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For over five decades, a remarkable find in paleontology has captivated researchers: a mass grave containing over a hundred rhinoceros skeletons that met their demise together 12 million years ago. Recent findings from a new study now provide insights suggesting that these ancient creatures didn’t just die in the same location; they also lived as part of a substantial herd. The evidence lies in their teeth.
A barn now shelters the rhino grave, protecting it from the elements. Photo: University of Nebraska State Museum
Rhinos Buried in Ash
The discovery is situated within the Ashfall Fossil Beds, approximately 160 kilometers from Sioux City, Iowa, formed during a catastrophic volcanic eruption in Yellowstone 11.9 million years ago. This eruption discharged a thick cover of ash that blanketed the surrounding environment, leading to immediate death for smaller animals, which succumbed to the suffocating ash.
In contrast, larger, more resilient animals such as the barrel-bellied rhino, Teleoceras major, experienced a more gradual demise. The volcanic ash, on a microscopic scale, possesses a sharp quality akin to tiny glass shards. As these animals inhaled the ash, they developed severe respiratory issues, eventually succumbing while seeking refuge at nearby watering holes. Ironically, the very substance that caused their deaths also preserved their remains in astonishing detail.
The initial discovery in 1971 by paleontologist Michael Voorhies and his wife Jane took place while they were exploring the eroded gullies of Northwestern Nebraska. In a stroke of fortune, Michael spotted a skull protruding from the ash, that of a baby rhinoceros, remarkably still attached to its neck and body.
By 1977, Dr. Voorhies returned to the site, which has since become a recognized national park and an ongoing excavation area. The arrangement of the fossilized remains reveals a chronological order of death, starting with small birds at the bottom, followed by horses and camels, with the rhinos being the last to fall victim. The site houses over 20 species and numerous skeletons, predominantly those of rhinos.
This bone map represents only a small section of the remains discovered at Ashfall. Photo: University of Nebraska State Museum
Insights from Tooth Enamel
Initially, researchers were uncertain whether the grouping of rhinos indicated distinct individuals from various herds converging on a common site or if they were parts of a singular, extensive herd. A team from the University of Cincinnati undertook investigations to clarify this ambiguity.
They analyzed tooth enamel samples from a selection of rhinoceroses, focusing on the isotope ratios present in the enamel. Variations in isotopes, which arise from differing neutron counts within the same element, can indicate environmental conditions and diet. By comparing the isotopic data from the rhinos to that of another species, a sabre-toothed deer, they gained insights into the dietary habits and movements of these ancient animals.
The results were striking. Analysis revealed that the sampled rhinos had consistently consumed local vegetation throughout their lifetimes, without evidence of significant long-distance travel, seasonal migration, or territorial shifts after reaching maturity. The isotopic comparison pointed toward a diet that likely included aquatic plants, suggesting that if T. Major had semi-aquatic tendencies, their movement was confined, corroborating the interpretation that they were part of a cohesive herd rather than a scattered collection of individuals fleeing a disaster.
Researchers meticulously collected samples from the large, robust teeth shown above. Photo: Ward et al
A Glimpse into Prehistoric Nebraska
Prior to the eruption, Nebraska’s landscape during the Mesozoic era was a sprawling savannah dotted with streams and watering holes that provided sustenance for grazing animals. Creatures like the towering Aepycamelus, a giant extinct camel, thrived by reaching for treetop foliage, while smaller three-toed horses such as Pseudhipparion gratum and Neohipparion affine grazed the ground cover below.
These grazing animals, particularly the younger specimens, faced predation from formidable hunters like Epicyon, often referred to as the “bone-crushing dog,” which could weigh up to 170 kilograms.
The scenes might have included immense herds of barrel-bodied T. Major, which could grow to lengths of four meters. Built more like modern hippos, they formed large groups, enjoying the muddy waters of their environment while effectively warding off threats from the predatory dogs.
Despite the catastrophic volcanic event, the species T. Major persisted for approximately another seven million years, only becoming extinct as shifting climate conditions transformed their once-lush habitats into harsher landscapes.
Source
explorersweb.com