Neoichnology of Tropical and Arid Scorpions: Environmental Impacts on Burrow Construction and Form

ABSTRACT 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 variability of burrows constructed by phylogenetically, geographically, and environmentally distinct scorpions. Five extant scorpions, Heterometrus spinifer, Pandinus imperator, Pandipalpus viatoris, Hadrurus arizonensis, and Paravaejovis spinigerus were studied through neoichnological experiments under varying substrate conditions. Burrow casts produced were described and compared across species and different substrate conditions. Tropical scorpions excavated sediment and carried it away from the burrow to produce open, straight-to-sinuous, subvertical tunnels to branching tunnel systems with single to multiple entrances and often chambers. Arid scorpions excavated with rapid leg movements to throw sediment behind the body to produce single to linked networks of U-shaped burrows as well as subvertical tunnels to tunnel networks with single to multiple entrances and rarely chambers. Changes in sediment composition and moisture 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 architecture suggesting that scorpions produce burrows of consistent form regardless of phylogenetic or environmental distance. The 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.