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

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 era(1-4). Here we report new archaeological, palaeoecological and botanical data indicating that during an increasingly drier mid-Holocene, at around 4,190 radiocarbon (C-14) 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 C-14 yr B P) is similar to, but earlier than, settlement patterns demonstrated in Amazonia(5-10), revealing a new and independent architectural tradition for South America.