Paleontologists have unearthed the fossilized remains of two new small-bodied pachycephalosaurines: one in the Dinosaur Park Formation of Alberta and the other in the Hell Creek Formation of Montana.
One of the new dinosaur species, named Sphaerotholus lyonsi, lived 75 million years ago in what is now Canada.
The other, Sphaerotholus triregnum, lived in the United States approximately 67 million years ago.
Both species belong to Sphaerotholus, a small dinosaur genus in the subfamily Pachycephalosaurinae within the family Pachycephalosauridae.
“Despite a poor representation in the fossil record, with their thickened frontoparietal domes and hypothesized head-butting behavior, Pachycephalosauridae are some of the most iconic dinosaurs,” said lead author Dr. Cary Woodruff, a paleontologist with the Phillip & Patricia Frost Museum of Science and the Museum of the Rockies, and his colleagues.
“While the true function of their unusual cranial domes continues to be debated, considerable research has focused on their ontogeny and diversity.”
“This work has been complicated by an unusual fossil record that is dominated by disarticulated cranial remains, with associated skeletons being exceptionally rare.”
“This pattern is likely to be the result of their small body size and taphonomic biases against the preservation and recovery of their delicate skeletons, and the robust and diagnostic nature of the bones that comprise their cranial domes.”
Sphaerotholus lyonsi and Sphaerotholus triregnum are each represented by an isolated squamosal, a skull bone found in most reptiles, amphibians, and birds.
“The holotype of Sphaerotholus lyonsi was collected on the north side of the Red Deer River, in the northeast region of Dinosaur Provincial Park, Alberta, Canada,” the researchers said.
“The holotype of Sphaerotholus triregnum was collected from the lower half of the Hell Creek Formation, around 45 km southwest of the town of Jordan in Garfield County,…
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