Skeletons of the Pampas
On a low knoll in the flat grasslands of the Argentine Pampas is Arroyo Seco 2, a significant archaeological sites. Excavations have uncovered the skeletal remains of more than 40 individuals. Radiocarbon dating of these human bones indicates they were buried over a long period, with some of the earliest dating to the Early Holocene, around 8,500 years ago. These burials make Arroyo Seco 2 one of the oldest known formal burial sites on the continent.
The scientific puzzle deepens with isotopic analysis of the remains. Studies of stable isotopes, particularly the ratios of Carbon-13 and Nitrogen-15 in the bone collagen, allow scientists to reconstruct ancient diets. The signatures in some of the Arroyo Seco skeletons suggest a diet that included a substantial amount of marine resources. This finding is unexpected, as the site is located more than 170 kilometers (105 miles) from the modern Atlantic coastline. The data implies these inland groups either undertook long-distance journeys to the coast to hunt or fish, or they maintained extensive trade networks with coastal populations. This evidence complicates the picture of typical inland hunter-gatherer subsistence in ancient South America.
Deep Time and Deeper Ancestry
The human story at Arroyo Seco 2 begins long before the burials. Deeper, older layers at the site contain a different kind of evidence: stone tools and the fossilized bones of extinct Pleistocene megafauna. Some of these animal bones, from creatures like the 4-ton giant ground sloth (Megatherium americanum) and the extinct horse species Equus neogeus, have fractures and cut marks made by human tools. Radiocarbon dating on these faunal remains places human activity at the site as early as 14,000 years ago. This makes Arroyo Seco 2 an important location for understanding the initial peopling of the Southern Cone, predating the Clovis culture of North America.
Ancient DNA extracted from the skeletons adds complexity. The genetic profile of the Arroyo Seco individuals includes Y-DNA haplogroup Q and mitochondrial haplogroups such as C1b, D1, and A2, which are common founding lineages for Indigenous peoples across the Americas. The reference to Australian populations in the hook points to a broader, continent-wide genetic mystery. A faint but distinct "Australasian signal" has been detected in some ancient and modern populations in the Amazon and along the Pacific coast. While this specific signal has not been reported directly in the Arroyo Seco individuals themselves, its presence elsewhere in South America suggests that the story of how the continent was populated is far from simple and may have involved multiple, ancient streams of people.