Dermal denticle dilemma

[digit]

18 minutes ago, Rockwood said:

But if all that appear to be clusters were fused like this the fish would be unable to move its tail.

 

These dermal dentices are not solely located on the tail--nor even the midline.

 

 

In stingrays the tail spine is simply a highly modified dermal denticle but they can appear in various regions all across the dorsal surface of the ray. They often do occur fused in clusters as with the object in question. Here is an example from Florida and a close inspection will show the small denticle toward the upper left side of the cluster is running counter current to the larger pair on the right side.

 

 

I've got contacts in the (extant) chondrichthyan research world and will see if this is a frequently observed thing or an odd mutation.

 

 

Cheers.

 

-Ken

 

[cck]

Thanks Ken! Exactly what I was wondering! I knew someone else had seen this… 

[digit]

All of my fused ray dermal denticles have been oriented and it is funny that the one I had closest at hand (a cluster of several) happened to show one of the reverse polarity.

 

I've dropped some imagery to my contact at the Shark Research Center and we'll see how quickly I get a reply given the holiday season toward the end of the year.

 

 

Cheers.

 

-Ken

[cck]

A few more shots of articulated clusters from a friend .. 

[Mahnmut]

Ok,

so now we know a lot more: while many denticles are solo players, clusters are normal for at least some locations of many species, and clusters containing "non-matching" orientations are not unheard of.

So it seems to me the only question remaining is if they are the norm for the species or some kind of rare abberrant form or pathology.

Looking forward to reading from Digits Contacts.

 

Best Regards,

J

[digit]

Just heard back from Gavin Naylor at the Florida program for Shark Research:

 

I believe this to be atypical. This said, denticles show tremendous variation across different parts of the body and can change from one form to another over a short section of skin. Also, remember that denticles (and teeth!) often flip their orientation as a response to injury. It is possible this individual may have sustained an injury in this area.

 

 

 

Cheers.

 

-Ken

[cck]

Thanks Ken.. and thanks to all for the discussion. Happy holidays!

[digit]

Always fun when an unusual fossil spurs discussion.

 

 

 

Cheers.

 

-Ken

[jpc]

I learned something today.  Thanks, y'all.

 

[digit]

9 minutes ago, jpc said:

I learned something today.  Thanks, y'all.

 

Me too. I like days like that.

 

 

 

Cheers.

 

-Ken

[Meganeura]

On 12/19/2022 at 8:55 AM, digit said:

Just heard back from Gavin Naylor at the Florida program for Shark Research:

 

I believe this to be atypical. This said, denticles show tremendous variation across different parts of the body and can change from one form to another over a short section of skin. Also, remember that denticles (and teeth!) often flip their orientation as a response to injury. It is possible this individual may have sustained an injury in this area.

 

 

 

Cheers.

 

-Ken

Wait - they flip their orientation? Teeth too? Does that mean you can technically find a fossil Ray mouth plate that’s shaped like a mirrored “U”? 

[digit]

Tooth reversal seems to be a localized phenomenon possibly with damage (rotation?) to the tooth germ. I don't see it being a larger scale mutation.

 

 

Cheers.

 

-Ken