Ancient Capybara Tooth Found in Chile’s Atacama Desert

The Atacama Desert in Chile ranks among the world’s driest environments, receiving nearly all of its limited moisture from fog drifting inland from the Pacific Ocean.

That makes it an especially unlikely setting for capybaras: enormous, guinea pig-like rodents with a strong affinity for water that have become internet favourites.

You may have seen capybaras relaxing in a yuzu-filled hot spring in Japan, yet South America is their natural home.

Across the continent, they inhabit wetlands surrounding the Amazon basin in every country except Chile. There, the Andes mountain range has effectively ‘walled off’ the Atacama.

Capybaras and water

Capybaras feed on aquatic vegetation and grasses growing along wetland edges, and travel through riparian corridors - ie., streams and rivers - in ‘herds’ of up to 20, rather like miniature hippos.

In every part of their range, capybaras are essentially inseparable from water.

For that reason, palaeontologists were astonished to uncover part of an 8.8-million-year-old capybara tooth in the Atacama Desert.

It represents the oldest capybara evidence ever discovered in Chile, as well as one of the oldest capybara fossils found anywhere.

The tooth fragment, from a third upper molar, belonged to an extinct capybara genus called Cardiatherium. These animals were prehistoric relatives of the modern capybaras known today (Hydrochoerus hydrochaeris).

It was recovered from sandstone within the Neogene Bahía Inglesa Formation in the Atacama Desert.

"Finding a capybara tooth in a marine deposit in what today is one of the driest regions on Earth is just freakish," says Priscilla Martinez, the study's lead author and geoscientist at the University of Arizona.

A wetter late Miocene Atacama Desert

The fossilised capybara tooth contributes to mounting evidence that, contrary to the assumption that the Atacama has been desert for 40 million years, it was a thriving wet ecosystem during the late Miocene.

"We have multiple lines of evidence indicative of really wet conditions that are typically associated with capybara today," says paleobiologist Mark Clementz of the University of Wyoming.

"The same deposits contain fossils of freshwater fishes and gavials (freshwater crocodiles)."

Researchers also identified minute pieces of silica, known as phytoliths, in the deposit. These provide revealing evidence of plants that once grew there and drew on groundwater.

The phytolith types found beside the capybara tooth point to palms, gingers and other flowering plants. Such plant life offers strong evidence that persistent freshwater once existed in the southern Atacama.

"All this supports the idea that there was enough of an ecological community to support capybara populations long term," Clementz adds.

"Finding this capybara – which I think everyone can agree is not a desert animal by any means – at that location is going to challenge many of the ideas about the Atacama's history."

The Atacama Desert therefore seems to have changed dramatically over the past 8.8 million years.

How capybaras may have reached Chile

Evidence of late Miocene capybaras has previously emerged from the opposite side of South America, on Argentina’s coast. During the Miocene, the Andes would have formed an even more formidable divide between the continent’s eastern and western coasts, leaving the animals’ presence on both sides something of a puzzle.

"Not only are the plateau lands of the Central Andes very tall, they're also extremely arid," says Martinez.

"So, if capybaras originated east of the Andes in this foreland region, how in the world could these short-legged rodents make it across?"

Rather than having crossed the Andes themselves, the researchers consider it more likely that a wetland route north of the mountains once crossed the continent, enabling capybaras to spread to either side of the range.

However, the animals that travelled east may have made the better choice for long-term survival, as the Atacama Desert is now inhospitable to a riparian rodent.

"The more we understand deserts, which are extremely sensitive to changes in climate, including shifts in monsoon intensity from year to year, the better we can predict how they fare long term," Martinez says.

"And if we can understand past climate changes that had nothing to do with humans, it gives us a baseline to work off of to understand how climate can evolve over time with humans in the mix."

The research was published in Scientific Reports.

This article was fact-checked by Rachel Garner and edited by Peter Dockrill. Although we take pride in our process, we are only human. If you notice an error, please let us know.