215-7 Neoichnology of the fecal pellets and casts of soil detritivores

Session: Coprolite Happens: Insights into Geobiology

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Abstract:

Invertebrate coprolites are relatively common within Cenozoic paleosols but their origin is often unclear. Neoichnological studies have provided valuable insight into the morphology of biogenic structures produced by different tracemakers, improving the interpretation of various trace fossils including coprolites. Modern soils are inhabited by numerous burrowing invertebrates that produce fecal pellets suitable for comparison. The purpose of this study is to document the size, shape, and placement of fecal pellets and casts made by modern soil detritivores for comparison with fossil fecal pellets from Paleogene to Neogene paleosols of the North American midcontinent. In this study, three millipede species, Chicobolus spinigerus, Orthoporus ornatus, and Tylobolus sp., and two earthworm species, Eisenia hortensis and Lumbricus terrestris, were studied in laboratory conditions. Specimens of each species were placed in separate sediment-filled enclosures. Fecal pellets of the millipedes were deposited on the sediment surface and collected directly from the enclosures. The earthworms were removed from their enclosure, rinsed off, and placed on a wet white paper towel in a container for 24 hours allowing them to deposit pellets. The morphology of the pellets was described qualitatively under a stereomicroscope and the length and width of the pellets were measured using digital calipers. Millipede pellets were pill-shaped with a spheroid to ovoid form, some having one end tapering to a point. Earthworm pellets were pill-shaped with an overall ovoid form. Millipede pellets were generally more cohesive, whereas the earthworm pellets often disaggregated after being deposited. The length and width measurements of both the millipede and earthworm pellets aligned with the size of the organism. The length-to-width ratio of millipede pellets ranged between 1 and 2, whereas earthworm pellets ranged between 0.5 and 4.5. The modern pellets were then compared to fossil pellets collected from paleosols of the Oligocene White River Formation. The morphology, length-to-width ratio, and dispersed distribution of the fossil pellets most closely resembled those of millipedes than earthworms. Coprolites in paleosols have the potential to provide valuable information related to understanding ancient biodiversity and soil ecosystems. Continued analysis of pellets produced by other modern soil detritivores will further aid in the interpretation of invertebrate coprolites.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8087

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