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What’s this peculiar skull-thingy?


Venefica1981

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Venefica1981

So, I found this in an area of TN where several marine fossils have turned up (various Gastropoda, trilobites, and more), but this was unearthed at the site of some serious deep water erosion and a small land slide at the banks of a lake. It looks to me like a skull of some sort, where the animal in question perhaps keeled over and laid for a looong time on its right side, hence the “squashing” of that surface. Apart from the somewhat mashed right side, and some chipping to the snout, it’s otherwise perfectly symmetrical. 

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Looks like weathered limestone, which would fit with marine fossils. Do you by any chance know the geologic age of the rock?

I don't really see a skull. For most of the time trilobites existed marine animals with skulls were rare.

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I could see why you would have picked it up. I think I would have too.  I'm not so sure it's a skull but maybe some better photos and a better description of the geology of the area may prove me wrong. 

 

Also Welcome!

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Sorry to say, but I believe this is a suggestively shaped rock as well. :shakehead:

 

Except for a few very small exceptions, most of the rock found in Tennessee is too old to have anything with a skull like this.  Below is a geological map of Tennessee for reference. 

 

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Venefica1981

Ok. I can live with that. The area in question is like 30 mins from the Gray Fossil site, so it seemed a possibility.

 

Out of curiosity, though, what would poorly preserved fossils look like? Such as those in acidic soil conditions? Is there leaching of the calcium, and would that form any kind of calcite projection around the bone? 

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I've never seen or read about 'runny' looking bone fossils. They typically just don't form in acidic soils.

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can we get a sharply focused pic of the surface of one of the white lamina? Could be something like bryozoan weathering out of the limestone.

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7 hours ago, Venefica1981 said:

Ok. I can live with that. The area in question is like 30 mins from the Gray Fossil site, so it seemed a possibility.

 

Out of curiosity, though, what would poorly preserved fossils look like? Such as those in acidic soil conditions? Is there leaching of the calcium, and would that form any kind of calcite projection around the bone? 

By “poorly preserved fossils” I am understanding you to mean fossils that have not stood the test of time. Fossils that have been exposed to the elements, geological processes, and in your example, acidic environments.

 

What they look like when exposed to the above mentioned all depends on how they were initially preserved. If the fossil is a mold or cast and is composed of the same material as the matrix it will weather and degrade the same as the surrounding rock. If the initial organism was replaced with some other mineral, it could degrade differently than the surrounding matrix.

 

Let’s look at your acidic soil example and assume the rock is limestone. Even weak acid will dissolve limestone, being calcium carbonate. Vinegar (a weak acid) will cause it to fizz and bubble fairly quickly. If the fossil itself is a mold or cast and essentially composed of limestone it would react the same as the surrounding matrix. However, let’s say the fossil is actually made of quartz  and the matrix is limestone. The quartz does not react with acid (well not with a weak acid anyway...) So the acid in the soil may dissolve the limestone, but the fossil itself would stay fairly intact. 

 

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8 minutes ago, Plax said:

can we get a sharply focused pic of the surface of one of the white lamina? Could be something like bryozoan weathering out of the limestone.

Agreed. This may be what the OP was basing her questions off of. More pics would help determine if these laminae are fossils or geological mineral layers. 

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Venefica1981

Sorry, I’ve been really busy and haven’t had time to take new pics or otherwise respond. I should have mentioned, in the OP, that I took this item over to a local fossil “expert”, who was certain that it was actually bone material...until I told him where I’d found it, and then he was suddenly dismissive. 

 

Does anyone know, offhand, what the estimated range of the Gray Miocene deposit is thought to be? Like, as in the circumference extending outward from the known sites? I read somewhere that only 1% or so has been explored so far, and I’m not far at all from there.

 

I would guess it’s a matter of layers, with the unexpected discovery of mammal fossils in an area previously only thought to contain marine stuff, no? The Gray site was only found by road excavation, and the uncovering of previously unexplored layers of rock. How often does this happen? It seems that unless publicized discoveries are verified by scientists, that people tend to be highly skeptical about the possibility of certain biological events, to the point of discounting them by the fact of being “unlikely”- although that’s not the same thing as “impossible”. 

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The first thing I would suggest is that you dismiss the local expert.

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Mark Kmiecik
2 hours ago, Venefica1981 said:

Does anyone know, offhand, what the estimated range of the Gray Miocene deposit is thought to be? Like, as in the circumference extending outward from the known sites? I read somewhere that only 1% or so has been explored so far, and I’m not far at all from there.

It's not really a matter of how far out it covers an area; it's a matter of how far down. Places where it is exposed at the surface may be in the few hundred or thousand square meter range. The area below ground that's farther down than you can dig without heavy equipment may be thousands of square miles, all of which contains fossils. The problem is getting to it. USGS (United States Geological Survey) topographical maps of your area will show what is exposed at the surface at any given location. Invaluable tool. Find them online, buy some, they will give you info you can't get anywhere else.

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