Rick E. Otto, University of Nebraska State Museum
Death was everywhere. Animal carcasses littered the landscape and sank into the area’s waterhole as ash swept away everything in its path. For some, death happened quickly; for others, it was slow and painful.
This was the scene after a supervolcanic eruption in Idaho, roughly 1,600 kilometers (900 miles) away. It was an explosion so powerful that it obliterated the volcano itself, leaving a crater 80 kilometers wide and spewing ash that was carried by the wind for long distances, killing almost everything that inhaled it. This was especially true here, at this location in Nebraska, where animals large and small were subjected to the explosion’s deadly emissions.
Eventually, all traces of this terrible event were buried; life went on, evolved and changed. That’s why, millions of years later in the summer of 1971, Michael Voorhies was able to enjoy another pleasant day of exploration.
Finding rhinos
He, like every summer between academic years, was creating a geological map of his hometown in Nebraska. This meant going from farm to farm and asking if he could walk the property to survey the rocks and look for fossils. “I’m basically a kid at heart, and being a paleontologist in the summer was my idea of heaven,” Voorhies, now retired from the University of Georgia, told Ars.
What caught his eye on one particular farm was a layer of volcanic ash—something prized by geologists and paleontologists, who use it to determine the age of deposits. But as he got closer, he also noticed the exposed bone. “Finding what was obviously a lower jaw still attached to the skull, now that was really quite interesting!” he said. “Mostly what you find are isolated bones and teeth.”
That skull belonged to a baby rhinoceros. Voorhies and some of his students returned to the site to dig further, uncovering the rest of the rhino’s fully articulated remains (meaning the bones of its skeleton were connected as they would have been in life). More digging produced intact skeletons of five or six more rhinos. This was enough to get National Geographic funding for a massive dig that took place between 1978 and 1979. Crews collected, among many other animals, an incredible total of 70 complete rhinoceros skeletons.
To put this in perspective, most fossil sites—even spectacular sites that preserve multiple animals—consist mostly of disarticulated skeletons, pieces of the puzzle that paleontologists painstakingly piece together. Here, however, was something that no other country had produced before: a large number of complete skeletons preserved where they died.
Realizing there was still much to discover, Voorhies and others appealed to the greater Nebraska community to help preserve the area. Thanks to hard work and substantial local donations, the Ashfall Fossil Beds park opened to the public in 1991, staffed by two full-time employees.
The fossils discovered have now been left in place, meaning they remain on display right where they are, protected by a massive structure called Hubbard’s Rhino Barn. Excavations inside the barn are carried out at a much slower and steadier pace than they were in the 1970s, largely because of the small, rotating number of seasonal workers—mostly college students—who dig further each summer.
Photos by Rick E. Otto, University of Nebraska State Museum
A complete ecosystem
Nearly 50 years of excavation and research have revealed the story of a cataclysmic event and its aftermath that took place in a Nebraska that no one would have known — one where species like rhinoceros, camels and saber-toothed deer were a common sight.
But to understand that story, we need to set the scene. The area we know today as the Ashfall Fossil Beds was actually a waterhole during the Miocene, an area frequented by a variety of animals. We know this because there are fossils of these animals in a layer of sand at the bottom of the waterhole, a layer that was not affected by the supervolcanic eruption.
Rick Otto was one of the students who dug up the fossils in 1978. He became Ashfall’s superintendent in 1991 and retired at the end of 2023. “There were animals dying of natural causes around the Ashfall waterhole before it happened volcanic ash storm,” Otto told Ars. which explains the fossils found in that sand. After being wiped out, their bodies may have been trampled by some megafauna visiting the waterhole, which would have “worked those bones into the sand.”