An 8.8-million-year-old fossilized capybara tooth discovered in Chile’s Atacama Desert challenges long-held geological assumptions about the region’s ancient climate. Unearthed at the El Morro site within the Bahía Inglesa Formation, the specimen provides the oldest record of these semi-aquatic rodents in coastal Chile, suggesting parts of the hyperarid landscape were once a lush, water-rich habitat.
Unearthing a Fossil in the Bahía Inglesa Formation
The discovery centers on a single, two-thirds-of-inch-long partial molar. Researchers identified the specimen as belonging to Cardiatherium, an extinct direct relative of modern capybaras. This finding shifts our understanding of Late Miocene epochs in South America.
“Finding a capybara tooth in a marine deposit in what today is one of the driest regions on Earth is just freakish,” explains Priscilla Martinez, a doctoral student at the University of Arizona and lead author of the study published in Scientific Reports.
The Atacama Desert is widely recognized as one of the most arid environments on the planet. Yet, the sediments surrounding the fossil at El Morro paint a vastly different picture. Deposited in a shallow marine environment between 7 and 10 million years ago, the formation sits near Cerro Ballena, a location globally renowned for its dense concentrations of prehistoric whale fossils.
Reconstructing a Lost Late Miocene Ecosystem
Capybaras are the world’s largest living rodents. They rely heavily on permanent freshwater sources, wetlands, and abundant vegetation to survive. Finding their ancestral remains in northern Chile forces a total revision of local paleoclimatic timelines, disputing the notion that the Atacama has remained continuously dry for 40 million years.
The isolated tooth did not emerge in a vacuum. Excavations at the same deposits yielded a trove of auxiliary biological indicators pointing to a humid, temperate environment:
- Fossils of freshwater fish and gavials, an extinct crocodilian lineage tied exclusively to permanent river systems.
- Microscopic silica structures known as phytoliths, which trace ancient plant tissues.
- Stable isotope evidence confirms that the area was dominated by C3 vegetation, including flowering plants and palms.
“Think sunny Southern California full of palm trees,” Martinez notes. “You don’t really expect the Atacama Desert to have palms, and we’re not sure if they were blooming extensively there, but they were definitely there.”
Navigating Geographical Barriers Across Ancient South America
The presence of these semi-aquatic herbivores on the Chilean coast raises immediate questions regarding their migration pathways. Modern capybaras live primarily east of the Andes. Even 8.8 million years ago, the towering mountain range would have formed a formidable geographical and climatic barrier.
To bypass this obstacle, researchers suggest the animals utilized low-elevation dispersion routes. Instead of traversing high, arid elevations, these ancestral rodents likely moved along a northern South American corridor. This pathway potentially stretched from modern-day Venezuela and Colombia through Ecuador and Peru, finally descending into northern Chile via extensive hydrological networks.
Such expansive river systems indicate that South America experienced drastically different continental drainage patterns during the Late Miocene. These persistent wetland connections allowed freshwater fauna to migrate freely across regions that are entirely disconnected today.
Broader Implications for Modern Climate Modeling
Beyond resolving the ancient biogeography of rodents, this fossil evidence offers critical baselines for contemporary environmental science. Deserts are exceptionally sensitive barometers for global climate shifts, reacting dynamically to year-to-year variations in regional monsoon intensity.
By studying how ancient arid ecosystems responded to major shifts without anthropogenic influence, researchers can better project how modern deserts will weather ongoing, human-driven climate change. The single capybara tooth from El Morro thus serves as an important piece of evidence, reminding modern scientists that even the most extreme environments on Earth carry records of radical ecological transformation.
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