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NUMBER 30 167
taken to contribute to the economy.
Applying these observations to the Mowry
Bluff sample leads to the following conclusions.
The 229 bison scapulae and the 6 deer metapodials
are rejected as estimators of species frequency
on the grounds that they owe their presence
in the site to their selection as tools. Twentyfive
of the remaining bison bones are assumed to
be interdependent but none of the deer bones. Of
the non-interdependent, nonspecially selected
bone fragments, 25 are bison and 10 are deer. In
each case the bones fall into eight skeletal categories.
It would seem, therefore, that on the basis
of this very small sample, conservatively, bison
were more than twice as frequent as deer. The
contrast would be even stronger in an animal
parts analysis.
Perthotaxic, Taphonomic, and Anataxic Bias
Vehik (1977) has considered the perthotaxic
implications of bone grease manufacturing on the
Plains and has produced a model of the kinds of
bone fragments likely to be recovered. She
(1977:171-172) concludes that, in addition to
large quantities of fingernail-sized bone chips,
there should be an absence of legs, feet, ribs and
vertebra, with the possible exception of the articular
ends of the long bones. However, she observes
that bone chips are not only found in bone grease
manufacturing sites. As an independent test for
the ancient presence of this technology, she proposes
that the organic components of bone chips,
which are boiled, and articular ends, which are
not, be compared. It should be remembered,
however, that the shafts and articular ends of
long bones start out with collagen fractions that
are somewhat different.
Nonhuman perthotaxic factors have also been
modeled. In general, once a bone fragment is
discarded it begins a transformation that will
eventually lead to its disappearance (or its transformation
into a fossil). In the presence of an
attritional agent, erosion is probably slow at first,
then increasingly rapid as the bone's integrity is
lost (Binford and Bertram, 1977:113, figs. 3, 10;
Brain, 1976). The denser the original bone fragment,
the longer the disappearance takes (see
Behrensmeyer, 1978, for a discussion of bone
weathering). This observation has led Binford
and Bertram (1977) and A. Gilbert (1979) to
predict that some of the variance in observed
bone frequencies compared to the proportion of
element types in a living animal must be the
result of the differing density of the various bone
elements. The relationship is extremely complex.
Imagine a situation in which an equal number of
several different bone elements are exposed to an
attritional agent. Each will tend to disappear at
a different rate. Because of these different rates,
the frequency proportions between the different
bone types will constantly change with time.
Binford and Bertram (1977) have developed a
mathematical model of this sort to predict the
proportions for the different elements of sheep
and caribou skeletons found on Navajo and Eskimo
sites after attrition by dogs.
A start has been made in modelling the taphonomic
conditions affecting bone deposits.
Buried bone undergoes gradual chemical alteration
that leads to a loss of physical integrity. Hare
(1980:218) conducted a simulation of the leaching
process, and concluded:
Qualitative observation during the simulation experiments
showed that, as water reacted with the protein in the
bone fragments, the bone fragments became progressively
chalkier and easier to break apart. Samples that had been
leached extensively were generally easy to crush and cut. In
the early stages of the reactions where collagen was still
present, the fragments would show the intact pseudomorphic
ghosts of the bone fragments. Bone strength and hardness
appeared only slightly less than that of fresh bone material.
As the reactions progressed the pseudomorphic ghosts looked
progressively less intact until there was no longer any pseudomorph
left—only a few scattered fragments of organic
material. At this stage there was substantially less strength
and hardness left in the bone fragment. The fragments were
somewhat chalky and easily crushed with the fingers.
Evidence now exists (D.W. Von Endt, Smithsonian,
pers. comm.) that indicates that organic preservation
is quite variable among bones of the
same type and species in the same site. In the
author's examination of a very small sample of