Need help with Pennsylvanian cephalopod from Texas

[BobWill]

I am having trouble putting a label on this cephalopod from the Upper Pennsylvanian, Graham formation, Finis Shale member, from Jacksboro Texas. The conch is crushed on the anterior end which distorts the apical angle but the intact posterior end shows an angle of around 12º and the cardinal ratio is about 2.

My first thought was bactrites but if that is the siphuncle it appears to be very near but not quite in contact with the ventral wall, which I thought was a requirement for the whole subclass.

It looks a little like the “doubtful” genus Cylobactrites with the foldlike ribs and missing ventral lobe, but the treatise shows those to be Mid-Denonian. Maybe the ribs could be described as annulations and the siphuncle as subventral making it a nautiloid like some Brchycycloceratidae but B. normale and B. curtum are all I see on the fauna list for the site and they have much large apical angles at around 22º and 40º.  Any ideas?

[Misha]

I am by no means an expert on cephalopods but could it perhaps be Mooreoceras? I have heard of them being found there and the shape, positioning of the siphuncle as well as the size seem similar to ones I have seen

[BobWill]

28 minutes ago, Misha said:

I am by no means an expert on cephalopods but could it perhaps be Mooreoceras? I have heard of them being found there and the shape, positioning of the siphuncle as well as the size seem similar to ones I have seen

Thanks for the suggestion. I had actually but in with my Pseudorthoceras until I noticed some differences so I looked at the possibility of Mooreoceras too. the siphuncle could be that far off-center and pass but it was the cardinal ratio that was just too high. There are about 5 chambers per unit conch diameter for Mooreocers and around 4 for Pseudorthoceras compared to 2 for this, if I am measuring that right. The most noticeable difference though is the annulations. They may not be coming through very well  in the photos well but they are quite distinct. They're what made me think of Brachycycloceras.

[erose]

Bob, do you have Pennsylvanian Cephalopods of Ohio?  There is a specimen with a tentative description that may be close

 

Brachycycloceras? cf. B.? spectrum Hansman, 1965 

 

There is a single image Pl. 1-2, fig. 7

 

 

[BobWill]

3 hours ago, erose said:

Bob, do you have Pennsylvanian Cephalopods of Ohio?  There is a specimen with a tentative description that may be close

 

Brachycycloceras? cf. B.? spectrum Hansman, 1965 

 

There is a single image Pl. 1-2, fig. 7

 

 

Thanks for the reference Erich but I don't have it. Could you see if that image shows annulations similar to what's circled on this unknown Brachycyloceras from Ben Neuman's pictorial guide on the DPS website? Even this one doesn't have the same cardinal ratio (at 5:1) as my new specimen (around 2.5:1). If your image shows sutures you can count the number of septa along a section on the shell for a distance equal to the diameter there to get the ratio.

 

[erose]

9 hours ago, BobWill said:

Thanks for the reference Erich but I don't have it. Could you see if that image shows annulations similar to what's circled on this unknown Brachycyloceras from Ben Neuman's pictorial guide on the DPS website? Even this one doesn't have the same cardinal ratio (at 5:1) as my new specimen (around 2.5:1). If your image shows sutures you can count the number of septa along a section on the shell for a distance equal to the diameter there to get the ratio.

 

Not the same image but similar specimen and transition from large annulations to small. The written description is what rang true for your specimen. I'll try to take a pic of the fig and page later today.

 

There are many similar taxa in the Pennsylvanian of Ohio and I would suggest that publication as a good one to add to our Texas references.  There is both a section on nautiloid and bacritoid cephalopods as well as ammanoid cephs.  Pretty sure some of Neuman's images came from this.

 

Pennsylvanian Cephalopods of Ohio, 1997, Bulletin 71, Ohio Department of Natural Resources. https://ohiodnr.gov/wps/portal/gov/odnr/discover-and-learn/safety-conservation/about-odnr/geologic-survey/publications-maps/geologic-records-center

 

PS although this one isn't, many useful references are available as downloads.

[cngodles]

Mooreoceras or Pseudorthoceras. There has been much debate about if these are the same species, with one (Pseudorthoceras) being juvenile. The body chambers can sort of rapidly expand at the end.

 

Here is the only reference I have that shows the difference. Also, its interesting that it appears someone marked a septal neck/opening in the middle, but the photo clearly shows one to the top center.

 

Here are three difference specimens lined up.

 

 

Another one, likely my best preserved length:

 

 

 

And, what I called Mooreoceras. The body chamber was much larger. But, it may just be a larger version of the other species?

 

 

[cngodles]

Sending you three pages from Pennsylvanian Fossils of North Texas, Mark McKinzie, John McLeod.

[cngodles]

5 hours ago, erose said:

Pennsylvanian Cephalopods of Ohio, 1997, Bulletin 71, Ohio Department of Natural Resources. https://ohiodnr.gov/wps/portal/gov/odnr/discover-and-learn/safety-conservation/about-odnr/geologic-survey/publications-maps/geologic-records-center

 

PS although this one isn't, many useful references are available as downloads.

 

You can call them or email them and order it. I think it was really affordable, something like $20 or so. People resell these elsewhere on the internet for 3-5X the price. The larger Fossils of Ohio was $30 I believe.

 

https://ohiodnr.gov/wps/portal/gov/odnr/discover-and-learn/safety-conservation/about-ODNR/geologic-survey/publications-maps/popular-publications