Paleontologists have described a new genus and species of pachycephalosaurid dinosaur based on five fossil specimens found in the Late Cretaceous Two Medicine Formation in Montana, USA.
A new species of dinosaur lived in North America during the Late Cretaceous era, about 75 million years ago.
Dubbed Brontotolus harmonythe ancient herbivore was about 3 m (10 ft) long.
He belongs Pachycephalosauridsa family of bipedal domed dinosaurs within the ornithischian clade Pachycephalosauria.
“The dome-headed ornithischian clade Pachycephalosauria has a distinctive set of morphological features,” said Dr. D. Cary Woodruff, a paleontologist at the Phillip and Patricia Frost Museum of Science and the Museum of the Rockies, and colleagues.
“They have a bipedal gait, a heterodont bite, ossified myoseptae in the tail, and their iconic thickened frontoparietal domes and ornamented skulls.”
“Most pachycephalosaurid species are known solely from cranial remains, and thus the anatomy, functional morphology, and systematic importance of the frontoparietal domes have received the most attention from paleontologists.”
“This clade is known exclusively from the Late Cretaceous of Asia and western North America, the latter containing a more diverse assemblage of pachycephalosaurids.”
“The oldest species from North America is Santonian in age. Akrotol was braveand the group appears to have diversified in the middle and late Campanian with an abundance of currently recognized species.”
Five copies are now attributed to Brontotolus harmony were found in Two formations of medicine in Glacier County, Montana.
“This new species is the first pachycephalosaurid from the Two Medicine Formation,” the paleontologists said.
Brontotolus harmonyThe massive dome indicates that it was the third largest pachycephalosaurid in North America.
“Phylogenetic analysis reveals this new species, distant from both Stegoceras And Pachycephalosaurus“, the researchers said.
“Thus refuting the hypothesis that this species represents any part of a series of ancestral lineages between Stegoceras And Pachycephalosaurus“
“However, the new species not only expands understanding of the morphology and diversity of pachycephalosaurids, but also shows that this clade contained relatively large body-sized species as early as the middle Campanian.”
Opening Brontotolus harmony reported in paper Published October 9, 2025 in Journal Zoological Journal of the Linnean Society.
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D. Carey Woodruff etc.. 2025. The first pachycephalosaurid from the Late Cretaceous Two Medicine Formation: influence of the Western Interior Seaway on the evolution of pachycephalosaurids in North America. Zoological Journal of the Linnean Society 205(2): zlaf087; doi: 10.1093/zoolinnean/zlaf087
