Pennsylvanian Goniatite from Texas

[BobWill]

I'm unable to identify these goniatites from the Finis Shale member of the Graham formation. Found at the Lost Creek spillway near Jacksboro Texas. At first I thought they were just extra large examples of Agathiceras sp. which can be found there because of the longitudinal lirae but I noticed some other differences. These are more evolute as well as being larger. They also have a larger whorl height to whorl breadth ratio at 1.11 to 1 compared to .85 to 1 for Agathiceras.

 

 

 

This one shows the larger umbilical diameter of 10mm

 

 

and here is a close-up of the longitudinal lirae with fine crossing radial lirae.

 

 

This shows it on the venter of another specimen

 

 

and here is the largest sample which would have had a diameter of around 77mm without the body chamber, much larger than Agathiceras which I believe can range from 8 to 30mm depending on the species.

 

I would appreciate any help with these.

 

 

 

 

 

 

 

 

 

[ClearLake]

Bob

Sorry I can't help you with an ID.  I'm afraid you are already way more familiar with these than I am.

 

Mike

[Mare Nostrum]

Hello,

You're right, the reticulate ornamentation (longitudinal lirae + transverse striae) confirms that this is clearly not a 'giant' Agathiceras. A reticulate or crenulate ornamentation exists in several families of goniatites. Here, given the age, locality, and general morphology of the specimens with biconvex striae (cf. the third and fourth photos), it is certainly a Schistoceratidae and most likely the genus Schistoceras.

Here, for comparison, the schistoceratid Branneroceras branneri with similar ornamentation. Left, a small specimen from Arkansas, and right, a large mature individual from China. The transverse striae are stronger in small specimens.

[BobWill]

10 hours ago, Mare Nostrum said:

Hello,

 

You're right, the reticulate ornamentation (longitudinal lirae + transverse striae) confirms that this is clearly not a 'giant' Agathiceras. A reticulate or crenulate ornamentation exists in several families of goniatites. Here, given the age, locality, and general morphology of the specimens with biconvex striae (cf. the third and fourth photos), it is certainly a Schistoceratidae and most likely the genus Schistoceras.

Here, for comparison, the schistoceratid Branneroceras branneri with similar ornamentation. Left, a small specimen from Arkansas, and right, a large mature individual from China. The transverse striae are stronger in small specimens.

 

 

 

Thank you mare Nostrum. I believe you are right. All of the images I had for Schistoceras were internal molds so they didn't show the ornamentation but I see in the Treatise description a reference to the reticulate surface so this fits. Of the ones on local fauna lists, S. missouriense looks like the best match for the whorl profile since S. hildrethi is a little too depressed like your S. branneri.