Straight shelled Cephlopod Nautiloid?

[grg1109]

I purchased a couple of buckets of fossil/rocks from a friend who found them in the Ohio/Indiana area...which he told me was Ordovician and Silurian.

Unfortunatly I've lost the paper that described where this section of fossil/rock came from.  At first I thought it was a Crinoid...upon further inspection I noticed that there were patterns along with the ridges.  So, I scribed it out of the rock.  I noticed that one end was slightly larger than the other and that it was on the "Oval" side.  There is a bit of pyritisation...especially inside the small end.  So, I'm not really sure ...but I found one similar on the internet(last photo).  It looks to be the same but would like your opinions.

Thanks

Greg

Edited June 27, 2021 by grg1109

[Tetradium]

34 minutes ago, grg1109 said:

I purchased a couple of buckets of fossil/rocks from a friend who found them in the Ohio/Indiana area...which he told me was Ordovician and Silurian.

Unfortunatly I've lost the paper that described where this section of fossil/rock came from.  At first I thought it was a Crinoid...upon further inspection I noticed that there were patterns along with the ridges.  So, I scribed it out of the rock.  I noticed that one end was slightly larger than the other and that it was on the "Oval" side.  There is a bit of pyritisation...especially inside the small end.  So, I'm not really sure ...but I found one similar on the internet(last photo).  It looks to be the same but would like your opinions.

Thanks

Greg

FYI nautiloid didnt evolute till much later. We just use cephalopods for Paleozoic era mainly. 

37 minutes ago, grg1109 said:

I purchased a couple of buckets of fossil/rocks from a friend who found them in the Ohio/Indiana area...which he told me was Ordovician and Silurian.

Unfortunatly I've lost the paper that described where this section of fossil/rock came from.  At first I thought it was a Crinoid...upon further inspection I noticed that there were patterns along with the ridges.  So, I scribed it out of the rock.  I noticed that one end was slightly larger than the other and that it was on the "Oval" side.  There is a bit of pyritisation...especially inside the small end.  So, I'm not really sure ...but I found one similar on the internet(last photo).  It looks to be the same but would like your opinions.

Thanks

Greg

Also cephalopods outer shells often don't preserve well so most fossils you see are of the inner segments which are much more calcium carbonate and thus harder. Nautilords outer shell are much more harder and their interior are hollows connected by pores. 

[grg1109]

1 hour ago, Tetradium said:

FYI nautiloid didnt evolute till much later. We just use cephalopods for Paleozoic era mainly. 

Also cephalopods outer shells often don't preserve well so most fossils you see are of the inner segments which are much more calcium carbonate and thus harder. Nautilords outer shell are much more harder and their interior are hollows connected by pores. 

So are you saying that this is the inside mold?  I accidently broke two segments from the small end while removing the matrix...the first one was pyritized inside of the outside layer on the smaller edge and also in the inside of the broken piece...the second contained pyritization on the smaller side and had calcium carbonate on the inside larger side.  Do you agree that it is a Dawsonoceras amycus?  Also, would this be a juvinille, adult or the small end of a much larger speciman?  I can't find out much information on this.

Thanks

Greg

Edited June 27, 2021 by grg1109

[Tidgy's Dad]

Without location details I would hesitate to tie it down to any species. 

I am fairly certain it is a nautiloid and that is the exterior surface detail that we are seeing, not an internal mold of the septa. 

 

[FossilDAWG]

2 hours ago, Tetradium said:

FYI nautiloid didnt evolute till much later. We just use cephalopods for Paleozoic era mainly. 

Also cephalopods outer shells often don't preserve well so most fossils you see are of the inner segments which are much more calcium carbonate and thus harder. Nautilords outer shell are much more harder and their interior are hollows connected by pores. 

There is so much incorrect here I feel I have to comment in case people take the wrong information away.

1. Cephalopods are a Class (Cephalopoda) within the phyllum Mollusca.  It includes nautiloids, ammonites, squid, octopuses, etc.  We do not just use cephalopods for Paleozoic forms, they extend from the Cambrian to the present day.

2. Nautiloids first appeared in the Cambrian, diversified extensively in the Ordovician, and persist to present.  The modern genus Nautilus evolved in the Cenozoic or possibly (according to a couple of researchers) maybe the Cretaceous.

3. There is nothing unique about nautiloid outer shells that cause them to not preserve well.  In many North American Ordovician formations conditions tended to cause all aragonitic shells to dissolve after shells were buried in the sediment on the sea floor.  This included not only cephalopods but also almost all gastropods and bivalves.  Such fossils are preserved as internal molds.  On the other hand shells made of calcite or phosphate did not dissolve and are preserved as mineralized fossils.  For example fossils of brachiopods, trilobites, corals etc from these formations look like the original shell (although the original calcite may have been replaced by other minerals over time), not internal molds.  Note that this reflects chemical conditions in the sediment, not a universal property of the nautiloid shell.  I other formations deposited under different conditions the nautiloid shell may be preserved as well as other mollusc shells.

4. The chambers of the nautiloid shell are formed by shell material developed into partitions called septa, the divide the interior of the shell called camerae.  The camerae are connected by a tube called the siphuncle that runs the length of the shell.  Perhaps this is what was meant by "pores".  The position of the siphuncle (in the middle of the shell, dorsal side, ventral side, etc) is important in identifying species.  Also the siphuncle may have deposits made of calcite, so sometimes the siphuncle may be well preserved when the rest of the shell (made of aragonite) is not.

 

Don

[grg1109]

I found the description of where this came from...New Point Stone Co., Napoleon Quarry, Napoleon, Indiana....Massie Shale...Silurian.

Greg

[Tetradium]

1 hour ago, FossilDAWG said:

There is so much incorrect here I feel I have to comment in case people take the wrong information away.

1. Cephalopods are a Class (Cephalopoda) within the phyllum Mollusca.  It includes nautiloids, ammonites, squid, octopuses, etc.  We do not just use cephalopods for Paleozoic forms, they extend from the Cambrian to the present day.

2. Nautiloids first appeared in the Cambrian, diversified extensively in the Ordovician, and persist to present.  The modern genus Nautilus evolved in the Cenozoic or possibly (according to a couple of researchers) maybe the Cretaceous.

3. There is nothing unique about nautiloid outer shells that cause them to not preserve well.  In many North American Ordovician formations conditions tended to cause all aragonitic shells to dissolve after shells were buried in the sediment on the sea floor.  This included not only cephalopods but also almost all gastropods and bivalves.  Such fossils are preserved as internal molds.  On the other hand shells made of calcite or phosphate did not dissolve and are preserved as mineralized fossils.  For example fossils of brachiopods, trilobites, corals etc from these formations look like the original shell (although the original calcite may have been replaced by other minerals over time), not internal molds.  Note that this reflects chemical conditions in the sediment, not a universal property of the nautiloid shell.  I other formations deposited under different conditions the nautiloid shell may be preserved as well as other mollusc shells.

4. The chambers of the nautiloid shell are formed by shell material developed into partitions called septa, the divide the interior of the shell called camerae.  The camerae are connected by a tube called the siphuncle that runs the length of the shell.  Perhaps this is what was meant by "pores".  The position of the siphuncle (in the middle of the shell, dorsal side, ventral side, etc) is important in identifying species.  Also the siphuncle may have deposits made of calcite, so sometimes the siphuncle may be well preserved when the rest of the shell (made of aragonite) is not.

 

Don

Ok I'm sorry. 

[FossilDAWG]

55 minutes ago, Tetradium said:

Ok I'm sorry. 

That's OK, no big deal. Every one of us has misspoken at times.  Also I learn something from this site every day. 

 

Don

[Tetradium]

1 minute ago, FossilDAWG said:

That's OK, no big deal. Every one of us has misspoken at times.  Also I learn something from this site every day. 

 

Don

True me too. I'm just deleted that one post so not to cause any confusion for other members. 

[FossilNerd]

1 hour ago, Tetradium said:

True me too. I'm just deleted that one post so not to cause any confusion for other members. 

No need to delete or hide the post. We all make mistakes and we all learn from them. I’ve made my fair share.  

[JohnJ]

1 hour ago, Tetradium said:

True me too. I'm just deleted that one post so not to cause any confusion for other members. 

 

Post unhidden.  We live and learn.