A NEW IN SITU ARTHROPLEURA TRACKWAY, DIPLICHNITES CUITHENSIS, FROM THE MIDDLE PENNSYLVANIAN UPPER FREEPORT COAL MEMBER, ALLEGHENY GROUP, HARRISON COUNTY, OHIO

An arthropleurid trackway (Diplichnites cuithensis) has been recovered in situ from a gray silty shale layer of the Upper Freeport coal member of the Allegheny Group in the roof of the Vail Mine, now closed, in Harrison County, Ohio. The trackway is straight-to-curved, c. 2.7 m long, and 9–9.5 cm wide, made by an animal estimated to be more than 30 cm long. The width is relatively narrow for an arthropleurid trackway but exceeds that of the leg span of the next largest Carboniferous millipedes, the euphoberiids and the palaeosomatids. Individual footsteps are robust, more robust than footsteps that would be expected to be produced by a euphoberiid. Footsteps are closely spaced, some overlapping and variable in shape, ranging from subrounded to oblong with a pointed interior. Although the best-known occurrences of larger arthropleurid trackways are associated with sandy deposits such as channel sandstones, the new occurrence, and many of the best-preserved body fossils of Arthropleura, are associated with finer-grained deposits including shales, concretions in shales, siltstones and coals. This dichotomy in the context of preservation may simply be due to the distinctive preservation of trackways, which are more likely to be identified in coarser, more-resistant rocks that have greater surface areas exposed, versus cuticular material that tends to be well preserved only in finer sediment that is more likely to preserve cuticular material but less resistant to weathering. The Upper Freeport coal was the last domal peat mass that formed in the Appalachian Basin, deposited during a phase of transition from the early Pennsylvanian (Bashkirian to Moscovian) wet interval to the late Pennsylvanian (Kasimovian-Gzhelian) dry period. The roof shale contains lycopods and diverse tetrapods, mostly aquatic. Thus the Arthropleura which produced the trackway was adapted to a climate that was perennially wet, and part of an ecosystem dominated by lycopods and a diverse assemblage of mostly aquatic vertebrates.