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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