NEOICHNOLOGY OF TROPICAL AND ARID BURROWING SCORPIONS: ENVIRONMENTAL IMPACTS ON BURROW CONSTRUCTION AND FORM

Studying extant tracemakers, environmental conditions, trace construction, and trace morphology is vital for ichnofossil interpretation. Many scorpions are known to burrow, but despite having existed since the Silurian, they have a poor trace fossil record likely due to a lack of understanding of modern scorpion traces. In this study, burrows of three extant scorpions, Heterometrus spinifer a tropical species from Asia, Pandinus viatoris a tropical species from Africa, and Paravaejovis spinigerus an arid species from North America, were studied to identify key burrow characteristics, determine if and how evolutionary distance changed burrow form, and determine how burrow construction and form was affected by soil properties. Tests were used to determine the burrowing techniques, behaviors, and trace morphologies of each species under natural conditions and under conditions of altered soil moisture and composition.

Scorpions were placed in 65-, 56-, 30-, or 10-gallon terrariums based on scorpion size for three experiments, each lasting 14-30 days. The experiments consisted of 1) substrate and moisture conditions based on natural conditions, 2) raising or lowering moisture content from natural conditions, and 3) increasing or decreasing sediment grain size from natural conditions. At the end of each experiment, the scorpions were removed and burrows were cast in plaster for qualitative and quantitative description and analysis.

Each species produced distinct burrow forms. Heterometrus spinifer and P. viatoris used similar excavation methods where sediment was gathered in the first two pairs of legs or chelicerae, dragged away, and dropped. Heterometrus produced open, straight burrows comprised of a single entrance and subvertical tunnel. Pandinus produced large diameter, sinuous, branching burrow networks with 1-3 entrances and chambers. Paravaejovis excavated by rapid movement of the first three pairs of legs in order to throw sediment behind the body. Burrows had 1-3 entrances and mostly consisted of U-shaped burrows or networks close to the surface with no chambers observed. Changes in soil properties generally reduced burrow production. Data collected in this study can be applied to ichnofossils found in continental strata to better understand ancient terrestrial ecosystems and environments.