Experimental Neoichnology of Burrowing Arthropods from Eolian Environments

In desert dune settings, body fossils are rare, leaving the bulk of interpretations of ancient eolian ecosystems to be based on ichnofossils preserved in a variety of lithofacies. While many ichnofossils are simple to interpret, there are many ambiguous biogenic structures that are not well understood. Among animals that occur in modern eolian environments, arthropods are the most common bioturbators and are the likely producers of these structures. Recent studies utilizing laboratory-based neoichnological experiments have been able to bridge the gap of understanding between observed behaviors, environmental conditions, and the three-dimensional burrows produced by different continental animals. However, most eolian ichnofossils are only expressed in two dimensions and were likely produced in loose substrates that do not conform to such an experimental approach. This study examined the activities, behaviors, and two-dimensional biogenic structures produced by six arthropod species, Hogna lenta, Orthoporus ornatus, Paragaleodes sericeus, Smeringurus mesaensis, Ammopelmatus cf. fuscus, and Eleodes armata, in loose sandy sediment of varying composition and moisture levels. Sediment composition varied in the proportion and distribution of sand, silt, clay, and organic matter. Sediment moisture varied in ranges of 0-5%, 8-12%, and 15-25%. Active substrate disturbance activities were observed and recorded as well as behaviors associated with biogenic structures. Biogenic structures produced by individual species were compared between the different moisture levels and substrate compositions to evaluate the effect of substrate on trace morphology. Biogenic structures produced by all species in layered trials were compared to each other to evaluate the control of tracemaker on trace morphology. The highest depth and total amount of bioturbation were compared between each species. Biogenic structures produced in these experiments were compared to identified ichnofossils and ichnofabrics found in eolianites from the Mesozoic found around the world. There were significant differences among biofabrics produced in different substrate conditions and several key controls were identified in produced distinct trace morphologies among the arthropod species. This study has helped to identify new potential behaviors and tracemakers in eolianite ichnofabrics and ichnofossils. Continual refinement of interpretation of ichnofossils will aid in the understanding of environmental conditions and the paleoecology of ancient eolian environments.