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minnbuckeye

Confused by Orthocone Cephalopods

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minnbuckeye

In the driftless areas of Minnesota, Iowa, and Wisconsin I find many Orthocone Cephalopods. Each one seems to have its unique way of being preserved, some as an outer shell, others with their internal anatomy showing. A few weeks ago Raggedy Man posted a cephalopod that looked to be a siphuncle to me. Bev on the otherhand thought it was a phragmocone. No experts chimed in so a conclusion was not determined. That following weekend, I did a little collecting in Iowa. The trip was highlighted with the finding of many cephalopods. As I cleaned the findings, my mind went back to Raggedy Man's post. The more I looked at these collections, the more I wanted to understand the anatomy exposed. I think my biggest frustrations are telling siphuncles from phragmocones. Are siphuncles always smooth surfaced? Should septa be seen in any unworn phragmacone? How does one differentiate phragmacone from the external surface of a cephalopod? Finally does anyone have a good site that ID's our local Ordovician cephalopods? Thanks for any input!!!!! Now enjoy my finds. By the way, since it IS football season, I HAD to use a BUCKEYE to size my cephalopods. If anyone is unfamiliar with a buckeye, it is a little bigger than an acorn. For any of you buckeyes, OH......DSC_0607.JPG

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minnbuckeye

2016-09-25.jpg

2016-09-252.jpg

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minnbuckeye

2016-09-254.jpg

DSC_0578.JPG

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minnbuckeye

2016-09-256.jpg

2016-09-255.jpg

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minnbuckeye

2016-09-253.jpg

2016-09-251.jpg

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minnbuckeye

DSC_0595.JPG

DSC_0596.JPG

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Fossildude19

This is the best diagram of cephalopod anatomy I have come across. 

 

post-2806-0-96430500-1375996410.jpg

 

I can't help much beyond that, ... and some of your items sure look confusing to me, as well. 

Here's hoping someone can chime in with more observations about your pieces.

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minnbuckeye

DSC_0604.JPG

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minnbuckeye

Notice the patch of bryozoan attached to this specimen

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fossiling

what is that object you used for size comparison? A nut or something?

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tmaier

A buckeye, which is a nut off the tree of a Hazel tree. They are about 25 mm diameter (an inch).



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fossiling

thanks!

paleoCOOL!

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Goatcabin15

orhocerus this fossil  is found in the ordovician rock .. here in cornwall they are found in devoniian layers they also occur in the silurian levels in shropshire and wales

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tmaier

A really nice collection, Minnbuckeye. I've collected in the Ordovician of southern Minnesota, and found some interesting stuff. You have a pretty good anatomy lesson on cephalopods there.

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abyssunder

I think that the one in the last picture is an orthoconic cephalopod siphuncle steinkern with part of the remnant phragmocone at one end (right side of the picture).

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Raggedy Man
51 minutes ago, minnbuckeye said:

DSC_0604.JPG

That a sweet piece Minnbuckeye! 

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Rob Russell

The one pictured in the bottom right hand corner of the group photo, which I believe is pictured individually first, may be endoceras. 

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FossilDAWG
50 minutes ago, minnbuckeye said:

2016-09-256.jpg

2016-09-255.jpg

These are examples of siphuncles of an endocerid nautiloid, possibly Endoceras.  What appear to be "sutures" on the outside are connecting rings where the septa met the siphuncle.  Kind of the reverse of suture lines, which formed where the septa met the outside shell.  Note that there is no siphuncle-like round structure visible in the end-on view.  This is a strong indication that you are looking at a siphuncle, though not foolproof.  Also the connecting rings tend to make a more inclined angle with the siphuncle, compared to the sutures, although again this is not always the case. 

 

Don

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FossilDAWG
2 hours ago, minnbuckeye said:

2016-09-25.jpg

2016-09-252.jpg

Here you can clearly see the siphuncle in the end-on view, still encased in the camerae (chambers formed by the septa).  The side view shows camerae and suture lines, the exterior of the shell has dissolved away.  Again, likely an endocerid.

 

Don

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FossilDAWG
2 hours ago, minnbuckeye said:

DSC_0604.JPG

In this specimen, the spike-like part is the siphuncle, and the ball on the end is a few remaining camerae.  The bryozoan growing on the siphuncle indicates a complicated taphonomic history:

1. The nautiloid died, was buried in the sediment, sediment filled the siphuncle and at least some of the camerae, and hardened (lithified) enough to keep the shape of the structures.  The curved mark on the siphuncle may have been made by some animal burrowing into the sediment.

2. The specimen was unburied, and eroded enough to expose the siphuncle, or perhaps the camerae at the end never filled with sediment.

3.  The bryozoan grew on the exposed siphuncle, which was a hard substrate suitable for attachment.  The fossil must have been exposed for some time for the bryozoan to reach this size.

4.  The fossil was reburied, and the enclosing sediment lithified to shale or limestone.

5.  400+ million years later erosion again exposed the fossil for you to find it.

 

Don

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CBOB

Wow!  Really great finds!  Thanks for sharing.  The "spike like" ceph is really an interesting one.

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Fossildude19
19 hours ago, FossilDAWG said:

These are examples of siphuncles of an endocerid nautiloid, possibly Endoceras.  What appear to be "sutures" on the outside are connecting rings where the septa met the siphuncle.  Kind of the reverse of suture lines, which formed where the septa met the outside shell.  Note that there is no siphuncle-like round structure visible in the end-on view.  This is a strong indication that you are looking at a siphuncle, though not foolproof.  Also the connecting rings tend to make a more inclined angle with the siphuncle, compared to the sutures, although again this is not always the case. 

 

Don

 

Thanks Don, for the cogent explanation of "what is what" with Minnbuckeye's  cephalopod fossils.

Fantastic job - I have learned a few things today. :)

Thanks again.

 

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minnbuckeye

Thanks to all that have tried to educate me further!!!!  To sum up what I think is correct:                                    

  

    1. The shells of the orthocone cephalopods are eroded away. So the ridges seen on my specimens is actually a mold of the inner chambered part of the phragmocone, not the surface of the cephalopod. 

     2. Siphuncles are not smooth (assuming no erosional forces) but show evidence of the suture pattern.  Again , they represent an infill of sediment in a hollow tube so an impression of the suture pattern occurs.

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