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University of Nebraska, Niobrara State Park, Fort Robinson, Arbor Lodge, Smith Falls
The Ashfall Fossil Beds of Antelope County in northeastern Nebraska are rare fossil site types called lagerstätten that, due to extraordinary local conditions, capture a moment in time ecological "snapshot" in a range of well-preserved fossilized organisms. Ash from a Yellowstone hotspot eruption 10-12 million years ago created these fossilized bone beds.
The Ashfall Fossil Beds are especially famous for fossils of mammals from the middle Miocene geologic epoch. The Ashfall Fossil Beds are stratigraphically part of the Serravallian-age Ogallala Group.
The site is now protected as Ashfall Fossil Beds State Historical Park, which includes a visitor center with interpretive displays and working fossil preparation laboratory, and a building over an ongoing excavation site featuring fossil Teleoceras (native hippo-like ancestral rhinoceros) and ancestral horses.
Ashfall Fossil Beds Wikipedia
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.
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. The state purchased the Ashfall site in 1987; it 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.
The remains of Teleoceras are so numerous and concentrated that the main section of Ashfall is called the "Rhino Barn". Other fossils at the "Rhino Barn" include the remains of horses and camels. Taxa discovered in the Ashfall deposits include:five genera of horse: Cormohipparion, Protohippus, Pseudhipparion, Neohipparion and Pliohippus
three genera of camelids: Procamelus, Aepycamelus and Protolabis
three genera of canids: Leptocyon, Cynarctus and evidence of scavenging from a bone-crushing canid, possibly Aelurodon
one genus of rhinoceros: Teleoceras
one genus of saber-toothed deer: Longirostromeryx
three bird species: crowned crane (Balearica exigua), rail and Apatosagittarus (miocene hawk resembling the now living secretarybird)
two species of turtle: Hesperotestudo and pond turtle