Preface
If you describe something with great accuracy, you describe it as closely as you can to what it is, to its true value. If you describe something with great precision, you do so in the greatest possible detail, even though that detail may not necessarily be the true value of the thing being described. Simon Winchester, The Perfectionists: How Precision Engineers Created the Modern World
Generally considered diagnostic of Late Prehistoric Toyah assemblages, Perdiz arrow points are characteristic of the transition from the Late Prehistoric to the Protohistoric. If larger Perdiz arrow points from Caddo burials are conceived of as products of trade and/or exchange with Toyah groups, then those with longer blade lengths provide inference to shifts in Caddo selective preference, while those with shorter blade lengths evince local approaches to resharpening and/or retouch that were uniquely Caddo. This study asks whether linear shape variables convey discrete regional resharpening strategies, whether morphological trajectories differ between the northern and southern behavioural regions, and whether morphological disparity differs between larger and smaller size classes, as defined by differences in blade length. Results demonstrate distinct regional resharpening strategies and divergent morphological trajectories for Perdiz arrow points included as Caddo mortuary offerings in the northern and southern behavioural regions. Perdiz arrow point shapes were not found to differ in the large size class between the northern and southern behavioural regions, demonstrating consistency in Caddo preference, or—alternatively—Toyah manufacture. However, differences in the small size class suggest discrete local approaches to resharpening and/or retouch by Caddo knappers. Caddo groups that occupied the southern behavioural region may have also been less selective, preferring Perdiz arrow points with a greater range of diversity in shape and size, while their counterparts to the north preferred a more standardized product.
Primary findings
Linear metrics
For this effort, the mean maximum blade length for Perdiz arrow points from each behavioural region was calculated and used to bin the sample into two groups (henceforth, size classes); one with a longer blade, and the other, shorter. Following the assignment of size classes, data were joined in advance of analysis.
The morphological form (shape + size) of the Perdiz arrow points was then split into shape (representing proportions between dimensions in an object) and size (sensu Klingenberg (2016)). Size and shape were calculated using the method of log-shape ratios proposed by Mosimann (1970), where the geometric mean is considered a proxy for size, and shape was calculated as the log of isometric size subtracted from the log of each linear/dimensional measure.
An ANOVA was subsequently used to assess shape as a function of size class.
## boxplots by size class
knitr::include_graphics('img/boxplot-linear.png')
## pca by size class
knitr::include_graphics('img/pca-linear.png')
Results
- Blade length differs significantly between large and small Perdiz arrow point
size classes in the northern and southern behavioural regions
- Shoulder width differs significantly between large and small Perdiz arrow point
size classes in the southern behavioural region, but does not differ in the northern behavioural region
- Width differs significantly between large and small Perdiz arrow point
size classes in the southern behavioural region, but does not differ in the northern behavioural region
- Thickness does not differ between large and small Perdiz arrow point
size classes from either behavioural region
- Stem length does not differ between large and small Perdiz arrow point
size classes from either behavioural region
- Stem width does not differ between large and small Perdiz arrow point
size classes from either behavioural region
## resharpening
knitr::include_graphics('img/img2/linresharp.png')
Geometric morphometrics
This analysis follows recent geometric morphometric analyses of Perdiz arrow points (Selden and Dockall, in review) and Gahagan biface morphology across the southern Caddo area and central Texas (Selden Jr., Dockall, and Shafer 2018; Selden Jr., Dockall, and Dubied 2020), where Perdiz arrow points and Gahagan bifaces have been found to differ in shape across the same geography as Caddo bottles (Selden Jr. 2018a, 2018b, 2019, 2021).
It also follows a recent geometric morphometric analysis in which Perdiz arrow points from the ancestral Caddo area were found to differ as a function of time, raw material, and burial context (Selden Jr et al. 2021; Selden Jr. et al. 2021).
Landmark data were aligned to a global coordinate system (Kendall 1981, 1984; Slice 2001), achieved through generalized Procrustes superimposition (Rohlf and Slice 1990) performed in R 4.1.3 (R Core Development Team, 2022) using the geomorph library v. 4.0.3 (Adams et al. 2017; Adams and Otarola-Castillo 2013; Baken et al. 2021). Procrustes superimposition translates, scales, and rotates the coordinate data to allow for comparisons among objects (Gower 1975; Rohlf and Slice 1990). The geomorph package uses a partial Procrustes superimposition that projects the aligned specimens into tangent space subsequent to alignment in preparation for the use of multivariate methods that assume linear space (Rohlf 1999; Slice 2001).
Principal components analysis (Jolliffe 2002) was used to visualise shape variation among the Perdiz arrow points. The shape changes described by each principal axis are commonly visualized using thin-plate spline warping of a reference 3D mesh (Klingenberg 2013; Sherratt et al. 2014).
## pca
knitr::include_graphics('img/img2/gm-pca.png')
To assess whether shape changes with size (allometry) or differs by size class, Procrustes ANOVAs (Goodall 1991) were run that enlist effect-sizes (zscores) computed as standard deviates of the generated sampling distributions (Michael. L. Collyer, Sekora, and Adams 2015). A residual randomization permutation procedure (RRPP; n = 10,000 permutations) was used for all Procrustes ANOVAs (Adams and Collyer 2015; M. L. Collyer and Adams 2018), which has higher statistical power and a greater ability to identify patterns in the data should they be present (Anderson and Ter Braak 2003). These results are detailed in Chapter 2.
## allometric (shape + size) trajectories by size class
knitr::include_graphics('img/allometric.traj.png')
A phenotypic trajectory analysis (Adams and Collyer 2007, 2009; M. L. Collyer and Adams 2007, 2013; Michael. L. Collyer, Sekora, and Adams 2015) was used to assess whether Caddo reduction or retouch trajectories differ between the northern and southern behavioural regions. The trajectory analysis was followed by an analysis of morphological disparity (M. L. Collyer and Adams 2020; Foote 1993; Zelditch et al. 2004) to identify potential differences in morphological diversity between size classes.
## Perdiz arrow point shape trajectories by size class
knitr::include_graphics('img/img2/trajectory.png')
Results
- Perdiz arrow point shape differs significantly between the large and small size classes in the northern behavioural region
- Perdiz arrow point shape differs significantly in the small size class between the northern and southern behavioural regions
- Perdiz arrow point size differs significantly in the large size class between the northern and southern behavioural regions
- Perdiz arrow point size differs significantly in the small size class between the northern and southern behavioural regions
- Allometry is significant, and the homogeneity of slopes test indicates that the slopes associated with large and small Perdiz arrow points from the northern and southern behavioural regions differ
- Modularity is significant
- Morphological integration is significant
- Results of the trajectory analysis demonstrate a significant difference between shape trajectories in the northern and southern behavioural regions
- Results of the morphological disparity analysis by shape demonstrate that the large Perdiz arrow points from the southern behavioural region occupy a significantly greater range of morphospace than the large and small Perdiz arrow points from the northern behavioural region
- Results of the morphological disparity analysis by size demonstrate that the large Perdiz arrow points from the southern behavioural region occupy a significantly greater range of morphospace than the large Perdiz arrow points in the northern behavioural region
Acknowledgments
I extend my gratitude to the Caddo Nation of Oklahoma, the Caddo Nation Tribal Council, Tribal Chairman, and Tribal Historic Preservation Office for their guidance related to the development of the scanning protocols, for permission and access to NAGPRA and previously repatriated collections, and for frank discussions related to language surrounding burial contexts associated with Caddo children. Thanks also to the Anthropology and Archaeology Laboratory at Stephen F. Austin State University for the requisite permissions and access to the NAGPRA items from the Washington Square Mound site and Turner collection, and to Tom A. Middlebrook for brokering access to the Perdiz arrow points from Caddo burials at the Morse Mound site. Thanks also to John E. Dockall, Michael J. Shott, Lauren N. Butaric, David K. Thulman, Timothy K. Perttula, Jon C. Lohse, C. Britt Bousman, Jeffrey S. Girard, Hiram F. (Pete) Gregory, Thomas R. Hester, Harry J. Shafer, Elton R. Prewitt, Bonnie L. Etter, Kersten Bergstrom, Christian S. Hoggard, Emma Sherratt, Dean C. Adams, and Michael L. Collyer for their constructive criticisms, comments, and suggestions throughout the development of this research program, and to the editors and anonymous reviewers for their comments and constructive criticisms, which further improved the manuscript.
Funding
Components of the analytical workflow were developed and funded by a Preservation Technology and Training grant (P14AP00138) to RZS from the National Center for Preservation Technology and Training, as well as grants to RZS from the Caddo Nation of Oklahoma, National Forests and Grasslands in Texas (15-PA-11081300-033) and the United States Forest Service (20-PA-11081300-074). Additional support for this project was provided by the Heritage Research Center at Stephen F. Austin State University.
Data management
The data and analysis code associated with this project can be accessed through this document or the GitHub repository, and is digitally curated on the Open Science Framework (DOI 10.17605/OSF.IO/85BU7). Images and additional information for all Perdiz arrow points used in this study can be viewed and downloaded from the digital comparative collection https://scholarworks.sfasu.edu/ita-perdiz/. The replicable nature of this undertaking provides a means for others to critically assess and evaluate the various analytical components of this study (Gray and Marwick 2019; Peng 2011; Gandrud 2014), which is a necessary requirement for the production of reliable knowledge.
Reproducibility projects in psychology and cancer biology are impacting current research practices across all domains. Examples of reproducible research are becoming more abundant in archaeology (Marwick 2016; Ivanovaite et al. 2020; Selden Jr., Dockall, and Dubied 2020), and the next generation of archaeologists are learning those tools and methods needed to reproduce and/or replicate research results (Marwick et al. 2019). Reproducible and replicable research work flows are often employed at the highest levels of humanities-based inquiries to mitigate concern or doubt regarding proper execution, and is of particular import should the results have—explicitly or implicitly—a major impact on scientific progress (Peels and Bouter 2018).
Colophon
This version of the analysis was generated on 2022-06-26 07:23:52 using the following computational environment and dependencies:
# what R packages and versions were used?
if ("devtools" %in% installed.packages()) devtools::session_info()
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## Head: [f548e2e] 2022-06-26: <edit struc>
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![Location of sites with Perdiz arrow points included in the study, extent of major drainage basins (Neches [brown], Sabine [maroon], and Red [navy] Rivers), and extent of the ancestral Caddo region (white). In the context of this effort, those sites from the Red River basin constitute the `northern behavioural region`, while those from the Sabine and Neches River basins represent the `southern behavioural region`.](img/img2/fig1.png)
