Millions of years ago during the middle of the Miocene epoch, a large volcanic eruption in what is now Idaho spread deadly volcanic ash and dust over a path hundreds of miles wide. In an ancient water hole almost a thousand miles away, some animals, particularly smaller ones, died shortly as the falling ash (and the glass particles it contained) quickly filled their lungs. Larger animals lived a few days longer, perhaps even weeks. A few scavengers survived long enough to prey upon some of the dead animals filling up the pond. But before long even the largest creatures met their end in and around the area, and the ash continued to fall, covering the bodies in a layer eight to ten feet thick that kept them preserved right where they died.
Roughly 12 million years later (in 1971), a paleontologist named Mike Voorhies noticed a baby rhinoceros skull sticking out of a volcanic ash layer exposed on a hillside in northeastern Nebraska. Several years later he came back to collect the skull, and he and his team uncovered not only the rest of the baby rhino body, but intact skeletons from dozens of ancient rhinos and other creatures, many perfectly preserved by the volcanic ash that was laid down shortly after the eruption. Later this paleontological treasure would become Ashfall Fossil Beds State Historical Park, and in 2006 it was designated a National Natural Landmark.
The discoveries at Ashfall Fossil Beds have given paleontologists something rare and priceless: fully intact, articulated skeletons of numerous ancient animals. While fossilized mammals, birds, and turtles have been discovered in Nebraska for many years (in fact it’s one of the very best places on earth to find them), there are relatively few examples of well-articulated skeletons, and even fewer complete skeletons. That all changed with the discovery at Ashfall, where dozens of skeletons that are complete or very close to it, have told us much about animal life during the Miocene epoch.
THE BONEBED
The original quarry excavation in 1978-79 uncovered dozens of Teleoceras, an ancient barrel-bodied rhino that probably behaved more like a hippopotomus than a modern day rhinoceros. As other extinct animals were also uncovered, researchers quickly realized that they had only uncovered a fraction of the likely bonebed.
Eventually the land was purchased by the state parks commission, who partnered with the University of Nebraska State Museum to build and run Ashfall Fossil Beds. Fundraising campaigns and some generous donors allowed the organization to build a huge “rhino barn” over a significant portion of the thick layer of ash that covered the ancient water hole. The barn serves several purposes: it helps preserve the delicate fossils in the ash bed as they are uncovered, it allows the public to easily access the site, and it allows paleontologists to continue their work exposing the fossil bed regardless of the weather conditions.
WHAT BONES/FOSSILS ARE FOUND AT THE SITE?
There have been dozens of types of animals found at Ashfall. The largest and most common is a herd of Teleoceras. An extinct rhinoceros with a horn, the large animal had a body like a modern hippo, and was thought to spend much of its time wallowing in the water. Because of the volume of fossils, paleontologists now have great insight into the social behavior of Teleoceras. Several adult males have been found, while many adult females and calves have been uncovered. Very few young adult males have been discovered, suggesting that these animals behave like some modern herd animals: a few males large males protect a herd of females and young, while young adult males leave the herd to go and find their own herd to lead.
In addition to Teleoceras, another type of hornless rhinoceros called Aphelops has also been found at Ashfall. Although hornless, this animal is much more like a modern rhinoceros. Only a few remains have been found so far, suggesting that Aphelops was probably not a frequent visitor to the waterhole at Ashfall.
Many ancient horses have been found in Nebraska, spanning a time period of many millions of years. In fact, the evolution of the horse in North America was of great interest to Charles Darwin. The first horses were small, roughly the size of a dog. As the climate and environment changed around them, they eventually grew to the very large size they are today. Through that time they also went through several other evolutionary changes, the most obvious being the loss of several toes. Early horses had four toes, but horse fossils found in North America show that over time horses began to rely solely on one large toe in the middle of the foot, while the side toes became smaller and eventually disappeared. Some of this evolution can be seen among the varieties of ancient horse that have been found at Ashfall. The largest, Neohipparion, was a three-toed horse that was likely a very fast runner. Cormohipparion also had three toes but was slightly smaller, and had shorter leg bones than Neohipparion. One of the more interesting horses found at Ashfall is Pliohippus, once the “missing link” and darling of evolution scholars because it was the first horse that showed how the vestigial toes of early horses disappeared over time.
The smallest horse found at Ashfall is also the most common, with over fifty individuals of all ages having been discovered. Pseudhipparion was about the size of a dog, and unlike most horse species, Pseudhipparion actually got smaller over time. A skeleton of Pseudhipparion was uncovered by a young researcher about two weeks ago at Ashfall.
Many other animals have also been found at Ashfall, including an ancient camel relative called Aepycamelus, also known as the “giraffe camel” for it evolved very long legs and a long neck. Aepycamelus is not related to giraffes, so it is a good example of convergent evolution, where animals who are not related evolve similar body features and behaviors based on living in similar environmental conditions. Dozens of specimens of ancient camels have been found at Ashfall, with the possible ancestor of modern camels Procamelus being the most abundant. While ancient elephants and gomphotheres (four-tusked elephant-like mammals) are found all over the state of Nebraska, only a few remains at Ashfall have been found. The largest carnivore remains that have been discovered at Ashfall belong to an animal called Ischyrocyon, or more commonly the “giant beardog.” The giant beardog is not closely related to either bears or dogs, but looked somewhat like a very large dog and walked flat-footed like a bear. This animal undoubtedly scavenged some of the carcasses at Ashfall before expiring.
Rhinos, horses and camels are the largest animals found at Ashfall, and among the most abundant. There are a lot of smaller animals that died first and are buried under the layer of large animals. This layer contains several species of extinct deer and dogs. Other small animals include a number of birds, amphibians, and turtles.
ARE THERE OTHER ACTIVITIES AVAILABLE AT THE FOSSIL BED?
In addition to the rhino barn, there is also a visitors center which offers a number of interesting interpretive displays, including some fossils from the early excavations. Among these are a baby Teleoceras fossil, an extinct saber-tooth deer skeleton, and camel fossil that shows how some of the larger animals at Ashfall suffered severe lung trauma before their deaths. There are quite a few fossil specimens in the visitor center, mostly from Ashfall but some mammoth and plesiosaur fossils come from elsewhere in Nebraska.
Two new buildings have been erected since the last time we visited a couple years ago. One is the Dickinson Heritage Center which has some displays and educational information and also a large dig pit that contains two complete casts of animals found at Ashfall Fossil Beds. There is another good dig play area outside near the new building that has been there for a while and contains several “bones” for children to dig. The new dig pit in the Heritage Center is excellent: it is much larger than the older dig pit and it is on the ground and easily accessible for small children. The new dig pit play area occupied my kids and plenty of others for quite a long time on our recent visit.
The other new building is on the opposite side of the Hubbard Rhino Barn; it had a few fossils to look at as well as a researcher sorting through microfossils from the site. All the researchers at Ashfall including the rhino barn and the visitors center were very friendly with the public and happy to answer questions as they worked.
One activity that we have enjoyed a couple times at Ashfall is a hike through the valley around the site. The trail takes about thirty minutes or so to hike and was very enjoyable as we walked on a trail through the tall grass. Bluebirds are common in the area and on our most recent visit, we saw one fly right in front of us!
EASE OF SEEING THE BONES:
It doesn’t get easier to see ancient bones still in the ground than at Ashfall! While the visitors center has a number of fossils on display, the rhino barn is very impressive to most visitors. The fossils are still in the ground as they are discovered, and researchers continue to work on the surface, brushing away volcanic ash while they hope to uncover more interesting animals from the Miocene. This is one of the best bonebeds to see fossils because the bones are not jumbled up like they are in many bonebeds. Instead the majority of the animals are fully articulated and visitors can see the entire skeletons very easily. It is an amazing place!
EDUCATION MATERIALS/DISPLAY INFORMATION/SIGNAGE:
There is a wealth of display information available at Ashfall. Not only is the signage good, but beautiful educational posters about many of the animals in the fossil beds are on display in the rhino barn, painted by noted Nebraska paleoartist Mark Marcuson.
DID MY CHILDREN ENJOY GOING?
Yes, my children enjoy going to Ashfall Fossil Beds. It is about a two and a half-hour drive from Omaha, but they never hesitate when I ask if they want to go. The first time they went they were fascinated by the skeletons in the bonebed, and we spent a lot of time looking at them and talking about them. In subsequent visits, the dig pits and hiking trails have occupied more of our time.
HOW MUCH TIME SHOULD I PLAN TO SPEND THERE?
It takes us about two and a half hours to get to Ashfall Fossil Beds from Omaha; once we are there we typically spend a couple of hours walking on the trail around the park and looking in the rhino barn and heritage center buildings. It’s a beautiful and very relaxing area to visit.
OVERALL:
The Ashfall Fossil Beds are a fascinating look at the animals that lived in North America during the late Miocene epoch about 12 million years ago. Unlike other famous fossil bonebeds such as the La Brea Tar Pits, at Ashfall the animals are still lying in situ. Even for those of us who live within easy driving distance, it is fun to go every year or two because research in the bonebed continues, and every year more ancient animals are exposed.
Rating Aspects of the Fossil bonebed:
Visibility of the Bones/Fossils on Display: (9.5 out of 10)
Ease of Getting to/Seeing the Bones: (10 out of 10)
Educational Materials/Display Information/Signage: (9 out of 10)
Activities/Play Areas for Children: (8 out of 10)
Allosaurus Roar 