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What are these protrusions on Elrathia?


Sagebrush Steve

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Sagebrush Steve

I'm going through a bunch of trilobite fossils I collected at U-Dig Fossils in Utah about 10 years ago to get practice removing matrix.  I started with this one because it's only a partial and would be no great loss if I messed up.  I'm pretty sure it's an Elrathia kingii but what I don't understand is the protrusion that runs almost the full length of the axial lobe on the left side.  It looks like it may have penetrated the animal in life.  But it could have been part of the axial lobe that was displaced after death?  There also looks to be a similar fragment along the right side of the axial lobe.  I haven't seen anything like these in the photos of E. kingii I've come across, does anyone know what this is?  The 3 photos show the feature under slightly different lighting.

E kingii 2.jpg

E kingii 1.jpg

E kingii 3.jpg

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Sagebrush Steve

Could it have something to do with molting?

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I'm going to guess that it is a piece of debris that got pushed in to the trilobite after it died. Notice the crease into the pygidium, that seems so strong it cut in to the carapace. I think this object has cut deeply all the way up the carapace. Don't know what the object is... a bit of shell or something?



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Sagebrush Steve
3 hours ago, tmaier said:

I'm going to guess that it is a piece of debris that got pushed in to the trilobite after it died. Notice the crease into the pygidium, that seems so strong it cut in to the carapace. I think this object has cut deeply all the way up the carapace. Don't know what the object is... a bit of shell or something?


 

Thanks, tmaier, that might be what it is.  What makes me uncertain are the raised features on the right side of the axial lobe that I've circled in the photo here.  They extend along the axial lobe and appear to circle around the pygidium,  They look like they are part of the trilobite, not something foreign.  It makes me wonder whether the ridge on the left was similarly attached to the left side of the lobe and broke away to get embedded where it now resides.  That's why I wondered whether it could all be part of the molting process.  The ridge on the left could be a portion of the exoskeleton that got crushed into the trilobite during molting and subsequent fossilization.  Apparently trilobites had problems molting according to this: https://www.sciencedaily.com/releases/2002/11/021125072153.htm.  Could it have died during molting and ended up like this?  I may be way off base so I'd be interested in hearing what anyone else thinks.

 

Outline.jpg

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I'm going to guess that the object on the left got pushed into the trilobite, and the ridge on the right is an arifact of that action. The object caused tension pull on the exoskeleton and it separated, allowing this ridge of something to be exposed. So the ridge on the right is caused by the crushing debris pressure on the left.

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