Bullet-shaped Pennsylvanian Fossil

[BobWill]

I found this possible cephalopod in the Upper Pennsylvanian Graham Formation at the Lost Creek dam Spillway near Jacksboro Texas. It is 30mm long with a round profile 12mm across.

 

 

 

 

The arrow in the picture below points to a portion of the inside layer that is broken away from the internal mold.

 

 

 

 

The arrows in the picture below point to two more layers outside of the first.

 

 

 

 

Here is a fourth layer on the outside of the others.

 

 

 

 

Here you can see the layers on the blunt end

 

 

 

 

This is the pointy end

 

 

 

 

The ridges in picture below are the only hint of any ornamentation.

 

 

 

At first I thought it was one of the enigmatic burrows we find there but they don't have all these layers or these ridges going around the shell just occasional linear grooved linings.

 

 

 

 

[erose]

Some sort of orthoconic cephalopod.

 

[abyssunder]

Maybe a belemnoid ?

[BobWill]

2 hours ago, abyssunder said:

Maybe a belemnoid ?

I thought they were Mesozoic but they had their origins with the Bactritoids. There was a Bactrites on the fauna list for Lost Creek but it was reassigned to a coleoid group with external shells because of shell wall ultrastructure...oh! Extra shell walls...I just looked up Shimanskya postremus and it has regularly spaced concentric ornamentation missing on mine but the examples I find pictures of are too fragmentary to tell the overall shape. This could be just a worn coleoid. Maybe you set me on the right track here. Anyone else have any of these?

[Ridgehiker]

We get similar shaped straight nautiloids in Carboniferous deposits. They can be smooth, grooved, rippled.  The blunt end in that photo has the outer thickness the same as a nautiloid.

 

However...not familiar with that formation

[doushantuo]

might be a protoconch,e.g. of a scaphopod,but then it would be a large one

and,potentially:Sphooceras

[Monica]

Hi @BobWill!

 

I would agree that what you have is some kind of cephalopod since there appears to be evidence of a siphuncle at the top (pointy end) of your specimen - see red circle below:

Now, maybe that area is just one of the outer layers that has broken off in that one small spot, but I think I can see a smaller, dark-grey-coloured circle within - perhaps that is the siphuncle?

 

Thanks for sharing!

 

Monica

[abyssunder]

There was also a coleoid named Rugobactrites jacksboroensis Mapes, 1979 in the Finis Shale.

 

" R. jacksboroensis : Upper Carboniferous – all of the specimens examined are from the Finis Shale Member of the Graham Formation, which is exposed in the northeast, east and southeast of Jacksboro, Jack County, Texas. This taxon was recovered from localities TXV-40 and TXV–56, which are located approximately 7 km southeast of Jacksboro (see Boardman et al. 1994, pp. 94–95 for more locality details).
Additional specimens were recovered at localities BBTXV–82 and BBTXV-86, which are located approximately 15 km east of Jacksboro and 4 km southeast of Jacksboro, respectively (see Boston 1988). Locality BBTXV–89 is a road cut located in eastern Young County that was collected and measured by Boston (1988). " - as stated in Harry Mutvei , Royal H. Mapes & Larisa A. Doguzhaeva (2012) Shell structures in Carboniferous bactritid-like coleoids (Cephalopoda) from South Central USA, GFF, 134:3, 201-216

 

Other candidates for the Graham Formation, Finis Shale Member (lower Virgilian) might be Bactrites finisensis and B. postremus.

 

" S. postremus : Upper Carboniferous – all of the specimens examined are from the Finis Shale Member of the Graham Formation, which is exposed in the northeast, east and southeast of Jacksboro, Jack County, Texas. Seven localities have produced specimens. Localities TXV-30, 34, 36 and 56 are given in Boardman et al. (1994, pp. 94–95). Locality TXV-200 is the Lost Creek emergency spillway located approximately 7 km northeast of Jacksboro (see Rice et al. 1996; Mapes and Mapes 1997 for additional details). For additional details on localities BBTXV 60 and BBTXV-89, see Boston (1988). "

[BobWill]

Thanks for this reference abyssunder . I didn't know about the other coleoid but it seems to come from other sites near Jacksboro so it would be nice to add it to the fauna list for Lost Creek Dam if that's what this is.

 

Does anyone know if a coleoid with an external shell has a siphuncle and if so where it is located. @Monica noticed the possible siphuncle and it is located near the center like a nautiloid. I believe a bactrites has a siphuncle near the venter but they may also be slightly central.

 

It was Shimanskta Doguzhaeva et al. 1999 who reassigned Bactrites postremus to the coleoid order and renamed it Shimanskya postremus  because of the shell wall ultrastructure but I also don't know whether nautiloids have that character or not for comparison.

[abyssunder]

In an older document (which I recommend for its excellent content) were described the morphological features of Bactritoids: phragmocone cross section and sutural configuration, apical angle, ornament, protoconch morphology, internal deposits, septal necks, siphuncle position, wrinkle-layer, cameral ratio, septal orientation, and color patterns.

 

" SIPHUNCLE POSITION
Within the cephalopods as a group, the position of the siphuncle is an important morphologic and taxonomic feature. This also holds true in the Bactritoidea.
Bactritoids generally possess a marginal siphuncle, but exceptions are known.
Within the Sinuobactritidae, there are two taxa, Turbobactrites eudoraensis and Dilatobactrites missouriensis, in which the siphuncle is submarginal, removed 1/6 to 1/10 of the corresponding diameter from the venter (Pl. 38, figs. 20 and 7, respectively). If it were not for the known phylogenetic origins of these two species, these taxa would probably have been placed in another subclass.
Additionally, Globulobactrites loveladyensis n. gen., n. sp. (PI. 41, figs. 7,9,12) has a siphuncle distinctly separated from the venter, although a shallow ventral lobe is present on the suture. The relationship between Annulobactrites n. gen. and Globulobactrites is only moderately close, but it is clear they are related, and Annulobactrites (Pl. 40, fig. 5) has a marginal siphuncle.
Shimansky (1954, 1962) described an exception to the general rule that bactritoids have marginal siphuncles in that the Permian taxon Hernibactrites is described as having a suture without a ventral lobe; therefore, by implication, the siphuncle is separated from the venter.
Erben (1964a) suppressed this genus as a primitive variant of Bactrites, which has a ventral lobe and marginal siphuncle.
Thus, even though it has been demonstrated that the overall concept of the Bactritoidea must accommodate specimens with nonmarginal siphuncles, the higher (subclass to ordinal) level concept of a marginal siphuncle can be retained as a general rule. " - Mapes R.H., 1979: Carboniferous and permian bactritoidea (cephalopoda) in North America. The University of Kansas Paleontological Contributions Article 64: 1-75

 

And another little document mentioning Rugobactrites jacksboroensis : Lost Creek Reservoir, Jacksboro, Texas, Finis Shale

 

[BobWill]

Thanks for the additional information abyssunder. The last document is what we use for a handout when Dallas Paleontological Society has a field trip to Lost Creek Dam. The line drawings are only marginally useful and some of the fossils there are not in the book the introduction is lifted from by Mark and John. The newest version of the book, Color Guide to Pennsylvanian Fossils of North Texas has nice color pictures of most of the fossils they could verify from this site but no bactrites. Apparently others have found some there.

 

The location of the siphuncle, if that's what it is, on this fossils suggests nautiloid. I will try to find something about whether coleoids with an external shell have one.