For years, the fossil record of pachycephalosaurs (dome-headed dinosaurs) has primarily consisted of fossilized skulls. In contrast, the postcranial remains of young pachycephalosaurs have remained largely unexplored. Recent paleontological findings have unveiled the youngest known example of a pachycephalosaur body, shedding light on how these fascinating dinosaurs grew and moved during their early months of life.
Reconstruction of the life of the pachycephalosaur individual CMNFV 22039 in a typical environment of the Upper Maastrichtian French Formation. Image credit: Caitlin Lindblad.
Paleontologist Brian Moore from Carleton University and his team noted that pachycephalosaurs predominantly comprised small, bipedal dinosaurs (ranging from 2 to 6 meters long) found in Asia and North America during the Santonian to Maastrichtian periods (85 to 66 million years ago).
This clade is particularly recognized for its unique frontal and parietal bones, which merge to create a bulbous dome on their skulls.
The cranial elements surrounding this dome are occasionally integrated into the structure, often featuring nodes, spikes, and other decorative traits.
Notably, the frontoparietal dome is the most resilient part of the pachycephalosaur skeleton (besides the teeth), resulting in a fossil record that heavily favors partial skull remains.
Consequently, much of the understanding regarding the ontogeny and phylogeny of pachycephalosaurs relies significantly on skull morphology.
The recently described pachycephalosaur specimen, cataloged as CMNFV 22039, dates back to roughly 67 million years ago during the Maastrichtian period of the Late Cretaceous.
This fossil was discovered in the French Formation, the youngest of the five Maastrichtian formations located in southern Saskatchewan, Canada.
Remarkably, this dinosaur was likely under a year old at the time of its death, marking it as the youngest known pachycephalosaur from fossil records.
“Despite its small size (estimated at just 90 centimeters or 3 feet), the skeleton displays several features characteristic of pachycephalosaurs,” the paleontologists confirmed.
These findings indicate that many traits used to identify adult pachycephalosaurs were present from a very young age.
Additionally, they provide insight into how juvenile pachycephalosaurs moved. In comparison to adults, the hindlimbs of juveniles were proportionately longer, suggesting that they had a more agile physique during their early development.
As the dinosaur matured, its body seemingly transitioned to the more robust proportions observed in adults, indicating a shift in physical capabilities as it increased in size and weight.
“The relatively long hind limbs of juveniles compared to those of adults imply a likely negative ontogenetic allometry in the hind limbs,” the researchers concluded.
The team’s findings are detailed in a paper published in the February 26th issue of the Journal of Vertebrate Paleontology.
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Brian R.S. Moore et al. Posterior skull of ontogenetically youngest known pachycephalosaur (Dinosauria: Ornithischia). Journal of Vertebrate Paleontology, published online on February 26, 2026. doi: 10.1080/02724634.2026.2616325
Source: www.sci.news
