Researchers have identified a fossilized capybara tooth dating back almost nine million years in the Atacama Desert of northern Chile, providing the oldest record of capybaras on the Chilean coast. The findings, published in Scientific Reports, challenge the long-held view that the Atacama has remained continuously dry for around 40 million years, and instead add to evidence that at least parts of the region experienced significant environmental changes on geological time scales. The capybara tooth is important because no other capybara fossils of a similar age have yet been discovered in Chile, making this tooth an important piece of evidence for reconstructing the region’s past ecosystems. Close view of the chewing surface of the fossilized capybara tooth described in the research article. The specimen measures about two-thirds of an inch long (scale equals 10 mm or 0.4 inches). Credit: Carolina Gutstein et al. “Finding a capybara tooth in a marine deposit in what is now one of the driest regions on Earth is just strange,” said lead author Priscilla Martínez, a doctoral student at the University of Arizona. According to the researchers, along with the other animal and plant fossils found at the site, the evidence points to an Atacama landscape very different from today’s arid environment, with a more complex history of changing climates and ecosystems across the region over millions of years. Capybaras are the largest living rodents in the world and are closely associated with freshwater environments; These semi-aquatic herbivores depend on surface water and wetland vegetation. Therefore, its presence in the modern Atacama, one of the driest places on Earth, would be very unexpected, according to the researchers. The tooth was discovered at El Morro, a fossil-rich site within the Bahía Inglesa Formation, where surrounding sediments were deposited in a shallow marine environment between 7 and 10 million years ago. The formation also includes Cerro Ballena, a site famous for its exceptionally rich concentration of whale fossils. The discovery raises questions about how capybaras arrived on the Chilean coast, given that their modern relatives are predominantly found east of the Andes and the mountain range would have already presented a substantial geographical and climatic barrier when the animal lived in the region. A paleoenvironmental reconstruction of a group of Cardiatherium, a genus of extinct direct relatives of modern capybaras, photographed in the late Miocene coastal wetlands and forest canopy of the Atacama Region in northern Chile. Freshwater crocodiles float in the river and seals can be seen sunbathing on the rocks while seabirds fly over the coast. – Credit: Mauricio Álvarez Instead of crossing the high, arid Andes, the study found evidence that capybaras may have dispersed throughout low-elevation environments around the northern tip of South America, potentially moving from what is now Venezuela and Colombia through Ecuador and Peru and into northern Chile. Other fossils from the same deposits provide additional evidence of a very different late Miocene climate, including freshwater fish and gharials, a group of crocodiles associated with freshwater habitats. The researchers also found phytoliths (microscopic silica structures formed within plant tissues) that reveal clues about the vegetation growing in the region at the time. Analyzes indicate that the landscape supported palm trees and other flowering plants, including dicotyledonous plants, in stark contrast to the sparse vegetation found in the Atacama today. Priscilla Martínez, a doctoral student at the University of Arizona, conducts field work on an ancient dry riverbed where minerals were found, demonstrating that standard temperate plants once covered the now-arid Chilean coast. Credit: Joao Gabriel Martínez López “Think of sunny Southern California full of palm trees,” Martínez explains. “You really don’t expect the Atacama Desert to have palm trees, and we’re not sure if they were flowering extensively there, but they were definitely there.” The findings could also provide broader insights into how desert landscapes respond to climate change, beyond the history of capybaras and the Atacama Desert, Martínez said. “The more we understand deserts, which are extremely sensitive to climate changes, including changes in monsoon intensity from year to year, the better we can predict how they will fare in the long term,” he said. Understanding past climate changes that occurred without human influence can also provide a basis for evaluating how these environments may change as a result of human-driven climate change. Cover image: San Pedro River Valley in the Atacama Desert. Credit: Erlantz Pérez Rodríguez/Getty Images
