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Over the last few weeks I have been preparing a nice xenacanth skull. Will continue to post updates as I go, but here it is so far!

 

The nodule was huge, so we started off by removing a small chunk to see if there was anything in the cross section. It was up a fairly steep embankment, so after we rolled it down I inspected it for any signs of fossils.

 

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Surprisingly, it had something in it! The nodules from this horizon are usually empty. It is hard to see in the photo, but it was clearly the cross section of a xenacanth skull. The distinctive bubbly texture of cartilage and weird looking teeth ruled out any of the other fish from this site. 

 

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Our car was already full by this point, so we decided to leave the rest of the nodule and take the smaller chunk to prepare and see if it was worth going back for more. After preparing this piece, it became clear that it was a nicely articulated (but slightly squished) skull! The nodules from this site tend to be shocking to extract and prepare since they splinter into pieces right through the fossils, but this one was surprisingly solid and nice to work on. The matrix was still incredibly hard, but good separation between the fossil and matrix made it much easier to air scribe than most others I've worked on from here. 

 

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After our success on the first chunk, we decided we needed the rest! It was too heavy for one (or even two) people to lift, se we had to slide it up to the work bench on a trolley.

 

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Here it is after bulk matrix removal with the angle grinder, plus some air scribe work.

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Some more work over the last couple of days

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And here it is currently! Still lots more to do, but it is coming out well. A pleasant surprise considering how terrible some other things from here have been to prepare. The nodule is incomplete, so we only have the skull and some vertebrae, but hopefully there is enough for some pectoral fins to fit in there somewhere. Time will tell!

 

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Amazing find!
 

:yay-smiley-1:

I had to look up Xenacanths as we don’t get them here. Amazing to find a skull with teeth! Will you use acid or air abrasion to finish off close to the bone or do scribes work well in this rock?

 

Im following this thread that’s for sure! 

 

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2 minutes ago, Doctor Mud said:

Amazing find!
 

:yay-smiley-1:

I had to look up Xenacanths as we don’t get them here. Amazing to find a skull with teeth! Will you use acid or air abrasion to finish off close to the bone or do scribes work well in this rock?

 

Im following this thread that’s for sure! 

 

Thank you!!

 

Scribes are the only way I can think to prepare this stuff. Air abrasion would be too harsh for the fossil. When scribing, the rock doesn't seperate cleanly from the fossil, it takes a bit of the surface with it, so not much more can be done to clean it further. A fresh coat of paraloid at the end will make it look nicer too, a lot of the white stuff is just dust!

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Excellent find and prep work.  Thanks for showing us.  I also had to look up Xenacanth.  

 

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Thank you all!! :)

 

Unfortunately a fish has appeared right where I want to scribe down, I can't bring myself to destroy it yet... would be nice to leave it but the rest of the xenacanth neurocranium might be more important. 

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Incredible can't wait to see how this turns out! I also had to look up xenacanth, such a cool find!

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Amazing find!  Teeth, spines and random fragments of cartilage are the only xenacanthid remains I have ever found. Cant wait to see your finish of the prep. 

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"There is no shortage of fossils. There is only a shortage of paleontologists to study them." - Larry Martin

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Some progress from today. The right side is coming out well, but I'm not sure how much of the meckel's cartilage can be exposed as it seems to dive underneath the palatoquadrate. The matrix is extremely hard so it takes a long time to remove!

 

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12 minutes ago, izak_ said:

Some progress from today. The right side is coming out well, but I'm not sure how much of the meckel's cartilage can be exposed as it seems to dive underneath the palatoquadrate. The matrix is extremely hard so it takes a long time to remove!

Looking great! The skull is emerging! Are the teeth in situ. Boy what a wonderful piece. So is the skull preserved cartilage? 
 

You can tell that rock is hard by the way it fractures and scribes. I know what slow going hard rock prep can be!

 

loving it.

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3 minutes ago, Doctor Mud said:

Looking great! The skull is emerging! Are the teeth in situ. Boy what a wonderful piece. So is the skull preserved cartilage? 
 

You can tell that rock is hard by the way it fractures and scribes. I know what slow going hard rock prep can be!

 

loving it.

 

Thank you! I'm glad you're enjoying :) 

 

From the cross section it seemed there were teeth still in situ, but they might be too deep to prep out. I will try to expose some at the end though! The main issue with this stuff is how fragile the actual fossil is, the rock is so hard that the only way it separates from the fossil is through it. This results in a tiny layer being removed from all of the cartilage, not an issue for larger elements but it can make it very tricky to prepare tiny teeth. Air abrasion would be wonderful but probably wouldn't work because it would simply blow the fossil right off the rock... an acid would be ideal, but I can't think of any that would work on this matrix. Thyoglicolic acid could be worth experimenting with but I doubt the iron content of the rock would be high enough for it to work. Nodules from higher horizons seem to be purely siderite, but this nodule appears much higher in silica (more of a chert?). It is super easy to accidentally blow pieces of cartilage off while removing matrix, but it seems easy enough to repair by mixing powdered cartilage scraped off the counterparts with paraloid and filling the gaps. 

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Interesting - so it’s not something that reacts to acetic acid. 

I have some concretions like that and I haven’t tried prepping them yet for the very challenges you have mentioned. Hard rock, thin delicate bones. 


Whatever you are doing is working from where I’m sitting!! 
 

I see what you mean about the teeth. You have already excavated the mouth and would have to go deeper to reach them. 

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2 hours ago, izak_ said:

Some progress from today. The right side is coming out well, but I'm not sure how much of the meckel's cartilage can be exposed as it seems to dive underneath the palatoquadrate.

 

You certainly do know your fish anatomy. I had to google those terms to see what you're talking about. What happened to that extra fish?

 

Greetings from the Lake of Constance. Roger

http://www.steinkern.de/

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2 minutes ago, Ludwigia said:

 

You certainly do know your fish anatomy. I had to google those terms to see what you're talking about. What happened to that extra fish?

I didn't before I started this project! I was just referring to the parts as lower jaw, maxilla, etc but it seems a whole different set of terminology is used on sharks. The extra fish is safe, it isn't in the way as much as I thought. 

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Very cool! Congrats on the awesome find and thanks for taking us along in your prep journey. It’s coming along to nicely! :b_wdremel:

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The good thing about science is that it's true whether or not you believe in it.  -Neil deGrasse Tyson

 

Everyone you will ever meet knows something you don't. -Bill Nye (The Science Guy)

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This is a very dope skull. What age is this material?

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54 minutes ago, NickG said:

This is a very dope skull. What age is this material?

Thank you! It is middle Triassic. 

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Amazing as usual :) 

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The jaws are very well articulated on this side so far! The orbit can be seen just to the right of the crack.

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:default_clap2:
 

Looking great! Having the orbits exposed really steps it up a notch!

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I just saw this now and I am quite amazed, I am following this for sure!

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Dipleurawhisperer5.jpg          MOTM.png.61350469b02f439fd4d5d77c2c69da85.png

I like Trilo-butts and I cannot lie.

 

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Starting with exposing some of the details on the right side. My finer airscribe broke today so won't be able to do much more precision work for a few weeks!

 

Before and after:

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I hope you’re able to expose some teeth. It’ll be interesting in case this happens to not be what you think it is.

 

What other fossil shark teeth are known from the geological unit this came from?

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6 minutes ago, NickG said:

I hope you’re able to expose some teeth. It’ll be interesting in case this happens to not be what you think it is.

 

What other fossil shark teeth are known from the geological unit this came from?

 

This time it's definitely a xenacanth (I swear!), there have been lots of loose teeth in the surrounding matrix. I'm not sure if I'll be able to expose teeth in the jaw itself due to how they're positioned and how the rock prepares, but fingers crossed! Shark teeth themselves aren't common in this formation and are always found with body fossils like this one. They are mostly found as complete skeletons (sometimes slightly disarticulated) within nodules. So far only the one species of xenacanth and one species of hybodont is known, but who knows what else will turn up! 

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