THE IDENTIFICATION AND INTERPRETATION OF MILLIPEDE-PRODUCED ICHNOFOSSILS USING ACTUALISTIC STUDIES

Millipedes are known from body fossils as early as the Silurian. Modern millipedes are an important part of global soil ecosystems suggesting that ancient millipedes were as well. Little is known, however, about millipede biogenic structures in either the modern or the fossil record. The burrowing behavior and biogenic structures of extant millipedes were studied in a laboratory setting for application to the study of ichnofossils. The goal of this research was to determine the connections between millipede morphology, burrow morphology, and environmental conditions.

Two burrowing millipede species, Lophostreptus rutilans and Orthoporus ornatus, were studied. Specimens were placed in large, substrate-filled terrariums in temperature-controlled rooms. The test animals were exposed to variations in soil moisture and substrate composition. Biogenic structures analyzed in the laboratory include subsurface burrows and chambers as well as surface tracks and trails. Burrow descriptions include the architectural and surficial morphologies, type of fill, complexity, and tortuosity. Architectural morphology includes general dimensions, cross-sectional shape, orientation, branching, and interconnectedness of burrow elements. Surficial morphology includes such structures as scratches, bumps, and linings on the burrow walls that record excavation methods and locomotion style.

The millipede species produced burrows with distinct architectural and surficial morphologies despite their similar body morphologies. Burrow morphology was controlled by excavation methods, trace-making behavior, and burrow occupation time, all of which differed between the two taxa. Substrate composition, consistency, and soil moisture also resulted in reproducible variation in burrow architecture. Biogenic structures produced by millipedes in the laboratory were used to interpret ichnofossils from paleosols in the late Pennsylvanian Conemaugh Group of Ohio. There are at least two distinct morphologies of millipede ichnofossils in Conemaugh paleosols suggesting the presence of at least two millipede taxa. Experimental results also allow the use of morphological variations of these ichnofossil to interpret substrate characteristics and improve the interpretation of the paleosols the millipedes inhabited.