Trampling as a cause of bone surface damage and pseudo-cutmarks

Bones of recent mammals in the Amboseli Basin, southern Kenya, exhibit distinctive weathering characteristics that can be related to the time since death and to the local conditions of temperature, humidity and soil chemistry. A categorization of weathering characteristics into six stages, recognizable on descriptive criteria, provides a basis for investigation of weathering rates and processes. The time necessary to achieve each successive weathering stage has been calibrated using known-age carcasses. Most bones decompose beyond recognition in 10 to 15 yr. Bones of animals under 100 kg and juveniles appear to weather more rapidly than bones of large animals or adults. Small-scale rather than widespread environmental factors seem to have greatest influence on weathering characteristics and rates. Bone weathering is potentially valuable as evidence for the period of time represented in recent or fossil bone assemblages, including those on archeological sites, and may also be an important tool in censusing populations of animals in modern ecosystems.

I present a statistical technique for determining the disarticulation sequence of vertebrate skeletons based on the relative numbers of different intact joints in an assemblage of bones. For remains of modern Topi (Damaliscus korrigum) on the margin of Lake Turkana, northern Kenya, the disarticulation pattern is very consistent. This sequence, on dry land, differs from that reported for bovids that have disarticulated in the presence of water. On land the bones first released as single bones are those moved least easily by currents of moving water. The last released are those moved most easily. I develop a model of random scattering that suggests that the rate of dispersion is great at high concentrations of bones and decreases rapidly as the distance between bones increases. This leads to a condition where scattering effectively stops. The area of more or less stabilised dispersion is dependent only upon the mean distance that each random event moves a bone. Tests show that it is unlikely that articulated units themselves are much involved in scattering, and scattering appears to take place throughout the course of disarticulation.