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Date: | Mon, 29 Sep 1997 09:00:47 +0100 |
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On Thu, 25 Sep 1997, Loren Cordain <[log in to unmask]> wrote:
>
> I would like to point out that relative components of ancient
> diets can be estimated utilizing stable carbon isotopic analysis (i.e.
> the 13C/12C ratio). 13C/12C analysis has been used to determine
> presumed dietary intake of Australopithecus robustus from 1.8 -1.0
> million years ago (1). The stable carbon isotope ratio (13C/12C)
> distinguishes the relative proportions of plants utilizing either the C3
> or C4 photosynthetic pathways.
<snip>
> Grasses are almost exclusively C4 plants whereas trees, shrubs and forbs
> are more generally C3 plants.
It is important to note that it is only **tropical** grasses, the grasses
of Europe and most of N. America are not C4 flora. This limits the
usefulness of this technique. There is also a very small shift in isotope
content from herbivore to carnivore, but this is much more difficult to
use, except in situations where there are one to one predator-prey
relationships.
> The carbon isotopes (13C and 12C) from
> plants are incorporated into the bones and teeth of the animals who
> consume these plants. Grass eating herbivores and the carnivores
> feeding on them can then be identified by the higher C13/C12 ratio they
> maintain in their bones and teeth. Lee-Thorp et al.'s data (1) suggest
> Australopithecus robustus consumed a mixed diet containing both C3 and
> C4 foods.
> Although, the interpretation is more difficult, strontium
> calcium ratios (Sr/Ca) have also been used to estimate dietary
> components of ancient diets (2).
Interpretation is in fact very much more difficult, as the Sr/Ca work is
rarely accompanied by assessment of postmortem changes to bone mineral. I
have a PhD student starting in a weeks time who will be taking a long hard
look at just what it is that Sr/Ca analysis is extracting from bones.
Andrew Millard
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Dr. Andrew Millard [log in to unmask]
Department of Archaeology, University of Durham, Tel: +44 191 374 4757
South Road, Durham. DH1 3LE. United Kingdom. Fax: +44 191 374 3619
http://www.dur.ac.uk/~drk0arm/
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