Overview
It has rightly been said that the most important question to ask of
any archaeological bone assemblage is "What are all these bones doing
here?". Unless and until we understand the range of processes by which
the assemblage that we recover from excavated deposits derived from a
number of formerly live animals, we have little hope of making a
fully-nuanced and soundly-based interpretation.
Prehistorians who study the deep past of humanity, dealing in
hundreds of thousands of years, are accustomed to undertaking detailed
taphonomic analyses of the animal bone assemblages that often accompany
the remains of our earliest ancestors. At the other end of the
timescale, we are much less likely to undertake such an analysis.
Yet
we should, not least because sites such as medieval towns or Iron Age
hillforts may yield prodigious quantities of bones from hundreds of
contexts, making it necessary to prioritise their study. Obviously, it
is essential that the most informative assemblages are given the
highest priority, but without a full taphonomic analysis, we cannot
state with confidence which assemblages will be the most informative,
nor what classes of information different assemblages may yield.
Processes
We start by subdividing the taphonomic trajectory of a bone
into a series of stages. First the animal dies, and the place and
circumstances of its death may markedly affect the chances of any bones
surviving in the archaeological record. Next the carcass undergoes transport.
In non-cultural situations, the transporting agency may be water,
scavengers or simply the trampling feet of passing animals. On
settlement sites, transport includes many of the human
activities that we seek to understand, such as butchery, food-sharing
and trade, and refuse disposal. Transport is followed by exposure,
the stage at which the bone is incorporated into a forming deposit.
This stage may be very brief, for example if a bucket-full of bone
waste is tipped into a cess-pit. More often, this is a period of time
during which bones are exposed to a particularly dynamic and
destructive range of processes. These may include trampling and
sub-aerial weathering, for example in a bone-strewn medieval backyard.
Once the bone is buried, the processes of diagenesis take
over, altering the bone chemically. In some burial conditions,
diagenesis may lead to complete destruction of the bone, leaving us
archaeologists with nothing to study. More often, the bone stabilises,
coming into chemical equilibrium with its surroundings. Once that
equilibrium has been attained, bone may survive for many thousands of
years, unless changes to the deposit, such as erosion and re-exposure,
lead to a change of equilibrium. Excavation is just such a change, of
course, and it is a common mistake in archaeology to assume that
because a piece of bone has survived for millennia in the ground, it
will survive for years or decades following excavation.
