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Stable isotope analysis has begun to make its way
into the study of anthropology. It is used as a method for reconstructing
the dietary and environmental context of human and animal remains.
It uses differences in relative proportions of carbon and oxygen
isotopes in animal and human bones dentition skin and hair to identify
aspects of the surrounding environment and the type of food consumed.
Differences in carbon isotopic ratios can be used to determine the
types of plants that were consumed. Differences in oxygen isotopes
can be used to indicate climatic change to group a number of animals
to a single location and to show seasonality or migration patterns.
This project involved the investigation of samples from three distinct
populations that originated in Africa. The first population was
from the Carlos Museum¡'s collection of Egyptian mummies.
The second population was from the Kulubnardi collection of Nubians
at the University of Colorado at Boulder. The third population was
from recently dead herbivores from Uganda North Tanzania and Kenya.
The data from the herbivore population showed a high degree of intra
and inter species variation for oxygen isotopes with a high degree
of overlap between the giraffe M1 the hippopotamus and the warthog.
The wide degree of variation for the warthog could indicates a greater
sensitivity to climactic changes that a migratory pattern was followed
or that there was an unknown stressor that lead to the high variation
of data values. The data from carbon isotopes shows a relatively
low degree of interspecies overlap. Both of the giraffe teeth had
ƒÔ18C values that were very close to those predicted
by Kingston of -10o/oo to ¡V25.5 o/oo for C3 plant consumers
(the mean for the giraffe M1 was ¡V13.36 and for the giraffe
P1 was ¡V8.09). The values for the warthog hippopotamus and
rhinoceros fell very close to those predicted by Kingston of 3.5
to ¡V2.5 o/oo for C4 plant consumers. The warthog probably
consumed a wider range of food as shown by its decrease in values
outside of the C4 range and may have supplemented its diet with
C3 plants or with some other type of food.
Many studies have identified strong correlations
between stable isotope ratios and vertebrate diets. Since the isotope
composition reflects what the animal eats it can be used to determine
the different types of environments that the animal occupied (Ambrose
1993, Katezenberg 1989). Differences in relative proportions of
stable isotopes of carbon and oxygen in animal bones dentition skin
and hair can be used to identify aspects of their diet and surrounding
environment. Isotopic fractionation is the change in isotopic ratios
between substrate and product that typically occurs in biological
and chemical processes. It can be used to differentiate between
plants utilizing different metabolic pathways as well as to identify
climactic conditions such as precipitation patterns temperature
and humidity (Schoenger 1995). Isotopic values in teeth are representative
of diet from an individual's early childhood during their tooth-forming
years (Wright 1998). Isotope values from bones show the average
value of diet over approximately the last ten years before the individual's
death. Values from skin show diet from the two to three weeks prior
to death. Values from hair that is closest to the root show values
from 1-2 weeks closer to death and can show a short chronology with
1cm of hair being approximately 2-3 weeks worth of growth (Hrdy
1978). Oxygen isotopic composition correlates with precipitation
but the relation between animal and isotope concentration may change
based on the species of animal and other factors may influence its
composition (Kohn 1999). Browsing and mixed feeding herbivores tend
to have more enriched 18O values when compared to grazing herbivores
but this can still vary between species (Sponheimer and Lee-Thorp
1998). Much of the differences in the proportion of carbon isotopes
in animals can be attributed to the types of plants that the animals
eat. There are three basic types of plants available to animals
for consumption: C3, C4, and CAM. Usually carbon incorporated into
plants is depleted in 13C relative to atmospheric CO2 which has
a composition of ¡V7.8 o/oo. C3 plants are usually the most
depleted and C4 plants are usually the least depleted. CAM plants
overlap both C3 and C4 ranges (Kingston 1999). The ƒÔ13C
values for animals are positively correlated with the values of
the plants that they eat and provide a basis for determining the
types of plants that make up an animal's diet as well as those found
in the surrounding environment. The values for modern herbivores
show an enrichment of about 12.5 o/oo relative to the plants that
they ate (Kingston 1999). Egyptians This aspect of the research
analyzed even mummies from the Carlos Museum's collection of Egyptian
remains. Samples from skin tooth hair and bone were collected. Five
of the mummies were from the 21st dynasty (1039-945 BCE). Of the
five individuals two were female and three were male. One of the
women was probably an upper class lady and Chantress of the Temple
of Amun. Of the three men two were believed to be temple priests
and the third a temple scribe. The sixth mummy was a child from
dynasty 25-26 (760-525 BCE) with a cleft palate. The seventh mummy
was a head from the late period. There is very little information
known about this individual. No other information is known about
this mummy. (Lacovara 2001). This analysis sought to identify the
basic sources of diet along with any seasonal or longitudinal variation
in diet. Nubians In this study we analyzed eighty rib samples from
the Kulubnarti collection of Nubians on loan from the University
of Colorado at Boulder. The remains from Kulubnarti are believed
to be made up of two distinct populations the S and R groups. The
bodies from the S group were excavated from the 21-S-2 cemetery
on Kulb Island which is located on the west bank of the Nile and
was not usually separated from the mainland except for during floods.
The bodies from the R group were excavated from a mainland cemetery
across the temporary waterway from Kulb and near a classic Christian
church (Adams 1999). Previous research has caused people to hypothesize
that the S and R groups represent diachronic populations with the
S group existing from 550-750 CE and the R group existing from 1000-1500
CE (Adams 1999). Recent reanalysis of grave textile and pottery
styles show that these two groups may actually represent a synchronic
population existing closer to the dates of the S group. Under this
hypothesis social stratification is the primary factor in any observed
differences. The purpose of analyzing the Nubians was to reconstruct
dietary composition and to test if there were any dietary differences
between the S and R groups diet across age ranges. Herbivores The
third population was from recently dead herbivores from Uganda North
Tanzania and Kenya. Two from the same giraffe Giraffa camelopardalis
one was an M2 tooth (G94) and the other was a P1 tooth (GP94) one
from a hippopotamus Hippopotamus amphibius (H1002) one from a rhinocerous
Ceratotherium simum (R1010) and one from a warthog Phacochoerus
aethiopicus (WM901) were analyzed. Giraffes mainly eat leaves preferably
from the Acacia tree. Hippos will primarily eat grasses preferentially
feeding on short grasses close to water. Rhinos will eat grasses.
Warthogs will eat grass roots berries tree bark and sometimes dead
animals (San Diego). Analysis of dental remains from these newer
teeth as well as of modern animal lifestyle patterns and existing
environmental conditions may lead to the formation of a pattern
for species analysis that can be applied to ancient remains.
Inorganic material:
Teeth and Bones
- React with 2% NaOHCl for 24 hours and rinse to neutral.
- Treat with 0.1M CH3COOH for 16 hours under a weak vacuum rinsed
to pH7 and freeze dry.
- React with pure H3 PO4 for 48 hours. Collect released CO2 analyze
using an irm-mass spectrometer.
Organic Material:
Bone
- Extract lipids using a 10:5:1 solution of CH3OH:CHCl3:H2O in
a soxhlet distillation unit for four hours.
- Demineralize using 0.5M HCl for 2-28 days at 40C.
- Extract humic acid using 0.1%KOH for 48-72 hours.
- Isolate 0.3-0.5mg of collagen to be sent to the mass spectrometer
for analysis.
Hair
- Extract lipids and resins by soaking the hair in a 10:5:1 solution
of CH3OH:CHCl3:H2O in a test tube for 30 minutes with the solution
changed every 10 minutes.
- Freeze dry and send the samples to the mass spectrometer for
analysis.
Skin
- Sonicate the skin twice to remove excess dirt and resin.
- Half of the skin samples were sent to be analyzed using the
mass spectrometer after sonication. The other half had lipids
extracted in the same manner as the hair.
Results have not yet been obtained for the Egyptian
mummies, the Nubians, and most of the herbivore teeth. All of the
data sets from individual teeth are statistically different but
graphical representation shows a large amount of overlap. One of
the most striking differences about the individual data sets is
how different the isotopic variation within the giraffe teeth. Oxygen
isotopes from the P1 tooth contain significantly more 18O than do
those from the M2 tooth. The hippopotamus tooth had the steadiest
values and was much lower than all of the other data points except
for the extreme low value of the warthog. These intertooth variations
could indicate seasonal changes. There was a relatively high degree
of difference between species for their relative proportions of
carbon isotopes. The data from the giraffe teeth had the lowest
proportionalities of carbon isotopes with the M2 tooth being significantly
lower than the P1. There was very little correlation between the
two giraffe teeth except that both of them had lower values than
all of the other animals. The warthog had a high degree of variation
within its values possibly due to its wider dietary range.
The data for oxygen isotopes indicates that there is a high degree
of interspecies overlap. The data sets from the hippopotamus the
rhinoceros and the giraffe M2 are relatively linear and the data
for the giraffe M1 and rhinoceros are very similar. There are not
enough data points for the intertooth variations in the giraffe
P1 to be analyzed. Changes in values could indicate changes in climactic
variation especially those values that are more than one standard
deviation away from the mean. The wide degree of variation for the
warthog could indicate a greater sensitivity to climactic changes
or that a migratory pattern was followed or that there was some
other stressor like a drought that lead to the large range of data
values. The data from carbon isotopes shows a relatively low degree
of interspecies overlap. Both of the giraffe teeth although different
from each other had values for the proportion of 13C that were much
lower than all of the other animals. These values are very close
to those predicted by Kingston 1999 for C3 consumers of -10 o/oo
to ¡V25.5 o/oo for C3 plants . The values for all of the animals
fell very close to those predicted by Kingston for C4 consumers
of -3.5 to ¡V2.5 o/oo. This verifies that giraffes primarily
ate C3 plants and warthogs rhinoceroses and hippopotami primarily
ate C4 plants. The warthog probably consumed a wider range of food
as shown by its decrease in values outside of the C4 range and may
have supplemented its diet with C3 plants or with some other type
of food. The giraffe teeth also indicate a wide degree of intertooth
variation that may need to be taken into account when comparing
these values to other giraffes. The data obtained in this project
will contribute to a basis for comparison with ancient remains.
Additional samples are needed to construct an adequate modern baseline
of African herbivores. Once this baseline has been created ancient
herbivore teeth remains can be compared with the modern ones in
hopes of better reconstructing environment and providing more scientifically
sound conjectures as to the environment that surrounded earlier
species. Data is still pending for the Egyptian and Nubian mummies.
Once available this data will contribute to a growing body of life
history data for both populations. Future directions for this research
include study of coprolites intestinal remains and DNA analysis.
Special thanks to the Michael C. Carlos Museum for providing samples
from Egyptian mummies and to Renee Stein for assistance in obtaining
those samples. To Dennis van Gerven of the University of Colorado
at Boulder for providing samples from Nubian populations. To George
Armelagos for assistance on this project to Diana Smay for help
with the Egyptian mummies and to Tanja Fabsits for help with the
microscope. This research is based upon work supported by the Howard
Hughes Medical Institute Grant No. 52003727.
Isotopes are atoms that have the same molecular number
but differ in molecular weight. These atoms can be found in the
atmosphere in things like carbon dioxide water and nitrogen. When
a plant produces its food it will take in some of the air. Diffferent
types of plants will incorporate different proportions of the isotopes
into their food. Stable isotope analysis uses the different proportions
in carbon nitrogen and oxygen isotopes to determine what type of
plant an animal was eating what sort of meat they were eating and
if there were any seasonal differences in rainfall. In this project
we studied Egyptian mummies Nubians and modern herbivores from Africa.
We only have some preliminary data on the herbivores. The data shows
that it is possible to discriminate between different types of animals
using stable isotope analysis and that it can be used to identify
what sort of plants that ancient animals ate.
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