For many years, the fossil record of pachycephalosaurs (dome-headed dinosaurs) has been dominated by fossilized skulls. The postcranial material of young pachycephalosaurs, by contrast, has remained almost entirely unknown. Paleontologists have now described the youngest example yet of a pachycephalosaur body, offering a look at how these dinosaurs grew and moved during their first months of life.
Life reconstruction of the pachycephalosaur individual CMNFV 22039 in an environment typical of the Upper Maastrichtian Frenchman Formation. Image credit: Kaitlin Lindblad.
“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.
“The clade is best known for the fusion of its frontal and parietal bones into an inflated dome.”
“The surrounding cranial elements are sometimes incorporated into this structure and are often adorned with nodes, spikes, and other ornaments.”
“Because the frontoparietal domes are the most taphonomically resistant parts of pachycephalosaur skeletons (except for teeth), the pachycephalosaurian fossil record is dominated by these partial cranial remains.”
“As a result, much of what is known about pachycephalosaur ontogeny and phylogeny is based largely on skull morphology.”
Catalogued as CMNFV 22039, the newly-described pachycephalosaurian specimen is approximately 67 million years old (Maastrichtian age of the Late Cretaceous epoch).
The fossil was found within the Frenchman Formation, the youngest of five Maastrichtian formations in southern Saskatchewan, Canada.
This dinosaur was likely less than a year old when it died, making it the youngest pachycephalosaur known from skeletal remains.
“Despite its small size (estimated total length of 90 cm, or 3 feet), the skeleton shows several characters diagnostic of Pachycephalosauria,” the paleontologists said.
The findings show that many of the features scientists rely on to identify adult pachycephalosaurs were already present very early in life.
They also hint at how young pachycephalosaurs moved: compared with adults, the juvenile’s hindlimbs were proportionally long, suggesting a more cursorial, or speed-oriented, build early in 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 said.
The team’s paper was published on February 26 in the Journal of Vertebrate Paleontology.
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Bryan R.S. Moore et al. The ontogenetically youngest known pachycephalosaur (Dinosauria: Ornithischia) postcranium. Journal of Vertebrate Paleontology, published online February 26, 2026; doi: 10.1080/02724634.2026.2616325