Ten thousand years ago, in the shadowy forests and plains of South America, vast beasts lumbered beneath the canopy. Among them was Notiomastodon platensis, a close cousin of elephants, whose massive feet padded across ancient landscapes where Chilean palms dropped heavy fruits and monkey puzzle trees raised their spiny crowns toward the sky. Their trunks tugged at branches, their broad molars ground pulp and seeds. And every step they took scattered life across the continent.
Then, suddenly, they were gone.
The extinction of South American mastodons wasn’t merely the disappearance of a charismatic giant; it was the silencing of a crucial voice in an ecological conversation that had been unfolding for millions of years. Now, in a discovery that stitches together threads of paleontology, botany, and modern conservation, scientists have uncovered the first direct fossil evidence proving that these extinct titans were fruit-lovers — and, more importantly, irreplaceable allies of the forests they once roamed.
The research, published this week in Nature Ecology & Evolution, is the culmination of painstaking detective work led by Erwin González-Guarda of the University of O’Higgins in Chile, in collaboration with researchers from IPHES-CERCA, the Universitat Rovira i Virgili, and the Universitat Autònoma de Barcelona. The team’s findings crack open a 40-year-old ecological mystery and echo a warning across the millennia: when giants fall, the consequences ripple through time.
The story begins in 1982, when biologist Daniel Janzen and paleontologist Paul Martin proposed a radical notion: that many tropical trees and plants evolved large, sweet fruits specifically to tempt hefty animals — mastodons, giant sloths, native horses — into swallowing their seeds and carrying them far and wide. These plants, they suggested, were now ecological orphans, left waiting for seed couriers that would never return. It was a beautiful theory, but for decades, solid fossil evidence remained elusive.
Until now.
The new study examined 96 fossil teeth from Notiomastodon platensis, gathered across more than 1,500 kilometers of Chilean terrain, from the northern coastal city of Los Vilos to the wild, rain-soaked expanses of Chiloé Island. Nearly half the fossils came from the storied paleontological treasure trove of Lake Tagua Tagua, a Pleistocene basin where ancient animals seem to have left behind echoes of their lives in mud and sediment.
These teeth — timeworn, cracked, but still telling their stories — became the key to unlocking the mastodon’s dietary secrets. González-Guarda’s team used a battery of modern techniques: stable isotope analysis, microscopic examination of dental wear, and the study of fossilized dental calculus — the hardened tartar that, astonishingly, can trap bits of ancient meals.
“We found starch residues and plant tissues typical of fleshy fruits, such as those from the Chilean palm,” said Florent Rivals, a paleodiet expert from IPHES-CERCA. “It’s direct proof that these mastodons frequently consumed fruit. They weren’t just grazing on grass or browsing leaves. They were critical partners in the regeneration of forests.”
Each method the team employed peeled back another layer of time. Microscopic scratches on enamel revealed the mechanical signatures of chewing soft fruits, while the chemical fingerprints locked into tooth enamel told tales of ecosystems teeming with fruiting trees. It was like reading a forgotten journal of South America’s lost megafauna.
“This is more than just knowing what they ate,” explained Iván Ramírez-Pedraza, who specializes in paleoenvironmental reconstruction. “These animals shaped the forest itself. They carried seeds over long distances, created new plant colonies, and influenced which species thrived. When they vanished, entire ecological networks began to fray.”
One finding hit especially hard. By feeding a machine learning model with their data, the researchers examined how plant species that once relied on mastodons for seed dispersal are faring today. In central Chile, where no large animals have stepped in to fill the mastodon’s ecological shoes, the outlook is grim: 40% of these plants are now threatened, a rate four times higher than in tropical regions where creatures like tapirs or monkeys still act as substitute seed couriers.
“Where that ancient partnership between plants and animals has been completely severed, the consequences remain visible even thousands of years later,” said study co-author Andrea P. Loayza.
Among the living casualties of this lost alliance are species like the towering monkey puzzle tree (Araucaria araucana), its prickly branches spiraling skyward in Chile’s temperate forests, and the gomortega (Gomortega keule), an endangered tree whose golden fruits once tempted mastodons to spread its seeds far beyond a single grove. Today, these plants cling to survival in fragmented, isolated pockets, their genetic diversity dwindling, their future hanging in delicate balance.
“Paleontology isn’t just about telling old stories,” Rivals said. “It helps us recognize what we’ve lost — and what we still have a chance to save.”
That message rings louder than ever as scientists grapple with modern extinctions and climate change. The echoes of mastodons still rustle through South American forests, carried by fruits whose size and sweetness were tailored for giants that will never return. The shapes of these fruits remain the botanical ghosts of a lost companionship.
So when a Chilean palm drops its massive fruit in the silent forest, no mastodon arrives to gulp it down, to transport its seeds over mountain passes or across rivers. The fruit rots on the ground, a monument to a partnership severed by extinction.
And in this fossil evidence — hidden for millennia in the crevices of ancient teeth — we finally hear the mastodon’s own voice reminding us that the past is not truly past. It lives on in seeds waiting to sprout, in forests yearning to be whole again, and in the lessons we must heed if we hope to keep our world’s intricate webs from unraveling further.
More information: Erwin González-Guarda et al, Fossil evidence of proboscidean frugivory and its lasting impact on South American ecosystems, Nature Ecology & Evolution (2025). DOI: 10.1038/s41559-025-02713-8