Here is a a patological Elrathia kingii with a nice bite mark. Trilobites with injurys are quite uncommon in the Wheeler  Shale of Utah. For this kind of injury is many times Anomalocaris referred as the creator but this seems to be implausible if we keep the strange circular mouth structure of Anomalocaris in mind. The bite mark on this trilobite looks like to be created by some kind of pincer or claw like tool.

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