MASTODONS, VERTEBRATE TAPHONOMY AND NUTRIENT CYCLING AT THE GRAY FOSSIL SITE

Fossil proboscideans present unique challenges to vertebrate taphonomy. Carcass decay processes in proboscideans are relatively complex and prolonged due to their large size and attractiveness to both macro- and micro-scavengers. Understanding these processes, and consequent implications for nutrient cycling, is further complicated by the occurrence of proboscidean remains in wet or saturated burial contexts, which have poor analogues in the neo-taphonomic literature. Multiple mastodons have now been discovered from the early Pliocene age Gray Fossil Site (GFS) in northeastern Tennessee, including the nearly complete skeleton of a large male that is estimated to have had a live weight of ~16 metric tons. We interpret this as a potential single-episode death event based on the following taphonomic and sedimentological data: 1) close association between large angular boulders and skeletal elements, 2) depositional indicators of rapid mass movement, 3) breakage patterns on bone and dentin that indicate dynamic loading, and 4) the prevalence of terrestrial vertebrate taxa in slide contexts. This scenario has profound implications for understanding the processes of decay and nutrient flow within the GFS sinkhole complex. If true, the mastodons were buried in a rockslide near the edge of the inundated sinkhole, limiting access to vertebrate scavengers and arthropod decomposers. Consequently, the primary means of decomposition is inferred to have been anaerobic microbial communities. The resulting influx of N and C into a small, closed freshwater basin may have led to anoxia and hypereutrophic conditions, with cascading impacts to aquatic organisms.