Results of stable isotope analyses are presented for the study of human subsistence in the lower basin of the Colorado River, Buenos Aires province, Argentina. This paper provides the most current state of knowledge concerning isotopic research in the study area, which in turn sheds new light on such a significant region as the Pampa-Patagonia transitional zone, spatially related to the Atlantic coast. In addition, information from the middle basin of the Negro River is incorporated in the analysis and discussion. Both the construction of an isotopic ecology and the prehistoric human diets derived from

The early peopling of the Americas has been one of the most hotly contested topics in American anthropology and a research issue that draws archaeologists into a multidisciplinary debate. In South America, although the background data on this issue has increased exponentially in recent decades, the core questions related to the temporal and spatial patterns of the colonization process remain open. In this paper we tackle these questions in the light of the quantitative analysis of a screened radiocarbon database of more than 1600 early dates. We explore the frequency of radiocarbon dates as proxies for assessing population growth; and define a reliable and statistically well supported lower chronological bound (not to the exact date) for the earliest human arrival. Our results suggest that the earliest chronological threshold for the peopling of South America should be between 16,600 and 15,100, with a mean estimated date~15,500 cal BP (post Last Glacial Maximum). Population would have grown until the end of Antarctic Cold Reversal stadial~12,500 cal BP at the time of the main extinctions of megafauna-, when the increase rate slows, probably as a result of the changes that occurred in the trophic niche of humans.

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