Youngest Pachycephalosaur Skeleton Reveals Insights into Dinosaur Growth

For many years, the fossil record of pachycephalosaurs – often referred to as dome-headed dinosaurs – has been largely defined by fossilized skulls. The postcranial material, or skeletal remains excluding the skull, of young pachycephalosaurs has remained scarce. Now, paleontologists have described the youngest example yet of a pachycephalosaur body, offering a new perspective on how these dinosaurs grew and moved during their earliest life stages.

Pachycephalosauria: A Brief Overview

“Pachycephalosauria comprises mostly small (between 2 and 6 m long), bipedal dinosaurs from the Santonian to Maastrichtian ages (85 to 66 million years ago) of Asia and North America,” said Carleton University paleontologist Bryan Moore and his colleagues according to research published in the Journal of Vertebrate Paleontology.

The clade is best known for the fusion of its frontal and parietal bones into an inflated dome. These domes are often adorned with nodes, spikes, and other ornaments. As the frontoparietal domes are the most durable parts of pachycephalosaur skeletons, the fossil record is dominated by these partial cranial remains.

Discovery of CMNFV 22039

Catalogued as CMNFV 22039, the newly-described pachycephalosaurian specimen is approximately 67 million years old, dating back to the Maastrichtian age of the Late Cretaceous epoch. The fossil was discovered within the Frenchman Formation, the youngest of five Maastrichtian formations in southern Saskatchewan, Canada as reported by NovaTaxa.

This dinosaur was estimated to be less than a year old when it died, making it the youngest pachycephalosaur known from skeletal remains.

Key Features and Insights

“Despite its small size (estimated total length of 90 cm, or 3 feet), the skeleton shows several characters diagnostic of Pachycephalosauria,” the paleontologists stated in their published paper. The findings indicate that many of the features used to identify adult pachycephalosaurs were already present early in life.

The research likewise provides clues about how young pachycephalosaurs moved. Compared to adults, the juvenile’s hindlimbs were proportionally longer, suggesting a more cursorial, or speed-oriented, build during its early life. As the animals matured, their bodies appear to have shifted toward the stockier proportions seen in adults, indicating a change in locomotion as they grew larger and heavier.

“The relatively long hindlimbs of the juvenile compared with those of adult pachycephalosaurs indicate probable negative ontogenetic allometry in the hindlimbs,” the researchers explained in the Journal of Vertebrate Paleontology.

Future Research

The team’s research was published on February 26, 2026, in the Journal of Vertebrate Paleontology. This discovery provides a crucial piece in understanding the growth and development of pachycephalosaurs, and further research will be needed to refine our understanding of their evolutionary history and behavior.