COMPLEX BURROWS OF SOIL DETRITIVORES: THE NEOICHNOLOGY OF THE MILLIPEDE NARCEUS GORDANUS

Paleosols rarely contain well-preserved body fossils due to sediment reworking, the abundance of decomposing microbes, and the soft-bodied nature of most soil animals. Ichnofossils are often the only evidence of life in paleosols making knowledge of burrow morphology critical to interpreting their paleoecology. Ichnofossils also represent organism response to the environment. Experimental work with modern soil animals allows ichnofossils to be used to interpret temperature, moisture, drainage, compaction, water table depth, oxygen content, and nutrient availability. Millipedes are known from the Silurian and have been identified from body fossils and rare surface traces. Members of the superorder Juliformia are well adapted to a fossorial lifestyle, but their burrows are poorly understood. Despite their wide geographic distribution and role as primary detritivores in modern ecosystems their fossil record is relatively poor. In this study, specimens of the millipede Narceus gordanus were placed in 30 and 65 gallon terrariums with varying substrate and moisture conditions. The substrates were composed of different concentrations of organic matter, clay, and carbonate sand. The sediment moisture was varied from 35% to 50%. After periods of 7 and 14 days, the specimens were removed and open burrows were cast with plaster. Narceus gordanus uses a compressive burrowing technique to produce vertical tubes, helical burrows, O-, J-, and U-shaped burrows. Few open burrows were produced in 35% moisture substrates indicating that N. gordanus burrows are not likely to be preserved in low moisture, loose soils. The burrow casts were described and measured including the number of surface openings, depth, length, slope, tunnel width and height, width-to-height ratio, circumference, complexity, and tortuosity. The burrows were compared using a Bray Curtis similarity analysis both with each other and with those of two other previously studied millipede species, Archispirostreptus gigas and Orthoporus ornatus, to identify millipede-specific burrow properties useful in identifying millipede ichnofossils. Neoichnological studies on terrestrial animals such as this can provide vital data to help interpret ancient ecosystems as well as enhance our knowledge of the lifestyles of some important fossorial groups.