Researchers: 9-Million-Year-Old Capybara Tooth Suggests Atacama Was Once Wet

Fossil Molar Discovered in the Atacama Desert

Live Science reported that a roughly 9-million-year-old tooth from a large, aquatic-loving cousin of today’s capybaras has been found by researchers in the Atacama Desert of northern Chile, Atacama Desert of northern Chile, Live Science reported. Previous indications that the Atacama—among Earth’s most arid environments—has not remained continuously dry over the past 40 million years are further supported by this fossilized molar.

The Tech TL;DR:

• A 9-million-year-old capybara relative tooth was unearthed in northern Chile’s Atacama Desert, challenging long-held aridity timelines.
• Researchers theorize the semiaquatic rodents migrated along western coastal wetlands rather than crossing the 18,000-foot Andes barrier.

The Discovery of an Extinct Capybara Relative in Northern Chile

The Atacama Desert occupies the northern third of Chile and is bounded by the Chilean Coast Range to the west and the Andes to the east. The hyperarid core’s monthly rainfall drops below 0.08 inches. Recent research estimates this core started forming between 47.8 million and 33.9 million years ago during the Mid- to Late-Eocene, preceding the formation of the Andes by approximately 20 million years.

Modern capybaras (Hydrochoerus hydrochaeris) live near stable freshwater sources and consume plants requiring significant moisture. Consequently, uncovering an extinct capybara relative (Hydrochoerus Cardiatherium) tooth in this region represents an unexpected paleontological anomaly. “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 doctoral student in the University of Arizona’s Department of Geosciences and co-author of the new paper, stated.

Sediment Layers and Botanical Evidence Supporting Ancient Moisture

The fossil specimen originates from a three-foot-thick sediment bed at El Morro, part of the Bahía Inglesa Formation. These sediments were deposited in a shallow sea between 10 million and 7 million years ago, a formation location that also holds Cerro Ballena, recognized as the world’s largest concentration of whale fossils.

To evaluate historical environmental conditions, researchers analyzed microscopic plant remains known as phytoliths, which are tiny accumulations of silica forming inside plant cells as roots absorb groundwater. Mark Clementz of the University of Wyoming noted the finding challenges established models of the Atacama’s history. Additional fossil evidence from the region indicates that crocodiles and freshwater fish also inhabited the area during the late Miocene.

Transcontinental Dispersal Pathways Across Western South America

The presence of a semiaquatic mammal in coastal Chile raises questions regarding its migration path, given that the Andes form an 18,000-foot-high barrier between modern capybara habitats and the fossil site. Rather than traversing the high-elevation plateaus, researchers theorize that ancient capybaras migrated along the western coast of South America by following connected wetlands, rivers, and low-elevation water sources.

Through an email message, University of Oregon Earth sciences professor Samantha Hopkins—who did not participate in the research—pointed out that the tooth’s dimensions rule out wind or water carriage over long distances unless a vast river network existed, thereby adding weight to the finding that the Atacama experienced a much wetter climate in earlier times.