Ancient graveyard reveals that rhinos once lived in 'super-herds'

Twelve million years ago, vast herds of rhinoceroses grazed the lush grasslands of what is now the North American Midwest. These barrel-bodied creatures – ancient rhinos known as Teleoceras major – flourished across the region, often gathering in large numbers near waterholes.

Today, a new study from the University of Cincinnati (UC) reveals they weren’t just occasional visitors to these sites – they likely lived and died in close-knit herds, much like modern hippos.

As a result, the research sheds new light on one of North America’s most extraordinary fossil sites: Ashfall Fossil Beds State Historical Park in northeast Nebraska.

Over 100 rhinoceroses left fossilized remains at this site, along with camels, horses, and other animals – all of which perished in the aftermath of a massive Yellowstone supervolcano eruption.

Unraveling an ancient rhino mystery

Since the park’s discovery in 1971, scientists have puzzled over why so many animal,s including rhinoceroses, were found clustered in the same place. Did they come from miles away, fleeing the growing disaster of falling ash? Or had they been living there all along?

“We found they didn’t move very much,” said Clark Ward, lead author of the study and a UC graduate. “We didn’t find evidence for seasonal migration or any evidence of a response to the disaster.”

Clues from rhino teeth

Ward, now a doctoral student at the University of Minnesota, used isotopic analysis of fossilized ancient rhino teeth to track their movements and environmental conditions. 

With guidance from co-authors and advisers Brooke Crowley at UC and Ross Secord at the University of Nebraska, Ward analyzed ratios of strontium, oxygen, and carbon isotopes – atomic fingerprints that can reveal everything from diet and rainfall to landscape use.

“By studying carbon in the animal, we can reconstruct carbon in the environment to understand what kinds of vegetation lived there,” Ward explained.

“We can use [oxygen] to reconstruct how wet or dry the environment was,” he added. “And strontium tells us where the animal was foraging because the ratio of isotopes is related to the soil and supporting bedrock.”

Together, these isotopic clues suggest the rhinos were long-term residents of the area, not migrants drawn by a natural disaster or seasonal food shifts. It appears they simply lived – and ultimately died – in the place they called home.

A supervolcano’s lethal reach

The mass death was triggered by ash from one of Yellowstone’s ancient supervolcano eruptions. The Yellowstone hotspot has erupted often over 12 million years, spreading ash hundreds of miles away.

“That ash would have covered everything – the grass, leaves, and water,” Ward said. “The rhinos likely weren’t killed immediately, like the people of Pompeii. Instead, it was much slower. They were breathing in the ash, and they likely starved to death.”

In contrast to the sudden catastrophe of volcanic pyroclastic flows, which instantly buried victims in ancient cities like Pompeii, the Ashfall rhinos suffered a slower, agonizing fate.

The ash settled into the landscape like snow, rendering food and water sources toxic or unusable. Over time, the animals succumbed to inhalation of ash and eventual starvation.

Fossils show scavenging by bone-crushing dogs, which came after the animals died. Ancient tracks from these 100-pound carnivores, along with tooth marks on bones, support this conclusion.

Social creatures in ancient herds

Teleoceras major was a one-horned rhino with a short, squat body and stubby legs. Like hippos, these rhinoceroses were grazers who likely spent much of their lives near water. Their massive size offered protection from predators, but their calves would have been vulnerable to attack.

The study’s findings have answered one long-standing question: Did these rhinos live alone or in groups? The presence of so many individuals, including adults and juveniles, supports the idea of herd behavior.

Rhino expert John Payne, who spent his career working with Sumatran rhinos in Malaysia, said the conclusion fits the species’ biology.

“I am not surprised that the analyses very strongly suggest that Teleoceras major lived in herds, given that this animal resembles the modern hippopotamus in form, and hippos live in herds of several tens of animals – with several herds in one geographical area,” Payne said.

Science comes full circle

For Ward, the study has a personal significance. As a child, he visited Ashfall Fossil Beds and later returned as an intern to help with fossil preparation and visitor education.

Now, his name is attached to groundbreaking research from the same site that once inspired his curiosity.

“I’m honored and privileged to have my name in science attached to the site,” he said. “As someone who used to go to Ashfall as a kid, it’s come full circle.”

Broader implications of the study

Though Teleoceras major is extinct, studies like this reveal ancient ecosystems and modern species’ responses to threats.

The broader implications of the research go beyond rhinoceroses. By studying how ancient animals responded to environmental change, scientists can better predict the impact of climate disruptions today.

Whether it’s ash, mercury, or climate change, the past remains a vital key to our future.

The study is published in the journal Nature Scientific Reports.

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