Ordovician, southwestern Wisconsin,

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This topic contains 9 replies, has 5 voices, and was last updated by  Julie Niederkorn 1 year, 7 months ago.

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  • #24045

    Julie Niederkorn
    Participant

    Not sure what this is.  I collected it in a roadcut in southwestern Wisconsin.  There was a trilobite on the rock and other Ordovician fossils.

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    #24049

    Jack Kallmeyer
    Moderator

    @julie-niederkorn  The reddish object in the first two photos is the glabella (central part of the cephalon) of a trilobite.  The third photo shows the pygidium of a trilobite.  Sorry I can’t tell you what the species is.

    Jack

    #24051

    Jeff Nolder
    Participant

    Hi again, Julie -I think the pygidium is Flexicalymene meeki.  The cephalon could be, as well, but there  isn’t enough exposed for me to be sure.  I’m glad you liked SW WI; hard to get good exposures here in the drifted area of SE WI.

    #24052

    Jim Chandler
    Participant

    The “Poka-dotted” fossils in photos 1&2 are bryozoans.

    Jim

    #24062

    Asa Kaplan
    Participant

    That pygidium is definitely not Flexicalymene! Note in this photo how triangular Flexicalymene‘s pygidium is, and how it terminates with a prominent bulb on the median lobe with hardly any posterior margin. The pygidium you show has many segments and a broad posterior margin — features typical of order Proetida, not Phacopida (of which Flexicalymene is a member). I was not able to locate an Ordovician trilobite to match your image, but I’ve included below an image of a pygidium that more closely matches the features I see in yours. (This pygidium belongs to Dikelocephalus, which is certainly not the trilobite in your hand.)

    Image result for flexicalymene pygidium

    https://upload.wikimedia.org/wikipedia/commons/d/df/Flexicalymene_meeki_pygidium_view.JPG

    https://upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Dikelocephalus_minnesotensis_pygidium_draw.png/440px-Dikelocephalus_minnesotensis_pygidium_draw.png

    #24063

    Asa Kaplan
    Participant

    The cephalon appears to belong to some ceraurine trilobite. For example, here is Ceraurus. Note the glabellar lobes and how they’re connected to the other parts of the cephalon.

    Specimen Photo

    http://strata.uga.edu/cincy/fauna/trilobita/Ceraurus.html

    #24064

    Asa Kaplan
    Participant

    Guide to trilobite morphology:

    https://www.trilobites.info/trilomorph2007.gif

     

    #24128

    Julie Niederkorn
    Participant

    Thanks everyone, I have never collected trilobite fossils before and really appreciate your help.  I was wondering if the pygidium is a Thaleops ovata?  The cephalon sure looks like the ceraurine-Ceraurus.

    <post bump> Any ideas, @jeff-nolder, @asa-kaplan, @jkallmeyer?

    #24339

    Asa Kaplan
    Participant

    Julie @julie-niederkorn, you have opened my eyes! I was assuming the entire fossil to be a pygidium, but now I take your point that it comprises the whole thorax plus the pygidium. And that makes it an excellent match for the thoracopygidium of Thaleops ovata. It also helps explain the outline that appears anterior to the thorax: It’s a cross-section through the cephalon. I note especially the robust right gena. For comparison:


    Congrats on your first complete trilobite, Julie 🙂

    #24340

    Julie Niederkorn
    Participant

    Thank you!  I am so excited to have found one!

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