Cambrian Arthropod Fossils from Mount Elk Group
"Mass Mortality of 8 Unequivocal Carapaces"

Arthropod

Phylum Arthropod, Euthycarcinoids (?) or Aglaspida (?)

Geologic Time: Upper Cambrian (about 510 million years ago)

Size (25.4mm=1 inch): Matrix: 15.7 by 7.2 by 1.5 inches

Fossil Site: Krukowski Quarry, Elk Mound Group, Mount Simon Sandstone, near Mosinee,Wisconsin


EuthycarcinoidsThis 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 is not an ichnofossil. Rather, it is the body fossil(s) 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. 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 picture presentation below covers eight unequivocal carapaces (numbered in the pictures) with many fine details preserved, especially considering the coarseness of the quartzite sandstone matrix. Depending on the carapace, body segmentation, tail, leg base and legs are noticeable.

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)
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Click pix to enlarge
Entire specimen
Carapaces 1 - 8
Left half
Carapaces 1 - 5
Right Half
Carapaces 5-8
Closeups
Carapace 1
Carapace 2
Carapace 3
Carapace 4
Carapace 5
Carapaces 6 and 7
Carapace 6
Carapace 7
Carapace 8

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