Herbivores survived millions of years of change - but now face a modern crisis
A herd of mastodons, rhinoceroses, and giant deer once roamed freely across Earth. Their lives shaped landscapes for tens of millions of years. In a sweeping new study, scientists examined fossil records from more than 3,000 large herbivores to see how their world shifted, and how it didn’t.
An international team of researchers led by Fernando Blanco at the University of Gothenburg discovered that herbivore ecosystems remained surprisingly steady for long stretches. But they also pinpointed two pivotal moments where the balance flipped.
Herbivores shifted during climate change
The first ripple hit around 21 million years ago. A land bridge emerged as the ancient Tethys Sea closed. Suddenly, elephants and relatives could walk from Africa into Eurasia. Other hoofed animals, deer, pigs, rhinos, joined them.
“The environmental pressure was so great that the entire system underwent global reorganization,” noted Blanco. At this point, hoofed communities didn’t collapse, they reassembled.
Larger browsing species with mid‑to‑high crowned molars became dominant. Network analyses of those fossil data reveal a shift to a new system across continents, the first major global transformation in herbivore functional types.
Roughly ten million years later, another reinvention unfolded, this time silently. A cooling, drying climate expanded grasslands worldwide. Forest‑dwelling browsers declined. Grazers equipped with tougher teeth spread.
A functional tipping point followed, reshaping the roles of herbivores again. Grazers and mixed feeders dominated, equipped with both high‑ and low‑crowned teeth. From then on, functional diversity began a long decline, a trend scientists trace onward through the Pleistocene and beyond.
Different species, same ecosystem structure
“It’s like a football team changing players during a match but still keeping the same formation. Different species came into play but they fulfilled similar ecological roles, so the overall structure remained the same,” explained Ignacio A. Lazagabaster of CENIEH in Spain.
Despite these transformations, the ecosystem backbone remained intact. Even as mastodons, woolly mammoths, and giant rhinos disappeared in the last 129,000 years, the roles they played weren’t lost.
The network models show that after these extinctions, community configurations, known as continental functional faunas, remained remarkably consistent.
That consistency holds through the last 4.5 million years, reflecting resilience through ice ages and environmental upheavals. Still, the team warns that modern biodiversity loss is happening much faster – and could trigger a third tipping point before ecosystems can adjust.
Why these transitions matter now
Functional diversity began declining around 10 million years ago, during the spread of C4 grasses and shrinking forests. As herbivores with specialized teeth rose to dominance, the global count of functional roles dropped by about 65 percent in roughly 5 million years.
The drop intensified around 2.5 million years ago with glacial cycles and major biotic exchanges, like the Great American Interchange.
Still, the overall shape of ecosystems held firm. The continents shared similar functional configurations even as roles vanished. But today, the authors caution, biodiversity is receding much faster. They warn that another irreversible reorganization may soon be triggered.
Herbivores and modern changes
Megaherbivores, those weighing more than a ton, have largely vanished. Proboscideans, which once numbered up to 33 species, now survive as just a handful. Yet scientists estimate that they comprised only about 15-18 percent of functional types in most regions. Their loss reduces ecosystem richness but didn’t break the system.
“We may soon reach a third global tipping point, one that we’re helping to accelerate,” said Juan L. Cantalapiedra of Spain’s MNCN.
The study highlights the importance of large herbivores in ecosystem function. Conservation efforts that protect or reintroduce them could help restore key ecological roles lost in recent millennia.
Signals from the fossil record
The fossil record offers a rare, long-term perspective on ecological resilience. By tracking traits like tooth morphology and body size across thousands of extinct herbivores, the researchers built a detailed picture of how animals responded to shifting environments over time.
The team’s data-driven approach captured how new species stepped into familiar roles, even after dramatic losses. The research reveals a disconnect between species loss and system collapse.
While many individual species disappeared, their ecological roles often lived on through new players. That buffering capacity is what kept herbivore ecosystems functionally stable for 60 million years. The question now is whether that same resilience can hold under today’s faster pace of change.
Protecting the roles of herbivores
Ancient ecosystem changes took thousands to millions of years to unfold. Humans are transforming biodiversity on century scales. This study shows that large herbivore communities can adapt to change – but only up to a point.
If current declines continue, we risk triggering a shift beyond recovery. Protecting the functional diversity of herbivores is as crucial as protecting population numbers.
Restoring or preserving herbivore populations may help systems stay resilient as conditions continue to change.
The study is published in the journal Nature Communications.
—–
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.
—–
