The bizarre, six-horned Uintatherium was once mistaken for a saber-toothed carnivore and an elephant.

Nature · Published 3 October 2026 Swipe more like this →

In short: During the Eocene, a massive, barrel-chested mammal roamed North America and Asia, sporting three pairs of bony, skin-covered horns and oversized canine tusks. Though it looked like a prehistoric monster, this herbivore was a puzzle to early paleontologists, who struggled to classify its strange, elephant-like and rhino-like anatomy.

Uintatherium lived during the Eocene epoch, with U. anceps inhabiting North America between 50.5 and 37 million years ago, and U. insperatus appearing in China between 48 and 37 million years ago. These animals were massive, reaching shoulder heights of 1.5 meters and weighing up to 4,500 kilograms. Their most striking feature was a series of six bony protrusions on the skull, which were likely covered in skin rather than keratin. Because these horns show signs of damage, researchers believe they were used in agonistic behaviors.

The creature's classification has been historically contentious. Early scientists like Edward Drinker Cope and Othniel Charles Marsh engaged in a fierce rivalry, naming a plethora of genera and species—such as Loxolophodon and Tinoceras—that were later found to be synonymous with Uintatherium. While early observers noted similarities to elephants, such as the large tusks and zygomatic arches, these traits are now considered products of convergent evolution. The animal possessed a small brain relative to its body size, with an estimated weight of only 290 grams.

Uintatherium was a graviportal animal, meaning its skeleton was adapted to support its immense weight. It lacked upper incisors, likely relying on a firm elastic pad to process vegetation, while its lower jaw featured bony flanges to support its large upper canines. These tusks, along with the horns and sagittal crests, were sexually dimorphic, with males exhibiting larger features. While some early theories suggested it might have had a trunk, the structure of its nasal passage indicates it likely had a flexible upper lip and a long, muscular tongue instead.

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