Tracing the Source of the Elephant And Hippopotamus Ivory from ...

Koch et al. (1995) reported on several isotopes (carbon, nitrogen, and strontium)
from elephants in Amboseli National Park, Kenya, to track dietary and habitat changes.
Time series were gathered by microsampling sequential growth laminations in molar
roots (because tooth dentine grows by accretion in elephants). The results are presented
in Table 5. There were no coherent temporal trends for the nitrogen isotopes, but the
δ 15 N values were as expected for elephants living in a semi-arid environment. The
carbon isotopes did change with time, showing a switch in the diet from browse to grass.
A negative correlation was observed between carbon and strontium isotope values
(Figure 37) as a result of two isotopically distinct regions within the park: the C3 rich
bushlands on Precambrian soils (low δ 13 C, high 87 Sr/ 86 Sr) and the C4 rich grassland on
Plio-Pleistocene volcanic and lakebed soils (medium to high δ 13 C, low 87 Sr/ 86 Sr). The
soils overlying the Proterozoic gneiss had Sr ratios of approximately 0.7067, whereas the
soils on the Plio-Pleistocene volcanic rocks were approximately 0.7048. At 0.70518 the
mean elephant Sr value is closer to the Plio-Pleistocene volcanic rocks, suggesting a
greater residence time in this region (see Figure 38 for map of study area).
The researchers also warn that ivory may be more isotopically variable than bone,
as illustrated by the carbon isotope data. They suggest that “in the face of such high
within-tusk variability, it may be difficult to characterize a tusk or ivory artifact on the
basis of a single, small (for example, 20 mg) isotopic sample. Isotopic discrimination
between populations could probably be obtained if multiple samples of different
geologically controlled isotopes (Sr, Nd, and Pb) were examined for each artifact” (Koch
et al. 1995: 1343). While this may hold true for elephants (particularly with carbon
isotopes) because of their seasonal diet and large home-range, hippopotami are much less
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