Secrets of Bolivian Amazon exposed
The 'forest island' known as Isla del Tesoro (Treasure Island) turned out to be the earliest evidence of human habitation in the region.
Image: University of Wollongong

The enigmatic ‘forest islands’ set amidst the grasslands of Bolivian Amazonia have yielded the earliest evidence of human habitation in the region.

Previously thought to be relict landforms cut away by shifting rivers, or long-term bird rookeries or termite mounds, these piles of freshwater snails, animal bones and charcoal are now known to have been built up over millennia, starting from at least 10,400 years ago, by ancient hunter-gatherers.

Using novel approaches drawn from archaeology, geomorphology and geochemistry, an international team of researchers, led by Dr Umberto Lombardo of the University of Bern, has conducted detailed excavations of a large mound known locally as Isla del Tesoro (Treasure Island).

Associate Professor Katherine Szabó from the University of Wollongong’s Centre for Archaeological Science and Dr Jan-Hendrik May from UOW’s School of Earth and Environmental Sciences were among the international team members.

Distinctive chemical signatures of human presence were recorded at high levels throughout the mound sediments, and studies of the animal bones and shells indicate they are the remains of ancient human meals. Team members said that Isla del Tesoro tells us that from over 10,000 years ago, hunter-gatherers were moving across the grasslands hunting a variety of mammals, catching fish and birds, and gathering large quantities of freshwater snails.

Over time, the refuse of these hunting and gathering forays built up forming mounds, which sat elevated above the floodplain. These refuse or ‘midden’ mounds in turn provided a habitat for local plants and animals, transforming them into the forest islands so recognisable in the landscape today.

It is highly likely that many more midden mounds lie buried beneath the metres of silts under the current savannah, according to the researchers.

Regularly flooded savannah landscapes such as those surrounding Isla del Tesoro have long been thought to be an inhospitable environment for early hunter gatherers. The densities of animal prey are lower and less predictable than in coastal areas, near stable watercourses or in forested areas where early South American archaeological sites are typically found. Dr Lombardo and colleagues’ work at Isla de Tesoro tells us that early South Americans moved across a wider variety of landscapes than previously thought, and adapted their ways of life to cope in these challenging environments.

The findings were published in PLOS ONE, access them here.

Editor's note: Original news release can be found here.