Santander, February 19th-22nd 2008 - Aranzadi

178
GREG CAMPBELL
The author assessed the marine shell from
Staple Gardens (51º3.9’N, 1°19.0’W: Site Code
AY93) in Winchester, central southern England.
The history and archaeology of this city are summarised
by James (1997). Founded by the Romans
shortly after their invasion of Britain in A.D. 43,
Winchester remained a major town until the decline
of Roman Britain in the later Fourth Century.
Winchester was the capital of an early English kingdom,
the first capital of a united England (from A.D.
927 until the Norman Conquest of A. D. 1066), and
has remained a major English town.
Oysters of the Roman period (A.D. 43 – circa
A.D. 410) from this site appeared to come in two
distinct shapes (Fig. 1). Occasionally the shell was
the ‘classic’ shape, rounded with the hinge small
and triangular (Fig. 1a). However, most were oval
(shell height was manifestly greater than shell
length) with large straight-sided hinges, resembling
those in the oyster genus Crassostrea (Fig.
1b). Most of these oval shells had changed shape
abruptly, usually in their third or fourth year. This
growth step could be slight (Fig. 2a), but in some
cases the shell changed from rounded to oval (Fig.
2b). Such a ‘step’ was also marked by a change in
the colour and spacing of growth-bands in the
hinge (Fig. 2c); in some cases the hinge changed
from a curved and triangular shape typical of O.
edulis to a broad and straight Crassostrea-like
hinge (Fig. 2d). A possible explanation of these
growth steps was a sudden change in habitat
during the life of the oyster.
Figure 1. Left (lower) valves typical of late Roman oyster (O. edulis) shapes
from Staple Gardens, Winchester. (a): round morphotype. Hmax 81 mm;
(b): oval morphotype. Hmax 88 mm.
The chief aim of this study was to determine
whether O. edulis shape is likely to vary significantly
with habitat. If the relationship between
habitat and typical shape is understood, the relationship
can be used to reconstruct habitat from
typical shape, a process familiar to palaeontologists
(e.g. Seilacher et al. 1985). Each species of
oyster exhibits a wide range of variation to suit
local conditions: this ecophenotypic variation is so
great that shell shapes and forms are not reliable
for distinguishing species, a situation lamented by
almost every oyster taxonomist (e.g.: Gunter 1950:
438; Yonge 1960: 78; Franc 1960: 2086; Galtsoff
1964: 18; Stenzel 1971: 1016; Harry 1985: 122).
Therefore there have been few biological studies
of shell shape variation with habitat in O. edulis.
However, ecophenotypic variation in the eastern
oyster Crassostrea virginica (Gmelin, 1791) has
been well-studied (e.g. Gunter 1938; Gunter 1950;
Galtsoff 1964), and is applied regularly to archaeological
shells to reconstruct habitat (e.g. Kent
1992). In contrast, the only readily available studies
of O. edulis variation seem to be those of the
archaeo-malacologist Winder (e.g. Winder 1992:
197), who found off-shore oysters were taller than
oysters from the adjacent large sheltered bay.
It was not certain that the perceived shape differences
in the Roman Winchester oysters were
genuine, since methods of determining shape
variation in O. edulis are not widely developed in
biology. Variety is so great that defining consistent
dimensions to measure can be controversial
(Stenzel 1971: 955-958). Another aim of this study
was to determine whether it is likely that there is a
simple way to measure O. edulis shells to make
shell shape objectively comparable between samples,
both biological and archaeological.
MUNIBE Suplemento - Gehigarria 31, 2010
S.C. Aranzadi. Z.E. Donostia/San Sebastián