Ashfall Fossil Beds

The Ashfall deposit preserves the fossilized remains of ancient animals that perished in a dense volcanic ash fall which occurred during the late Miocene, approximately 12 million years ago; the animals had come 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 (1,600 km) west of the Ashfall site. A large number of very well preserved fossil Teleoceras (extinct hippo-like relatives of rhinos), small three-toed and one-toed horses, camels, and birds have been excavated. Many animals were preserved with their bones articulated; one rhino still bears her unborn fetus, while others retain the contents of their last meal.

The bones of the animals show features that indicate that the animals died of lung failure induced by inhaling volcanic ash. 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 carcasses, 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.

Fossil of a Teleoceras in volcanic ash.

Paleontologists working on the site

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. In 1971, University of Nebraska State Museum paleontologist Michael Voorhies was walking with his wife Jane through a series of gullies on Melvin Colson's farm in northeastern Nebraska and made this discovery.[6][7] The Nebraska Game and Parks Foundation purchased the Ashfall site in 1986.[8] Ashfall Fossil Beds State Historical Park opened in 1991.[7] The site was declared a National Natural Landmark on May 9, 2006.[9]

The park's Hubbard Rhino Barn opened in 2009. The 17,500-square-foot (1,630 m²) pavilion lets visitors observe as paleontologists carry out excavations of new discoveries exactly where the fossilized remains lie preserved.[10] Specially constructed walkways afford visitors an unobstructed close-up view of paleontologists at work during the summer field season.

The remains of Teleoceras are so numerous and concentrated that the main section of Ashfall is called the "Rhino Barn".[11] Other fossils at the "Rhino Barn" include the remains of horses and camels.[12] Taxa discovered in the Ashfall deposits include:

• five horse genera: Cormohipparion, Protohippus, Pseudhipparion, Neohipparion and Pliohippus
• three camelid genera: Procamelus, Aepycamelus and Protolabis
• three canid genera: Leptocyon, Cynarctus and evidence of scavenging from a bone-crushing canid, possibly Epicyon
• one rhinoceros genus: Teleoceras
• one saber-toothed musk deer genus: Longirostromeryx
• three bird species: Balearica exigua (a crowned crane), Apatosagittarius (a hawk resembling the living secretarybird), and Anchigyps (a scavenger related to Old World vultures)[13]
• three turtle species: Hesperotestudo (a large tortoise), Sternotherus (a musk turtle) and Chrysemys (a painted turtle)[12]

• Gray Fossil Site
• List of fossil sites
• Pipe Creek Sinkhole

Wikimedia Commons has media related to Ashfall Fossil Beds.

• Ashfall Fossil Beds State Historical Park Nebraska Game and Parks Commission
• Ashfall Fossil Beds State Historical Park University of Nebraska State Museum
• Ashfall Fossil Beds Skeleton Map University of Nebraska State Museum
• Cenozoic Geology of Idaho: "The Bruneau-Jarbidge Eruptive Center, Southwestern Idaho" by Bill Bonnichsen (pages 251-268) Idaho Bureau of Mines and Geology