NEOICHNOLOGY OF SCORPIONS: CONSISTENT BURROW MORPHOLOGY ACROSS CLADES AND ENVIRONMENTS

Scorpions are intermediate predators in numerous terrestrial environments, and many are temporarily to permanently fossorial. As a result, they play key roles in terrestrial food webs, in soil development, and as ecosystem engineers. However, scorpions have a poorly described ichnofossil record likely due to an inadequate understanding of their trace morphology. Critical to correcting this is assessing the level of variability of burrows constructed by phylogenetically, geographically, and environmentally distinct scorpions. Seven extant scorpions, Heterometrus spinifer, Pandinus imperator, Pandipalpus viatoris, Uroctonus mordax, Hadrurus arizonensis, Paravaejovis spinigerus, and Smeringurus mesaensis were studied through neoichnological experiments in sediment-filled terraria under varying substrate conditions. Casts of the burrows produced by these species were described qualitatively and quantitatively and then compared to each other and across different substrate conditions. Scorpions from tropical to temperate settings excavated by gathering sediment and carrying it away from the burrow produce open, straight-to-sinuous, subvertical tunnels to tunnel networks with single to multiple entrances and often chambers. Scorpions from semiarid to arid settings excavated by rapid movement of the legs to throw sediment behind the body to produce single to linked networks of U-shaped burrows as well as subvertical to helical tunnels or tunnel networks with single to multiple entrances and rarely chambers. Across the studied scorpions, changes in sediment composition and moisture content tended to reduce burrow production but did not significantly alter burrow morphology. All scorpion burrows, regardless of species, bore a moderate-to-high similarity despite differences in excavation styles and qualitative aspects of architecture suggesting that scorpions produce burrows of consistent form regardless of phylogenetic or environmental distance. Scorpion burrows possess distinct features that allow their recognition in the absence of tracemaker. This result of these studies provides key ichnotaxobases of scorpion burrows which can be used to identify them in the fossil record and improve interpretations of ancient terrestrial ecosystems and environments.