A capybara tooth from coastal Chile puts standing water in the Atacama 9 million years ago
Priscilla Martinez's team pulled the tooth from a marine deposit at El Morro in northern Chile. Freshwater fish, gavials and palm phytoliths from the same beds carry more of the argument than the tooth does.
The Scientist · Science desk
What happened
- A fossilized tooth from a capybara that lived almost 9 million years ago in what is now the Atacama Desert is the first and oldest record of the rodent in coastal Chile, where none live today.
- The tooth came from sediments deposited in a shallow marine environment between 10 million and 7 million years ago at El Morro, part of northern Chile's fossil-rich Bahia Inglesa Formation.
- The same deposits yielded fossils of freshwater fishes and gavials, freshwater crocodiles, which the authors read as independent signs of persistently wet conditions at the site.
- The paper, in Scientific Reports, questions the textbook account of the Atacama as one of Earth's oldest continuously dry regions, an estimate that runs back some 40 million years.
Why it matters
- What it limits constraint A continuity claim breaks on its wettest documented gap, and this one is dated to about 9 million years ago, which leaves the older 31 million years of the record untested by the fossil either way.
- What's now possible capability Obligate semiaquatic animals plus phytoliths give aridity work a local water-presence check that does not depend on isotopes or sediment chemistry, and it can be applied wherever such fossils are preserved.
- Who has to decide decision Anyone extending El Morro's wet signal to the desert as a whole now has to argue the step explicitly, because the deposit that produced the tooth is a coastal marine one.
- What it limits constraint With a single specimen and no other capybara material from that stretch of coast, the strength of the reconstruction sits with the associated freshwater fossils and plants, not with the rodent.
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What makes the tooth a climate claim is what a capybara needs to stay alive. Rodent specialists call them obligate semiaquatic herbivores that indicate persistent riparian ecosystems [6]. They are the largest living rodents, native to South America, and today they live east of the Andes in low-elevation wetlands, their core range roughly outlining the Amazon basin [7]. Their way of life ties them to standing surface water, wetland vegetation and movement along creeks and rivers [8].
The tooth itself came out of the wrong rock for that habitat. The beds at El Morro were deposited in a shallow marine environment between 10 million and 7 million years ago [4], so where the animal was buried is not where it lived. Fresh water comes in with the rest of the assemblage. "We have multiple lines of evidence indicative of really wet conditions that are typically associated with capybaras today," said Mark Clementz of the University of Wyoming, a co-author. "The same deposits contain fossils of freshwater fishes and gavials (freshwater crocodiles)" [17]. The team also recovered phytoliths, the silica bodies that form inside plant cells as roots take up dissolved silica from groundwater, and co-author Caroline Strömberg of the University of Washington matched them to palms and other flowering plants, including dicots, nothing that grows in the Atacama now [13][14]. "Think sunny Southern California full of palm trees," Martinez said [15].
The 40-million-year figure and the fossil do not sit at the same scale. If the region's dryness began 40 million years ago and the tooth dates to about 9 million, then 31 million years of that record run before the wet interval and are untouched by it [19]. The tooth's age is bracketed rather than measured directly, inside a three-million-year depositional window [20].
The animals also had to get there. Geologists estimate the Andes rose to about 18,000 feet, roughly 5,500 metres, before capybaras appeared, walling the Atacama off from the eastern lowlands that hold the animal's range today [11][18]. "Not only are the plateau lands of the Central Andes very tall, they're also extremely arid," Martinez said. "So, if capybaras originated east of the Andes in this foreland region, how in the world could these short-legged rodents make it across?" [12] The authors propose they went around, counterclockwise through low-elevation wetlands from today's Venezuela into Colombia, Ecuador and Peru, then into northern Chile [21].
The record rests on one tooth. "We don't have any other evidence of capybaras in that part of coastal Chile," said co-author Barbara Carrapa, Martinez's doctoral adviser at the University of Arizona [10]. The published account does not say how long the wet conditions lasted or how far inland they extended [16]. I would put weight on the wet coastal setting at El Morro, which three independent fossil lines support, and much less on the 40-million-year continuity figure being wrong, because that case needs deposits of the same age from inland sites and the paper describes a coastal one [4][2].
What to watch
- Deposits of the same 10-to-7-million-year window from inland Atacama sites, with or without freshwater fossils, would test whether the wet interval was regional or coastal.
- A second capybara specimen from El Morro or elsewhere on the Chilean coast would turn one stray animal into evidence of a resident population.
- Whether aridity reconstructions revise the 40-million-year continuity estimate or restrict it to parts of the desert the fossil does not sample.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence72
- Adoption
- Not scored
- Hype gap+20
- Incentives30
- Confidence65
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
A fossilized capybara tooth from an animal that lived in the Atacama Desert in northern Chile almost 9 million years ago provides the first and oldest record of a capybara in coastal Chile, a country where no capybaras live today.
- [2]
The discovery calls into question the longstanding textbook version of the Atacama Desert as one of the oldest continuously dry regions on Earth, dating back an estimated 40 million years.
- [3]
The work is published in the journal Scientific Reports.
- [4]
The fossil was found in a layer of sediments deposited in a shallow marine environment between 10 million and 7 million years ago at a site called El Morro, part of the Bahia Inglesa Formation.
- [5]
The Bahia Inglesa Formation also hosts Cerro Ballena, or Whale Hill, recognized as the world's largest concentration of whale fossils.
- [6]
Scientists specializing in capybaras describe them as obligate semiaquatic herbivores that indicate persistent riparian ecosystems.
- [7]
Capybaras are the largest living rodents, native to South America, and today thrive east of the Andes in low-elevation wetlands, with their core range roughly outlining the Amazon River basin.
- [8]
The capybara's semiaquatic lifestyle tightly links it to persistent surface water, wetland vegetation and the ability to migrate along riparian corridors along creeks and rivers.
- [9]
"Finding a capybara tooth in a marine deposit in what today is one of the driest regions on Earth is just freakish," said Priscilla Martinez, the study's lead author and a doctoral student at the University of Arizona Department of Geosciences.
- [10]
"We don't have any other evidence of capybaras in that part of coastal Chile," said co-author Barbara Carrapa, a professor of geosciences and Martinez's doctoral adviser.
- [11]
Geologists estimate that long before capybaras appeared roughly 9 million years ago, the Andean mountain chain rose to 18,000 feet, effectively walling off the Atacama Desert from the eastern lowlands that stretch across parts of Venezuela and Colombia to northeastern Argentina and Uruguay, the animal's current range.
- [12]
"Not only are the plateau lands of the Central Andes very tall, they're also extremely arid," Martinez said. "So, if capybaras originated east of the Andes in this foreland region, how in the world could these short-legged rodents make it across?"
- [13]
The team unearthed phytoliths, microscopic accumulations of silica that form inside plant cells and tissues as they absorb dissolved silica from groundwater through their roots, which co-author Caroline Stromberg, a professor at the University of Washington, analyzed to identify the plants that made them.
- [14]
The phytolith evidence pointed to palms and other flowering plants, including dicots, not anything that would grow in today's Atacama Desert.
- [15]
"Think sunny Southern California full of palm trees," Martinez said.
- [16]
The published account does not report how long the wet conditions persisted or how far inland they extended.
- [17]
"We have multiple lines of evidence indicative of really wet conditions that are typically associated with capybaras today," said Mark Clementz, head of the Department of Geology and Geophysics at the University of Wyoming and a study co-author. "The same deposits contain fossils of freshwater fishes and gavials (freshwater crocodiles)."
- [18]
An Andean elevation of 18,000 feet is about 5,500 metres.
- [19]
If the Atacama's dry record began 40 million years ago and the tooth dates to about 9 million years ago, 31 million years of that record predate the wet interval the fossil indicates.
- [20]
The depositional window for the host beds spans three million years, so the tooth's age is bracketed within that interval rather than dated directly.
- [21]
The authors propose that capybaras took advantage of low-elevation wetlands connecting their original range along coastal areas, going counterclockwise around northern South America from today's Venezuela into Colombia, Ecuador and Peru, then into northern Chile.
Sources
2 independent publishers whose own reporting we read for this story.
- discovermagazine.com9-Million-Year-Old Capybara Tooth From Chile Hints at Unexpectedly Wet Conditions in the Ancient Atacama Desert
1 article · September 18, 2026
- phys.orgCapybaras in the desert? Fossil casts doubt on Atacama as world's oldest continuously dry region
1 article · September 17, 2026
Topics and entities
Topics
- Vertebrate Paleontology
- Phytolith analysis
- Paleoclimate
Entities
- Carolina Gutstein
- University of Arizona
- Atacama Desert
- Caroline Stromberg
- Fosfatos de Caldera
- Scientific Reports
- University of Wyoming
- Priscilla Martinez
- Universidad Santo Tomas
- Bahia Inglesa Formation
- University of Washington