Extant Squatina nebulosi (Clouded Angelshark) jaw

[MarcoSr]

Here is a Squatina nebulosi (Clouded Angelshark) jaw that I recently acquired. The jaw is 9.5” wide and 6.25” inches high. I normally take a labial view picture of the jaw but to really see the teeth in this Squatina jaw I took a lingual view picture. Here is the overall jaw:

To better see tooth details double clique the below pictures. If you mouse over the pictures you will see the file name which has additional positional information.

The lower jaw had areas of cartilage that displayed the distinctive prismatic structure pattern:

Squatina nebulosi does not have symphyseal teeth.

Lower jaw symphysis:

However there is an odd tooth in this lower jaw next to the A1.

To distinguish a Squatina anterior tooth from a lateral tooth you need to be able to see the base of the root which is very difficult with the teeth in the jaw. I’m sure the upper A1, A2 and A3 are anterior teeth and the lower a1 and a2 teeth are anterior teeth. I’m not really sure if Squatina have posterior teeth. The last tooth in each row does look like it could be called a posterior. However for now, I’ve called that tooth a lateral.

Here are the upper jaw A1, A2 and A3 teeth left and right side:

Continued in the next reply.

Marco Sr.

Edited January 20, 2016 by MarcoSr

[MarcoSr]

Here are the lower jaw a1 and a2 teeth left and right side:

I’m calling the lower 3^rd and 4^th teeth anteriors. Here are the lower jaw a3 and a4 teeth left and right side:

Continued in the next reply.

Marco Sr.

Edited January 11, 2016 by MarcoSr

[MarcoSr]

Here are the upper jaw lateral teeth left and right side:

Here are the lower jaw lateral teeth left and right side:

Continued in the next reply.

Marco Sr.

Edited January 11, 2016 by MarcoSr

[MarcoSr]

Here are the lower jaw lateral teeth left and right side Continued:

I can see 5 rows of upper teeth.

I can see 5 rows of lower teeth:

The upper jaw has 11 tooth files left and 10 tooth files right of the symphysis

The lower jaw has 10 tooth files left and 10 tooth files right of the symphysis

Unlike a lot of shark genera, Squatina teeth do not show a lot of evident variation. However, to get a complete feel for Squatina nebulosi jaws and teeth you would really need to look at a lot of different jaws from different localities.

Marco Sr.

Edited January 11, 2016 by MarcoSr

[Coco]

Hi,

On your 2nd pic, we call "tissu gingival" in french, perhaps in English "fabric (tissue) of the gum", what you name cartilage. I don't think it is cartilage because it is really very light, little thick, not hard when the shark is alive. This little membrane protects the teeth which are in formation (not still active)

Coco

[MarcoSr]

Hi,

On your 2nd pic, we call "tissu gingival" in french, perhaps in English "fabric (tissue) of the gum", what you name cartilage. I don't think it is cartilage because it is really very light, little thick, not hard when the shark is alive. This little membrane protects the teeth which are in formation (not still active)

Coco

Coco

That is very interesting. It definitely looks like the tissue does protect the forming teeth. What is interesting is that this tissue has the prismatic pattern that I associate with fossil shark cartilage. Do you see that prismatic pattern also in any of your jaws? I find very thin fossilized bits of material that have that same prismatic pattern. So is it this shark membrane fossilized? Can cartilage also be soft tissue like this membrane? Does other shark tissue which is not cartilage have the same prismatic pattern. I now have a lot of questions that I hope a TFF member can answer.

Marco Sr.

[Auspex]

Sounds like a working definition of "cartilage" is in order...

Any anatomists care to weigh in?

[MarcoSr]

I've looked at a lot of different papers on shark cartilage on the web. I did learn some interesting things. Sharks have both calcified and non calcified cartilage.

Everything which follows in quotes comes from KEMP WESTRIN 1979 Ultrastructure of Calcified Cartilage in the Endoskeletal Tesserae of Sharks:

There are three types of calcified cartilage in sharks: "(1) globular calcification, considered to be an early stage of mineralization both ontogenetically and phylogenetically; (2) prismatic or granular calcification, the type which forms the tesserae; and (3) areolar calcification, occurring in the vertebral centra of Euselachii."

"Endoskeletal tesserae (Applegate, '67; Kemp et al., '75; Kemp, '77) or Kallzpluttchen (Roth, '11; Weidenreich, '30; Bargmann, '39; Schmidt, '52) are blocks of calcified tissue which contribute rigidity to the cartilaginous skeleton of elasmobranchs and holocephalans."

So the prismatic calcification is what adds the rigidity to the shark's cartilaginous skeleton. From further reading, this prismatic calcification is a thin layer of calcified cartilage which overlies the non calcified cartilage. The fact that the prismatic calcified cartilage is in thin layers helps explain the thin pieces of fossilized cartilage I find with the prismatic pattern.

Although this is all very interesting to me, it doesn't explain why a thin membrane protecting the forming teeth would display the prismatic pattern.

Marco Sr.

[MarcoSr]

Sounds like a working definition of "cartilage" is in order...

Any anatomists care to weigh in?

I second Chas' call for an anatomist to weigh in.

Marco Sr.

[Auspex]

... it doesn't explain why a thin membrane protecting the forming teeth would display the prismatic pattern.

Bio-Kevlar? It would have to be pretty tough to withstand the cutting edges of that which it is 'protecting'.

[MarcoSr]

Bio-Kevlar? It would have to be pretty tough to withstand the cutting edges of that which it is 'protecting'.

Chas

It makes very logical sense that a really tough membrane would be needed to protect forming teeth and itself from damage from the teeth. I still would like to know if this thin membrane is a calcified form of cartilage. Hopefully a TFF member will know the answer.

Marco Sr.

[Coco]

Hi,

When I prep a selachian jaw, I automatically remove this membrane to see all teeth. I never seen this prismatic calcification on them because it is really solf. This tissue is really thick and solf. I think you see these prismatic forms because this tissue dried, what leaves them visibles.

I will try to see if my fishmonger can give me a head of a little and common shark (Scyliorhinus for example) which I could photograph...

Coco

[MarcoSr]

Coco

This is the only jaw so far that I've seen this prismatic pattern. If you could take pictures of the membrane that would be great. What I really like about TFF is I learn new things all the time, like about this membrane which covers the forming teeth which I didn't know before you posted it.

Marco Sr.

[Auspex]

...I think you see these prismatic forms because this tissue dried, what leaves them visibles...

I wonder whether desiccation is what makes this structure visible? Does un-desiccated shark cartilage from, say, the snout show it?

[Coco]

Hi,

Does un-desiccated shark cartilage from, say, the snout show it?

Can you repeat your question with another way please ? I don't understand very well

Coco

[Auspex]

Hi,

Can you repeat your question with another way please ? I don't understand very well

Coco

Maybe in drying, the structure of cartilage becomes more evident?

[Coco]

Hi,

Ah OK. I never seen these structure because I remove it all the time. I can't reply...

Coco