Asymmetrical Dinosaur Skull Discovery Turns Paleontology Assumptions on Their Head

Hannah’s skull.
Credit: Scott Persons.

University of Alberta paleontologists uncover spiky skull—and overturn long-standing assumptions in identifying horned dinosaurs.

A team of researchers at the University of Alberta has unearthed a well-preserved Styracosaurus skull—and its facial imperfections have implications for how paleontologists identify new species of dinosaurs.

The skull was discovered by Scott Persons in 2015, then a graduate student in the Department of Biological Sciences, during an expedition in the badlands northwest of Dinosaur Provincial Park.

Nicknamed Hannah, the dinosaur was a Styracosaurus—a horned dinosaur over five meters in length with a fan of long horns. UAlberta paleontologists led by Robert Holmes, professor in the Department of Biological Sciences, have learned much from those horns—because they aren’t symmetrical.

“When parts of one side of the skull were missing, paleontologists have assumed that the missing side was symmetrical to the one that was preserved,” explained Persons. “Turns out, it isn’t necessarily. Today, deer often have left and right antlers that are different in terms of their branching patterns. Hannah shows dramatically that dinosaurs could be the same way.”

The differences in the skull’s left and right halves are so extreme that had the paleontologists found only isolated halves, they might have concluded that they belong to two different species

“The skull shows how much morphological variability there was in the genus,” said Holmes. Like the antlers of modern deer and moose, Hannah shows that the pattern of dinosaur horns could vary significantly—meaning some fossils that were once assumed to be unique species will have to be reevaluated.

Stumbling upon a skull

Tradition dictates that the person who finds an important dinosaur specimen gets to give it a nickname. “Hannah the dinosaur is named after my dog,” explained Persons, now a professor and museum curator at the College of Charleston. “She’s a good dog, and I knew she was home missing me while I was away on the expedition.”

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