Shell imprint, fragment, geode or other?

[anonaddict]

location: aarhus, denmark

found: loose beach rock

units: metric

 

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Ive found this rock and am wondering if it is an ammonite or nautiloid fossil of some kind due to the shape.

I've marked the shape I'm seeing here

 

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the shape is fairly vague however i took notice of it due to the different surface texture as seen under magnification here

 

 

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compares to the surface texture of the rest of the rock seen below

 

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as always any information on the specimen is appreciated

 

Edited 34 minutes ago by anonaddict