CAMBRIAN COPROLITES: A RECORD OF NON-ANOMALOCARIDID GNATHOBASIC PREDATION

Cambrian coprolites provide important evidence of the diet and body size of predators and scavengers. Unfortunately, coprolites are extremely rare and difficult to recognize. In order to identify a bona fide Cambrian coprolite, one needs to thin-section or slab the fossil and falsify the hypothesis that it is: i) part of a circular to cylindrical debris-lined resting trace such as Bergaueria; ii) a spherical to blob-like regurgitation; iii) a premortem aggregation of complete individuals (e.g., a chain- or sphere-like aggregation of Waptia); iv) a elongate or flattened lined burrow; and v) the elongate weathered edge of a mm-thick skeletal hash bed, bounded by overlying and underlying shale.

Coprolites from the Latham Shale and Poleta Formations (E. Cambrian, CA) and Burgess Shale (M. Cambrian, BC) pass these criteria. Coprolites are 0.5-1 cm wide, 3-8 cm long, and are composed entirely of crushed trilobite, brachiopod, hyolithid, and other skeletal material. They do not contain complete individuals and are isolated from adjacent and over/underlying laminations by shale in which no other skeletal debris occurs. Coprolites are elongate to capsule-shaped, taper along their long axis, are compressed or boudin-shaped along their short axis, and do not exhibit evidence of sediment filled interiors (e.g., like many collapsed lined burrows). They are similar in size and shape to elongate putative coprolites from the Emu Bay Shale (E. Cambrian, S. Australia) and Marjum Formation (M. Cambrian, UT).

Because anomalocaridids had a soft mouth which could not close, and because they had soft preoral appendages, they could not have produced these coprolites. Neither could priapulids, which did not crush biominerlized prey and are not known to have scavenged skeletal debris. More plausible producers are arthropods with robust gnathobasic appendages, such as Sidneyia inexpectans (Burgess Shale, BC), Utahcaris orion (Spence Shale, UT), or redlichiid trilobites (global distribution). Sidneyia and Utahcaris have gut contents consisting of crushed trilobite, ostracods, hyolithids, and other phosphatic skeletal debris – making their linkage to these coprolites plausible. Retrodeformation of coprolites into cylindrical bodies also matches well with the interpreted gut size of these arthropods.