A METHOD TO ESTABLISH THE PROVENANCE OF BONES AFTER COLLECTION: IMPLICATIONS FOR TAPHONOMY, BIOSTRATIGRAPHY, AND PALEONTOLOGICAL RESOURCE MANAGEMENT

The temporal and spatial context of a fossil bone (its provenance) can be obscured by many processes, natural and human. Bones may be reworked from one horizon to another or recovered from geologically complex or mixed sediments. In addition to these problems, the increasing value attached to fossils encourages commercial exploitation of limited and in many cases protected resources, and such exploitation can cause problems such as incomplete or false stratigraphic and locality information. Many such problems could be addressed though reliable and quantitative post-collection tests of provenance. Earlier studies have suggested that the trace element composition of fossil bones reflects the local depositional environment and therefore could be used to indicate provenance, but limits of resolution were not previously tested. Research on a large and well-documented sample of bones from Pleistocene excavations in Kenya, East Africa, demonstrates how trace element chemistry of fossil bone can be used as a natural tracer or fingerprint to uniquely characterize all bones from a single depositional unit and/or excavation site. Most bones from a single depositional unit of c.1000 yrs duration can be correctly assigned to their original excavation site, even when excavations are separated by <100 m laterally. Despite this high level of geochemical resolution within a single depositional unit, bones from successive stratigraphic levels also can be distinguished accurately on the basis of trace element chemistry. Such high levels of resolution may not be reproducible in all depositional settings (and certainly not in marine settings), but we see no geological reason why the geochemical variation in our test site should be unusually high.; hence, the observed REE variation are likely representative of levels of variation that would be expected in other terrestrial vertebrate-bearing deposits. This is supported by the fact that all previous studies of bone REE geochemistry have successfully discriminated between depositional horizons. This method (which requires <0.005g of bone) can be used to assess mixing within populations of fossil bones, to test provenance (and therefore age) assignments, to indicate deliberate alteration of fossil bones, and to identify fossils that have been collected or traded illegally.