Protichnites eremita unshelled? Experimental model-based neoichnology and new evidence for a euthycarcinoid affinity for this ichnospecies

Abstract

Protichnites eremita from the Cambrian Elk Mound Group of Wisconsin is reinterpreted based on new material and trackway experiments. Two new forms of P. eremita suggest that the discrete medial imprints of these traces could be produced by the segmented postabdomen of euthycarcinoids from the same deposit. Form 1 could have been produced by a pair of euthycarcinoids traveling together, like in limulid amplexus, where both individuals made imprints with their postabdomens. In this scenario, if one individual held its postabdomen to the left side, it is possible to produce left-handed shingling in trackways and angled segmentation of each medial imprint. Form 2 could have been produced by a single animal traveling in arcing or tightly looping paths. Experimentally-produced medial imprints yield morphologies that are consistent with both trackway forms. Thus, it seems more likely that P. eremita was produced directly by the animal's body (alone or paired) rather than by employing hermit-like behavior.