Fossil hunting brings to mind hot deserts and painted badlands, but Nebraska is one of the best places in the United States to find fossils from the Cenozoic — the Age of Mammals, from 66 million years ago to today. One of its finest sites is Ashfall Fossil Beds in Antelope County, in the state's northeast, where hundreds of beautifully preserved skeletons of extinct rhinos, horses, camels and other animals lie in volcanic ash about 11.93 million years old. Some are still in the ground where visitors can see them, many almost perfectly articulated.
A waterhole and a distant eruption
The fossil beds lie in the Ash Hollow Formation, about 12 to 5 million years old, in the Miocene epoch. 11.93 million years ago the site was a waterhole on a broad savanna, home to many mammals — some familiar-looking, others not, most from groups no longer native to North America.
Then a massive eruption hundreds of miles away, in what is now southwestern Idaho — from the same volcanic system that now lies beneath Yellowstone — sent a plume of ash across the continent. Around Ashfall, as much as a foot (30 cm) fell.
The animals died in order of size, and the layers record it:
| Layer | Who | What happened |
|---|---|---|
| Bottom | small animals | suffocated early; their bones were often smashed by larger animals trampling the waterhole |
| A few inches higher | horses and camels | bigger lungs let them live longer, but breathing ash killed them — and left telltale marks on their bones |
| Top | a herd of rhinos, Teleoceras major | gathered at the water and grew too weak to leave; with nothing left to trample them, their skeletons are the least damaged |
Wind kept blowing ash into the waterhole until the carcasses were buried.
Dozens of skeletons left in place and exposed in relief. Photo by V. Santucci, National Park Service
What has been found
More than 20 species have come out of the ash, with more in the older sands below — though far less well preserved.
| Group | Finds |
|---|---|
| Rhino Teleoceras major | by far the most common; 100+ studied |
| Horses | five species — the smallest, Pseudhipparion gratum |
| Camels | four species |
| Birds | four species, including 40 crane skeletons, some with feathers and gut contents |
| Dogs | two species |
| Reptiles | a turtle and a large tortoise — a sign the area rarely froze; lizards found as gut contents of birds of prey; a snake |
| Others | a musk deer, a mole, a mouse (also as gut contents) |
Many rhinos are preserved in three dimensions, showing broad, hippo-like bodies; some still have grass in their mouths and bodies. They seem to be several small herds of all ages and sizes, mostly females. Bone-cracking dogs and other big predators left few bones, but their dung, tooth marks and footprints show they were there.
History of the site
| Year | |
|---|---|
| 1920s on | locals report finding fossil bones nearby |
| 1953 | a partial rhino skull turns up in sandstone below the ash |
| 1971 | heavy rain exposes a baby rhino skeleton, found by paleontologist Michael Voorhies |
| Late 1970s | expeditions collect more than 120 articulated skeletons |
| 1986 | the Nebraska Game and Parks Foundation buys the site |
| 1991 | Ashfall Fossil Beds State Historical Park opens |
| 2006 | the site becomes a National Natural Landmark |
| 2009 | the Hubbard Rhino Barn opens |
The park, run by the University of Nebraska State Museum, sits in rolling farmland near Verdigre Creek and is open from early May to early October. The 17,500-square-foot Rhino Barn covers part of the bonebed — with about forty rhinos exposed — so visitors can watch paleontologists documenting, preparing and conserving skeletons in place. The waterhole's full extent is still unknown, and more species are likely to turn up.
National Natural Landmarks
The Park Service's National Natural Landmark Program recognizes, and supports the voluntary protection of, outstanding biological and geological sites. Landmarks are designated by the Secretary of the Interior and owned by many public and private stewards. Fossils have contributed to the designation of 59 of them, spanning early marine life 510 million years ago to mammals of 40,000 years ago.
Ashfall is one of 59 landmarks designated chiefly for fossils. Photo by V. Santucci, National Park Service
Sources
Based on "Paleontology of Ashfall Fossil Beds National Natural Landmark," by Justin Tweet, NPS partner paleontologist with the American Geosciences Institute, Park Paleontology News, Fall 2023, National Park Service; rewritten in hubnx's own words.
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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