EXPERIMENTAL NEOICHNOLOGY OF MODERN SOIL ANIMALS: KEYS TO INTERPRETING CONTINENTAL TRACEMAKERS AND RECONSTRUCTING ANCIENT SOIL ECOSYSTEMS

Modern soils contain diverse ecosystems that include micro- and macrofauna engaged in a variety of behaviors that produce abundant and distinct biogenic structures. Our knowledge of ancient soil ecosystems, however, is limited despite the preservation of biogenic structures in even Early Paleozoic paleosols. The interpretation of ichnofossils, including the tracemakers, behaviors, and environments that influenced their production requires the study of modern organisms. While there are numerous neoichnological studies with marine organisms, few have involved terrestrial animals. The lack of understanding of the biogenic structures produced by modern continental organisms makes the interpretation of continental ichnofossils difficult.

This project involved the study of scorpions (Pandinus imperator, Heterometrus spinifer, Hadrurus arizonensis), whip scorpions (Mastigoproctus giganteus), millipedes (Orthoporus ornatus, Archispirostreptus gigas), salamanders (Ambystoma trigrinum, A. opacum), and skinks (Chacides ocellatus, Mabuya multifasciata). The animals were placed in large, sediment-filled terrariums for up to thirty days during which their behaviors and resulting biogenic structures were observed. Biogenic structures produced in the aquaria included subsurface burrows and chambers as well as surface tracks and trails. Open burrows were cast with plaster while surface and soft sediment deformation structures were preserved with a sodium silicate solution. Descriptions of the of subsurface structures included basic architecture, bioglyphs, depth, slope, total length, tunnel width, height, and circumference, complexity, and tortuosity.

The biogenic structures included a diverse assemblage of shafts, ramps, U-, J-, and Y-shaped burrows, helical burrows, mazeworks, and boxworks. On average, each species produced three distinct morphologies. The quantitative aspects of the burrow morphologies were then compared using nonparametric statistics to determine if the burrow casts could be differentiated based on tracemakers, behaviors, and environmental conditions. The results from these experiments provide a vital dataset for assessing the paleoecology of ancient soil ecosystems through the improved interpretation of continental ichnofossil assemblages.