New Mexico Geological Society Annual Spring Meeting — Abstracts

L. F. Brady named the trace fossil Scolecocoprus in 1947 for specimens from the lower Permian Coconino Sandstone along the Little Colorado River near Cameron in northern Arizona. He named two ichnospecies, the type ichnospecies S. cameronensis and another ichnospecies, S. arizonensis. Scolecocoprus is a burrow. Brady considered Scolecocoprus to be a series of closely packed and aligned fecal pellets (coprolites) that filled a burrow. However, later workers regarded Scolecocoprus as a horizontal, backfilled burrow and treated it as a synonym of Taenidium (e.g., D’Allesandro and Bromley, 1990; Keighley and Pickerill, 1994). We question that synonymy for S. cameronensis, because S. cameronensis has a very coarsely segmented (annulated) structure without the meniscate backfill characteristic of Taenidium. S. arizonensis, on the other hand, is likely based on a specimen of Taenidium. Nevertheless, the type ichnospecies of Scolecocoprus is distinct from Taenidium, so we consider Scolecocoprus to be a valid name.

Scolecocoprus has long been known only from two occurrences in Arizona. We report its first record outside of Arizona, from the lower Permian Abo Formation in Socorro County, New Mexico at NMMMNH (New Mexico Museum of Natural History) locality 13833. Here, we collected three specimens of S. cameronensis: (1) NMMNH P-103036, one string of segments in convex hyporelief with segments that are 4-6 mm wide; (2) P-103037, somewhat disaggregated segments in concave epirelief with segment widths of about 10 mm; and (3) P-103038, two slightly sinuous, nearly parallel strings of segments in convex hyporelief; segment widths are 5-10 mm.These burrows are non-branching, non-meniscate, and lined, with sediment packages longer than wide. The sediment fill within the burrows is similar to the surrounding (host) rock in color and grain size. We explain this fill as “sediment pass-through” as the creature was moving through nutrient-poor sediment (also suggested by the lack of color change of the sediment filling the burrow). The newly discovered New Mexico specimens occur in very fine-grained red sandstone (siltstone) stratigraphically high in the lower Permian Abo Formation, making them the oldest known occurrence of Scolecocoprus.

Brady (1947) believed that Scolecocoprus cameronensis was the feeding burrow of a large worm, possibly an oligochaete, living in a damp sand dune environment (Coconino Sandstone). Frank DeCourten (1978) re-evaluated S. cameronensis and concluded that Brady’s specimens may not have come from the Coconino Sandstone and that the burrows were made by suspension-feeding organisms restricted to shallow marine environments.However, the burrow fill indicates that the tracemaker of Scolecocoprus was likely a deposit feeder, not a suspension feeder. As the Abo specimens were found within a few meters of the first dolostone of the Yeso Group, marine influence cannot be ruled out at this point. So, was Scolecocoprus terrestrial, marginal marine, or a facies crosser?

The identity of the trace maker remains uncertain. It likely was a deposit-feeding worm, but modern analogs have proven to be elusive.

References:

1. Brady, L.F., 1947, Invertebrate tracks from the Coconino Sandstone of northern Arizona: Journal of Paleontology, v. 21. no. 5, p. 466-472.
2. D’Alessandro, A. and Bromley, R.G., 1987, Meniscate trace fossils and the Muensteria-Taenidium problem: Palaeontology, v. 30, part 4, p. 743-763.
3. DeCourten, F.L., 1978, Scolecocoprus cameronensis Brady (1947) from the Kaibab Limestone of northern Arizona: a re-interpretation: Journal of Paleontology, v. 52, no. 2. p. 491-493.
4. Keighley, D.G., and Pickerill, R.K., 1994, The ichnogenus Beaconites and its distinction from Ancorichnus and Taenidium: Palaeontology, v. 37, part 2, p. 305-337.