Strontium isotope ratios in fossil teeth from South Africa: assessing laser ablation MC-ICP-MS analysis and the extent of diagenesis

This study tests the precision and accuracy of laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) for measuring strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) in fossil teeth from Swartkrans and Sterkfontein in South Africa, and explores the extent of diagenesis in these specimens. Compared to solution MC-ICP-MS or thermal ionization mass spectrometry (TIMS) methods, LA-MC-ICP-MS can be faster and less expensive, but has lower precision and accuracy. We found that ⁸⁷Sr/⁸⁶Sr ratios in fossil rodent teeth measured by LA-MC-ICP-MS were offset from solution values by a mean of 0.0005 ± 0.0010 (2σ). Because of the very wide spread of biologically available ⁸⁷Sr/⁸⁶Sr ratios (∼0.710 to ∼0.790) in the region, LA-MC-ICP-MS is more than sufficient for assessing the geographic origins of the fossil rodents. The concentration of strontium in modern and fossil enamel from the area is statistically indistinguishable, as is the range of ⁸⁷Sr/⁸⁶Sr ratios in modern rodents and fossil rodents from Swartkrans. Thus, there is little evidence of diagenetic Sr in the fossil enamel. In contrast, the fossil dentine may contain up to ∼50% diagenetic strontium, although many dentine ⁸⁷Sr/⁸⁶Sr ratios are still far removed from the background cave value of 0.729. We propose that LA-MC-ICP-MS will also be of use for investigating the geographic origins of other, non-rodent fossil teeth from the Sterkfontein and Swartkrans collections, and may prove of similar utility at other suitable sites.     

Burning damage and small-mammal human consumption in Quebrada del Real 1 (Cordoba, Argentina): an experimental approach

The zooarchaeological study of small-vertebrate consumption requires a taphonomical approach to differentiate animal bones that were incidentally incorporated from those that were intentionally exploited in the past human subsistence. In order to make this distinction, the relationship between archaeological small-rodent burned bones and prehistoric human behavior was explored using an experimental cooking study as a modern analogue. During the cooking experiment the entire carcasses of three guinea pigs (Cavia porcellus) and two yellow-toothed cavies (Galea leucoblephara) were placed in the coals of an open fire that simulate a real campfire, rotating their positions until the meat was completely cooked. Subsequently, the intensity of burning damage and the loss of skeletal elements were analyzed at macroscopical levels. The data was used to identify cooking evidence in the Ctenomyidae and Caviidae rodent bones recovered from Quebrada del Real 1 (ca. 6000-300 BP, Córdoba, Argentina). Remarkable similarities between the archaeological and analogical records were found, including the distinctive burning pattern on the distal extremities of the unmeaty long bones (e.g, radii and tibiae), the high frequency of broken incisor teeth and the loss of autopodium elements. Based on these comparative results, it is suggested that the small-rodent assemblages of QR1 were primary accumulated by humans though butchery, cooking and consumption related activities. Extending this study to other archaeological sites in South America may help to identify the prehistoric bone collectors of these small-animals.     

Taphonomic analysis of rodent bone accumulations produced by Geoffroy's cat (Leopardus geoffroyi, Carnivora,Felidae) in Central Argentina

Rodent prey remains recovered from Geoffroy's cat (Leopardus geoffroyi) scats were analyzed in order to identify taphonomic features produced by this predator. The analysis includes a year-long sampling discriminated by the seasons. Modifications produced by digestion are heavy. Taphonomic variables in samples discriminated by the seasons did not show major differences with respect to the total sample; thus, scats collected in any season clearly show the modifications on the bones of prey rodents made by Geoffroy's cats. The results presented here and its interpretation could be extrapolated to an analysis of zooarchaeological or paleontological assemblages.     

The influence of screen mesh size,and size and shape of rodent teeth on recovery

It is suggested with increasing frequency that rather than the industry standard of 1/4 inch mesh, zooarchaeologists use 1/8 inch or even 1/16 inch mesh to insure more complete recovery. These suggestions are based on the implicit assumption that the body size of a taxon and the probability that the remains of that taxon will be recovered are positively correlated. Size of skeletal specimens provides a more direct measure of recovery probability and accounts for the fact that not all skeletal elements in a body are the same size. Frequencies of eight kinds of rodent teeth representing three genera recovered from the Marmes archaeological site in southeastern Washington State, USA, correlate strongly with tooth size despite the use of 1/25 inch mesh screens. Shape of tooth types measured is insufficiently varied to reveal more than a general relationship between shape and recovery frequency. Choice of an appropriate screen mesh should consider the nature of a deposit, research goals, and cost efficiency.