RECOGNIZING FOSSIL BURROWS OF LARGE SPIDERS: NEOICHNOLOGY OF TARANTULAS

The Mygalomorphae, a suborder of heavy bodied spiders that includes tarantulas, first appears in the Triassic. While burrowing is common among mygalomorphs, fossil burrows are not well-documented likely due to an incomplete understanding of the morphology of modern spider burrows. The goal of this study is to describe the morphology of burrows produced by tarantulas and to compare them to the burrows of other large terrestrial arthropods as well as vertebrates with the purpose of improving the interpretation of continental ichnofossils and ancient soil ecosystems. This project involved the study of the burrowing behaviors and burrow morphologies of Hysterocrates gigas, Pelinobius muticus, and Aphonopelma chalcodes (Araneae: Theraphosidae). These tarantulas inhabit tropical and subtropical forests, scrublands and grasslands, and semi-arid deserts, respectively. Individual tarantulas were placed into sediment-filled terrariums under stable temperature and moisture conditions according to their environmental preferences. The tarantulas were observed for two- to six-week periods after which they were removed and the open burrows were cast with plaster, excavated, and described. Descriptions of the burrows included basic architecture, dimensions, bioglyphs, complexity, and tortuosity. All three of the studied species constructed burrows by excavating sediment using their chelicerae and first two pairs of walking legs. The burrow openings were circular to elliptical and lined with thin layers of silk. The burrows produced consisted of 1) H. gigas: vertical shafts with large ovoid chambers near the sediment surface and at depth, 2) P. muticus: interconnected networks of branching tunnels along a single plane, and 3) A. chalcodes: straight to curved, subhorizontal tunnels. The three species of tarantulas each produced burrows with a distinct morphology which allowed them to be distinguished from one another. The tarantula burrows as a group were also unique in comparison to the burrows of trapdoor spiders, scorpions, whip scorpions, and skinks produced in similar experiments. Data collected from these experimental neoichnological studies can be applied to ichnofossil assemblages found in continental paleoenvironments in order to better interpret the paleoecology of ancient soil ecosystems.