yet offered any explanation nor information to me about what these could be, and HOW they could be in the limestone, but almost perfectly restored by the HCL back to how they must have been when living, or at least very close to it... They look absolutely like they are freshly died specimens, but they are millions of years old!!

How is this possible Please help me understand, anybody!

Below is some video I recorded with digital microscope and uploaded to youtube showing 2 or 3 of the specimen I collected from the fluid once there was no more reaction dissolving the limestone. You will see how soft the pieces are when I accidentally tear one with the straight pin I used to move the specimen under the microscope. I believe that I placed them on paper towel for the recording.



I am really scratching my head on this one, and would greatly appreciate any wisdom on ANY aspect of this by any Sages of any the Sciences that wouldn't mind imparting onto my barely hobbyist's level of understanding of anything relating to "Rocks."

I'll try to keep this fairly brief, but I want to give all the information I can think of that might help the more knowledgable among us more readily solve the handful of mysteries this created for me. I won't list any here as the title pretty much says it all.

I found this kinda "fin shaped"(with some flat surfaces too) piece of limestone while artifact hunting a local field here in Howard County, Indiana. I only carried it home because I mistakenly thought it might have been worked into some ancient tool of some kind, based on it shape. After cleaning it up, I could see a couple possibly metallic inclusions and wanted to know how large and of what they were so I started rubbing away at the soft limestone around those "metal" bits with a stiff bristle brush.

Progress was fairly steady that way, but I thought I would speed the process up, and at the same time, would be able to rule out typical metals if the inclusions dissolve away with the limestone in a strong acid solution. So I prepared an acid bath and introduced the whole stone, allowing it to soak for a few hours. After a while I could see that it was a fossil's positioning inside the rock that gave it the unique, man-made looking shape, and it was not a stone tool of any kind. So I returned it to the acid bath to see how much more of the fossil(s) I could expose.

When I checked on it later is when I was able to see that there was a lot more of the "metallic" bits exposed, some looking very much like teeth or spikes of some kind, and also visible then was a fairly large(by Indiana fossil standards at least)partially intact, if not fully complete, marine fossil specimen of some kind. There were also various impressions made visible on the parts of the surface that looked like fibers in some areas, and there were spots that looked like scales and imprints looking like modern fish fins to my untrained eyes. The most noticeable features that became exposed in the acid bath would probably have to be the many pockets of, not impressions of, but clusters of delicate but thick fibrous bristles were becoming exposed and would fall away after continued contact time with the acid solution, which eventually prompted me to remove the sample from solution, then rinse and neutralize any residual to preserve what may still be left within the limestone matrix(most likely for later destruction by some other means) for now.

But in the time leading up to that, during my subsequent checkups, I started to notice an increasing amount of debris particles of various size, shape, and structure, floating around in, and on top of the solution. A lot of which looked consistent with being remnants from some of the fibrous and scaley-looking fin-like surfaces that had been exposed.

At some point, I decided to collect a couple samples of this debris so I could see what they looked like under magnification, and take some photos and/or video if interesting. And that is what leads up to here.

I have selected several high-res photos, mostly under magnifications of either roughly 20x or close to 45x both alternately, as well as standard macro-mode pictures and some in standard field format. They will be posted just below the linked video I made, posted right below here. It shows the compiled video clips that I recorded under magnification. First showing clips of the fleshy tentacle bits, then are clips of the magnified portions of the source limestone inclusions prior to most of the acid treatments. Altogether the video is about 9 minutes long, and I apologize for not editing it down to a shorter length but apart from no more than 2 or 3 focusing hiccups, the clips give a good of data and depth, and are arguably worth the time to watch. I leave that up to your discretion.

If you can tell me what th main fossil is, whether there's multiple fossils, what are the squishy bits, and how in the world did they come from fossils in limestone, please do, as I can assure you that I am largely lacking in my level of education on geological sciencerety...

Thank you

 

[Red-Coat]

Very interesting.

The only thing I can suggest is that you are finding various remnant microfossils from squid-like belemnitic cephalopods which would likely be Jurassic in age. Most commonly, these are onchyites and statoliths, but also other chitinous or calcareous structures that survived when the soft body portions of the animal decomposed, leaving them as isolated microfossils. The most common preservation is by replacement with aragonite (which dissolves readily in acid) but they may also be replaced by silica (which is highly resistant to acid).

Unlike modern squid, these animals didn’t have suckers on their ten arms (tentacles), but between 30-50 tiny chitinous hooks for grasping slippery prey, known as onchyites. Chitin often has a fibrous structure. Some examples:

Statoliths were small, dense, calcareous structures found in the balance organs of the head area that helped the animals sense gravity and maintain balance. Some examples:

 

[Derk]

Oh, Wow! Those have got to be what they are. Amazing!
I think there is every one of those shapes from the bottom 2 example pages that were sticking out all over the stone. I was calling them horns, or spikes, or some looked like mandibles and pinchers kinda. Now I will know exactly what those were.

Which begs the only question that still remains a mystery(to me anyway). Is it not so bizarre then to find the soft fleshy body 'casings(?)' both intact and very fleshy/soft/pliable, left behind, and undissolved by the acid reaction?

Maybe this part of it makes more sense than I am giving to it. But that part of the explanation still eludes me. I cannot find ANY instances of that result being mentioned by anyone so far. But it HAS to be a very common occurrence considering how common it must be to have someone submerging hunks of fossil containing limestone in HCL.

I would think that you would see these soft fleshy rehydrated skins of these organisms more often than not when dissolving stones that way. Can anybody find a reference to similar findings that, much like Morels, apparently like to crawl back into the ether whenever I get near... Lol!

And thank you Mr. Red-Coat! You definitely manifest the magic from the mystery! And now I'm set to learn more history.

 

[Red-Coat]

Hi again Derk.

I don't have an explanation for what you are observing but here's a couple of AI-generated answers that I haven't explored in more detail (and bear in mind that AI is a long way from infallible):

Are chitinous fossils made pliable by hydrochloric acid?
Yes, chitinous fossils and organic-walled microfossils can be made pliable and extracted from rock matrices using acids, including hydrochloric acid (HCl).
Extraction Method: Chitin is highly resistant to acid, allowing paleontologists to dissolve the surrounding limestone or carbonate rock matrix (using HCl or acetic acid) without destroying the fossil itself.
Resulting Texture: After the mineral matrix is removed, the remaining organic (chitinous) fossil is often flexible, pliable, and capable of being manipulated, rather than brittle.

Are chitinous fossils rare?
Chitinous fossils are considered relatively rare in the geological record compared to mineralized fossils (like bones or shells), primarily because chitin is a labile organic biopolymer that typically degrades quickly after an organism dies. However, under specific conditions—such as anoxic (oxygen-free) environments—chitin can survive for hundreds of millions of years.
Abundance vs. Preservation: While chitin is the second most abundant naturally occurring polymer on Earth (after cellulose), it is rarely reported in the fossil record because it is easily degraded by bacteria.
Conditions for Survival: Chitin preservation often requires special conditions, such as early cementation of sediment or anoxia, which prevent microbial decay.

 

[Older The Better]

I think red coat covered it but I was thinking the same, I wouldn’t say they are the original creatures complete make up, but a combination of what the fossil was made of and the acid reaction removing and altering all the other stuff. still cool though. I tried to dissolve limestone with acid one time and it just dissolved everything at pretty much the same rate fossils included guess I don’t have the right chemistry around here.