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Some guy

Orthocone Identification [SOLVED]

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Some guy

Found this fossil in a creek in middle Tennessee. I originally thought it was a crinoid column, until user ynot pointed out that it was more than likely an orthocone shell. Judging from where it was found, it seems to be from the Ordovician.

So now my question is: what species of orthocone do you think it is? Note the size (5 1/2" long, 2" wide) and the segmented pattern.

 

Thanks for the help!

 

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RenderedContent-310C947F-FF65-4F84-9CAF-9A49A63F65B7.JPG

RenderedContent-BFEAD69B-B3B9-45AC-AFCD-57D436792255.JPG

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ynot

Orthocone cephalopod.

 

Tony

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Some guy

My god, I think you're right. Any idea as to what its species may be?

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ynot

Sorry, but My knowledge does not go that far. Others will chime in with that information.

Tony

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Some guy

Alright. Thanks a ton for the help!

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Fossildude19

Welcome to the Forum. :)

 

Knowing what county it was found in could help with pinning down a time frame - orthocone cephalopods were very diverse through time. ;) 

That said, your cephalopod may be too worn to make a definitive ID possible. 


Regards,

 

EDIT: Here is a geologic map of Tennessee.

 

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Fossildude19

If it was found in central Tennessee, it could be Ordovician in age. 

 

That could point to something like Actinoceras sp. or Endoceras sp. 

Regards,

 

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Some guy

Thanks for the warm welcome and the map! 

 

The fossil was was found in Rutherford County, which means it was from the Ordovician.

And frankly, knowing that I may be holding a genuine Ordovician orthocone fossil makes the 7-year-old Nigel Marvin watcher inside me giggle uncontrollably.

 

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DevonianDigger

I agree with Tim, looks like Actinoceras sp., but it's too worn to know for sure I think. Very nice either way!

 

Welcome to TFF!

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FossilDAWG

Can we see the other side?  Judging from the end views the "bottom" might show the siphuncle in longitudinal section, which would be more useful than the view already posted that shows only the septa.

 

Don

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Some guy

Here's the underside:

 

 

 

IMG_0535.JPG

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FossilDAWG

Thanks.  I am fairly confident in saying this is an endocerid such as Endoceras though there are other genera in the group.  I say this because of the large straight-sided siphuncle without secondary deposits, the shallow camerae, and the relatively large size of the specimen.  It is definitely not an actinocerid, as those nautiloids have large siphuncles that expand in ring-like structures into the space in each cameral chamber (so the siphuncle looks like a series of rings stuck together), they are almost filled with secondary deposits, and they contact the exterior shell on one side (the ventral) where the ring-like segments are conspicuously flattened.  In actinocerids, the siphuncle was a large heavy structure that weighted the shell down so the ventral side lay flat on the sea floor.  It is also not a michelinocerid as those nautiloids had relatively small centrally located nummuloid (bead-like) siphuncles.  We can exclude oncocerids because the shell is not conspicuously curved, and the oncocerids had small bead-like siphuncles that ran along the outside of the curve.  The straight parallel sides exclude genera such as Gomphoceras and Westonoceras.

 

Don

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Fossildude19
23 minutes ago, FossilDAWG said:

Thanks.  I am fairly confident in saying this is an endocerid such as Endoceras though there are other genera in the group.  I say this because of the large straight-sided siphuncle without secondary deposits, the shallow camerae, and the relatively large size of the specimen.  It is definitely not an actinocerid, as those nautiloids have large siphuncles that expand in ring-like structures into the space in each cameral chamber (so the siphuncle looks like a series of rings stuck together), they are almost filled with secondary deposits, and they contact the exterior shell on one side (the ventral) where the ring-like segments are conspicuously flattened.  In actinocerids, the siphuncle was a large heavy structure that weighted the shell down so the ventral side lay flat on the sea floor.  It is also not a michelinocerid as those nautiloids had relatively small centrally located nummuloid (bead-like) siphuncles.  We can exclude oncocerids because the shell is not conspicuously curved, and the oncocerids had small bead-like siphuncles that ran along the outside of the curve.  The straight parallel sides exclude genera such as Gomphoceras and Westonoceras.

 

Don

 

 

Great information, Don. 

Thanks for chiming in on this thread. 

I always learn something when you post. :) 

Regards, 

 

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Some guy
34 minutes ago, FossilDAWG said:

Thanks.  I am fairly confident in saying this is an endocerid such as Endoceras though there are other genera in the group.  I say this because of the large straight-sided siphuncle without secondary deposits, the shallow camerae, and the relatively large size of the specimen.  It is definitely not an actinocerid, as those nautiloids have large siphuncles that expand in ring-like structures into the space in each cameral chamber (so the siphuncle looks like a series of rings stuck together), they are almost filled with secondary deposits, and they contact the exterior shell on one side (the ventral) where the ring-like segments are conspicuously flattened.  In actinocerids, the siphuncle was a large heavy structure that weighted the shell down so the ventral side lay flat on the sea floor.  It is also not a michelinocerid as those nautiloids had relatively small centrally located nummuloid (bead-like) siphuncles.  We can exclude oncocerids because the shell is not conspicuously curved, and the oncocerids had small bead-like siphuncles that ran along the outside of the curve.  The straight parallel sides exclude genera such as Gomphoceras and Westonoceras.

 

Don

Wow. Very good information there Don. I think you've found the creature we needed. 

 

I guess that's it, then. Thanks so much for the help, everyone!

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