Ashfall Fossil Beds

 5 August 2022

On our way back from our summer trip to see family near Chicago, we wandered somewhat further west to Augusta, Missouri (great gallery and great wines) and northeastern Nebraska, before spending the weekend with my brother and his family in Minneapolis. We've been trying to visit the Ashfall Fossil Beds since 2017, but we were either passing nearby on the wrong day (closed Mondays) or the wrong season (open mid-May through mid-October). It was worth the effort to finally make it to the site.

Ashfall Fossil Beds State Historical Park & National Natural Landmark is located in northeastern Nebraska. The fossil beds were created by ashfall from a huge volcanic eruption 11.2 million years ago in what is now southwestern Idaho. This eruption, 1000 times larger than the 1980 Mt. St. Helens one, was caused by the same hotspot that now sits under Yellowstone National Park. The ashfall was about 18 inches thick in this region, but the Ashfall Fossil Beds collected a much deeper layer (up to 12 ft) because the ash filled in a waterhole as it blew around. As a result, the fossil beds are layered with skeletons of animals that died over the course of a month or two. Since whole animals were covered by ash and the site was not disturbed by running water or destroyed by ice age glaciers (which came within 8 miles of the site), the skeletons are complete, intact, and tell paleontologists much about the climate and ecology of this area 12 million years ago.

At that time this area held wildlife now associated with African savannas such as the Serengeti. Rhinos, elephants, horses, camels, deer, antelopes, canids, felines, rodents, large birds, and a giant tortoise roamed these plains.

While the surrounding land is mostly flat, Verdigre Creek has created a system of small ravines. This erosion exposed the fossils.

The original discovery was made in 1971, and this area was systematically excavated and examined over the next few years. The photo shows the earliest trenches and pits.

Today the Hubbard Rhino Barn covers the most important part of the site.

A view of the fossils protected by the Rhino Barn from the upper viewing level.

In the Rhino Barn, several of the skeletons are marked - and have been given names. #1 is a young adult male barrel-bodied rhino ("Tusker", Teleoceras). #2 is a large 3-toed horse (Cormohipparion), whose left front foot is under the legs of #1. #3 is an adult female rhino ("Sandy") with baby ("Justin"). #4 is a juvenile rhino that shows evidence of scavenging after death; the bones were moved between death and burial. #5 is a juvenile rhino. (Click on the image to see a larger image.)

A few of the skeletons have been removed, carefully mounted, and displayed behind plexiglass.  This is Pliohippus, a three-toed horse whose outer toes have nearly disappeared - a link between 3-toed horses and modern horses.

Skeleton #29: A large 3-toed horse (Neohipparion) lying next to scavenged camel bones and a partial skeleton of a small 3-toed horse (Pseudohipparion).