12 Million Years Ago

Overview of fossil site shown on live camera

Skeletons in situ labeled

2019-08-25 Sunday

Today was one of those days when we really feel as if we found a gem that hardly anyone seems to know about. We have waited for a year to get back to Nebraska to see Ashfall Fossil Beds State Park, and today was the day. We left our campground at 9:30, for a 2.5 hour drive (which took us 3 hours, with a stop for gas and slower speed than the speed limit allows.) As soon as we got out of the outskirts of York, the scenery became more and more rural until we felt we were driving into the middle of nowhere. The towns were all tiny, with no gas stations or much of anything, really. There was only one sizable town during the entire 135 mile drive.

Adult female barrel-bodied rhino

The park itself is in a gorgeous setting of hills, ravines, and green everywhere. And SO QUIET-- when we got out of the RV in the parking lot, all you could hear was the breeze and the crickets. Standing there with the cool air blowing lightly and the green hills all around, I would have been happy to just sit and drink it in for an hour or so. But of course, I was too eager to go see the fossils.

12 million years ago, the area of Ashfall was a semi-tropic area, and there was a water hole in that spot. The area was populated by a lot of mammals which are extinct relatives of our living rhinoceros, horse, camel, dog/cat (they have the same ancestor!), and loads of smaller mammals as well as birds. At that time, a volcano erupted in what is now southwest Idaho, and the volcanic ash blew eastward, settling as it came. A significant amount of it fell in what is now the Ashfall area. The animals in the neighborhood of the water hole died in that area--first the birds and small mammals, then the medium ones, and finally the largest, the rhinos. The winds blew the volcanic ash over the dead animals before the bones could be moved by weather or by carnivorous animals, and so as the ash hardened, the bones stayed as intact skeletons. The smaller animals with less lung capacity were affected by the ash in the atmosphere sooner, and the scientists think it took 4-6 months for the largest animals to be affected. Until they died, they were breathing what was essentially toxic ash, and many of them show signs of some kind of lung disease (I’m not sure how they can tell, but apparently they can) because they were breathing it longest, and inhaling the fallen ash with the grasses which they grazed on (most of them, other than the dogs, were herbivores.)

Bird (Crane) skeleton with lizard in its stomach

Complete skeleton of 3-toed horse

Unborn baby rhino in adult female

Because the bodies were protected by the ash, which is like crushed glass in texture, tiny details of the animals were preserved. So besides the skeletons being intact, there are details such as females with unborn fetuses still inside them (it was one of these skeletons, which is on display in Lincoln, which clued us in to the Ashfall area last year.) There is also one baby with the mother which seemed to be in a position to be nursing, with its head up under the ribcage of the mother animal. It is just amazing to see so many of these large animal skeletons totally complete. They are being preserved with a cement around them, because the bones are mostly not petrified. The exteriors are hard, but the interiors can crumble, and so the bones can be easily damaged. The first large group of animals to be uncovered were removed to protect them, but now the plan is to leave them where they are found for educational purposes. The site has student interns working there in the summer, slowly uncovering more of the site (I am so jealous-- I would love to work there!) The whole set up reminds me very much of the Mammoth Site in Hot Springs, SD, which we visited back in 2007.

Cassie checks out a petrified rhino bone

Baby rhino skeleton displayed at visitor center

We looked at the displays in the small visitor center for 20 minutes or so to get oriented to what we would be seeing, but we spent most of our time in the Rhino Barn, as it is called. The rhinos are the most common animal to be found at Ashfall. They have found (I think I remember reading) about 48 females, but only 6 males, and about 48 young rhinos. They think that maybe the rhinos behaved like some other modern animals, where there is one dominant male with a “harem” of females and their babies, which would account for the gender imbalance. In the case of other animals known to have this kind of social group, young males gather in “bachelor herds”, and they have found a group of all male rhinos about 150 miles away from Ashfall which supports this theory. I remember something similar was true with the mammoths-- the find in Hot Springs was mostly adolescent males, and they think that the females drove the males out of the herd and they fell into the sinkhole where they were found.
I took a lot of photos, and Joey and I both talked to the young intern from University of Montana who was working there today. He was answering a lot of questions from other visitors (there weren’t many of us, though!) and also had been working in the dig area when we first arrived. Besides the dig area itself, there were a lot of poster-size panels on the wall with color drawings of all the animals which had been found in the area (they found over 200 skeletons in the first dig--located outside the current Rhino Barn--alone!) There were also electronic displays around the railing which showed drawings of the various skeletons, giving their descriptions and (I loved this part) the name of the volunteer or student who had found each one! They are all numbered, and the skeletons left in situ are numbered correspondingly so you can see a number in the dig area, and then look at the details of what kind of animal it is, on the electronic display.

All in all, I think we spent 3 hours at the site, including drinking in the surroundings and reading the information panels outside describing the landscape (the entire area outside is, of course, part of the area covered with ash, but that layer is not visible except just around the Rhino Barn, where the ground is dug out to allow a sidewalk to walk “through the millenia” as we descended to the ash layer.

The animals species at the site did not become extinct-- they existed in other parts of what is now Nebraska and elsewhere, where presumably the ash was not as thick. So gradually many of these animals returned the the area, and their bones have been found in layers above the ashfall layer. Gradually the climate changed, the animals evolved or became extinct, and time went on. But the unique circumstances at the Ashfall area have given an incredible opportunity to see these animals without having to piece them together from various skeletal remains. We were totally in awe of the site, and felt it was well worth driving the side roads to find it.

We left the park at 5:00 (closing time!) and drove about an hour west until we found a small public campground in the town of Atkinson. Tomorrow will be a long day driving to the Black Hills.