Twelve million years ago, a massive herd of rhinos gathered at a watering hole in what is now northeastern Nebraska. But when a distant volcanic eruption at Yellowstone blanketed their food sources with ash, the species didn’t leave as expected, a new study finds.

Instead, the aftermath of the eruption killed more than 100 rhinos and preserved them in a state park.

The fossils were discovered in 1971 but a new study published April 4 by researchers at the University of Cincinnati used the teeth of 13 Teleoceras major (T. major) rhinos to analyze the herd’s migration habits — or lack thereof.

“We found they didn’t move very much,” lead author Clark Ward said in an April 8 news release by the university. “We didn’t find evidence for seasonal migration or any evidence of a response to the disaster.”

The species of “short-legged, barrel-bodied” rhinos lived on grass and other vegetation in the Miocene epoch, the study said. This herd defied some of the typical habits of rhinos such as the expected seasonal or long-distance migration and the size of the herd.

However, the study identified one major factor that kept the approximately 100 rhinos in what is now known as Ashfall Fossil Beds State Historical Park in Antelope County — a water source.

The semi-aquatic creatures needed easy access to water, according to the study, which likely deterred them from making the trek across different habitats.

Scientists determined this sedentary lifestyle by T. majors through an analysis of the isotopes, carbon and oxygen present in their fossilized molars, the study said.

They compared the isotopes of the soil and bedrock of the region to those in the teeth to determine if the rhinos had moved, and therefore eaten, in another place, according to the study.

In this case, the study found there was no long-distance migration or even a substantial seasonal move, though a short-distance move was not ruled out.

The climate at the time could have allowed the large herd to forage year round, researchers said.

But when volcanic ash blew hundreds of miles east from Yellowstone, it coated the rhinos’ food and water sources, according to the study.

“That ash would have covered everything: the grass, leaves and water,” Ward said in the news release. “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.”

Though the researchers involved in the study said they were surprised by the T. major’s lack of migration, one rhino expert said the findings add to an ongoing debate about the animal’s migration habits.

“I am not surprised that the analyses very strongly suggest that Teleoceras major lived in herds given that this animal resembles modern hippopotamus in form and hippos live in herds of several tens of animals — with several herds in one geographical area,” John Payne, who studied endangered Sumatran rhinos in Malaysia, said in the news release.

The study was published in the Nature Journal Scientific Reports and was conducted at the University of Cincinnati. It was authored by Ward, Brooke Crowley and Ross Secord.

Antelope County is about a 160-mile drive northwest from Omaha.

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