1 week Ago By Billings Gazette
Rhinos that roamed North America roughly 12 million years ago gathered in large herds, evidenced by the 100 that died around a water hole in what is now Nebraska following a huge eruption of the Yellowstone supervolcano. Entombed at the , teeth from the rhino fossils were analyzed by researchers at the University of Cincinnati for clues to how they lived. Since the discovery of the rhinos in 1971, scientists have wondered what drew so many animals together in the same place.
Did they converge from far away? “We found they didn’t move very much,” said Clark Ward, a UC graduate and lead author of the study, published in the Nature journal . “We didn’t find evidence for seasonal migration or any evidence of a response to the disaster.” Yellowstone volcano’s supereruption The disaster was an eruption of the Yellowstone volcano when it was located in what is now southern Idaho.
The hotspot has traveled across North America as the Earth’s crust has moved. The hotspot is now located in Wyoming, surrounded by Yellowstone National Park, and helps fuel the park’s many geysers and hydrothermal features. As many as 12 massive supereruptions of the Yellowstone volcano have been identified between 8 and 12 million years ago as the hotspot worked its way across the Snake River Plain.
The ash that killed and then buried the Nebraska rhino herd is called Ibex Hollow Tuff, spreading its airborne deposits as far west as off the California coast, south to the Gulf of Mexico and across much of the Midwest. As much as a foot of ash fell in northeastern Nebraska initially, a distance of 700 miles from the explosion, with more ash deposited by wind after the eruption. “That ash would have covered everything: the grass, leaves and water,” Ward said in a news release.
“The rhinos likely weren’t killed immediately like the people of Pompeii. Instead, it was much slower. They were breathing in the ash.
And they likely starved to death.” “Smaller animals were killed early on, suffocated by the ash; their fossils are found at the bottom of the ash layer and are often smashed or broken up due to trampling by larger animals in the waterhole,” according to a . “Larger animals with bigger lungs lived longer but were killed by the effects of breathing the ash, which left telltale marks on their bones.
” When North America was tropical At the time, Nebraska would have been a tropical or subtropical grassland with areas of trees, not unlike today's African savannas where modern hippos thrive. Horses, camels, a large tortoise and other animals – more than 20 species – have also been found buried in the ash. Several species of lizards were found as gut contents in birds of prey; a snake; four bird species, including 40 crane skeletons, some with preserved feathers and gut contents; two species of dogs; a mole; a mouse (also as gut contents); four species of camels; and a musk deer have been unearthed.
Large herds of Teleoceras major also wandered the region – one-horned rhinos resembling hippos, standing only about 3.5-feet tall at the shoulder but about 10 feet long. Weighing as much as 2,000 pounds, the animals were grazers.
Because of their size, they had few predators in the Miocene epoch, Ward said. But their calves would have been vulnerable to hyena-like predators called bone-crushing dogs. Some of the specimens found at the Nebraska site bear evidence that scavengers removed portions of their carcasses after they died.
And ancient tracks and scat from the 100-pound dogs have been found there. Ward and study co-authors Brooke Crowley at UC and University of Nebraska professor Ross Secord examined ratios of isotopes of strontium, oxygen and carbon in fossil teeth to track the movements of the long-extinct animals across landscapes. Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons.
Grass or leaves that rhinos and other animals eat contain similar ratios of isotopes as the soil and bedrock where plants grow that allow researchers to determine where the animals fed, sometimes with surprising precision depending on how variable the vegetation and geology are. “By studying carbon in the animal, we can reconstruct carbon in the environment to understand what kinds of vegetation lived there,” Ward said. Oxygen tells scientists about climate, particularly rainfall.
“We can use it to reconstruct how wet or dry the environment was,” Ward said. “And strontium tells us where the animal was foraging because the ratio of isotopes is related to the soil and supporting bedrock.” Park is open May through October Ashfall Fossil Beds is situated in rolling farmland drained by nearby Verdigre Creek.
There are reports of people finding fossil bones in the immediate area of the fossil beds going back to the 1920s, including a partial rhino skull found in a sandstone bed below the ash in 1953, according to the Park Service. It wasn’t until the 1970s that the fossil beds were uncovered by scientists. In 1971 erosion by heavy rains exposed a skeleton of a baby rhino.
Expeditions in the late 1970s collected more than 120 articulated skeletons from the site. Visitors to the state park, created in 1991, can see the animal skeletons still being uncovered, some of them largely intact. Artist Gary Staab created statues of two battling rhinos and an ancient tortoise that can also be seen at the park.
The site is managed by the University of Nebraska State Museum and is open to visitors from early May through early October..
