Twelve million years ago, in ancient Nebraska, short, round hippos, elephants, three-toed horses, many types of camels and oreodonts roamed the grasslands. But a thousand miles away, unknown to these animals, a supervolcano erupted, spewing rock and ash into the sky. Over the next days and weeks, the ash carried downwind of the eruption continued to fall steadily.
The Ashfall Fossil Beds were first discovered in 1953, although the area was known for the bones found in a specific spot by farmers for years. That spot was called Bone Hill and it was believed that this was where cattle went to die. That's because any bones found, unlike most fossil bones were not mineralized. Farmers thought that meant they were recent.
Donald Peterson and his father James were hired by a farmer to plant rye in fields near Bone Hill. At the base of Bone Hill, Donald and James discovered the skull of an animal eroding out of the cliff face. They decided to contact University of Nebraska State Museum about their discovery and this led paleontologists Lloyd Tanner and Henry Reider to visit the site. They were able to identify the skull as that of a rhinoceras, which once roamed the Great Plains of North America! Although Tanner and Reider made field notes and noted the location of the skull, which they took back to the museum, their notes were eventually lost.
It wouldn't be until 1971 that geologists Mike and Jane Voorhies, who were mapping the area, would discover the jawbone of a baby rhino within the ten foot thick layer of volcanic ash. It was known that rhinoceras roamed what is now Nebraska over thirty million years ago. However, fossils were a rare find.When he returned the next day to remove the fossil, he discovered the entire skull and saw a vertebrae as well. Jane did not return to the area because it was covered in poison ivy. (They eventually named it Poison Ivy Quarry.) It would be another six years before Mike returned to Poison Ivy Quarry, this time with a small team of paleontologists to help him. They would uncover the complete skeleton of the baby rhino and more skeletons. Over the next few weeks they would remove the skeletons of a dozen rhinos and three horses, taking them to the museum.With the help of John Boellstorff, who worked for the Nebraska Geological Survey, the ash was dated at approximately 10.5 million years, plus or minus 1.5 million years. At this time they did not know the source of the volcanic ash.
The following year, Mike Voorhies again returned with a bulldozer to remove the rock and soil topping the ash layer. Over the next four months, they uncovered fifty-eight rhinos. So began the remarkable discoveries that led Voorhies and other scientists to piece together the catastrophic events that led to what became known as the Ashfall Fossil Beds.
Scientist, Alison Pearce Stevens weaves together the fascinating events that paleontologists believe occurred at a watering hole almost 10 million years ago, after the eruption of a supervolcano. Stevens, who has a Ph.D in ecology, evolution and animal behaviour begins the story with the discovery of rhino bones and then goes on to describe the work of Mike Voorhies as he and other paleontologists, students and interns worked to excavate the Ashfall Fossil Beds.
Along the way, Stevens provides her young readers with information about many different aspects of the research. For example she explains how scientists dated the volcanic ash, how evidence from the skeletal remains of the animals indicated they suffered from Marie's disease and what that suggested about how they may have died.
Paleobotanists were able to use seeds in the ash to determine what the environment was like at the time of the eruption. Evidence from diatoms, tiny plant-like algae that form glass shells, helped paleobiologists determine that the water hole filled during the rainy season and dried up when the rains stopped. The distribution of types of animals who died at the water hole helped scientists determine that grazers like rhinos were more affected by the ash than browsers like deer. Michael Perkins, a geologist at the University of Utah had studied ash beds from Utah and many surrounding states. Mike Voorhies asked Perkins to try to determine where the volcano that produced the ash beds in Nebraska was located.
Stevens shows her readers the many facets of paleontological and geological research and how geologists can piece together an event based on the information fossils, rocks and other features provide. The explanations are simple and easy to understand. There are the black and white illustrations by Matt Huynh as well as some black and white photographs of the Ashfall beds excavated over the years and housed in a special building constructed to protect them.
Budding geologists and those interested in earth history will enjoy this well written, engaging and informative book about a unique event in North American natural history. Stevens has included a Glossary, Author's Note and an Index at the back of the book.
Further information may be found at
Rhino Resource Center's copy of Mike Voorhies 1978 paper, A Miocene Rhinoceros Herd Buried in Volcanic Ash.
Alison Pearce Stevens article from Science New for Students, Rhinos, Camels and Bone-Crushing Dogs Once Roamed Nebraska.
Rhinos In Nebraska by Alison Pearce Stevens
New York: Henry Holt and Company 2021