Two Major Events Shaped Herbivores Over 60 Million Years — Yet Their Role Remains Unchanged

Over the span of 60 million years, vast herds of large herbivores have roamed, transformed, and reshaped Earth’s ecosystems. These creatures, ranging from mastodons and giant deer to ancient rhinoceroses, have played pivotal roles in maintaining ecological balance, sculpting habitats, and influencing the evolutionary trajectories of countless species. A groundbreaking study led by researchers from the University of Gothenburg and published in Nature Communications now reveals how these colossal herbivore communities endured immense environmental upheavals, maintaining ecological stability despite successive waves of extinctions and migrations.

Large herbivores are more than just giants walking the landscape; they act as key ecosystem engineers. Their feeding habits affect vegetation cover, seed dispersal, and nutrient cycling. For millions of years, these dynamics have sustained diverse ecological functions, ensuring the resilience of habitats from dense forests to sprawling grasslands. However, the fossil record chronicles two profound shifts that deeply influenced these communities’ composition and ecological roles—events that underscore the delicate equilibrium between biodiversity and environmental change.

The first significant ecological revolution occurred approximately 21 million years ago. Geological shifts, specifically the closure of the ancient Tethys Sea, forged a land bridge connecting Africa and Eurasia. This corridor unlocked mass migrations of ungulates—hoofed mammals—across continents. The dispersal included ancestors of modern elephants, which had previously been confined to Africa. As they ventured into new territories spanning Europe and Asia, they encountered competing species such as deer, pigs, and rhinos. This faunal interchange rewired food webs and redefined ecological niches on a global scale. Intriguingly, despite the profound rearrangements in species distribution, the overall functional framework of herbivore communities remained robust.

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About 10 million years ago, Earth underwent yet another dramatic transformation. A prolonged cooling trend rendered the planet drier, triggering extensive expansion of grasslands at the expense of forests. This climate trajectory favored the evolution and proliferation of grazers adapted to these open habitats—species equipped with specialized dentition to cope with abrasive grasses. Concurrently, forest-dependent herbivores declined, leading to a contraction in the functional diversity of ungulates. The transition marked a critical turning point in the evolutionary saga of these large herbivores, yet, remarkably, ecosystems retained their intrinsic structure even as species composition shifted.

To unravel this complex evolutionary narrative, the international team undertook an unprecedented meta-analysis of fossil data encompassing over 3,000 species of large herbivores. By integrating paleontological records across temporal and spatial scales, the researchers could reconstruct patterns of species turnover and ecological roles through deep time. This approach allowed them to disentangle the interplay between species identity and functional roles within ecosystems, revealing that shifts in species were often compensated by others fulfilling similar ecological functions.

Fernando Blanco, the study’s lead author, emphasized the implications: “We observed that while species came and went over millions of years, the overarching ecological roles within large herbivore communities persisted. The foundational framework of ecosystem function did not collapse, underscoring a resilience that defies the dramatic environmental and faunal upheavals that have punctuated Earth’s history.” This resilience reflects a dynamic balance, where ecological redundancy and evolutionary adaptability safeguard ecosystem integrity.

Ignacio A. Lazagabaster, co-author from Spain’s CENIEH research center, illustrated this concept vividly, likening ecosystems to a football team that substitutes players but retains the same tactical formation. “Even though individual species were replaced, the ecosystems maintained their structural integrity because new species assumed similar ecological roles. This functional continuity is the keystone of resilience.”

However, this ecological robustness faces unprecedented challenges in the contemporary era. The last 129,000 years witnessed the extinction of some of the largest terrestrial mammals—including mammoths and giant rhinos—which, despite their absence, did not immediately dismantle ecosystem structures. Today, though, anthropogenic pressures—habitat destruction, climate change, and accelerated biodiversity loss—are causing species declines at a pace never before witnessed in the fossil record. These rapid transformations could push ecosystems beyond their adaptive thresholds.

Juan L. Cantalapiedra, senior study author from Spain’s MNCN, warned, “Natural ecosystems have evolved with a remarkable capacity to adapt over millions of years. However, the speed and scale of current changes are extraordinary. If we continue on this trajectory, we risk triggering a third global tipping point—a collapse of ecosystem function that could be irreversible.” This sobering perspective calls for urgent conservation efforts that recognize not only species survival but the preservation of ecological functions.

The study’s findings also illuminate fundamental principles in ecology and evolutionary biology. They highlight the concept of functional redundancy—the presence of multiple species that perform similar roles—which acts as an insurance mechanism against environmental variability. Moreover, the research demonstrates how macroevolutionary processes and biogeographical events interplay to shape ecosystems over geological timescales, providing crucial insights into how biodiversity loss today might reverberate through ecological networks.

This expansive research sets a new benchmark for understanding faunal evolution by moving beyond species counts to examine the persistence of ecological roles. It challenges traditional narratives focused solely on extinction, reframing ecosystem change as a dynamic process where function can be maintained through rearrangement and replacement. However, the looming question remains: How long can this resilience endure in the face of accelerated human-driven environmental change?

In conclusion, as we stand at a crossroads in Earth’s ecological history, understanding the legacies of past environmental shifts and their impact on large herbivore ecosystems is more relevant than ever. The interplay between species extinction and ecological functionality as revealed by this study underscores a vital message—preserving biodiversity is not merely about individual species, but about maintaining the complex web of interactions that sustain life on our planet. The next chapters in this saga are unwritten, and humanity’s choices will determine whether large herbivore communities—and the ecosystems they underpin—continue to thrive or unravel.

Subject of Research: Not applicable

Article Title: Two major ecological shifts shaped 60 million years of ungulate faunal evolution

News Publication Date: 5-Jun-2025

Web References: 10.1038/s41467-025-59974-x

Image Credits: Illustration: Fernando Blanco

Keywords: Large herbivores, ecological resilience, functional diversity, faunal evolution, environmental shifts, ungulates, extinction, migration, ecosystem function, biodiversity loss, paleontology, climate change

Tags: ancient mammal migrationsbiodiversity and extinctionecological balanceecological stability over timeecosystem engineeringenvironmental upheavalsfossil record insightsherbivore evolutionlarge herbivores impactnutrient cycling in ecosystemsseed dispersal mechanismsTethys Sea geological changes