Jump to content

Confused by Orthocone Cephalopods


minnbuckeye

Recommended Posts

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

Link to comment
Share on other sites

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.

    Tim    -  VETERAN SHALE SPLITTER

   MOTM.png.61350469b02f439fd4d5d77c2c69da85.png      PaleoPartner.png.30c01982e09b0cc0b7d9d6a7a21f56c6.png.a600039856933851eeea617ca3f2d15f.png     Postmaster1.jpg.900efa599049929531fa81981f028e24.jpg    VFOTM.png.f1b09c78bf88298b009b0da14ef44cf0.png  VFOTM  --- APRIL - 2015  

__________________________________________________
"In every walk with nature one receives far more than he seeks."

John Muir ~ ~ ~ ~   ><))))( *>  About Me      

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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).

" We are not separate and independent entities, but like links in a chain, and we could not by any means be what we are without those who went before us and showed us the way. "

Thomas Mann

My Library

Link to comment
Share on other sites

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

Finding my way through life; one fossil at a time.

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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.

 

    Tim    -  VETERAN SHALE SPLITTER

   MOTM.png.61350469b02f439fd4d5d77c2c69da85.png      PaleoPartner.png.30c01982e09b0cc0b7d9d6a7a21f56c6.png.a600039856933851eeea617ca3f2d15f.png     Postmaster1.jpg.900efa599049929531fa81981f028e24.jpg    VFOTM.png.f1b09c78bf88298b009b0da14ef44cf0.png  VFOTM  --- APRIL - 2015  

__________________________________________________
"In every walk with nature one receives far more than he seeks."

John Muir ~ ~ ~ ~   ><))))( *>  About Me      

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...