A Summer Internship at Ashfall Fossil Beds Adrienne

The Barefoot Paleontologist: A Summer Internship at Ashfall Fossil Beds Adrienne Stroup MUS 670 11-1-12 A catastrophic event took place in Nebraska nearly twelve million years ago, one that would be concealed in time and earth until 1971. A paleontologist named Michael Voorhies set out to map the stratigraphy of sediment layers in northeastern Nebraska, when he noticed a small fossil, which marked the start of one of the great discoveries in vertebrate paleontology. The jaw of a juvenile rhinoceros jutted out of the eroding hillside, and remarkably so was the rest of the skull. Excavation soon revealed that the entire skeleton of the animal was attached and completely articulated, something that is almost unheard of in the science of paleontology. Even more surprising was that it was not the only one. Over two hundred complete skeletons were removed in the late 1970s and accessioned into to the University of Nebraska’s State Museum collections in Lincoln. The site proved to be larger than anyone had expected, about one and half football fields in length. As more and more fossils were uncovered, it was decided that they would remain in-situ on permanent display. The farm on which these fossils were discovered became the site of a unique institution; a joint project between the University of Nebraska-Lincoln (UNL) State Museum and the Nebraska Game and Parks Commission, combining the features of a natural history museum and a state park. A Visitor Center and an enclosure for the fossil bed, affectionately dubbed the Rhino Barn, were built and in 1991 the park was opened to the public. Ashfall Fossil Beds State Historical Park allows visitors to see a fossil site, celebrated world-wide for its incredible preservation of a fairly complete Miocene ecosystem, a waterhole where animals gathered to seek relief from ash filling the air and settling over Nebraska from the eruption of a super volcano. The volcano erupted in southwestern Idaho and its ash settled across the Midwest. It only fell for a few days but its effect on Nebraska would last millions of years. Barrel bodied rhinos, giant tortoises, three toed horses, camels, and saber-toothed deer are just a few of the dozens of species that have been found there. As one of seven interns, I had the pleasure to work with Dr. Voorhies for most of the summer, benefiting from his wealth of knowledge about the site. As an emeritus curator of the UNL State Museum and retired professor, he spends many hours volunteering at the park. In fact, only two permanent employees, Rick Otto and Sandy Mosel, run the entire facility. The park really depends on the interns to continue excavating in the Rhino Barn, sorting for microfossils in the Discovery Shelter, preparing fossils in the Prep Lab, and above everything else provide educational experiences and make ourselves available to answer visitors’ questions. The Rhino Barn houses the remaining part of the site, more than half of which remains unexcavated. When the park opened in 1991, the original barn was much smaller; basically it was a two bay garage. Soon the excavation had to be halted when everything inside was uncovered, though the site extended far beyond its foundation. Three years ago, fundraising efforts allowed for a new 17,000 square foot building to be constructed. The Theodore F. and Claire M. Hubbard Family Foundation gave UNL over a million dollars to build the new facility, and thus it was officially named the Hubbard Rhino Barn. According to Dr. Voorhies, the Hubbards are very active philanthropists, and they have donated large sums of money to not only build the new barn, but the Discovery Shelter as well, in addition to helping out the Omaha Zoo and other science education efforts throughout Nebraska. The new barn allows visitors to view what has been uncovered in the past, as well as see new discoveries being made every day. We work very closely with the fossils and have to be extremely careful when walking through the ash bed, therefore we are asked to work barefoot. In fact, we are discouraged to even walk through the previously excavated section of the ash bed. This is because walking through it will cause loose ash to become airborne and settle on the fossils, and then the entire ash bed has to be dusted off with soft brushes. The bigger risk is the possibility of tripping and stepping on a fossil, which would surely break it. Typical fossils are created when mineral-rich ground water, sometimes called “hard water,” penetrates organic material that has been quickly buried, such as animal bones. As the organics decay the minerals are left behind, creating an exact replica of the bone out of rock. Sand is superb for the fossilization process, but ash, which is volcanic glass, does not allow ground water to seep through it as easily. Therefore, only the outside layer of bone in the ash bed is fossilized; the inside, which is porous with a honeycomb-like structure, is still original bone. This is both helpful and problematic when excavating. Each intern is assigned an area to excavate, digging only through the bottom two feet of ash to the contact between the ash and the sand layers. Here is where we find the fully articulated skeletons. When we think we have found bone, our first clue is a smooth texture and a slightly different color. Here is where we slow down and examine the area by tapping the surface with a scalpel. Bone will make a sharper, hollow sound as opposed to the dull thud when tapping surrounding ash. By keeping our scalpels parallel with the ground surface we are less likely to gouge and crack the fossilized but fragile outer layer of bone. Instead, the scalpel usually glides right over the fossil. Visitors often remark on how tedious it must be to sit inches away from the ash and scrape away at it for hours in crouched positions, but it goes rather quickly, especially since most of the ash is very soft. Small tools are used to remove the layers of ash and then brushes and scoops collect the loose ash into buckets, which are dumped into a skid loader hopper that is finally deposited into a ravine on the park property. Great efforts are made to keep the ash from getting kicked up into the air, but over time the ground water seeping through the ash layer rendered it more dense so there is little risk of breathing in too much ash inside the barn. In addition, many people ask if fossils are also found beneath the ash bed, and if we will eventually remove all of the skeletons to get to them. Fossils are found in the lower sand layer, but excavation in the barn focuses on the Ashfall event. The older fossils beneath the ash were deposited before the event and are only individual scattered bones, not complete skeletons. Furthermore, if the Ashfall specimens were removed there would be no fossil bed to see and little reason to have a state park. Seeing the animals in the exact, unchanged positions is unique and tells us much more about the site and what happened there than if all the skeletons were removed and reassembled elsewhere. When visiting a museum, many people are unaware that the fossilized bones on display often come from many different individuals to create a complete skeleton. When found, the bones are usually scattered around and some may be missing. The classic example is the Brontosaurus, which was renamed Apatosaurus, meaning deceptive lizard, because for over a hundred years the dinosaur had the wrong skull attached to it at Yale’s Peabody Museum. At Ashfall, the entire animals are perfectly preserved, and there is no mistake that the rhinos and horses looked the way they did. One interesting thing about working in the barn was realizing how different the styles of excavation are between archaeology and paleontology. When Rick showed me around and told me where to begin excavating, I felt a little lost. There was no datum stake to record excavation depth below ground surface, no string lines to indicate the boundaries of my workspace, no need to dig in perfectly level ten-centimeter levels, and no paperwork. The field work that I had done in the past was much more regimented, which is logical since the data collected would be the only remaining evidence of the site after construction begins, at least with the cultural resource management I have been contracted to do in the past. There is a reason why one of our phases of fieldwork is called “Data Recovery.” At Ashfall, the site is mapped periodically, and nothing is removed, so the documentation is a little more relaxed. We do not even screen the ash after digging. Since we work so closely to the ash, anything small would be noticed, but there is a bigger reason and one that further explains the story of Ashfall. The animals died over a period of four to six weeks. The smallest of which, such as the birds and turtles, succumbed to the ash’s effects within a few hours of the fall. Wind blew the ash around like snow where it drifted and settled into the lowest point on the landscape, which is why almost eight feet of ash is found at Ashfall, further indicating that it was a watering hole. In two to three weeks the camels and horses would have died and lastly the rhinos, around four to six weeks. Therefore, the smallest animals are more likely to be found in the top of the sand layer, with the larger animals in the initial two feet of ash.

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