A new genus and species of pachycephalosaur dinosaur has been identified by paleontologists from five fossil specimens found in the Late Cretaceous Two Medicine Formation in Montana, USA.
This newly identified dinosaur roamed North America during the late Cretaceous period, approximately 75 million years ago.
Named Brontothorus harmony, this ancient herbivore measured around 3 meters (10 feet) in length.
It is classified within the Pachycephalosauridae, a family of bipedal, dome-headed dinosaurs belonging to the ornithischian clade Pachycephalosauria.
“Pachycephalosaurs are a unique ornithischian clade characterized by distinct morphological features,” stated paleontologist D. Carey Woodruff, Ph.D., from the Philip Patricia Frost Museum of Science and the Museum of the Rocky Mountains, along with colleagues.
“These traits include bipedalism, heterodentary dentition, ossification of the caudal muscular septum, as well as the distinctive thickened frontoparietal dome and decorated skull.”
“Most pachycephalosaurid species are primarily known from cranial remains, making the anatomy, functional morphology, and phylogenetic significance of the frontoparietal dome particularly intriguing for paleontologists.”
“This clade is exclusively identified from Late Cretaceous Asia and western North America, with the latter showcasing a more diverse assemblage of pachycephalosaur species.”
“The oldest North American species is the Santonian variant, Acrotorus odeti, and this group evidently diversified during the middle to late Campanian period, resulting in a wealth of presently recognized species.”
A total of 5 specimens attributed to Brontothorus harmony were unearthed in the Two Medicine Formation located in Glacier County, Montana.
“This new species represents the first pachycephalosaur discovered from the Two Medicine Formation,” the paleontologists noted.
The notable dome structure of Brontothorus harmony positions it as the third largest pachycephalosaur in North America.
“Phylogenetic analyses indicate that this new species is significantly distinct from both Stegoceras and Pachycephalosaurus,” the researchers remarked.
“Thus, this species is not closely related to Stegoceras or Pachycephalosaurus.”
“This discovery not only enhances our understanding of the morphology and diversity of pachycephalosaurs but also highlights that this clade included relatively large species sizes during the early Middle Campanian.”
The finding of Brontothorus harmony is detailed in a paper published on October 9, 2025, in the Zoological Journal of the Linnean Society.
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D. Cary Woodruff et al. 2025. The first pachycephalosaurs from the Late Cretaceous Two Medicine Formation: Influence of the Western Interior Seaway on the evolution of North American pachycephalosaurs. Zoological Journal of the Linnean Society 205 (2): zlaf087; doi: 10.1093/zoolinnean/zlaf087
Source: www.sci.news
