Evidence for cultivar adoption and emerging complexity during the mid-Holocene in the La Plata basin

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Multidisciplinary investigations at the Los Ajos archaeological mound complex in the wetlands of southeastern Uruguay challenge the traditional view that the La Plata basin was inhabited by simple groups of hunters and gatherers for much of the pre-Hispanic era1,2,3,4. Here we report new archaeological, palaeoecological and botanical data indicating that during an increasingly drier mid-Holocene, at around 4,190 radiocarbon (14C) years before present (bp), Los Ajos became a permanent circular plaza village, and its inhabitants adopted the earliest cultivars known in southern South America. The architectural plan of Los Ajos during the following Ceramic Mound Period (around 3,000–500 14C yr bp) is similar to, but earlier than, settlement patterns demonstrated in Amazonia5,6,7,8,9,10, revealing a new and independent architectural tradition for South America.

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Figure 1: Maps showing the position of the study area and locations of archaeological sites within the study area.
Figure 2: Topographical maps of the study site.
Figure 3: West wall stratigraphic sketch of Mound Gamma block excavation and part of trench.
Figure 4: Selected phytoliths and starch grains.


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Supported by grants from the National Science Foundation, Wenner-Gren Foundation for Anthropological Research, Smithsonian Tropical Research Institute, and the University of Kentucky Graduate School. J.I. received support from the Comisión Nacional de Arqueología, Ministerio de Educación y Cultura, Uruguay and the Rotary Club of Lascano, Rocha, Uruguay. We thank T. Dillehay, C. Mañosa, E. Moreno, H. Ciganda and G. Uriarte for their support.Author contributions J.I. directed the multidisciplinary research and conducted the archaeological, lithic and phytolith analyses. I.H. undertook the starch grain analysis, C.L. did the pollen analysis, O.M. directed the lithic debitage and ceramic analysis, A.R. carried out the faunal analysis and E.A. collected and identified the selected plant species to build the phytolith reference collection of southeastern Uruguay.

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Correspondence to José Iriarte.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Methods (DOC 22 kb)

Supplementary Tables 1 and 2

Supplementary Table 1. Detailed Phytolith Counts and Percentages from Mound Gamma; Supplementary Table 2. TBN Trench Cross-shaped Phytoliths Discriminant. (DOC 329 kb)

Supplementary Figure Legends (DOC 23 kb)

Supplementary Figure 1

View of (a) the central part of Los Ajos from S to N and (b) the TBN crescent-shape rise trench excavation in progress from N to S. (JPG 69 kb)

Supplementary Figure 2

Selected pollen and phytolith percentage diagram from Los Ajos core. (JPG 75 kb)

Supplementary Figure 3

Plant-grinding tools from Mound Gamma. (JPG 54 kb)

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