Ammonite ID 2

[KimTexan]

Here is a 2nd ammonite found right near the first one, but a few years earlier. Can anyone tell me what the crystalline component is?

This is from the Edwards Formation near Rio Vista, TX.

I think it's one of my favorite ammonites because of the crystalline material. I'd kind of like to bleach the crystals to clean it up, but I'm not sure if that's possible.

[Macrophyseter]

I may be wrong, but I think that this could be a goniatite, based on the shell pattern and what I'm guessing of the possible shape of the shell opening (which is covered by matrix).

That size is pretty darn big, making it quite rare. Nice find!

[Anomotodon]

@Macrophyseter is right, suture lines are really goniatite-like. But Edwards formation, according to the internet, should be Cretaceous? Maybe it's an ammonitid ammonite from Acanthoceratoidea with secondary-primitive suture lines? Like a worn Coilopoceras or Tissotia. They normally have ceratite-like suture lines, but they should look similar on worn specimens, like this one. Ammonite looks really nice though!

Here is a picture of Tissotia from the internet

[doushantuo]

tex

[doushantuo]

[KimTexan]

18 minutes ago, Anomotodon said:

@Macrophyseter is right, suture lines are really goniatite-like. But Edwards formation, according to the internet, should be Cretaceous? Maybe it's an ammonitid ammonite from Acanthoceratoidea with secondary-primitive suture lines? Like a worn Coilopoceras or Tissotia. They normally have ceratite-like suture lines, but they should look similar on worn specimens, like this one. Ammonite looks really nice though!

Here is a picture of Tissotia from the internet

I believe Edwards is the lower Cretaceous. It's right near an area with a complex formation that also has Duck creek formation mixed in with a number of other layers, but I tend to think this is from the Edwards. I could be wrong. I'm not an expert.

[KimTexan]

This was found in Southeast Johnson County, which is in North central Texas near the Brazos.

[BobWill]

The goinatites were extinct by the end of the Permian. This ammonite appears goniatite-like but you are not really seeing sutures.The lines you see are the edges of the septa where they have been worn down past the sutures. The septum is nearly flat at the center and becomes more and more wavy as it nears the inside surface of the shell with the maximum folding at the shell wall where the sutures are.

 

 

Edit: If the ammonite is evolute enough you might be able to see some of the suture pattern by removing the matrix in the umbilicus to reveal the early whorls.

[Anomotodon]

7 minutes ago, BobWill said:

The goinatites were extinct by the end of the Permian. This ammonite appears goniatite-like but you are not really seeing sutures.The lines you see are the edges of the septa where they have been worn down past the sutures. The septum is nearly flat at the center and becomes more and more wavy as it nears the inside surface of the shell with the maximum folding at the shell wall where the sutures are.

This makes sense! So this can be any monomorphic ammonite? Not just from the pseudoceratitic type?

[BobWill]

14 minutes ago, Anomotodon said:

This makes sense! So this can be any monomorphic ammonite?

Yes but it may be pretty hard to identify without the sutures and any preserved ornamentation. Even the whorl profile can change as an ammonite grows. For example an Eopachydiscus will have a profile much like this one on the early whorls and become much thicker with a more rounded ventral surface as it matures.

[bone2stone]

The crystalline structure is most likely calcite.

Never the less, ain't dat cool.

Not sure just what bleaching the calcite would do, but I can tell you don't use an ultra sound device.

I tried cleaning some calcite material from the Eagleford and it crumbled.

The stuff out of the Edwards material may be a little more stable than the calcite found in the Austin chalk stuff

but I would be cautious when cleaning any specimen you prize.

 

Bob has a good grasp of weathering and the effects of exposure.

The limestone sorta weathered away more rapidly than the crystalline area and left the chambering

effects as you found it.

 

[Uncle Siphuncle]

Could this be a weathered Eopachydiscus from the basal Duck Creek?  I think in the area where collected, the Edwards begins transitioning to the Goodland facies, and between the Ked and Kgd, I'm not used to seeing ammos approaching this size except for Oxytropidoceras, which would still show some finely spaced ribs on the less weathered side, so I don't think we are looking at an Oxy.  I have seen brown calcite in geodized chambers of ammos from the Kdc. 

[BobWill]

4 hours ago, Uncle Siphuncle said:

Could this be a weathered Eopachydiscus from the basal Duck Creek?  I think in the area where collected, the Edwards begins transitioning to the Goodland facies, and between the Ked and Kgd, I'm not used to seeing ammos approaching this size except for Oxytropidoceras, which would still show some finely spaced ribs on the less weathered side, so I don't think we are looking at an Oxy.  I have seen brown calcite in geodized chambers of ammos from the Kdc. 

Good process of elimination Dan. I've seen Mortoniceras that big but not often and the whorl profile is wrong. All of the other disc-shaped ammos are smaller than this and with the ventral change I mentioned above we can probably even say it's an immature Eopachydiscus.