A fossilized capybara tooth discovered in northern Chile’s El Morro sediment beds reveals that the hyper-arid Atacama Desert supported wetlands, palms, and freshwater crocodiles roughly 9 million years ago. Reported in Scientific Reports, the finding disrupts the long-held consensus that the region has remained continuously dry for an estimated 40 million years.
Unearthing a Capybara in a Marine Deposit
Finding the remains of the world’s largest living rodent in a coastal marine sequence strikes researchers as completely unexpected. “Finding a capybara tooth in a marine deposit in what today is one of the driest regions on Earth is just freakish,” notes lead author Priscilla Martinez, a doctoral student in the University of Arizona’s Department of Geosciences.
The specimen itself—measuring roughly two-thirds of an inch long—was pulled from a three-foot-thick sediment layer at El Morro. This site sits squarely within the Bahía Inglesa Formation, a geological treasure trove famously known for hosting Cerro Ballena, or Whale Hill, recognized as the world’s largest concentration of whale fossils.
Local residents historically gathered unusual fossils from the region to sell to private collectors, scattering historical evidence across distant hands. Fortunately, local merchants recognized the scientific value of specific specimens and donated them to researchers, putting the capybara tooth into the hands of Carolina Gutstein, head of paleontology at the Chilean mining company Fosfatos de Caldera and professor at Universidad Santo Tomás in Santiago.
Reconstructing a Lost Ecosystem of Palms and Crocodiles
The sediment layers didn’t just preserve a solitary mammalian tooth. Microscopic plant remains called phytoliths—tiny silica structures formed inside plant cells as roots pull dissolved minerals from groundwater—survived the millennia, offering a botanical snapshot of the ancient coastline.
Caroline Strömberg, a co-author and professor at the University of Washington, analyzed these microfossils to map out the historical flora. The data pointed directly to palms and other flowering dicots, painting a picture starkly removed from today's barren environment. “Think sunny Southern California full of palm trees,” Martinez explains. “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.”
Additional fossil records within the same strata solidify the picture of an aquatic-friendly environment. Co-author Mark Clementz, a paleobiology expert and head of the University of Wyoming’s Department of Geology and Geophysics, points out that the deposits also yielded remains of freshwater fishes and gavials, which are freshwater crocodiles. Together, these clues confirm that there was enough of an ecological community to support capybara populations long term.
Navigating Around the Andes Mountains
The presence of capybaras on Chile’s coast raises compelling questions regarding geographic distribution. Modern capybaras and their guinea pig relatives are native to South America, yet the massive physical barrier of the Andes Mountains separates the modern Atacama from traditional habitats east of the range.
“Not only are the plateau lands of the Central Andes very tall, they’re also extremely arid,” Martinez states. “So, if capybaras originated east of the Andes in this foreland region, how in the world could these short-legged rodents make it across?”
Researchers propose that the animals bypassed the high altitudes entirely. The hypothesis suggests that capybaras journeyed across low-elevation wetlands connecting their original range to northern Chile’s coast, potentially traveling in a counterclockwise route from Venezuela.
As scientists continue analyzing the Bahía Inglesa Formation, this 9-million-year-old tooth forces a reevaluation of South America’s climatic history, proving that even the driest places on Earth once sustained water-bound ecosystems.
