Lithic morphological organisation: Gahagan bifaces from the Southern Caddo Area

Abstract

This analysis of Gahagan biface morphology enlists the three largest samples of Gahagan bifaces, to include that of the type site (Gahagan Mound) as well as the Mounds Plantation and George C. Davis sites. Results indicate a significant difference in Gahagan biface morphology at the Mounds Plantation site when compared with Gahagan bifaces from the Gahagan Mound and George C. Davis sites. Tests for allometry and asymmetry were not significant. The test of morphological disparity indicates that Gahagan bifaces produced at the Mounds Plantation site occupy a more restricted range of morphospace than those produced at Gahagan Mound, providing indirect evidence for standardisation and diversity in Caddo biface production. While the sample includes a wide range of morphological variability, the test of morphological integration indicates that Gahagan bifaces are significantly integrated, meaning that those traits used to characterise their shape (blade and base) vary in a coordinated manner. These results articulate with a shift in Caddo bottle morphology over the same geography, potentially indicating two previously unrecognised and morphologically-distinct lithic and ceramic production areas.

A quantitative assessment of intraspecific morphological variation in Gahagan bifaces from the southern Caddo area and central Texas

“…Superficially, this constellation of landmarks and semilandmarks appears similar to the 2D configuration used in the previous study (Selden Jr. et al, 2018). However, this landmarking protocol captures the morphological variation that articulates with axial twisting introduced by knappers through the practise of bifacial beveling (Figure 9) (Selden Jr., 2020).…”

“…This contribution follows a recent study of Gahagan biface morphology that enlisted the three largest samples in the southern Caddo area from the Gahagan Mound (16RR1), George C. Davis (41CE19), and Mounds Plantation (16CD12) sites ( Figure 1) (Selden Jr. et al, 2018). The results of that study indicated a significant difference in shape between Gahagan bifaces found at the Mounds Plantation site compared with those found at the Gahagan Mound and George C. Davis sites (Selden Jr. et al, 2018, Figure 7).…”

“…The series of geometric morphometric studies focused upon Caddo ceramics has capitalised on the morphological variation that occurs along a single plane; however, 3D data were required to systematically identify the widest vessel profile. The Gahagan bifaces used in the previous study come from many of the same contexts as the Caddo bottles, and were found to differ in morphology across the same shape boundary (Selden Jr. et al, 2018;Selden Jr., 2019b, Figure 15.1). The current study leverages a suite of analytical tools that have allowed for the incorporation of morphological attributes associated with beveling, which occurs with some regularity along the lateral edges of Gahagan bifaces.…”

“…Landmark-based geometric morphometric methods are ideal for research designs that incorporate questions of complex 3D geometry. Examples from the literature cover a broad scope of artefact categories including projectile points (Shott, 2011;Shott and Trail, 2010), bifaces (Archer and Braun, 2010;Archer et al, 2015Archer et al, , 2016Selden Jr. et al, 2018), percussive tools (Caruana et al, 2014), flake scars (Sholts et al, 2012), flake tools (Archer et al, 2017), handaxes (Lycett, 2009;Lycett et al, 2010Lycett et al, , 2015Lycett and von Cramon-Taubadel, 2013;Wang et al, 2012), and Caddo ceramics (Selden Jr. et al, 2014;Selden Jr., 2017, 2018b,a, 2019a).…”

“…While an interesting aside, the residue does pose a problem for an analysis of 3D geometry. The initial research design (3D) was thus revisited, leading to a reconfiguration of the previous analysis as a 2D geometric morphometric study (Selden Jr. et al, 2018), enlisting a landmark configuration similar to that used The same basic constellation of landmarks was employed for this undertaking; however, unlike the previous iteration where landmarks were projected onto a 2D spline, landmarks in this iteration were plotted directly on the 3D spline, providing a means of capitalising on shape variation introduced through the practise of beveling. This configuration of landmarks will be revised for subsequent analyses, where additional semilandmarks will be added to capture morphological attributes associated with latitudinal and longitudinal cross-sections.…”