Ashfall Fossil Beds
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The Ashfall Fossil Beds of Antelope County in northeastern Nebraska are among the rare preservation sites called Lagerstätte, which preserve ecological "snapshots" from a brief moment in time, due to extraordinary local conditions that have preserved a range of fossilized organisms undisturbed.
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[edit] Bruneau-Jarbidge event
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. The fall of ash drifted downwind from the Bruneau-Jarbidge supervolcano eruption (in present-day Idaho), nearly 1,000 miles (1600 km) west of the Ashfall site. 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 bears her unborn fetus, while others retain the contents of their last meal.
The animals, in effect, choked to death; the bones of the animals show telltale marks recognized by veterinarians as signatures of poor breathing. The smaller animals with smaller lung capacity were the first to die, and the larger animals were the last. Bite-marks on some bones show that local predators (the carnivorous bone-crunching dog Aelurodon) 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 rapidly-accumulating ash, windblown into deep drifts at low places like the waterhole site, remained moderately soft. The ash preserved the animals in three dimensions; not even the delicate bones of birds or the carapaces of turtles were crushed. Above the layer of ash, a stratum of more erosion-resistant sandstone has acted as "caprock" to preserve the strata beneath.
[edit] Preservation
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 Ashfall site became Ashfall Fossil Beds State Historical Park in 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. The site was declared a National Natural Landmark on May 9, 2006<ref>Acting Interior Secretary Scarlett Designates Ashfall Fossil Beds A National Natural Landmark. United States Department of the Interior (2006-05-09). Retrieved on 2006-06-11.</ref>
[edit] Species
The remains of Teleoceras are so numerous and concentrated that the main section of Ashfall is dubbed the "Rhino Barn". Other fossils at the "Rhino Barn" include the remains of horses and camels. Taxa discovered in the Ashfall deposits include:
- five species of horse: Cormohipparion, Protohippus, Pseudhipparion, Neohipparion and Pliohippus
- three species of camel: Procamelus, Aepycamelus and Protolabis
- three species of dog: Leptocyon, Cynarctus and Aelurodon
- one species of rhinoceros: Teleoceras
- one species of saber-toothed deer: Longirostromeryx
- three bird species: crowned crane, rail and secretary bird
- and two species of turtle: Hesperotestudo and pond turtle
[edit] See also
[edit] References
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[edit] External links
- Ashfall Fossil Beds - University of Nebraska State Museum
- 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 Historical Park
- NebraskaStudies.org - Ashfall
- Paleobiology Database: Ashfall Fossil Beds: Clarendonian - Miocene, Nebraska
