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ToeKnee

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I found these in the McGregor member of the Platteville formation in SW Wisconsin.  Endoceras?

 

5cf5dbce4767a_Endoceras3-Plattevilleformation-MineralPointWI.thumb.jpg.54544eaa71db842bfc20b7c5b1dcb537.jpg

5cf5dbce4767a_Endoceras3-Plattevilleformation-MineralPointWI.thumb.jpg.54544eaa71db842bfc20b7c5b1dcb537.jpg5cf5dbcf3c474_Endoceras1-Plattevilleformation-MineralPointWI.thumb.jpg.4e4103c56201efcc17d5b36b3788128f.jpg5cf5dbd06559e_Endoceras2-Plattevilleformation-MineralPointWI.thumb.jpg.08d6b367730c832c95a4fd265e7293f2.jpg5cf5dbd1d3c60_Endoceras4-Plattevilleformation-MineralPointWI.thumb.jpg.91ef8797cb34bf5e7781f34ffd7faae6.jpg

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Beautiful specimens! Could you take more photos from the sides of the first one? Curious to see if there's any preservation of the siphuncle and it's location if it is. Endocerids are characterized by a ventral siphuncle. Again, really cool finds, they definitely have the size going for them!

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I think the last picture shows the siphuncle (between 6 and 8 of the meter).

So last one should be orthocone Nautiloid.

As CSimpson said, more detailed photos are needed from the sides to be sure.

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After a little scrubbing I think I can make barely make out the siphuncle on the first one.  One the left side of this image.

 

 

5cf735a4e4778_Endoceras1.1-Plattevilleformation-MineralPointWI.thumb.jpg.724943f85ed119824bd16fc1969b4a94.jpg

 

The last image of the longest one definitely seems like it's there.  Here's a closer picture of the end of that one.  From about the 5 to 8" marks in this image looks like the siphuncle.  As for the shorter of the three I'm not really seeing anything standing out on that one.  I might cut a smidge off the end of that one with the saw.  If there were no evidence of a siphuncle what else would they be?  

 

5cf736a1ade59_Endoceras3.1-Plattevilleformation-MineralPointWI.thumb.jpg.6673d78d8867736c87d540d14fa307d0.jpg

 

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Even without any evidence of the siphuncle preserved, the uniform morphology as well as especially the septa preserved shows that they are nautiloid orthocones. I should have asked before to also see a better photo of the siphuncle from your fifth photo in which you already have done so. I honestly was more focused on the first photo just due to the sheer size of it. We just wanted to see the location of the siphuncle, also with a bit more research, you can see how it maintains a general tube shape through the phragmocone. Not gradually bulging in the segments like in Actinocerida, which is another large order of orthocones. Finally, after doing some research on the Platteville Formation, seeing that they have indeed found Endoceras specimens, I feel confident enough to say that these are Endoceras. I would be curious to see what others would say as well. Aside from size and siphuncle morphology, there's a lot of variables that differentiate nautiloid orthocones such as septa spacing, gradual tapering of the phragmocone, etc.

 
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