A beautiful small GASTROPOD and a nautiloid with an unusual form

[PaleoOrdo]

In my last fossil hunting trip to a late ordovician site in the Oslo field I found these 2 fossils. One with a small spiral form, size 1 cm in diameter, seems to be a gastropod, and the bigger one what seems to be a nautiloid with an unusual form, size about 7-8 cm long. Anyone seen something like these before?

First the small gastropod or maybe it is a nautiloid too?

A small part fell of, so one can see if it has a sihuncle or not, I took these photos of it with a microscope, the first most clear in the cross section:

 

And here is the bigger nautiloid, with the (for me) unusual form:

 

 

[Fossildude19]

Nautiloid shapes can vary, quite a bit. 

 

Image from HERE.

 

[PaleoOrdo]

Thank you for the figure, Tim!  It was very helpful when I google articles and pictures online.  It seems I found an orthoconic brevicone nautiloid, and from the Katian period in late Ordovicium.  I read some articles today and yesterday to find the genus of this bigger nautiloid (6-7 cm long). From my limited knowledge of the different brevicone nautiloids, I think it is the genus Gompoceras.  I though first it could be a Discosorida, for example Landeroceras, but I could nt find any picture or description similar to my speciemen. AlsoI did nt see an speciemen of Gompoceras which is fully identical to it yet online. If it is a Gompoceras, then it is quite unusual find, at least for Ordovicium. This is a genus which is not yet assigned to a family.  According to fossilwork.org it is found only 11 speciemen in the world, and 1 only from Ordovicium. As I understand it is several species of Gompoceras, but I do nt know which one it can be. Could it be interstion for a researcher to look at it?

I am grateful for any viewpoint or advice on this subject.

Martin

[PaleoOrdo]

I took a picture of the small spiral form with my microscope. Could it be the siphuncle we see here in the color , indicating that it is a very small nautiloid? Or can nautiloids never be so small? Anyone know the smallest found fossil size of nautiloids?

[Fossildude19]

Nautiloids can be very small. 

Squares in photo 5 mm x 5 mm.

 

 

That said, I'm pretty sure your item is a gastropod steinkern. 

[PaleoOrdo]

I understand and I think you are right. Thank you, Tim.