The Atacama Desert in northern Chile is one of the driest places on Earth, where some areas receive almost no rain. Yet, a roughly nine-million-year-old tooth discovered in an ancient deposit is offering scientists a glimpse of a very different past, when wetlands, vegetation and freshwater habitats supported a large, semi-aquatic rodent.
According to Live Science, researchers identified the fossil as belonging to an extinct relative of modern capybaras, adding to evidence that the Atacama was not always hyperarid.
A surprising fossil in the desert
The Atacama's extreme dryness is partly linked to its geography. The Chilean Coast Range blocks moisture from the Pacific, while the Andes restrict moisture from the Atlantic. However, geological research suggests that the region's aridity began developing millions of years before the Andes reached their present heights.
The fossil belonged to a capybara relative identified as Hydrochoerus and Cardiatherium, which lived during the late Miocene. Modern capybaras, the world's largest rodents, depend on freshwater habitats and vegetation, making the discovery particularly significant.
Evidence of an ancient wetland
The tooth was found in a geological layer containing evidence of a shallow marine environment that existed between about seven million and 10 million years ago.
Researchers have also discovered microscopic plant remains called phytoliths, suggesting that palms, grasses, gingers and other flowering plants once grew in the region. Fossils of freshwater fish and crocodiles provide further evidence that wetlands and waterways periodically spread across parts of the desert.
How did the animal get there?
The discovery raises questions about how the animal reached northern Chile. The Andes, with elevations reaching around 5,500 metres, formed a formidable barrier between its likely habitats farther east and the fossil site.
Researchers suggest that the animals may have travelled along South America's western coast, moving between wetlands, rivers and other freshwater habitats. The tooth's size also makes long-distance transport by wind unlikely, while water capable of carrying it would point towards a wetter environment.
A changing picture of the Atacama
The fossil does not mean the entire Atacama was once lush. Instead, it adds to evidence that parts of the region experienced significantly wetter conditions during the late Miocene.
For a desert now defined by water scarcity, the discovery offers a reminder that landscapes can undergo dramatic environmental changes over geological time. A single tooth has provided another clue to a period when water-dependent mammals could survive in what is now one of Earth's driest regions.
