Abstract
A unique ichnofossil assemblage from Pennsylvanian-age sandstones near Eaton Rapids, Michigan, USA, comprises straight-to-curved traces preserved in convex hyporelief, with the transverse ridges and median grove associated with the ichnogenus Arthrophycus. The Michigan traces show some branching or pseudo-branching (also known from other Arthrophycus specimens) and are among the smallest structures (millimeters in diameter) attributed to this ichnogenus. The orientation of the Michigan Arthrophycus burrows is distinct from other ichnospecies of this taxon in the pronounced co-planar alignment of the burrows, as opposed to the multiplanar, interweaving, “bundled” nature typical of the ichnogenus. On this basis we assign the Michigan specimens to a new ichnospecies of Arthrophycus. The “paralleling behavior” of the new taxon may reflect a strategy of the tracemaker to avoid previous burrows and reflect differences in resource availability or current energy. This new taxon supports previous records of the occurrence of this ichnogenus in Upper Carboniferous strata.
ACKNOWLEDGMENTS
We thank Roger Laylin of the Central Michigan Lapidary and Mineral Society for bringing these specimens to our attention, Kristian Fauchald of the Smithsonian Institution for generously sharing his time and expertise on modern polychaetes, and Anna Kay Behrensmeyer (SI) and Robert Anstey (MSU) for helpful discussions and suggestions. This article was much improved by the thoughtful critiques of Luis Buatois and Renata Netto.