We conducted a stable isotope study of bone collagen extracted from leporids and white-tail deer. Our samples include modern deer and both modern and prehistoric leporids.

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OVERVIEW
We conducted a stable isotope study of bone
collagen extracted from leporids and white-tail
deer. Our samples include modern deer and both
modern and prehistoric leporids.
Proxy data, including pollen analysis at Boriack,
Weakly, and Patschke bogs (Bousman 1998 Camper
1991 Nickels and Mauldin 2001) and stable
isotopes analysis of paleosols and humins from
Medina River and Halls Cave (Nordt et al. 2002,
Cooke 2005), that reflect long-term, large-scale
climate patterns are commonly used to reconstruct
paleoecological conditions (shown in figures
below). Yet prehistoric hunter/gatherers adapted
to short-term (e.g., seasonal, yearly) local
conditions. Stable carbon isotope analysis of
collagen from cottontails (Sylvilagus sp.) and
jack rabbits (Lepus californicus), both common in
Texas archaeological sites, has the potential to
monitor these short-term local conditions. Change
in leporid collagen signatures should track
ecological shifts at short temporal and limited
spatial scales.
Leporids occupy small lifetime home ranges (ca
300-500 ha French et al. 1965 Smith 1990), have
short lives, typically less than three years
(Feldhamer 1979, French et al. 1965), and consume
both C3 and C4 vegetation depending on the
nutritional value and water content of available
plants. Leporid bone collagen should reflect
local diet during their brief lifetime.
Plants that use a C3 or C4 photosynthetic pathway
produce distinct carbon isotopic signatures. The
?13C of C3 and C4 plants average -26 and -12,
respectively (OLeary 1988). Measurements of
carbon isotope ratios in collagen extracted from
herbivore bones can provide an estimate of the
relative contribution of C3 and C4 plant groups
in the herbivore diet. As these two different
plant pathways are favored by different
environmental conditions, with C4 plants more
common in warm, arid settings, and C3 plants more
common in cooler, moister settings, the relative
contribution of C3 and C4 plants in herbivore
bone collagen can provide data to reconstruct
aspects of past vegetation and climate.
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Is There Gold in Them Thar Hares? Using Small
Herbivores from Archaeological Sites in
Paleo-ecological Reconstruction Cynthia Munoz,
Leonard Kemp, Raymond Mauldin and Robert
Hard Center for Archaeological Research and
Department of Anthropology, University of Texas
at San Antonio
SAMPLE
Seventeen prehistoric samples (11 jack rabbits
and 6 cottontails) were collected from 41MM340, a
stratified Late Archaic site located in Milam
County, Texas (Mahoney and Tomka 2001 Mahoney et
al 2003 see Kemp 2008). Multiple radiocarbon
dates suggest that hunter/gatherers occupied this
site between 2430-3050 BP (Mahoney and Tomka
2001) during a portion of the Late Archaic. As a
control, one modern jack rabbit was collected
from Val Verde County, Texas. One modern
white-tail deer (Odocoileus virginianus) was
collected from the Edwards Plateau region of
Central Texas.
METHODS
Bone samples were cleaned using a Dremel tool, to
remove exterior surface, followed by repeated
ultrasonic baths. Samples were dried, then
crushed to small fragments with a mortar and
pestle.
Branson Ultrasonic Cleaner
Jack rabbit femur
Weighed samples were decalcified with 0.5N HCL
for 30 hours, followed by multiple washes with
double distilled water. Samples were treated with
0.1N NaOH for 30-60 minutes to remove humic acids
and lipids, followed by multiple washes.
Collagen samples were solubilized with 0.01N HCL
at 70ºC in an Ecotherm oven for 11 hours.
Samples in HCL
Ecotherm oven
Solubilized collagen was freeze-dried under
vacuum resulting in a cotton-like product.
Approximately 0.550 mg of each sample was
analyzed by a Thermo Finnigan DeltaPlus XP Stable
Isotope Ratio Mass Spectrometer (IRMS). Raw
sample values were normalized against external
standards.
Stable Isotope Ratio Mass Spectrometer
Freeze dried collagen
Labconco freeze-dryer
This research is sponsored by the National
Science Foundation. Data and detailed results
regarding this poster as well as future analyses
and results can be viewed at http//car.utsa.edu/R
esearch/isotoperesearch.html.
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RESULTS
Because archaeological bone has a high potential
for postmortem diagenetic alteration and collagen
degradation, each sample was evaluated for
collagen integrity using the atomic ratio of
carbon (C) to nitrogen (N) (Ambrose 1990 Ambrose
and Norr 1992).
Samples with a CN ratio lower than 2.9 or higher
than 3.6 exceed the accepted threshold suggested
by analysis of modern and archaeological samples
(see DeNiro 1985 DeNiro and Schoeninger 1983
DeNiro et al. 1985 Schoeninger and DeNiro 1984).
Results from five samples (shown in blue on the
figure to the left) are outside this range and
were not considered in our paleoclimate analysis.
Twelve samples from the metatarsal of a single
modern deer sample were processed to assess the
accuracy of analytical procedure and overall
precision (shown to the right). White-tail deer
primarily feed on C3 vegetation (Davis and
Schmidly 1994). Two samples of this deer were
also processed by Geochron, an outside lab,
returning values of -20.0 and -19.6. The
results of 11 jack rabbit and 6 cottontail
samples point to a diet more concentrated in C4
plants and C3 plants, respectively.
While the ?13C values obtained to date for the 17
leporid archaeological samples from site 41MM340
preclude any detailed discussion of temporal
patterning of past-vegetation, the ?13C values
(shown below) show a wide range (-10.66 to
-21.47) with some leporids clearly having a diet
dominated by C3 vegetation and others having a C4
signature.
CONCLUSIONS
Preliminary analysis of collagen from site
41MM340 and from modern deer demonstrate that the
bone collagen extraction protocol and isotope
analytical techniques produce comparable and
isotopically homogeneous carbon isotope values
with a high degree of accuracy and precision. The
processing and analytical procedures produced
consistent ?13C values from bone collagen
extracted from white-tail deer, an animal with a
known diet. CN ratios for modern samples were
all within acceptable range and contaminated
prehistoric samples were identified as such by
unacceptable CN ratios. While this initial
analysis was limited to a small sample of
herbivores, from a single site, the analysis of
additional samples from other dated prehistoric
sites in Texas should allow a detailed
consideration of shifts in the mean ?13C values
from archaeological periods at site level, as
well as a documentation of vegetation and climate
variability. Stable carbon isotope composition
extracted from leporids can yield ecological
reconstructions at scales informative of local
conditions.