What is a Ptychodus ''oral scale'' ?

[Jaybot]

I recently found this very odd tooth which I originally thought was a fragment of a Ptychodus tooth.

Well, after a bit of research, I gave up (temporarily) on ID'ing it- until last week I stumbled upon this https://www.researchgate.net/figure/Representative-remains-from-upper-Jetmore-Chalk-of-Republic-County-Kansas-A-tooth-of_fig2_325131838      image on ResearchGate while researching for a different fossil.   I instantly recognized #B in that image as the id for my mystery tooth, and apparently it's a 'Ptychodus oral scale'.

 

  This brings me to my actual question (sorry for the long intro).  What is a Ptychodus Oral Scale??

Also, are these rare, and any guesses as to which species it would have belonged to?

 

 

Attached is my specimen, found in glacial deposits which have shark teeth eroded from the Kansas Chalk formations:

 

 

 

@Jared C@LSCHNELLE@Mikrogeophagus

 

 

[Mikrogeophagus]

Not informed on oral scales, so I can't help much here and I don't know if that specimen is an oral scale. My guess is they are placoid scales (abrasive denticles or tooth-like structures on shark bodies) located around the mouth. Placoid scales are something I have only seen in 1 locality so I assume they are pretty rare. They are generally small and fragile so it would make sense that they don't preserve often.

[ThePhysicist]

Mind the length scale in the figure. What you found is more than an order of magnitude larger than the "oral scale" depicted; that should rouse skepticism for your ID. I think yours is more likely to be a broken tooth.

[Jaybot]

On 9/8/2024 at 11:21 AM, ThePhysicist said:

Mind the length scale in the figure. What you found is more than an order of magnitude larger than the "oral scale" depicted; that should rouse skepticism for your ID. I think yours is more likely to be a broken tooth.

Sorry for the late reply.  Your right, I forgot to check the scale bar

 

So, if this isn't an 'oral scale', then does anyone know what kind of Ptychodus tooth would look like this?

I haven't seen anything that has a root quite like this one.

@LSCHNELLE@Jared C have you two found anything like this down there in TX?

Thank you in advance!

[LSCHNELLE]

I have not to my knowledge found dermal denticle scales of Ptychodus. I think it might be difficult to rule out that this is not just a posterior tooth of a Ptychodus that's been damaged on the top of the crown. My understanding is they're usually just tens of microns in size. So yours appears to be too large.

 

Here is what Shawn Hamm says about Type B scales in NMMNH Bulletin 81: "Type B scales have thin and broad crowns bearing posteriorly pointed projections and an expanded and rhombic-shaped root. There are five to six raised parallel ridges that run from the anterior to posterior edges of the crown. This type of scale is interpreted as a drag reducing scale like those found on the ventral and dorsal sides of the body (Becher! et al., 1986: Rasch i and Tab it. 1992) of fast-swimming sharks."

Edited Thursday at 01:24 AM by LSCHNELLE
Added a picture

[Jaybot]

14 minutes ago, LSCHNELLE said:

I have not to my knowledge found dermal denticle scales of Ptychodus. I think it might be difficult to rule out that this is not just a posterior tooth of a Ptychodus that's been damaged on the top of the crown. My understanding is they're usually just tens of microns in size. So yours appears to be too large.

 

Here is what Shawn Hamm says about Type B scales in NMMNH Bulletin 81: "Type B scales have thin and broad crowns bearing posteriorly pointed projections and an expanded and rhombic-shaped root. There are five to six raised parallel ridges that run from the anterior to posterior edges of the crown. This type of scale is interpreted as a drag reducing scale like those found on the ventral and dorsal sides of the body (Becher! et al., 1986: Rasch i and Tab it. 1992) of fast-swimming sharks."

Thank you for your informative response!  I suppose if it's a posterior tooth, that could explain the odd root shape.

Thanks again,