ABSTRACT

An integral part of the fossil crab assemblage described as the Dakoticancer Assemblage consists of fossil fecal material.

Large coprolites (about 10 mm in diameter) are represented by (1) hemicylindrical feces which usually contain fish remains and (2) cone-shaped spiraled coprolites which contain no hard remains.

Small coprolites (1.0 mm diameter and smaller), called fecal pellets, are ubiquitous and occur as ovoids, rods, and tapes. The ovoids are all prolate with some being smooth-surfaced and variable in size and others having undulatory surfaces. Rod-shaped pellets occur as small, smooth-surfaced and large, longitudinally striated cylinders. Tape-like castings of round or rectangular cross-section are uncommon.

The small coprolites are found in and around crabs and molluscs preserved as apatite concretions. The pellets are often found along trails associated with open burrows; one of which preserves the impression of a segmented burrower.

The large coprolites are interpreted to be the decayed remains of the feces of a vertebrate predator which preyed principally on fish. The fecal pellets are interpreted as the feces of deposit-feeding organisms which burrowed through the decaying, sediment-filled corpses of crabs and molluscs. The enrichment of the area of the corpses in phosphates may have been instrumental in the formation of the apatite concretions which preserve the Dakoticancer Assemblage.