STH Micro Matrix

[digit]

2 hours ago, Meganeura said:

Oh they’re probably just lower Carcharhinus then!

Which usually resemble Negaprion brevirostris (Lemon Shark) in shape but a closer look shows fine serrations which can be used to distinguish. I'm actually going through some of my old STH material preparing for a donation to the FLMNH and I was surprised not to see Negaprion in the ELASMO faunal list for STH. I'll have to do a bit more research but for now those are probably Carcharhinus sp.

 

 

Cheers.

 

-Ken

[Nimravis]

@digit Ken those are fantastic pictures, I wish I had that skill.

[JulieNC]

Those are fantastic!

[digit]

1 hour ago, Nimravis said:

@digit Ken those are fantastic pictures, I wish I had that skill.

All it takes is a digital microscope, 3 software packages, and about an hour per completed image.

 

 

Cheers.

 

-Ken

[Nimravis]

52 minutes ago, digit said:

All it takes is a digital microscope, 3 software packages, and about an hour per completed image.

 

 

Cheers.

 

-Ken

Lol

[Meganeura]

7 hours ago, digit said:

All it takes is a digital microscope, 3 software packages, and about an hour per completed image.

 

 

Cheers.

 

-Ken

An hour!!!!

[digit]

2 hours ago, Meganeura said:

An hour!!!!

Yup. And I've got hundreds of images.

 

First ones probably took me 2 hours but I got more efficient as I went along.

 

 

Cheers.

 

-Ken

[Notidanodon]

22 hours ago, digit said:

I believe earlier discussions on STH mentioned that Negaprion was too young of a genus for the Round Mountain Silt at STH.

 

http://www.thefossilforum.com/index.php?/topic/95769-lemon-or-black-tip-or-shark-teeth-ernst-quarry/

 

 

 

Hey, you probably excelled when they did the lesson on shapes in pre-school.

 

 

The roots on Galeorhinus are fairly distinctive in that the root is pretty much on the lingual side of the tooth--rather mustache shaped split with a large nutrient groove. While there is some similarity to Abdounia (which I believe is Paleocene-Eocene) the worn root on Daniel's symphyseal (probably parasymphyseal) is more consistent with the root on Galeorhinus.

 

 

 

Cheers.

 

-Ken

 

I thought the nutrient groove was too wide for galeorhinus but I suppose that’s due to erosion   Thanks!

[digit]

Erosion of the roots is always a consideration as that is the least durable part of shark teeth. I've noticed that Galeorhinus teeth have particularly porous roots that often do not survive well. Looking through some Shark Tooth Hill micros and probably 95% of the Galeorhinus have no root material at all. Of course, even the larger teeth at this locality often have very fragile roots. I've heard that the iron-rich preservation that often produces such lovely reddish to amber colorations does not seem to provide as stable a mineralization as in other locations. The "Fire Zone" preservation often makes for teeth with ruby red blades but roots that usually require stabilization.

 

 

Cheers.

 

-Ken

[siteseer]

On 6/15/2023 at 3:23 AM, Meganeura said:

Thanks Jess! @digit confirmed that one of my teeth at the very least was in fact Raja - it had very wide roots. Apologies for the poor picture:

 

 

As far as the Mustelus vs Rhinobatus - I’ve definitely got a few with the good root structure still so I’m glad to have those as reference teeth!

 

Much appreciated on the info though. I’ll have to see if I can find any Gymnura teeth. And of course, keep looking for even smaller teeth!

 

I didn't want to sound too critical about the quality of the photo because I know how tough it can be to not only get a clean shot of a small/tiny tooth but to get it from very particular angles.  Teeth almost always want to lean at least slightly out of the best view,

 

Yes, that looks like Raja from that angle.  It's a tough tooth to get, and when you get one, the root or crown is often chipped or worn.

 

 

 

[siteseer]

On 6/15/2023 at 11:27 AM, Notidanodon said:

Does anyone have another opinion on that tope shark tooth  

 

Maybe a view of the labial side would help.  To me the cusp base is leaning slighting so I'm not sure it's a symphyseal tooth.  In that tooth position the cusp is vertical.  I have one or two from my own screening.  I can try to get a shot.  Otherwise, I agree that it's Galeorhinus.

 

 

[siteseer]

On 6/15/2023 at 3:29 PM, digit said:

Which usually resemble Negaprion brevirostris (Lemon Shark) in shape but a closer look shows fine serrations which can be used to distinguish. I'm actually going through some of my old STH material preparing for a donation to the FLMNH and I was surprised not to see Negaprion in the ELASMO faunal list for STH. I'll have to do a bit more research but for now those are probably Carcharhinus sp.

 

 

Cheers.

 

-Ken

 

Yes, I've always been skeptical of any obsevation that Negaprion is present in the bonebed.  The teeth shown are always in the size range of Carcharhinus lowers from the site and I haven't found even a piece of what appears to be a lemon as you find when you hunt the Bone Valley Formation.

 

However, I can't rule it out because you do find "classic" Negaprion from the Rosarito Beach Formation in the Ensenada area of Mexico and that formation is about the same age.  Furthermore, a friend once found Negaprion in a layer above the STH Bonebed.  Negaprion is a warm water shark so we would expect it to be rare or absent in a layer representing a warm-temperate environment, Hemipristis being uncommon-rare there as a possible line of evidence of that.  World limates were on a cooling trend around the time of the Round Mountain Silt deposition but there were undoubtedly El Nino years and/or warmer phases within that trend so we'd have to keep an open mind even after many years of seeing what has come out of the bonebed.

 

[digit]

My diagnostic feature for separating Negaprion teeth from Carcharhinus lowers in Florida material has always been to look for faint serrations. Negaprion have none and Carcharhinus have some (though often faint). I've recently had a chance to look through some small teeth (though not micros) from STH and separated out all of the distinctive genera. I was then left with the carcharhinid types and was separating out the "lemons" as I knew them. That's when I did a little searching on this forum when I didn't see Negaprion in the faunal list on Elasmo.com.

 

 

Cheers.

 

-Ken