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Norki

Late Cretaceous Marine Gastropod

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Norki

Gastropods seem to be quite rare in the tracts of the Bearpaw formation I'm familiar with, so I'm incredibly curious about this lone specimen, the only one I've found. I found it in a hard layer of small conglomerated bivalves, pteria linguiformis, I believe, in sandstone dating roughly to the Campanian-Maastrichtian border. The specimen was collected from the western half of Diefenbaker Lake in southern Saskatchewan.

Anyway, here are the photos. If more angles are needed please let me know:

 

27705d2f4b.JPG

 

bee3c1a975.JPG

 

Pteria linguiformis (?), which constituted the conglomerate:

 

e612bf3e5a.JPG

 

Thanks for your time.

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caldigger

Being a steinkern it may be difficult to get a definitive ID on it without any identifiable outer ornamentation.

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Norki

Are you sure that it's a steinkern? Most of the surface is glossy and completely unlike the fairly coarse matrix, and appears to sheathe it. Many of the pteria also have some thin shell preserved...

But of course I know nothing about gastropods, so I'm totally inclined to take your word for it. What are the signs that typically indicate that a gastropod fossil is a cast?

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FranzBernhard
1 hour ago, Norki said:

completely unlike the fairly coarse matrix

It is very often the case, that the sediment filling of a shell is somewhat finer then the surrounding matrix (especially if the matrix is rather coarse grained). Your gastro-steinkern looks to be composed of fine to medium sized, hardened sand.

 

1 hour ago, Norki said:

Most of the surface is glossy

This is also not unusual for steinkerns. 

 

1 hour ago, Norki said:

Many of the pteria also have some thin shell preserved...

Yes, I can see it!

 

1 hour ago, Norki said:

What are the signs that typically indicate that a gastropod fossil is a cast?

No shell preserved, but a solid piece of rock. Narrow gaps between the winding (first pic). A hole, where the columella should be (second pic).

Franz Bernhard

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FranzBernhard

@Norki,

some time ago, I have posted this steinkern at its beginning... You can see the process of exfoliation of the shell, something you may have seen on your bivalves.

http://www.thefossilforum.com/index.php?/topic/69298-gastropod-miocene-badenium-ca-15-ma-of-the-styrian-basin/

Franz Bernhard

 

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Norki
8 minutes ago, FranzBernhard said:

@Norki,

some time ago, I have posted this steinkern at its beginning... You can see the processe of exfoliation of the shell, something you may have seen on your bivalves.

http://www.thefossilforum.com/index.php?/topic/69298-gastropod-miocene-badenium-ca-15-ma-of-the-styrian-basin/

Franz Bernhard

 

That's really interesting. I've definitely seen lots of examples of exfoliation on the bivalves and ammonites I've found - it actually seems to be less common to find fully exfoliated casts of the larger molluscs where I usually go, which may be why I automatically assumed that would also be the case with the gastropod.

Either way, thank you both for the information. I'll have to keep an eye out for more of these next time I'm out collecting... :)

Edited by Norki

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Ludwigia
2 hours ago, Norki said:

Are you sure that it's a steinkern? Most of the surface is glossy and completely unlike the fairly coarse matrix, and appears to sheathe it. Many of the pteria also have some thin shell preserved...

But of course I know nothing about gastropods, so I'm totally inclined to take your word for it. What are the signs that typically indicate that a gastropod fossil is a cast?

Yes that is a steinkern, as Franz has already described. It's also possible that the glossy surface means that it is in the process of being transformed into calcite, as is the case with many internal molds.

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