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Heteromorph

I have been doing more research on my unidentified Middle/Upper Coniacian heteromorph ammonite that I posted pictures and information on here, and with lots of papers and information from Keith Minor I think that I have narrowed it down to two ammonite genera, Neocrioceras and Pseudoxybeloceras. He sent lots of very helpful papers including Kennedy and Cobban's 1991 paper Coniacian ammonite faunas from the United States Western Interior. It includes pictures and information on 3 species of Neocrioceras and one species of Pseudoxybeloceras from the Coniacian Western Interior. Keith also emailed me some information that I will show here. 

 

At first I thought that my specimen could be Smedaliceras durhami which is so far known only from the Campanian Burditt Formation of south Texas. That was way out there and Keith didn't even consider that possibility because of how out there that suggestion was. Then I saw pictures on the internet of an Allocrioceras hazzardi specimen from Utah that did look similar to mine. The main problem with that theory is that A. hazzardi doesn't have lateral tubercles, so scratch that. It was after exchanging emails with Keith that I came to my aforementioned conclusion, that my specimen is either of the genera Neocrioceras or Pseudoxybeloceras. After studying Kennedy and Cobban 1991 a bit further it seems to me that Neocrioceras (Schlueterella) sp. most closely resembles my specimen. N. sp. has one set of lateral and ventral tubercles on both sides of the specimen respectively. The tubercles connect groups of 2-3 ribs. Between the tuberculate groups there are up to 6 finer non-tuberculate ribs. At first I said that on my specimen there were 7 non-tuberculate ribs between the tuberculate ones but on closer examination the tuberculate ribs come in groups like N. sp. with one tubercle connecting two ribs. In reality my specimen has 6 non-tuberculate ribs between each tuberculate group consisting of two ribs. The main difference that I notice is that my specimen has much weaker lateral tubercles than N. sp.

 

Interestingly, Neocrioceras is not known from the Austin Chalk but there are a couple Pseudoxybeloceras specimens reported from the Santonian stage of the Austin Chalk in central Texas. The main reason why I don't think my specimen is Pseudoxybeloceras is because the species P. dispar, the only species of this genus reported from the Coniacian Western Interior in Kennedy and Cobban 1991, is quadrituberculate on every rib with no ribs being non-tuberculate. But I will say that I have not seen nor read any detailed descriptions of the Pseudoxybeloceras species found in the Austin Chalk so I still consider it a very possible candidate, though my specimen is considerably older. @Wrangellian, I know that you have experience with this genus from the Santonian. What do you think? 

 

In this post I also include 3 pictures of 2 different inoceramid specimens I found along with my heteromorph specimen. I sent Keith these pictures to help pin point my heteromorph's stratigraphic position in the Coniacian. Anyone have any ideas on what species they are? From what I am hearing from Keith my ammonite specimen could be a bit older than the Prionocycloceras gabrielense zone if these inoceramids are in the Magadiceramus subquadratus group. 

 

I will update this thread when I receive more information. 

 

Here are the edited relevant emails from my exchange with Keith:

______________________________

Keith Minor, February 17.

 

Hi Heteromorph,

 

According to Kennedy et al., Phlycticrioceras douvillei and P. oregonensis are junior synonyms of P. trinodosum.
 
P. trinodosum has been found in several areas around the Cretaceous Tethys Sea.
 
According to Walaszczyk, The Trinodosum Zone is middle Coniacian, which is consistent with the level that you are finding your specimens. 

Cremnoceramus ranges up into the middle Coniacian. However, I think that the clams that you have are probably Magadiceramus, probably M. subquadratus group. So the heteromorphs are slightly lower than the Prionocycloceras gabrielense's that you are finding, and your Texanitine could actually be Protexanites shoshonense, which would be about the right level.
 
Also, I didn't put two and two together, but that big piece of a heteromorph that you showed me may actually be Neocrioceras, which doesn't have tubercles, or Pseudoxybeloceras, with small tubercles that fade on the body chamber.
 
I hope this helps!

 

Keith

______________________________

Heteromorph, February 22. 

 

Here are two websites with the pictures of the alleged Allocrioceras hazzardi specimen that I found pictures of online. The more I look at the pictures the less I think that the specimen is really A. hazzardi. I have never seen another A. hazzardi specimen that looks like it and all the descriptions that I have read on the species don't indicate this kind of variation. I now believe that it was misidentified, but I wonder what you think.
 
 
 
So, do you have an opinion as to what species my specimen is? For me I am having trouble deciding between Pseudoxybeloceras (Pseudoxybelocerasdispar or Neocrioceras sp. What I do know is that the alleged A. hazzardi specimen from Utah very much resembles mine. 
 
Thank you for all your help!
______________________________
Keith Minor, February 22.
 
Hi Heteromorph,
 
I see the images. Yes, that is definitely Allocrioceras hazzardi. It ranges from the Upper Turonian (Prionocyclus hyatti Zone) to the Upper Coniacian (Prionocycloceras gabrielense Zone). I don't know of any Santonian species.
 
Hazzardi is probably the descendant of Allocrioceras annulatum from the Upper Cenomanian. Kennedy also described A. conlini, but I'm not sure that this is a separate species. I attached (as a Google Drive link) Kennedy's review of Eagle Ford ammonites (Texas). You can see that the ribs are all the same size in annulatum, but in hazzardi, the the spine-bearing ribs are bigger, and also hazzardi is a larger species.
 
I double checked to see if Hamites and Anisoceras ranges up into the Coniacian, but they disappear in the Cenomanian (as far as I can tell), so these genera can be ruled out.
 
However, Neocrioceras and Pseudoxybeloceras are genera that need to be considered. I have some papers on these, I think from South Africa. I'll find those when I have time. There's a couple of Pseudoxybeloceras specimens from the Austin Chalk from central Texas (Santonian).
 
Kind regards,
 
 
Keith
 
______________________________
P1 - Inoceramid oyster 
fullsizeoutput_6c37.thumb.jpeg.038b14cd42ec20e05f1580376856a229.jpeg
 
P2 - Same inoceramid oyster showing more clearly the perpendicular ribbing.
fullsizeoutput_6c39.thumb.jpeg.c72b6a268ddb1a2f44a49a8e5d2bf625.jpeg
 
 
 
 

 

 

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Heteromorph

P3 - Different inoceramid specimen. Possibly different species from P1?

DSCN6237.JPG

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doushantuo

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Heteromorph
48 minutes ago, doushantuo said:

Very interesting. I see some similarities to mine with a few of those. Thanks! 

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doushantuo

you might like this:Checa on M(edit: -agadiceramus) sculpture formation

magauydgesllifernakristlanthc.jpg

 

Europe and the USA in the Coniacian/Santonian:

edit:83,5 Ma reconstruction

 

eudgesllifernakristlanthc.jpg

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doushantuo

279451 (1).pdf

(outtake below,approx 1,5 Mb)

eudgesllifernakristlanthc.jpg

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doushantuo

Cretusa

(Ward et al GSA Bull)

outtake:

eudgesllifernakristlanthc.jpg

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BobWill

I had a closer look at all my Inoceramus fossils and don't see wrinkles on any of mine. They're all from formations of the Lower Cretaceous though. They are clams rather than oysters.

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Wrangellian

I don't know enough about the ammonites from lower down in the column than my native Santonian (which I have a hard enough time with), but if I found that ammo in my area I would (tentatively) label it Pseudoxybeloceras. The other pics you showed of similar items with different names throw everything into question for me. If we could see more of those inoceramids we could narrow down an ID, but, like your ammo, I'd prefer to refer to the publications for your area/formations rather than compare to mine. They do look very similar. That smaller inoceramid (Sphenoceramus?) looks very much like ones I'm finding in my local Santonian but there's not enough to really tell.

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Wrangellian

BTW I believe we're seeing only the internal mold on that larger inoceramid? So that would be the inner surface. Not sure how much the outer surface would differ.

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Heteromorph
44 minutes ago, Wrangellian said:

BTW I believe we're seeing only the internal mold on that larger inoceramid? So that would be the inner surface. Not sure how much the outer surface would differ.

Yes, that is just the steinkern. From my experience if it had the shell it wouldn't be that different, though it would be prettier. 

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Wrangellian

Probably not very different, but I think I've seen that kind of 'ribbing' on the internal side more than the external. I may be wrong, I'd have to go and look at some of my specimens.

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