CLIMATIC AND ENVIRONMENTAL CONTROLS ON BONE WEATHERING: TIME-AVERAGING, ACCUMULATION HISTORIES, AND ECOLOGICAL INSIGHT

Establishing acquisition patterns of taphonomic damage on biological hard parts can provide data towards establishing accumulation histories of death assemblages. For vertebrate assemblages, patterns of bone weathering (BW) have often been used in this way, though few settings have been examined to test BW variability due to climatic and environmental controls. I use the large-mammal (ungulate) death assemblage of Yellowstone National Park (YNP), Wyoming, to establish BW characteristics in a temperate climate. Transects in four habitats (grasslands, forests, river-margins, and lake-margins) provided data on patterns of BW in different habitats and microenvironments. Carcasses with known postmortem ages and radiocarbon dating of additional bones provided data on weathering rates. Bones in YNP progress through six stages of weathering comparable to those in semi-arid, tropical settings (Amboseli, Kenya). While the initial trajectory of BW is highly similar between YNP and Amboseli, overall BW rate is depressed in YNP leading to centennial-scale bone survival. Bone weathering is highly variable on small geographic scales (including different surfaces of single bones). Even minor burial slows BW. Differences in the weathering stage frequency distribution among habitats are minor and best explained by variation in rates of BW and burial, and changes in ungulate habitat use over time. Bones start un-weathered and BW increases with time polygonally such that severely weathered bones result from extended postmortem weathering durations; though not all bones with extended postmortem ages are deeply weathered. Thus, while bones in early stages of BW may be from wide ranges of postmortem ages, bones in the most advanced weathering stages can be confidently assumed to be of relatively extended postmortem age. Though sensitive to climatic and environmental heterogeneities, patterns of BW can contribute to the ecological interpretations of vertebrate death assemblages.