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Climate-driven dietary change on the Colorado Plateau, USA and implications for gender-specific foraging patterns

Citation

Louderback, Lisbeth (2021), Climate-driven dietary change on the Colorado Plateau, USA and implications for gender-specific foraging patterns, Dryad, Dataset, https://doi.org/10.5061/dryad.w9ghx3fq3

Abstract

Complementary archaeological and paleoenvironmental datasets from North Creek Shelter (Colorado Plateau, Utah, USA) are analyzed using the diet breadth model, revealing human dietary patterns during the early and middle Holocene. Abundance indices are derived from botanical and faunal datasets and along with stone tools, are used to test the prediction that increasing aridity caused the decline of high-return resources. This prediction appears valid with respect to botanical resources, as high-ranked plants drop out of the diet after 9800 cal BP and replaced with low-ranked, small seeds. The prediction is not met, however, with respect to faunal resources: high-ranked artiodactyls are consistently abundant in the diet. The effects of climate change on dietary choices are also examined, finding that increased aridity coincides with greater use of small seeds and ground stone tools, but not with increases in low-ranked fauna, such as leporids. The patterns observed from the North Creek Shelter botanical and faunal datasets may reflect different foraging strategies between men and women, thus accounting for the discrepancy that low-ranked plant resources became increasingly abundant in the diet without a corresponding decrease in abundance of high-ranked artiodactyls. If so, then archaeological records with similar datasets should be re-examined with this perspective.

Methods

Faunal Dietary Patterns

Faunal remains were recovered from a total of 53 substrata across strata II through VI.  Previous evaluations of NCS faunal remains did not properly account for taphonomy, thereby potentially including non-cultural taxa (e.g. carnivores and rodents) in analyses of diet breadth. This was avoided by using the annotated data records and segregating specimens into human and non-human accumulations based on burning and cut marks as cultural markers. Taxa were included using the lowest taxonomic category that could be assigned with confidence. Taxa represented by a single specimen in any given substratum were excluded in order to minimize the effects of an accidental movement of specimens across strata.

Botanical Dietary Patterns

Macrobotanical remains (e.g. seeds, seed coats, fruits) were recovered by flotation analysis from hearth features (n=156) excavated from 38 substrata spanning all cultural strata (II - VI). Identification of certain families is made possible by their diagnostic characteristics such as the thick, ovoid and large seed coats of Pinaceae or the angular, elongated and small achenes of Asteraceae. Certain genera are also identified in this way; for example, the lenticular, beaked and rimmed seeds of Chenopodium. C. berlandieri was isolated from all other Chenopodium spp. seeds because it has a distinctive reticulate pericarp and seed coat patterning (Holmgren et al. 2012).  Rhus sp. (sumac) seeds are ovoid with a radicle bulge (these specimens are distinctively striated, perhaps due to pericarp impression).  In three cases are materials identified to species, Atriplex confertifolia (shadscale) by its two-winged fruits, Achnatherum hymenoides (Indian ricegrass) by its distinctive flask-shaped achene, and Solanum jamesii by its distinctive starch granules (Louderback and Pavlik 2017). Unidentified and indeterminate seeds and fruit are not included in the dietary analyses. The lowest possible taxonomic level was determined by using contemporary reference material from herbaria, seed reference collections, as well as plant specimens gathered at the study site itself.

Ninety-four ground stone tools spanning strata V and VI were analyzed for starch granules. The majority of tools were made from sandstone (88%), with quartzite (6%), volcanics (5%) and granite (1%) comprising the remainder. The weight of the tools varied from 4 grams to approximately 13.5 kilograms (see Louderback 2014 for ground stone inventory and data). Starch granules were extracted following the protocols outlined in Louderback (2014) and Louderback et al. (2015) and granules were identified using the approached outlined in Louderback et al. (2017). Only starch granules with eccentric hila have been positively identified (Louderback and Pavlik 2017). Because there is no way to determine an absolute count of starch granules, NISP is based on the number of ground stone tools that yielded identifiable granules in each substratum. For example, in substratum Vt, three of the twenty ground stone tools bore granules assigned to Solanum jamesii and, therefore, the NISP value for S. jamesii in substratum Vt is three.

Funding

National Science Foundation, Award: BCS-1262835