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In Nebraska, there is a unique place called Ashfall Fossil Beds, where around 12 million years ago, a massive volcanic eruption—650 km³ of expelled material—covered a wetland in ash, trapping and fossilizing a large number of animals, including over 100 rhinos. Since its discovery in the 1970s, researchers have wondered why so many animals were found in a single location. Did they live in herds? Was it a seasonal gathering linked to a varied diet that encouraged movement? Or had they come together seeking refuge from the ash?

A recent study attempted to answer these questions by closely examining the fossilized teeth of one of those rhinos: Teleoceras major. This species, endemic to North America during the Clarendonian—part of the North American land mammal age—was a rhino with a single horn, a stocky body, and short legs. All Teleoceras species exhibited sexual dimorphism in their lower second incisors: females had smaller, rounded tusks, while males had larger, pointed ones, possibly used in fighting or displays to gain mating privileges.

The study focused on the remains of 13 adult individuals (8 ♀ and 5 ♂), specifically the M2 and M3 molars. From the tooth enamel, researchers extracted material to measure three stable isotopes: carbon (δ¹³C) to determine diet, oxygen (δ¹⁸O) to infer climate and water intake, and strontium (⁸⁷Sr/⁸⁶Sr), which reflects local geology and helps detect potential geographic movement.

Results showed a diet based almost entirely on C3 plants, typical of humid, wooded environments, with no signs of C4 plant consumption. Oxygen values varied with seasonal water changes, but strontium values remained homogeneous, indicating constant use of the same territory, with no signs of migration from geologically distinct areas. More detailed analyses on serial samples confirmed this ecological stability.

T. major lived within a limited area of a few dozen km² and did not migrate regionally. It was sedentary and closely tied to aquatic environments, much like modern hippos. The lack of isotopic evidence for immigration supports the idea that all sampled individuals were local—likely part of a large herd—killed in the same catastrophic ashfall event.

See You Soon, and Good Science!