Distinguishing sheep and goats using dental morphology and stable carbon isotopes in C4 grassland environments

Distinguishing between sheep and goats in C-4 grass environments using new dental morphology criteria and enamel bioapatite stable carbon isotope ratios (delta(13)C) was tested on 35 modern individuals from the Central Rift Valley of Kenya. Two morphological criteria on the second and third lower molars, one of which had been previously partially described by Halstead et al. [Journal of Archaeological Science 29 (2002) 545], were found to be highly reliable in this population. Identification of species using carbon isotope ratios is made possible in some circumstances by differences in the feeding behavior of sheep, which are mainly grazers, and goats, which are mainly browsers. In environments where C-4 grasses predominate, sheep include a higher proportion of C-4 plants in their diet, and thus have higher delta(13)C values than goats. In the present study, the annual range and seasonal variation of carbon isotope ratio of diet of sheep and goats was measured from intra-tooth sequential analysis. Although the ranges of goat and sheep delta(13)C values overlap, those higher than -3.4 parts per thousand all belong to sheep; values lower than -5.2 parts per thousand all belong to goats. There is no overlap of the mean delta(13)C values by tooth, which range from -11.8 parts per thousand to -4.2 parts per thousand for goats, and from -3.1 parts per thousand to -1.3 parts per thousand for sheep. These results suggest that carbon isotope analysis of bone collagen and/or apatite will also distinguish sheep from goats in tropical C-4 grasslands. Application of the delta(13)C criteria to archaeological material must be restricted to C-4-dominated environments, and where potential access to C-3 plants (mobility, foddering) can be assessed. The utility of these morphological and isotopic criteria for differentiating sheep and goat breeds in other regions remains to be evaluated. (c) 2005 Elsevier Ltd. All rights reserved.