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minnbuckeye

Unknown Gastropod

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minnbuckeye

I had to make a trip to the "big" city of Rochester, Mn today. As I drove by a new building site that exposed some Decorah Shale, I had to make a stop.  The Decorah Shale is an impervious layer that keeps pollution from seeping into deeper rock layers and contaminating our ground water. Obviously, building permits are being obtained without adherence to the zoning which prevents interuption of this great geologic feature! I will drink my own water but collect fossils from these ill conceived sites. While visiting such a site, I discovered this tiny gastropod that I can not identify. 

  

DSC_1266-002.thumb.JPG.e360a86e4dde6798b13cdc799b987c21.JPG

 

 2020-10-014.thumb.jpg.1a6cdb11cff5470a53a69950189ab389.jpg

 

 

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Fossildude19

Are you sure it's not a nautiloid/goniatite?

Looks a bit like Phragmolites, to me. :unsure:  

 

@minnbuckeye

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minnbuckeye

@Fossildude19, you hit the nail on the head!!!!! Thanks

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Fossildude19
59 minutes ago, minnbuckeye said:

@Fossildude19, you hit the nail on the head!!!!! Thanks

 

Glad to help.  :) 

 

But, just so you know, it is a gastropod, (Bellerophont) not an ammonoid as I initially stated. 

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minnbuckeye

@Fossildude19, I didn't want to question that even though I knew Bellerophonts are gastropods. Just glad for an ID. I tried to narrow it to genus and species. It looks like P triangularis but this occurs in the Platteville. It also is close to P obliquus which does occur in the Decorah, but is stated NOT to be found in our area. Any thoughts?????

 

Mike

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ClearLake

Mike

If you really think it is one of those two species, here are some drawings out of Ulrich, E. O., and W. H. Scofield. 1897. The Lower Silurian Gastropoda of Minnesota where they were both described.  First one is P. triangularis and second it P. obliquus

image.png.ffc9af9069a5919fcec096095cfcda87.png  Note the triangular shape in 22 (hence the name)

 

image.png.c56949fdf4b5f426e5b7407134581dd5.png

 

If it were just a choice between those two (I have not looked at any other options), I'd go with Phragmolites obliquus.  And since it is found in the Decorah, that seems logical.  

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minnbuckeye
4 hours ago, ClearLake said:

I'd go with Phragmolites obliquus

That is my best assumption

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