Fossils recently excavated from a site in Uruguay provide tantalising evidence for the presence of human hunter-gatherer societies nearly 30,000 years ago.
It is widely accepted that the first people to colonise the Americas migrated from Siberia into Alaska across the Bering Land Bridge during the Late Pleistocene, some 12-15,000 years ago. However, the unexpected discovery of a large collection of megafaunal bones at a site in Uruguay points towards a far earlier date for the first human habitation in South America.
The site at Arroyo del Vizcaíno was first exposed during a severe summer drought in 1997. As the water dried up, a mysterious bed of gigantic bones was revealed. Some material was quickly collected, including a clavicle belonging to the extinct giant ground sloth (Lestodon armatus). Intriguingly, this bone clearly showed human-made cutting and scraping marks. However, palaeontologists had a frustrating wait until 2011 before the site could be properly excavated.
A team from Universidad de la República Montevideo ultimately recovered and analysed over 1,000 bones from the site. Most of these remains belonged to the giant ground sloth, but also included fossils from other extinct giant mammals such as glyptodonts (related to armadillos), the hippo-like toxodon and a sabre-toothed cat. But some of these fossils also revealed an extraordinary interaction with humans.
The assemblage of bones reflected those found in other human kill sites, with most of the remains belonging to prime adults rather than young or old individuals. There was little evidence that bones were carried to the site by water; instead it seems that the area was used by humans as a dump-site for animal carcasses. Incredibly, several of the bones clearly featured deep, sharp marks exactly like those produced by human tools. And further evidence that these animals were hunted for food was provided by the discovery of fragments of stone tools, including a scraper which showed signs of wear from use.
But the greatest revelation came with the radiocarbon dating of the bones, which put the age of the site at between 27,000 and 30,000 years old. This corroborates the dating of cave paintings and ceramic art from Serra da Capivara National Park in Brazil, some of which were created over 25,000 years ago. Together these findings provide evidence that humans arrived in South America far earlier than thought, with one theory suggesting that people came via ocean crossings from Africa.
However, the authors remain cautious about the implications of these findings until more evidence can be gathered, and acknowledge that the marks on the bone may simply be a result of natural processes mimicking human tools. The team hopes to continue excavating the rest of the site and plan to create a new museum to exhibit the valuable remains.
Reference: Fariña RA, Tambusso PS, Varela L, Czerwonogora A, Di Giacomo M, Musso M, Bracco R, & Gascue A (2014). Arroyo del Vizcaino, Uruguay: a fossil-rich 30-ka-old megafaunal locality with cut-marked bones. Proc. R. Soc. B, 281 (1774) PMID: 24258717