A Window into the Cambrian: Exceptionally Preserved Arthropods from Quebec and Wisconsin

Arthropods from the Late Cambrian Potsdam Group of Quebec and the Elk Mound Group of Wisconsin are possibly the earliest known phyllocarids and euthycarcinoids. Unlike most Phanerozoic soft-bodied fossils, the arthropods are preserved in 3-D in fine to medium grained, sub-angular to well-rounded, clean quartz arenites. These sandstones represent a suite of emergent sand- and tide-flats in which significant numbers of arthropod and other invertebrate trackways, mass strandings of medusae, and microbially textured surfaces occur. These fossils offer insight into the preservation of soft-bodied animals in lithologies that are typically not thought of as conducive to lagerstätte-style preservation.

Because there are relatively few described species of Paleozoic aglaspidids, phyllocarids and euthycarcinoids, larger scale questions in arthropod evolution are unresolved – for example, it is not known whether crustaceans are monophyletic or paraphyletic, or where the exact systematic affinity of Euthycaricnoidea lies. In order to help elucidate some of these relationships, the Elk Mound and Potsdam fauna is described and the systematic position of the new phyllocarids and euthycarcinoids is resolved using parsimony analysis and morphological data.

Protichnites and related arthropod trackways in aeolian facies of the Potsdam of Quebec represent the first evidence for animal terrestrialization; some of the new phyllocarid and euthycarcinoid arthropod body fossils are at the terminus of similar traces, potentially offering the opportunity to link animals to behaviors within specific paleoenvironments.