NEOICHNOLOGY OF THE DESERT SCORPION HADRURUS ARIZONENSIS: BURROWS TO BIOGENIC CROSS-LAMINATION

Bioturbation by terrestrial animals is common in arid and semi-arid continental environments. While predatory arthropods constitute a large portion of the burrowing fauna in these environments, their subsurface biogenic structures are relatively unknown in the fossil record. Scorpions have comprised a significant portion of the diversity of predatory arthropods in arid and semi-arid environments from the Late Paleozoic to the Recent. Many of these animals are active burrowers and likely have a substantial, if unrecognized, trace fossil record. This project involved the study of the burrowing behavior and trace morphologies of the desert scorpion Hadrurus arizonensis (Scorpiones: Caraboctonidae). Individual animals were placed into large, sediment-filled terrariums under stable air temperature and moisture conditions for two- to three-week periods after which open burrows were cast with plaster, excavated, and described. Detailed descriptions of the subsurface structures included basic architecture, bioglyphs, complexity, and tortuosity. Additional experiments were run with differing soil composition, compactness, and moisture to evaluate the animal’s behavioral response to altering environmental conditions. Specimens of H. arizonensis burrowed by scratching and kicking loose sediment from the subsurface to the surface with the first two to three pairs of walking legs. The subsurface biogenic structures produced consisted of isolated to interconnected U-shaped burrows, simple tunnels, and helical shafts. In the process of excavating the burrows, the desert scorpions produced a hummocky surface topography as well as structures in sandy sediment that resembled lamination and ripple cross-lamination. Increasing substrate compactness, moisture, and clay content increased the complexity and tortuosity of the preserved burrows. Decreasing these variables reduced the complexity of the subsurface structures and reduced the likelihood of their preservation as well as increasing the abundance of biogenic cross-lamination. Data collected from these and similar experimental studies can be applied to ichnofossil assemblages found in semi-arid to arid paleoenvironments in order to better interpret the paleoecology of these ancient soil ecosystems.