COMPLEX ICHNOFABRIC PRODUCED BY LARVAL TO ADULT BEETLES: MODERN AND ANCIENT EXAMPLES

Interpretation of continental ichnofossils is often hindered by our limited knowledge of traces produced by many modern continental animals, thus inhibiting our understanding of ancient continental ecosystems. Actualistic studies of the relationships between tracemakers, environment, and trace morphology improves this understanding. This project documented the traces produced by burrowing beetle species from their larval to adult life stages under varying environmental conditions. Experiments were used to observe the burrowing techniques, behaviors, and trace morphologies of each species under their natural conditions and how these aspects changed when sediment composition, moisture, and compaction were altered.

The beetle larvae burrowed through intrusion, compression, and excavation techniques using their head, appendages, and abdomen to produce open to backfilled burrows. The burrows included open to meniscate backfilled, straight to sinuous shafts and tunnels with compression linings, and false branching. Before pupation, the larvae produced spherical to ellipsoidal, unlined chambers. After pupation, adult beetles burrowed to the surface using their walking limbs to produce passively to back-filled, shafts as well as near-surface, ellipsoidal chambers.

These results highlight the ability of a single trace maker to produce a variety of different trace morphologies. In this case, changes in trace morphology were caused by differences in trace function, such as the preparation of pupation chambers, and changes in trace maker morphology, such as the transition from larval to adult life stages. The variety of traces produced did not reflect a high biodiversity, but the high bioturbation potential of individual beetle species. The repeated sequence of burrow production from their larval to adult stages resulted in high levels of bioturbation where multiple individuals were involved in a single experiment. Despite the continuous overlap of new traces over old ones, the nature of the trace origin and function could be discerned. This allowed for the reconstruction of the history of ichnofabric production, providing a model for comparison to ancient examples such as those from the Permian Dunkard Group, Eocene to Oligocene White River Formation, and the Miocene Pawnee Creek Formation of Colorado.