Peace River micro matrix sort: shark dermal denticles

[debivort]

[edit: TLDR: DD1-DD13 are denticles. Everything else is likely not.]

Here are the candidate shark dermal denticles from my Peace River micro matrix sort (grid lines are 1mm):

• DD1-DD13: quite certain in the ID, but can the species be identified?

• DD14-DD19: Less confident about these more idiosyncratic specimens. DD16 might just be very worn, or possibly just a lookalike piece of phosphate. might DD17 be a steinkern? Its ridges seem shaped like the other denticles, but the material appears different.

 

Additional idiosyncratic specimens, two orientations each. I am uncertain if they are denticles:

• DD20 seems to have ridges, but texture is rough

• DD24 has a promising profile, but ridges aren't obvious

• DD23 has a rough "base," visible in the lower shot, and overall conical form.

 

What do y'all think?

Edited May 4, 2023 by debivort
added outcome of discussion as a TLDR.

[Al Dente]

5 hours ago, debivort said:

DD1-DD13: quite certain in the ID, but can the species be identified?

I agree that these are denticles. I’m not sure if you can ID them to species. I’m not sure what the other fossils are or if any of them are denticles.

[MarcoSr]

I also agree that your top picture has dermal denticles.  However, I'm not 100% convinced that they are shark even though the features match shark dermal denticles.  Most shark dermal denticles (placoid scales) are less than 1mm (usually less than .5 mm) with only a few shark species with larger ones.  Rays also have dermal denticles which can get a lot bigger.  However, a lot of small ray dermal denticles look like thorns.

 

Marco Sr.

[digit]

8 hours ago, debivort said:

• DD14-DD19: Less confident about these more idiosyncratic specimens. DD16 might just be very worn, or possibly just a lookalike piece of phosphate. might DD17 be a steinkern? Its ridges seem shaped like the other denticles, but the material appears different.

 

The ones on the left 5-ridge and 7-ridge are dermal denticles. These are the size and shape of those we find in various localities in Florida. Here are some images from the Montbrook site.

  

  

 

  

 

The specimens DD14-DD19 are not dermal denticles. DD14 looks like a worn bit of root from a myliobatid tooth plate. DD18 looks like a steinkern from a tiny barnacle. DD19 is suggestive but the part that would be the attached base looks too large and not like a dermal denticle.

 

Your additional specimens are either worn dasyatid teeth or blobs of phosphate mimicking denticle-like shapes.

 

Dermal denticles from sharks are tricky and tedious to find as they are all on the millimeter scale--you did well to find a nice baker's dozen of them.

 

 

Cheers.

 

-Ken

 

[debivort]

Thanks @digit @MarcoSr and @Al Dente! I am happy with my set of 13 denticles. This paper (Diversity of dermal denticle structure in sharks: Skin surface roughness and three-dimensional morphology) documents substantial variation in denticle size across the body, so I imagine what has happened is that all the normal sized denticles fell through the mesh, leaving only the >mm "big ones" behind.

I'm satisfied to relegate the rest of the candidates to the discard pile, except perhaps DD19. Pretty sure that's a body fossil and not an imprint. Will follow up with some additional photos and perhaps y'all can suggest an ID there.

@digit I have many likely dasyatid teeth to share later. While googling to ID those, I thought I found a morphological match in saw fish oral teeth (ptychotrygon). I realize the chronology is off, but are there similar, more modern saw fish oral teeth to find in Peace River material?

[Al Dente]

1 minute ago, debivort said:

While googling to ID those, I thought I found a morphological match in saw fish oral teeth (ptychotrygon). I realize the chronology is off, but are there similar, more modern saw fish oral teeth to find in Peace River material?

 

There should be Pristis and Anoypristis teeth in the Peace River, but they are tiny. Most in the 1 millimeter and smaller range.

[digit]

9 hours ago, debivort said:

I'm satisfied to relegate the rest of the candidates to the discard pile, except perhaps DD19. Pretty sure that's a body fossil and not an imprint. Will follow up with some additional photos and perhaps y'all can suggest an ID there.

It's something potentially interesting and could use additional images.

 

9 hours ago, debivort said:

I have many likely dasyatid teeth to share later. While googling to ID those, I thought I found a morphological match in saw fish oral teeth (ptychotrygon). I realize the chronology is off, but are there similar, more modern saw fish oral teeth to find in Peace River material?

Dasyatid teeth are ubiquitous in every micro-matrix locality with a marine component. There are pointed (breeding) male forms and female/non-breeding male forms. There are also a good number of wedgefish teeth which can be discerned by the droopy uvula in the margin of the enamel. Much less commonly are the smaller members of the Rhinopristiformes--guitarfish in the family Rhinobatidae.

 

Al Dente is correct in that Pristis and Anoxypristis rostral "teeth" (actually highly evolved dermal denticles) are infrequently found in the Peace River. I have searched (probably 30+ gallons) of Peace River micro-matrix looking for oral teeth from either of these sawfishes and haven't found a single specimen I could assign to those. A friend on the forum sent me some Cretaceous micro-matrix (from out of state as Florida is not blessed with fossils that old). That particular matrix is chocked full of Ptychotryogon oral teeth of all sizes showing a large range in size distribution. I had hoped that picking some matrix where those were richly sprinkled would tune my search image so that I wouldn't miss them if sawfish orals turned up in any Florida micro-matrix. So far, they seem rarer than hen's teeth.

 

Would enjoy seeing any oddities that are making you think sawfish.

 

 

Cheers.

 

-Ken

[digit]

9 hours ago, debivort said:

This paper (Diversity of dermal denticle structure in sharks: Skin surface roughness and three-dimensional morphology) documents substantial variation in denticle size across the body, so I imagine what has happened is that all the normal sized denticles fell through the mesh, leaving only the >mm "big ones" behind.

I've looked down as small as #50 mesh (1/50" or ~0.5 mm) and mostly found sand grains with no increase in really tiny shark dermals. I may need to get some bulk (sandy) matrix from the Peace again and run it through my stack of sifting screens and focus on the tiny stuff between #20 mesh and #50 mesh to specifically see if any micro-dermals appear. At that scale most of the rest of the fossil material is restricted to tiny (and often fragmentary) fish teeth and nothing much else.

 

The paper mentioned above is relatively recent and I'm going to see if I can request a full-text PDF. Thanks for the pointer.

 

 

Cheers.

 

-Ken

[Meganeura]

How is it I sort through 12lbs of teeny tiny micro matrix and find 2 denticles, but I send you 2lbs and not only do you find 13 denticles, but you find a nurse shark tooth too???? 

[debivort]

19 minutes ago, digit said:

I'm going to see if I can request a full-text PDF. Thanks for the pointer.

Let me know if you get stuck. I can get a copy for you through our library or ... walking down the hall?

[digit]

18 minutes ago, debivort said:

Let me know if you get stuck. I can get a copy for you through our library or ... walking down the hall?

I've made a request through ResearchGate. If the authors don't get back to me in a reasonable amount of time I may lean on you for access.

 

 

Cheers.

 

-Ken

[debivort]

Here's the undersides of the denticles. (Sadly I lost track of the original order, so they only correspond as far as 5-ridge and 7-ridge).

 

cc @Meganeura

[debivort]

Here is the mysterious DD19:

Front:

:

 

Back:

 

Top-down

 

Side:

 

Bottom:

 

The bottom looks somewhat cancellous to me.

 

cc @digit

 

2023-05-04 21-15-22 (B,R8,S4).tif

Edited May 5, 2023 by debivort
remove extraneous .tif file

[digit]

From the bottom they could be missed on the picking plate. The ones in the Peace River are rather river polished and the bases are worn down considerably. You'll notice that in the images of the specimens from the Montbrook site (above) which are much less worn, the bases of attachment are much more prominent.

 

 

Cheers.

 

-Ken

[digit]

5 minutes ago, debivort said:

The bottom looks somewhat cancellous to me.

 

My previous reply was made about the reverse view of the dermals--your post snuck in just as I posted my reply.

 

I see what you mean about the possible cancellous view. could be this is a broken piece off of something larger. I've looked at it from several angles and I cannot think of anything I recognize that matches this shape. May remain a mystery....

 

 

Cheers.

 

-Ken

[debivort]

2 minutes ago, digit said:

May remain a mystery....

Very good- I will file at away as such for now. Thanks digit!