Abstract
Strontium isotopes (87Sr/86Sr) in tooth enamel reflect the geological substrate on which an animal lived during tooth development. Therefore, strontium isotopes of teeth in fossil cave accumulations are potentially useful in determining whether an animal was native to the vicinity of the site or was brought in by other agents such as predators from farther afield. In this study, we tested the ability of strontium isotopes to help determine the origins of fossil rodents in Gladysvale Cave, South Africa. First, biologically available 87Sr/86Sr ratios were established using modern plants recovered from three geologically distinct areas, the Malmani dolomite, the Hekpoort andesite/basalt, and the Timeball Hill shale, all of which were found to be significantly different. Strontium isotope values were then measured on tooth enamel of rodents from a modern barn owl (Tyto alba) roost in Gladysvale Cave. The results clearly distinguished modern owl roost rodents that came from local dolomite (67%) versus those from other geological zones. We then measured strontium isotope values of enamel from 14 fossil rodent teeth from Gladysvale Cave. The average and range of values for the fossil rodents is similar to that of the modern owl roost rodents. Fifty-seven percent of the fossil rodents probably derived from the local dolomite, while others were brought in from at least 0.8 km away. A pilot study of 87Sr/86Sr ratios of fossil rodent teeth from Swartkrans Member 1 and Sterkfontein Member 4 indicates that 81% and 55% of those rodents, respectively, are from the local dolomite substrate. Overall, this study shows that strontium isotopes can be a useful tool in taphonomic analyses by identifying non-local individuals, and has great potential for elucidating more of the taphonomic history of fossil accumulations in the dolomitic cave sites of South Africa.
Copeland, S R