Today's blog is about how a 9 million-year-old tooth gave more insight that the Atacama desert wasn't always a deser, because it belonged to a prehistoric rodent who loved water. Prehistoric Capybaras are classified as rodents who resemble oversized guinea pigs.
(Illustration: Paleoenvironmental reconstruction of a group of Cardiatherium, a genus of extinct, direct relatives of modern capybaras, pictured in the late Miocene coastal wetlands and forestry canopy of the Atacama Region of northern Chile. Freshwater crocodiles float in the river, and seals can be seen basking on rocks while seabirds soar above the shoreline. Credit: Mauricio Alvarez) Freakish' discovery of 9 million-year-old capybara tooth supports idea that Atacama wasn't always a desertSCIENCE NEWS, By Damien Pine Edited by Laura Geggel, Laura Mondragó, October 8, 2026
Researchers have discovered a roughly 9 million year old tooth belonging to a large, water-loving relative of modern day capybaras in the Atacama Desert of northern Chile. The fossilized molar adds to previous evidence suggesting that it's unlikely the Atacama Desert (in Chile), one of the driest places on Earth, was continuously dry for the last 40 million years.
The Atacama Desert, possibly the oldest desert on Earth, takes up the northern third of Chile. It's bounded by the Chilean Coast Range to the west, which blocks rain from the Pacific Ocean, and the enormous Andes to the east, which obstruct rain from the Atlantic Ocean. The driest part of the desert's hyperarid region gets less than 0.08 inches (2 mm) of rainfall a month.
Recent research estimates the Atacama's hyperarid core started forming between 47.8 million and 33.9 million years ago, in the Mid- to Late-Eocene, 20 million years before the Andes formed. It suggests the mountain ranges weren't the cause for the desert's aridification, and may have only intensified it.
Capybaras (Hydrochoerus hydrochaeris) — the world's largest rodent — exclusively live close to stable freshwater sources and feed on plants that also require water to grow, so the discovery of an extinct capybara relative (Hydrochoerus Cardiatherium) tooth in the Atacama Desert is very strange.
"Finding a capybara tooth in a marine deposit in what today is one of the driest regions on Earth is just freakish," Priscilla Martinez, a geoscientist at the University of Arizona and co-author of a new paper describing the discovery, said in a statement. The authors propose a scenario in which the capybaras took advantage of low-elevation wetlands connecting their original range along the coastal areas going "counterclockwise" around the northern portion of South America – from today's Venezuela into Colombia, Ecuador and Peru, into northern Chile.
"We have multiple lines of evidence indicative of really wet conditions that are typically associated with capybara today," said professor Mark Clementz, paleobiology expert and head of the Department of Geology and Geophysics at the University of Wyoming and is one of the study's co-authors. "The same deposits contain fossils of freshwater fishes and gavials (freshwater crocodiles)."





































