Nautiloid? Help Id please

[PaleoOrdo]

I found this stone with some unknow pattern in the Kalvsjøen formation, Oslo field (late Katian, in late Ordovicium). Can it be two nautiloids or alge? It is some small gastropods there too. The length of the longest "nautiloid" is about 7 cm.

[pachy-pleuro-whatnot-odon]

Looks like a pair of orthocones to me...

[Rockwood]

Conularid ?

[Fossildude19]

Not sure these are well preserved enough to hazard a guess. 

 

[PaleoOrdo]

It is not well preserved, but I think the thickness of the edges and the horisontal bands or lines indicate perhaps that is not conularids, but nautiloids.

[PaleoOrdo]

In the same formation I found this fossile, which is more clearly a nautiloid, an ortoconic? Anyone have an idea of which genus or species it might be?

[val horn]

the last fossil bothers me more, because the central circles dont fit  any cephalopod that I know of,  maybe there is an expert who will recognize the fossil

[FossilDAWG]

The last couple of photos show an actinocerid nautilod.  The "circles" are segments of the siphuncle, which are very inflated and filled with deposits (except for a narrow central canal) in actinocerids.  There are quite a few genera in this group, including Actinoceras, Kochoceras, Armenoceras, and on and on.  A more precise ID would require some investigation of the relevant literature to see what has been described from the local formations.

 

Don

[pachy-pleuro-whatnot-odon]

35 minutes ago, FossilDAWG said:

The last couple of photos show an actinocerid nautilod.  The "circles" are segments of the siphuncle [...]

 

Cool! I thought it might be something like that, but really have no experience with episodes whatsoever. Learned something new today, so thank you! 

[minnbuckeye]

Here is a photo from wikipedia of just the siphuncle of these critters. From here it is easy to see what you have, which is a nice find!! 

 

Mike

 

 

[FossilDAWG]

Looks like a sideways stack of very stale doughnuts!  Yummy!

 

Don

[PaleoOrdo]

Thank you, Don and Mike, for the explanation.

Maybe it is not the genus Actinoceras, because according to an article in Wikipedia about this genus its siphuncle is ventral of the center but away from the ventral margin, while my speciemen is at the margin (if I can assume that the fossil's edge or outer layer is not partly eroded?), also its siphuncle tends to decrease in diameter towards the adult part of the phragmocone, again opposite to my speciemen. Maybe it can be a Kochoceras (family Actinoceratidae ) which is relatively short, breviconic, and the ventral, or under, side is strongly flattened with prominent lobes. Its siphuncle is proportionally very large and in broad contact with the ventral wall, as in my speciemen. In addition, its age range is according to fossilworks 449.5 to 443.7 Ma, which cover the age of the formation (445-446 Ma).

But there are in all nine families of Actionocerida. I found one article by Trygve Strand (THE UPPER ORDOVICIAN CEPHALOPODS OF THE OSLO AREA ) which says it is found a Armenoceras (Armenoceras holtedahli) in 'the Gastropod limestone' in the Oslo region, "etage 5a", which is the same age as the actual formation, at a different location. But he descibe that specis as have siphuncle "near ventral margin" with 8-9 chambers, and width of the conch in lateral direction through the center of the siphuncle is 54 mm at the upper end, which is wider than my speciemen. Each chamber is also higher. 

I can see 12 chambers in my speciemen, possibly 13. Maybe a few more is invisible in the apex part. It seems also that the siphuncle is smaller. However, he mention another Armenocera, A. richardsonim from the Selkirk member of the Red River formation of southern Manitoba which has bigger siphuncle, with "height to width index 20-25 (30 in holtedahli)". But I not understand what is the meaning of these numbers to compary with my speciemen. Any help is appreciated.

 

[PaleoOrdo]

In the same formation I found this speciemen, is this also a actinocerid nautilod? The length is 5cm, and it seems to be complete.

 

 

[PaleoOrdo]

I think the last nautiloid above belongs to the family Cyrtogomphoceratidae, in the order Discosorina (new name: Discosorida) or it is an Oncoceratida.  According to JERZY DZIK: PHYLOGENY OF THE NAUTILOIDEA, Discosorida differ from the endogastrically curved representatives of the Oncoceratida in compressed shell. Can anyone please look at my speciemen, and determine if it is compressed or not. 

[PaleoOrdo]

I tend to think that it is not depressed, or not strongly depressed, because it has few chambers each of which is not low relative to the whole shell. On the other hand the chambers are not structured horisontally the whole way. The genus is not included in Trygve Strand's paper on upper ordovician nautiloids in the Oslo region. However, a genus called Strandoceras (in the family Cyrtogomphoceratidae, order Discosorida), mentioned by Walter Sweet ("THE MIDDLE ORDOVICIAN OF THE OSLO REGION, NORWAY 10. Nautiloid Cephalopods" p.166-170), who describe a few species which have many of the same properties, such as Protophragmoceras tyriense, a species of Strandoceras from the Darriwilian stage in Middle Ordovicium. This article is unclear about the age assessments of the fossils of this genus found in my Hadeland area (although he correctly says that the genus is found in both Middle and Upper Ordovicium), but he has one relevant picture (p.167) of the species Strandoceras strandi, which is most similar to my speciemen. However, there are also some differences with this one and my found speciemen: the ventral side is more and clearly flat in my speciemen, the size of the specimen (Sweet's speciemen are bigger overall), the shape of the siphuncle (mine, although unclear, seems quite circular, while Strandoceras strandi is oval), and the number of chambers (clearly fewer in mine). Moreover, my speciemen is from very late in Upper Ordovicium. Anyone who knows about other relvant species of Strandoceras than those here mentioned or any paper on this genus?

Picture of Strandoceras strandi:

 

 

[PaleoOrdo]

Here is two other nautiloids from the same formation and the same location, late Katian. The first one seems to be broken off a part, size about 6cm long. Anyone have an idea of which family or order they belong to?

The second one seems more complete, it is strongly curved or coiled on the visible side (ventral side?), where the suture pattern is visible. The other side of the rock has nothing visible. Maybe it is an exogastric formed nautiloid?

[PaleoOrdo]

I post two more photos of the second nautiloid, to show that the bending is not along a straight axis or it is because of wear and tear?

 

[PaleoOrdo]

Another picture, side view, shows the compressed shape. It seems unusually much compressed. I guess it is an Oncocerid, which often is a somewhat compressed cyrtoconic brevicone nautiloid. But this is just a guess. In the north Europe it was not so common with cyrtoconic nautiloids in Ordovicium, and I cannot find much litterature about this order.  

[JimB88]

On 4/14/2021 at 3:09 AM, PaleoOrdo said:

I found this stone with some unknow pattern in the Kalvsjøen formation, Oslo field (late Katian, in late Ordovicium). Can it be two nautiloids or alge? It is some small gastropods there too. The length of the longest "nautiloid" is about 7 cm.

 

The bigger one could be a Gonioceras..which were a flattened bottom dwelling ceph..kinda like today's Flounder

[PaleoOrdo]

The next nautiloids I found in this formation, most of them preserved in almost two-dimentional view, is first these compressed and not wholly displayed ones. I have no idea to which order they belong to. Any opinion very much appreciated. The first is very compressed, diameter is 3 cm wide at the broadest part. I do not know how this shape would look like in a good 3-D view.

A close up of the connecting lines:

The second is about the same size, a little smaller, but less compressed:

 

The third a little bigger, about 4cm in diameter, similar to the first one in overall shape:

Next, the forth, same stone as the second, a little bigger:

The same from a different angle, showing a second nautiloid, on top of the bigger and a very small one below it:

 

The fifth and the sixth, also in the same stone as the second. The fifth with a different shape, oval, size is 2,5 cm long, with only 3 chambers:

THE SIXTH, (orthoconic?), 3 cm long, 1 cm wide:

[PaleoOrdo]

Could the brown pattern on top of the nautiloid in the last photo, and in the 4th last photo, be the internal mould, the siphuncle, of another nautiloid? It looks similar to patteren in the photo posted above by Mike.

[Robert Mahorney]

I found these in ordovician lebanon limestone in Tennessee. I believe their actinoceras but I'm no expert.

[PaleoOrdo]

Your first and third pictures seems most interesting. It would be necessary for a determination to know where you found them or the formation. Was it in middle Tennesse? According to my limited knowledge the Lebanon limestones are the oldest rocks in Middle Tennessee and age is Lower Ordovician (Chazyan).  Hence, the nautiloids you found, if they are actinocerida, must be among the oldest of this order (much older than my late Ordivician species). I am not sure if they are Actinoceras, which is one of seven known genera in the family Actinoceratidae, belonging to the order Actinocerida (actinocerida nautiloids became up to 3 ft or 90 cm and even larger in the silurian, it was 20 genera in the peak middle Ordovicium). There is about 45 species of the genus Actionoceras.

     Some Actionoceras, but not all, are fusiform (tapering toward each end) with the diameter decreasing from the anterior end of the phragmocone toward the aperture. That maybe is not the case with your speciemens (uncertain in 1st picture which lack a part near living chamber, but definitely not in the 3rd). 

     Chambers of this genus are short and contain cameral deposits which are more concentrated apically (near the smaller end, opposite of living chamber part). That seems clearly to be the case for the first picture. However, according to several websites this genus lived in the middle and late Ordovician and later (fossil works: Age range: 466.0 to 336.0 Ma), while your formation is early Ordovician (?). It could then be an "ancestor" of Actionoceras, an early Armenoceras. The big siphuncle is characteristic of Actinocerida.

     I think your speciemen is interesting, because the derivation of the Actinocerida remains enigmatic and debated. Could you find out more precisely which formation it was found in the Lebanon limestone. Is it late early Ordovician? If so, it is interesting, because the origins of the actinocerids (Georginidae - 472-458 Ma) first appear late in the Early Ordovician (Cassinian Stage, late Floian).

 

Your last picture seems to be gastropods, not nautiloids.

I am also not an expert.

 

[Robert Mahorney]

Could be either Lebanon or Carter's idk. It's just my best guess from research. Maybe Ross formation. Heres exactly where I found them in a creek behind houses. Dose anyone know or have the ability to cross reference this location.

[PaleoOrdo]

I hope someone have more knowledge than me of the locations and formations in the area (I read somewhere that it is several ordovican strata there) can cheked this out. And also check out what I wrote above if possible. Thanks for show an interesting find!