This plate is one of the most unique trace fossils to come out of a sensational sandstone formation in Central Wisconsin that was once a tidal beach, resulting in the distinctive ripples you see on the surface. At present, it is generally accepted that the age of this sandstone unit is Middle Cambrian and thus represents an outlier of the Mount Simon Sandstone. This quarry has been producing some intriguing trace or ichnofossils, including huge madusae, tentacled jellyfish, Climactichnites and the diplichnites you see here, among others.

The depositional environment in this quarry varies from very shallow marine to aerial. This is very significant as these arthropods may have been some the very first large organisms and carnivores to abandon their marine habitat to utilize the terrestrial environment. If verified to be Middle Cambrian, these could be the earliest arthropod tracks thus far found in the fossil record, earlier than the Cambrian-Ordovician trackways from Canada described in the May 2002 issue of Geology.

The tracks appearing as wide dimples are called Diplichnites. The uniqueness of this plate is twofold: 1) such a long, straight, single trackway; 2) the obvious large size of the animal, since the sides of the tracks are some 2 inches apart, much larger than most tracks in the quarry. Note that this is a large specimen and is the convex half of the fossil that is preferred by most (part and counterpart are not usually recovered from the working quarry). The trace has had a subtle stain applied.

These tracks have been very popular at the Tucson fossil show, especially with museum curators. A publication is forthcoming describing these trackwaytypes to be submitted to the Journal of Paleotology.