MICROTAPHONOMY AND GEOMICROBIOLOGY OF PHOSPHATIC COPROLITES AND RECENT SCAT

Analysis of modern and fossil carnivore scat by SEM and EDX shows a calcium phosphate matrix adhering to both fossil and modern bone fragments. This reprecipitate of the prey's calcium phosphates liberated during the acidic phase of digestion has entrapped and cemented together other gut contents including hair, essentially plastering them to the bone surfaces. The hair entrapped in the modern scat samples appears little modified by digestion and retains good cuticular scale morphology, while the cuticle of hair entrapped in the fossil samples appears to have been partially digested by the actions of fungal hyphae and shows some degree of biomineralization. Where the matrix has cracked open, hairs are revealed laying in natural hemi-cylindrical molds that often preserve the impressions of the hairs' cuticular scale patterns. On the broken matrix surfaces small spherical spaces interpreted as having been formed by gas bubbles commonly occur. These two characters provide bio-structural markers that narrow the window of formation of this phosphatic matrix. A number of carbonate mineral forms also occur on the fossils and in the surrounding sediment including needle-fiber calcite, micrite, and hollow crystalline tubes. Various fungal reproductive structures and other microbes are also present.

In addition to the distinctive corrosive tissue modification and loss that characterizes digested microvertebrate skeletal remains, the recognition that the mineralization of scat can be successional is important. A distinction is made among 1) mineralization that could occur within the digestive tract of the carnivore, 2) biomineralization that occurs due to the activities of colonizing microbes after scat deposition and 3) diagenetic mineralization after burial. This microtaphonomic suite of characters could potentially identify digested bone fragments as coprocoenotic, even if a coherent bolus shape has not been maintained. Continued identification of the consortia of biomineralizing microbes that colonize scat and skeletal remains may yield important insights into the variability of fossil preservation.