TAPHONOMIC SIGNATURES OF MASS MORTALITY IN A KENYAN LARGE MAMMAL DEATH ASSEMBLAGE

The fossil record includes deposits resulting primarily from mass mortality events as well as time-averaged assemblages incorporating both attritional and pulsed mortality. Although taphonomic analysis of fossils can reveal a great deal about circumstances of death and burial, studies of modern analogues combined with modeling of time-averaging effects are needed to evaluate varying contributions of attritional vs. mass mortality input. In 2009, the large ungulates of Amboseli National Park, Kenya, experienced catastrophic drought mortality, with loss of 70-95% of the standing populations of wildebeest, zebra, and buffalo. This provided a rare opportunity to examine the influence of mass mortality (MM) on a modern bone assemblage. In 2010, we sampled the Amboseli death assemblage using surface surveys in four habitats; swamp margin (N=4), plains (N=7), woodland (N=5), and bush (N=3). All surveyed areas were previously sampled between 2002 and 2004 under conditions of attritional, non-pulsed mortality (NPM). We found no differences in species richness or body-size distributions between the MM and NPM death assemblages. The MM death assemblage had a significantly positive number of dead individuals in Weathering Stages 0 and 1, reflecting recent skeletal input. This pulse of fresh bones was observed in swamp margin, bush, and woodland habitats, but not in the plains, likely indicating intra-habitat differences in where animals died during the drought as well as variation in predator and scavenger activity. The MM death assemblage had significantly higher concentrations of bones on the landscape and higher proportions of undamaged bones, both indicative of scavengers (chiefly spotted hyena) overwhelmed by the glut of available carcasses. Ontogenetically younger individuals were recovered in greater numbers in the MM bone assemblages, which we attribute both to greater drought susceptibility of young animals and the lower levels of destruction by overwhelmed scavengers. This first taphonomic comparison of MM and NPM large mammal death assemblages from the same ecosystem provides a starting point for identifying similar variations in skeletal input processes in fossil accumulations.