Protichnites

Protichnites is an ichnogenus of trace fossil consisting of the imprints made by the walking activity of certain arthropods. It consists of two rows of tracks and a medial furrow between the two rows. This furrow, which may be broken, set at an angle, and of varying width and depth, is thought to be the result of the tail region contacting the substrate.

Sir Richard Owen, the noted British paleontologist and anatomist who coined the term “Dinosauria”, based Protichnites on trackways that were shipped to him from the Cambrian Potsdam Sandstone of Quebec. He was correct in recognizing that these were the oldest footprints on land, having been produced in intertidal and supratidal environments during what would now be called Cambrian times.

Owen first thought that these trackways were made by tortoises, but new material convinced him that “articulates” (a group that included the arthropods) were responsible. He further suggested a kinship with Limulus, the modern horseshoe crab. Additional material was collected in Quebec, Ontario, New York and Missouri for the next 150 years without a single fossil of the maker of these traces. Finally, body fossils of potential makers were found in two of the same quarries that preserved Protichnites from the Elk Mound Group of Blackberry Hill, Wisconsin, and the Potsdam Group of Melocheville, Quebec. The animals, Mosineia macnaughtoni and Mictomerus melochevillensis, were euthycarcinoids, extinct arthropods that may have given rise to the mandibulates. Fossils that clearly tie euthycarcinoids to Protichnites were then found at Blackberry Hill.

It is possible that other extinct arthropods, such as members of the Aglaspidida, may also have produced some of these trackways. Trilobites have been suggested as well; however, no trilobites have been found thus far in the strata that contain this ichnogenus. Similar trackways are present in post-Cambrian strata; however, those are seldom referred to as Protichnites.

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