Richard Musgrove
Dr Richard Musgrove is a zoologist and science journalist. He writes for Cosmos and Double Helix.
The fossilised teeth from herds of massive hippo-like rhinos (Teleoceras major) have revealed their grazing habits and movement patterns on the ancient North American savannah during the Miocene Epoch.
Nebraska’s Ashfall Fossil Beds State Historical Park, an active research and dig site, provides a window into life around the mid-Miocene 12 million years ago. As the name suggests, the fossil beds were formed by ash, in this case, originating from what must have been a massive eruption of the Yellowstone super volcano, 1100 km away. Hundreds of herbivores, including rhinos, horses and camels, perished and were entombed and preserved.
“That ash would have covered everything: the grass, leaves and water,” says doctoral student, Clark Ward. “The rhinos likely weren’t killed immediately like the people of Pompeii. Instead, it was much slower. They were breathing in the ash, which was piling like snow, about 30cm deep. And they likely starved to death.” Windblown ash continued to fall on Nebraska long after the initial eruption, he adds.
T. major was a 1.8 tonne, 4m-long, one-horned rhino, a grazer, with a barrel-shaped body and stubby legs like a hippo. And like hippos, Ward says, they spent a lot of time in and around water.
More than 100 rhinos were found fossilised around the remains of a single waterhole, says Ward, who wanted to know why. Why were they all in the same place? Were they seeking shelter? Modern rhinos don’t form herds.
He used stable isotopes from their fossil teeth to track the rhinos’ movements across the landscape, in collaboration with Dr Brooke Crowley of the University of Cincinnati and Dr Ross Secord of the University of Nebraska.
Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons. Strontium, oxygen and carbon isotopes are incorporated into bones and tooth enamel over time and vary predictably with soil and bedrock, diet and environment.
“By studying carbon in the animal, we can reconstruct carbon in the environment to understand what kinds of vegetation lived there,” Ward said. Oxygen reveals climate, particularly rainfall, he adds.
“We can use it to reconstruct how wet or dry the environment was,” Ward says. “And strontium tells us where the animal was foraging because the ratio of isotopes is related to the soil and supporting bedrock.”
But no differences were found in foraging ecology or landscape use before and after cow-calf separation for males or females, say the researchers
“We found they didn’t move very much. We didn’t find evidence for seasonal migration or any evidence of a response to the disaster.” Being semi-aquatic also meant they were tied to water, perhaps grazing along edges of waterholes and their connecting streams and rivers, like hippos do today, he says.
The Australian rhinos are similar
The rhino-sized Diprotodon, Australia’s extinct wombat relative, moved more. Great herds of these 3 tonne, 4m long grazers roamed across the country during the last Ice Age, dying out about 25,000 years ago. In 2017, University of Queensland researchers, analysing the same three stable isotopes from fossil teeth, reported that Diprotodons migrated about 200km per year, .
“You’ve heard of the old saying ‘You are what you eat?'” lead author, Dr Gilbert Price asks. “As it turns out, you are where you eat, too.”
Movement patterns are also found through analysis of these isotopes in modern animals, from caribou to kangaroos
Rhino expert Dr John Payne has spent his career working on endangered Sumatran rhinos in Malaysia. Payne, who was not involved in the research, says: “I am not surprised that the analyses very strongly suggest that T major lived in herds given that this animal resembles modern hippopotamus in form and hippos live in herds of several tens of animals — with several herds in one geographical area.”
The study was published in the Nature journal Scientific Reports.
