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Pennsylvanian gastropod?


KCMOfossil

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This specimen is from the Winterset Limestone Member in the Kansas City Group, Pennsylvanian Subsystem. It is somewhat fragile (I broke off two small pieces and then repaired it), so I have not be able to remove it from its matrix. The fossil is about 2x1 cm. There are small brachiopods and a bit of fan bryozoan on the rock as well. I have not seen any other fossils like this one in the area. It might be a gastropod, but the “base” of the fossil seems oblong, as though it came to a point (but is now broken) and the fossil does not really look spiral (although it is hard to tell). There are two photos of the front view; in addition there is a photo from the right side and another from the left side.  Any help regarding identification will be appreciated.

 

 

top measure.jpg

right side.jpgleft view.jpgfront view.jpg

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Welcome to the forum......:)

It almost looks like a trilobite  to me.....Is that possible.....:headscratch: 

Tony
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It DOES look like a piece of trilobite cephalon :headscratch:But in the second picture there seems to be a "folding in" that might be more suggestive of gastropod... Neat find!

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I agree with Trilobite, ... possibly Phillipsia sp. or Ameura sp.?

@piranha - advice needed. :)

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Thanks so much. When I first broke this fossil out of the small boulder it was in, I thought the material the fossil was made of looked like some of the trilobytes I had seen before in this area, but the presentation fooled me.  I can see now, however,  that the two ridged "bulge" on top is the eye and the eye ridge.  The narrowing on the left side would be the beginning of the Genal spine.  I have two other partial cephalons and 10 or so pygidiums--so this fossil will definitely go on the shelf beside those. 

 

Thanks again,

Russ

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Nice specimen.

 

With magnification, there may be individual lenses visible in the compound eye, like this:

 

post-6808-0-06695900-1404117022.jpg

Context is critical.

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Thanks, Missourian, for the suggestion.  Upon close examination I do not see any lenses on my specimen--perhaps next time.  

 

Would you agree that my specimen is an Ameura missouriensis?  Is that the species of the specimen in your photo?

 

Russ

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16 hours ago, abyssunder said:

If there are no visible lenses of the compound eye, then is not an Ameura missouriensis = Phillipsia missouriensis.

I've been meaning to ask about this. Does the cornea on holochroal eyes follow the contour of the lenses, and is it commonly preserved?

 

The only drawing I've been able to find is on this page:  http://www.trilobites.info/eyes.htm

It shows the cornea conforming to the shape of the lenses.

 

I was curious if I'm seeing the complete eye or just the lenses in trilobite fossils.

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18 hours ago, KCMOfossil said:

Thanks, Missourian, for the suggestion.  Upon close examination I do not see any lenses on my specimen--perhaps next time.  

 

Would you agree that my specimen is an Ameura missouriensis?  Is that the species of the specimen in your photo?

 

Russ

 

The lack of visible lenses is due to the degree of preservation (i.e. recrystallization) of fine structures in that bed in the Winterset. (The example I included is a rather large specimen from the Westerville Limestone.

 

And I would agree with Ameura missouriensis. I used to call them A. major, but it seems those two species are synonymous. Plus, in my experience, trilobites in the Winterset of KCMO have been exclusively Ameura.

 

Context is critical.

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Incredible. Thanks Doushantuo. 

 

If the eyes detected vibration as well as light, it's interesting that they disappeared entirely on some of the endobenthic trilobites.

 

Is there any literature on sensory organs of eyeless trilobites?

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Reading what I can find on the ventral eyes of the horseshoe crab. They seem to have been repurposed for other uses :).

 

If trilobite eyes detect vibration, would it be necessary for them to be external in the benthic variety? Curious if they could have been internalized in the absence of light. Would there be any way to tell in the fossil record?

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On 9/23/2016 at 4:11 PM, abyssunder said:

Late Paleozoic Trilobites from Kansas and Nebraska - Robert E. Swisher, 2007.pdf

Thanks, abyssunder, for the links.  The article by Swisher gives a nice distribution evaluation beside his Kansas City Group stratigraphy (p.6).  I'm quite sure that my specimen is from the Winterset formation because I found it at a common collecting site and I have a stratigraphy of the site.

 

The thread on trilobite eyes was also very interesting.  The photos are particularly helpful.  I had never realized how much variety there is in the eyes.

 

Russ

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