06 June, 2012

Burrows and burrowing in Hadrurus arizonensis

Daniel Hembree and co-workers have recently published a paper describing the forms and shapes of Hadrurus arizonensis Ewing, 1928 (Caraboctonidae) burrows. The authors are geologists (and/or palaentologists), and the angle and terminology of this papers is somewhat different from what I'm used to from the traditional scorpion literature. I must admit there are quite a few terms in the paper that unknown to me (but praise Google for being a helpful friend ;)

The goal of the paper is both to learn more about scorpion burrows, but also to aid in the recognition of scorpion burrows in the fossil record and to determine if aspects of palaeoenvironment can be ascertained by variations in scorpion burrow morphology.

The paper also has a nice mini-review of scorpion burrowing behavior and several pictures of burrow castings showing the form and shape of Hadrurus burrows.

Bioturbation by terrestrial animals is common in arid and semi-arid continental environments. Scorpions have comprised a significant portion of the diversity of predatory arthropods in these environments from the Late Paleozoic to the Recent. Many scorpions are active burrowers and likely have a substantial, if rarely recognized, ichnofossil record. This project involved the study of the burrowing behaviors and trace morphologies of the scorpion Hadrurus arizonensis (Scorpiones: Caraboctonidae). Individual animals were placed into sediment-filled terrariums for two- to three-week periods after which burrows were cast, excavated, and described. Descriptions of the subsurface structures included architecture, dimensions, bioglyphs, complexity, and tortuosity. Additional experiments were run with differing sediment composition, density, 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 with the first two to three pairs of walking legs. The subsurface biogenic structures produced consisted of subvertical ramps, U-shaped burrows, helical burrows, and mazeworks. In the process of excavating the burrows, the desert scorpions also produced a hummocky surface topography as well as structures in dry, sandy sediment that resembled lamination and ripple cross-lamination. Increasing clay content and sediment density increased the complexity of burrow architectures produced. Reducing these variables limited the complexity of the burrows, reduced their likelihood of preservation, and increased the abundance of biogenic cross-lamination. Data collected from these and similar experimental studies can be applied to terrestrial ichnofossil assemblages in order to better interpret the paleoecology of ancient soil ecosystems.

Hembree DI, Johnson LM, Tenwalde RW. Neoichnology of the desert scorpion Hadrurus arizonensis: burrows to biogenic cross lamination. Palaeontologia Electronica. 2012;15(1):1-34. [ Free full text]

Thanks to Jahn Hornung for informing me about this paper!

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