Geometric Morphometrics – Lithics

The study of form may be descriptive merely, or it may become analytical. We begin by describing the shape of an object in the simple words of common speech: we end by defining it in the precise language of mathematics; and the one method tends to follow the other in strict scientific order and historical continuity. — D’Arcy Wentworth Thompson (1915)

In addition to the geometric morphometric (GM) analyses of ceramics, I am also working to explore whether–and to what extent–lithic traditions and ceramic traditions change at the same pace. While the initial goal of the lithic analysis is to identify and expound upon potential morphological transitions, much effort is being put into identifying shifts in the shape, form, allometry, and asymmetry of specimens that occur across two or more artifact categories.

Interactive citation network for applications of geometric morphometrics in archaeology. Access and explore the interactive version here.

A recent study of Gahagan bifaces from the Gahagan Mound, Mounds Plantation, and George C. Davis sites in Louisiana and Texas demonstrates the utility of this approach, where the Mounds Plantation specimens were found to differ significantly from those produced at the other two sites.

Mean consensus configuration (black) with Procrustes residuals (gray) superimposed by Generalized Procrustes Analysis for a, Mounds Plantation; b, Gahagan Mound; c, George C. Davis; and d, all specimens.

Morphological disparity is also significant between the Mounds Plantation and Gahagan Mound samples, indicating that the Gahagan Mound sample occupies a greater range of morphospace. While not significant, the George C. Davis sample also demonstrates a greater range in Gahagan biface shape when compared to the Mounds Plantation sample. Thus, Caddo Makers at Mounds Plantation may have employed a more standardized approach to Gahagan biface manufacture.

Archaeology Principal Components Analysis of Gahagan Bifaces (Caddo) from the Mounds Plantation, Gahagan Mound, and George C. Davis sites geometric morphometric
Principal components analysis (PCA) for Gahagan bifaces from the Gahagan Mound (red), George C. Davis (black), and Mounds Plantation (green) sites.

In addition to differences in shape, flaking techniques used by Caddo makers at Mounds Plantation also differ, and–while not explored in depth for this paper–raw material choice also appears to differ at Mounds Plantation.

Comparison of mean consensus configurations for Gahagan biface shape by site at; a, Mounds Plantation (gray) and Gahagan Mound; b, Mounds Plantation (gray) and George C. Davis; c, Gahagan (gray) and George C. Davis.

From these very basic examples, we see much promise for extending our geometric morphometric studies to include dart points. Similar to my efforts with ceramics, I am capitalizing on both 2D and 3D data from across the East Texas region (prior to synthesizing these data in a larger network analysis), since there is a veritable wealth of readily accessible data available in the published–and gray–literature. While I have conducted a few small-scale (site specific) tests of correlation between the 2D /3D ceramic data with meaningful results, more studies of this kind are needed.

Illustration of flake scars on a Gahagan biface from the Gahagan Mound site in Northwest Louisiana.

Access the poster associated with this project here, and the publication here.

More information regarding a similar analysis for Caddo bottles here.