Identifying accurate artefact morphological ranges using optimal linear estimation: Method validation, case studies, and code

A fundamental goal of archaeologists is to infer the behaviour of past humans from the attributes of the artefacts they left behind. The archaeological record is, however, fragmented and often provides a partial record of the total artefacts produced by a given population. In turn, there is potential for population-level morphometric data, and therefore behavioural inferences, to be biased relative to the trends realised in the past. This includes morphological range data which are important for identifying similarities and differences between artefact groups, and for contextualising artefacts relative to external variables such as human anatomy, ecology, climate and chronology. Here, we investigate whether optimal linear estimation (OLE) modelling can be used to accurately identify the upper and lower limits of artefact morphological ranges (including those represented by sparse datasets). First, we test whether OLE reliably identifies morphological ranges using randomly sampled subsets of ‘known and complete’ replica artefact assemblages. Using morphometric data from lithic, ceramic, and metal archaeological case studies, we then identify how much further the upper and lower form limits of these artefact types would have been in the past, relative to the ranges evidenced by excavated (i.e., known partial) records. Validation tests demonstrate OLE to be capable of providing broadly accurate estimates for the true morphological range of artefact assemblages. Estimate accuracy increases relative to the percentage of the total assemblage used and the method is shown to function well using as few as five records (k) from an assemblage. The case studies reveal how OLE can overhaul or reinforce our understanding of artefact morphological ranges. In some instances, it is clear that the archaeological record provides a highly accurate representation of artefact morphological ranges and the overlap between artefact groups. For others, it is demonstrated that our understanding of the extreme artefact forms produced by past people is likely inaccurate