The Ashfall Fossil Beds of Antelope County, northeastern Nebraska, are among the rare preservation sites called Lagerstätten, which preserve ecological "snapshots" from a brief moment in time, due to extraordinary local conditions that have preserved a range of fossilized organisms undisturbed.

The Ashfall deposit preserves 10-million-year-old (Miocene) fossil mammals who suffocated in a dense volcanic ashfall where they came to a waterhole seeking relief. Some of the best-preserved fossil rhinos, small three-toed horses, camels, and birds found anywhere have been excavated, still with their bones articulated, one rhino still bearing her unborn foetus, others retaining the contents of their last meal. The rapidly accumulating ash, windblown into deep drifts at low places like the waterhole site, has remained moderately soft, preserved them in three dimensions, not crushing even the delicate bones of birds or the carapaces of turtles. Above the ashfall, a stratum of more erosion-resistant sandstone has acted as "caprock" to preserve the strata beneath.

Bite-marks on some bones show that local predators scavenged some of the carcases, but no predator remains have yet surfaced. There are also abundant clues to the region's ecology, indicating a savanna of grassland interspersed with trees that luxuriated in a warmer, milder climate than today's.

The fall of ash drifted downwind from a volcanic eruption in the Rocky Mountains, in Idaho, hundreds of miles to the west.

The first hint of the site's richness was the skull of a juvenile rhinoceros noticed in 1971 eroding out of a gully at the edge of a cornfield. The precious site has been protected as Ashfall Fossil Beds State Historical Park since 1991. Newly uncovered fossils are being left exactly as they are found: specially constructed walkways afford visitors an unobstructed close-up view of paleontologists at work during the summer field season.

External links

• Mike Voorhees, "Ashfall: Life and Death at a Nebraska Waterhole Ten Million Years Ago" from University of Nebraska State Museum Notes Number 81 (February 1992)
• Nebraska Game and Parks Commission: Ashfall Fossil Beds State Park
• NebraskaStudies.org: Ashfall