Penn Dixie - gastropod or ammonoid?

[Monica]

Hello there!

 

I visited @Malcolmt yesterday and he was nice enough to clean up some of my stuff from Penn Dixie (mid-Devonian), including the specimen below.  I'm not exactly sure what it is, so I was hoping that someone out there will be able to help me with identifying this little guy, which I think is either a gastropod or a ammonoid - what do you think?  These are all pictures of the same specimen, just from different angles.  And it's pretty small - only 5mm across at its widest point.  Maybe @DevonianDigger can help?

 

 

Thanks for your help!

 

Monica

 

PS - We found a definite gastropod - a Platyceras of some sort - just barely exposed on the side of one rock, but it's kind of twisted and weird-looking, so Malcolm is going to work on it a bit more - after it's done, I'll post pictures of that little guy, too.

 

 

[ynot]

Looks like a nautilus to Me.

Is it pyrite?

Looks very nice.

[Fossildude19]

I would go with Tornoceras uniangulare, with the shell material pyritized.

Maybe Jay or someone else can weigh in.  

 

Nice find, Monica!

Thanks for posting it. 

[Kane]

Just to throw in a small wrinkle here, but wouldn't there be evidence of suture ornamentation if this was Tornoceras uniangulare? I've never found one at PD, so I'm not sure if perhaps the sutures don't show up on the ones that appear there. 

[DevonianDigger]

I'm leaning toward nautiloid as well, but I don't see the sutures that would usually indicate the T. uninagulare. Unfortunately, I am currently in Wisconsin, away from all of my references and would want to check Wilson to see if there was another alternative. Regardless of what it is, it's a really nice piece. Malcolm did a great job on it—as always! Looks like there's a tiny piece of Bellacartwrightia plurae sitting under it too!

[Fossildude19]

3 minutes ago, Kane said:

Just to throw in a small wrinkle here, but wouldn't there be evidence of suture ornamentation if this was Tornoceras uniangulare? I've never found one at PD, so I'm not sure if perhaps the sutures don't show up on the ones that appear there. 

Kane, I'm not sure. I've always thought that they had shell material covering the sutures, and that it isn't always preserved, like in some ammonites. 

I could be totally wrong on this, however. 

[DevonianDigger]

It's possible that it's a gastropod and that the spire is facing down into the matrix and thus not visible. Looking at it more, I see no signs of sutures, but it does look like growth lines.

[DevonianDigger]

Platyostoma sp.?

 

The thing that has me leaning most toward gastropod is that if you look at the aperture, it appears to be perfectly intact with no signs of pieces being broken off. The T. uninagulare, along with most of the goniatite species from the area have an overhang on the aperture that would have to have been broken off. If it weren't the aperture that we were seeing, it most likely would show evidence of the suture pattern where it broke rather than just being smooth and well-rounded.

 

It's not a common find from the site, and these are just my thoughts. My gut is saying gastro. (Pun intended.)

[Fossildude19]

8 minutes ago, DevonianDigger said:

It's possible that it's a gastropod and that the spire is facing down into the matrix and thus not visible. Looking at it more, I see no signs of sutures, but it does look like growth lines.

Could be that, or something like Naticonema?  I guess we'd need to see it prepped out further. 

However it does appear to be planispiral, to me.  

 

 

 

[FossilDAWG]

I'm also leaning towards a gastropod.  I've never seen an ammonoid from the Hamilton Group that preserves the exterior shell well enough to completely obscure the sutures, the aperture looks wrong for an ammonoid, and it's hard to be sure but the shell doesn't look perfectly planispiral.  In other words it seems that the inner whorl is not symmetrically contained within the outer whorl, rather it seems to stick up a bit.  This would be expected of a gastropod with a low spire, whereas an ammonoid would be perfectly planispiral (no heteromorphs in the Hamilton Group as far as I know).

 

Don

[Monica]

Wow - thanks for all of the responses!!!  I'm happy with either a gastropod or an ammonoid since it would be a first of either for me from Penn Dixie!!! 

(Although, I guess if it's a gastropod, that means I'll have two since Malcolm and I found another one that didn't appear to be a gastropod until he started prepping it.  However, the one that Malcolm's working on is definitely a Platyceras of some sort, and it looks completely different from this specimen, so I would still be pretty darned excited if the specimen pictured in this thread is a gastropod!!!)

 

So, should I see if @Malcolmt can prep it out further - would that be helpful?  I don't want to bug him too much, though, so if it's identifiable in its current state then I'd be happy to leave it as-is...

 

By the way, @ynot - it is indeed pyritized - so pretty 

[Fossildude19]

Good points, Don. I suppose that the top two whorls could have broken off. 

 

The Goniatites at Deep Springs Road do not always show the sutures, however. (Another Hamilton group site) 

 

 

Photo courtesy of Pagurus

 

 

[Rockwood]

1 hour ago, Monica said:

I'm happy with either a gastropod or an ammonoid since it would be a first of either for me from Penn Dixie!

Have you tried mini world (thought to be a low oxygen environment) to the left of the entrance ? Surface collecting is how I found a small ammonite there.

[Monica]

On 7/24/2018 at 1:37 PM, Rockwood said:

Have you tried mini world (thought to be a low oxygen environment) to the left of the entrance ? Surface collecting is how I found a small ammonite there.

There's something next to the entrance of Penn Dixie?  I've never noticed, but I'll keep my eyes peeled the next time I visit...

[Tidgy's Dad]

Lovely specimen, whatever it may be! 

[DevonianDigger]

On 7/26/2018 at 7:33 AM, Monica said:

There's something next to the entrance of Penn Dixie?  I've never noticed, but I'll keep my eyes peeled the next time I visit...

 

When you first come in, if you go to the left, past the storage container into that flat dirt area and look closely, the ground is loaded with pyritized goodies. Mostly just worm poop, but some orthoceras, goniatites, bivalves, and gastros. I've even found a few enrolled Greenops barberi pyritized up there.