Large, complex burrow systems from freshwater deposits of the Monongahela Group (Virgilian), Southeast Ohio, USA

A large burrow complex is described from the Monongahela Group (Upper Pennsylvanian) in southeastern Ohio. The burrow complex consists of a branching network of elliptical to circular, horizontal tunnels, 1–18 cm in diameter, occurring on a single horizontal plane. The tunnels branch to form X-, T-, and Y-junctions with branch angles between 60 and 130°. Branching produces multiple polygonal galleries up to 60 cm wide connected by small horizontal tunnels. Vertical shafts connecting the galleries to the surface are not preserved. Tunnel surfaces are irregular with circular to elliptical nodes and depressions, elongate ridges and grooves, and 1.5–4.0 cm wide nodular patches typically located at branch points. The occurrence of these burrow complexes in the Monongahela Group represents one of the largest examples of a branching burrow complex older than the Cretaceous. The Monongahela burrow complexes are preserved within a succession of floodplain and palustrine sediments suggesting a freshwater habitat for the tracemaking organisms. Potential tracemakers of the Monongahela burrow complexes include a variety of Pennsylvanian crustaceans and vertebrates. The presence of these and similar Paleozoic ichnofossils indicate a long and complex evolutionary history of the trace-making behaviors associated with the construction of large, open burrow networks.