Heritage, Volume 9, Number 2, Spring 1991 Page: 16
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show little beyond scatters of discarded
tool flaking debris, burned rock, bone, snail
shells, and charcoal. This latter item is
treasured by archaeologists for its potential
in accurate radiocarbon dating and wood
species identification. A lingering mystery
of the Toyah people is their lack of cemetery
sites, common in earlier periods. This
may reflect their increased nomadism and
lack of prescribed territory. Their mortuary
ritual may also have entailed a means of
disposal of the dead, such as scaffold burial,
which left no archaeological evidence.
The above is what we have learned from
excavation. The principal technique in recent
years has been to open sites with large
horizontal block excavations, one excavation
square after another in a grid pattern,
until a wide area of a site, its features,
and artifacts are exposed. This is more appropriate
than other excavation techniques
because it allows for the identification
of discrete activity areas within a site.
The more advanced technological
analyses, especially those of archaeological
chemistry, offer means of taking the information
from the excavations further
and actually offering explanations for the
data. A good example of this is lipid analysis.
Lipids are fatty acids that are often
preserved on the faces and edges of tools.
From their analysis, it is possible to determine
the type of material on which the tool
was used. These new and sometimes arcane
sciences in combination point toward the
environment and changes in plants, animals,
and cultures of the region as an explanation
for the Late Prehistoric bisonhunting
pattern in South and Coastal
Specifically, why did bison range into
the Coastal Plains of South Texas after
A.D. 1200. Evidence from geomorphological
studies suggests that there was an
environmental change which made the
land favorable for bison. Apparently there
was a substantial dry period about a thousand
years ago. This long-term drought had
an effect on the Post Oak Savannah,
which-with its dense trees and thick
brush understories-constituted a biological
barrier between the High Plains and the
Coastal Prairie. The 200 year span between
the start of the dry period and the advance
of the bison allowed enough time for the
dense underbrush to thin, become grassier,
and thus provide both quality fodder and a
more open landscape conducive to bison
16 HERITAGE * SPRING 1991
Living floor of a Toyah horizon site. Painstaking wide horizontal excavation is the principal method
for discovering the prehistoric bison hunters of South Texas.
Two types of studies have yielded assessments
of prehistoric grassland quality in
southern Texas. The first of these is the examination
of phytoliths, which are microscopic
silica grains found in the leafy parts
of plants. These microfossils, which are
preserved long after the rest of the plant has
deteriorated, are chemically separated
from soil samples and identified under
high-power light microscopes or electron
microscopes. The results from these analyses
show a general increase in grasses,
especially in flood plain settings, with an
associated decrease in trees and shrubs at
about the same time as the geomorphological
evidence points to dry conditions.
The second of these techniques, stable
carbon isotope analysis, allows for identification
of the types of grasses that were
actually consumed by prehistoric bison in
From the way grasses synthesize carbon
atoms during photosynthesis, they can be
broken into two types: 3 Carbon pathway
(C-3) or 4 Carbon pathway (C-4). As
bison graze, the isotopic signature of the
particular grasses consumed are incorporated
in their living tissues, which
includes the organic component of their
bones. Through the use of this method the
ratio of C-3 to C-4 grasses consumed during
an animal's lifetime can be measured.
Since C-4 grasses fair much better in hot,
dry conditions, it is not surprising that they
would constitute the bulk of the animals'
diet. A typical ratio would be in excess of
The most interesting result from this
analysis was that isotopically the dietary
patterns of bison on the High Plains of the
Panhandle were very similar to those in
southern Texas, despite the marked difference
in the grass species present in the
two areas. Based on this evidence it appears
that bison dietary preference was not tied
to particular species of grasses but to the
type of photosynthetic pathway.
This setting in southern Texas would
have been a prime environment for bison,
but what spurred the bison to move from
their previous territories on the High
Plains? The drying trend on the Coastal
Prairie also operated on the High Plains.
There, however, it placed stress on the
already well-populated bison herds and the
grasses that were their food sources.
One biological solution to the problem
was wider ranging to pursue richer stands of
grass. The xeric interval broke what had
previously been the Post Oak Savannah
barrier between the High Plains and the
Coastal Prairie, and the bison ranging
southeastward naturally moved into what
was, for them, a lush environment indeed.
They moved down the corridor between
the Brazos and Colorado rivers, which
head in the High Plains and spread out
eastward and southward.
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Texas Historical Foundation. Heritage, Volume 9, Number 2, Spring 1991, periodical, Spring 1991; Austin, Texas. (texashistory.unt.edu/ark:/67531/metapth45424/m1/16/: accessed August 23, 2017), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting Texas Historical Foundation.