Identifying bilateral pairs of deer (Odocoileus sp.) bones: how symmetrical is symmetrical enough?

Identifying bilaterally paired bones in zooarchaeological collections rests on the assumption that left and right skeletal elements from the same organism will be symmetrical. Bilaterally paired bones in an individual are, however, typically asymmetrical to some degree, demanding that the question “How symmetrical is symmetrical enough to identify a bilateral pair?” be answered with control data. The degree of symmetry chosen, or tolerance, will influence both how many true pairs in an archaeological collection are not identified (type I error) and how many false pairs are identified (type II error). Bivariate measures of 60 pairs of astragali and 48 pairs of distal humeri of deer (Odocoileus virginianus and O. hemionus) indicate that both sorts of error are frequent even when a conservative level of tolerance (≤average asymmetry) is used. Simulation of an archaeological collection indicates that as sample size increases, frequencies of both kinds of error increase. Application of the matching criteria and tolerance level to an archaeological collection underscores that the analytical requirements of identifying paired bones are steep.