Cambrian Arthropod Fossil from Mount Elk Group

This is a fossil for the advanced collector and/or ichnologist and/or museum. Prior to purchase, please review the Cambrian Shadows theme park section to gain the background to put the presentation below in context. Additionally, you can see the ichnofossils nomenclature chart to learn the technical terms that are used.

This arthropod carapace is not an ichnofossil. Rather, it is the body fossil of the putative arthropod track maker of Protichnites and Diplichnites trace fossils coming from the Krukowski quarry, which exposes the Elk Mound Group of the Mount Simon sandstone in central Wisconsin. This Cambrian arthropod with body segmentation and tail has resemblance to the enigmatic euthycarcinoids and aglaspids. The Protichnites and Diplichnites tracks found at the site are possibly the oldest terrestrial footprints in the fossil record.

This is one of only 10 fossils (and arguably the best) that will be made available. The remainder of the small layer is currently being used for research. The amphibious arthropods come from an interstitial desiccation layer between sandstone bedding planes (see ichnofossil nomenclature chart), where they are preserved as ventral, hyporelief body fossils.

The desiccation zone was likely created by the ingress of fine sediment, clay or mud in a trough, in which the creatures became entrapped and then perished; scratch marks on some specimens attest to the animals struggling to escape. We can hypothesize that, sandwiched between sand layers, the chitin exoskeletons of the arthropods filled with very fine sand and sediment even as mud and silt leached away, leaving the sandstone body molds to be preserved for the past half billion years.

The pictures shows one unequivocal carapaces with three possible Rusophycus (i.e., arthropod resting place), which are ichnofossils.

Also see: Cambrian Shadows

Good Reference:
Vacarri, N.E., Edgecombe G.D. and Escudero C., Cambrian origins and affinities of an enigmatic fossil group of arthropods, Nature 430, 554 - 557 (29 July 2004).