The brand-new dinosaur types resided in North America throughout the Late Cretaceous date, some 75 million years back.

Called Brontotholus harmonithe ancient herbivore was roughly 3 m(10 feet )long.

It comes from Pachycephalosauridae, a household of bipedal, dome-headed dinosaurs within the ornithischian clade Pachycephalosauria.

“The dome-headed ornithischian clade Pachycephalosauria has a distinct suite of morphological functions,” stated Dr. D. Cary Woodruff, a paleontologist at the Phillip and Patricia Frost Museum of Science and the Museum of the Rockies, and coworkers.

“They consist of a bipedal gait, heterodont dentition, ossified myosepta in the tail, together with their renowned thickened frontoparietal domes, and ornamented skulls.”

“The bulk of pachycephalosaurid types is understood solely from cranial remains, and as such the anatomy, practical morphology, and methodical value of the frontoparietal domes have actually gotten the most attention amongst paleontologists.”

“The clade is solely understood from the Late Cretaceous of Asia and western North America, with the latter hosting the more varied assemblage of pachycephalosaurids.”

“The earliest types from North America is the Santonian-aged Acrotholus audetiand the group obviously diversified in the Middle to Late Campanian, with an abundance of presently acknowledged types.”

5 specimens now appointed to Brontotholus harmoni were uncovered in the Two Medicine Formation in Glacier County, Montana.

“This brand-new types is the very first pachycephalosaurid from the Two Medicine Formation,” the paleontologists stated.

Brontotholus harmoni‘s enormous dome shows that it was the 3rd biggest North American pachycephalosaurid.

“Phylogenetic analyses recuperate this brand-new types far-off from both Stegoceras and Pachycephalosaurus,” the scientists stated.

“Thus, refuting the hypothesis that this types makes up any part of an ancestor-descent series in between Stegoceras and Pachycephalosaurus“

“However, the brand-new types not just increases understanding of pachycephalosaurid morphology and variety, however reveals that this clade consisted of reasonably big body-sized types as early as the Middle Campanian.”

The discovery of Brontotholus harmoni is reported in a paper released on October 9, 2025 in the Zoological Journal of the Linnean Society

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D. Cary Woodruff et al2025. The very first pachycephalosaurid from the Late Cretaceous Two Medicine Formation: impacts of the Western Interior Seaway on North American pachycephalosaurid advancement. Zoological Journal of the Linnean Society 205 (2 ): zlaf087; doi: 10.1093/ zoolinnean/zlaf087